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  The objective of this study is to investigate the performance and emissions in a pilot-ignited supercharged dual-fuel engine, fueled with different types of gaseous fuels under various equivalence ratios. It is found that if certain operating conditions are maintained, conventional dual-fuel engine combustion mode can be transformed to the combustion mode with the two-stage heat release. This mode of combustion was called the PREMIER (PREmixed Mixture Ignition in the End-gas Region) combustion. During PREMIER combustion, initially, the combustion progresses as the premixed flame propagation and then, due to the mixture autoignition in the end-gas region, ahead of the propagating flame front, the transition occurs with the rapid increase in the heat release rate


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  A transported probability density function (PDF) method and a photon Monte Carlo/line-by-line (PMC/LBL) spectral model are exercised to generate physical insight into soot processes and spectral radiation characteristics in transient high-pressure turbulent n-dodecane spray flames, under conditions that are relevant for compression-ignition piston engines. PDF model results are compared with experimental measurements and with results from a locally well-stirred reactor (WSR) model that neglects unresolved turbulent fluctuations in composition and temperature. Computed total soot mass and soot spatial distributions are highly sensitive to the modeling of unresolved turbulent fluctuations. To achieve reasonable agreement between model and experiment and to capture the highly intermittent nature of soot in the turbulent flame, it is necessary to accurately represent mixing and the low diffusivity of soot particles. This is accomplished in the PDF framework using a mixing model that enforces locality in the gas-phase composition space, while not mixing the transported soot variables. The results suggest that mixing is at least as important as kinetics in controlling soot formation and evolution in high-pressure turbulent flames. Regarding radiation, radiant fractions and global influences of radiation in these flames are relatively small. Nevertheless, an examination of spectral radiative heat transfer provides valuable insight into the nature and modeling of radiation in high-pressure turbulent combustion systems. There are complex spectral interactions that are revealed using PMC/LBL. CO2dominates the total radiative emission and reabsorption, but most of the emitted CO2radiation is reabsorbed before reaching the walls. On the other hand, most of the emitted soot radiation reaches the walls, but soot radiation is a small contribution overall; H2O dominates the radiation that reaches the walls. Global turbulence–radiation interactions (TRI) effects are small, but radiative emission from soot increases by approximately a factor two when TRI are considered. Radiative transfer contributes both to energy redistribution in the vessel and to wall heat losses. The results suggest that a simple model that considers soot radiation and the principal CO2and H2O spectral bands might be sufficient to capture the key influences of radiation in engine CFD. It is expected that these findings will contribute to the development of truly predictive CFD models for engines and other high-pressure turbulent combustion systems.


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  Multidimensional Modeling of Combustion and Knock in Spark-Ignition Engines with Detailed Chemical Kinetics


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  A G -equation-based multidimensional combustion model incorporating detailed chemical kinetics was developed and implemented in KIVA-3V for spark-ignition (SI) engine simulations. The integrated model simulates the turbulent flame propagation, pollutant formation, flame quenching and knocking combustion processes in SI engines, and was applied to both homogeneous charge and direct-injections (DI) SI engines. The G -equation method is employed to track the position of the mean turbulent flame front surface. A progress variable concept is introduced into the turbulent flame speed correlation to account for the laminar to turbulent evolution of the spark kernel flame. The laminar flame speed correlation was also updated to take the mixture stratification effect into account. A new method based on tracking the subgrid-scale burnt/unburnt volumes of the flame-containing cells is proposed for the primary heat release calculation. In the post flame zone, detailed hydrocarbon fuel oxidation mechanisms coupled with a reduced NO x mechanism are applied for modeling secondary heat release and NOx formation. The chemical kinetic mechanisms are also applied in front of the flame front for engine knock modeling. The detailed iso -octane mechanism used to simulate gasoline fuel combustion was validated using ignition delay test data in a shock tube and measured pressure data of a gasoline homogeneous charge compression ignition (HCCI) engine. The SI engines used for model validation include a Caterpillar propane engine, a two-stroke marine GDI engine and a Ford engine operating in both port-fuel-injection (PFI) mode and DI mode. Good agreement between simulated and measured in-cylinder pressure traces and engine-out emissions was obtained over a wide range of operating conditions. Based on model validation, knocking combustion processes in the Ford engine under boost conditions was modeled. Knock mitigation strategies using cooled EGR and split-injection were assessed based on the numerical study. As an independent topic, a semi-implicit numerical solver for detailed chemistry was developed aiming at improving computational efficiency. The present solver was successfully applied to diesel engine simulations and 40–70% CPU time savings were achieved compared to the standard CHEMKIN.


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  Numerical investigation on the evaporation of droplets depositing on heated surfaces at low Weber numbers


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  The evaporation of water droplets, impinging with low Weber number and gently depositing on heated surfaces of stainless steel is studied numerically using a combination of fluid flow and heat transfer models. The coupled problem of heat transfer between the surrounding air, the droplet and the wall together with the liquid vaporisation from the droplet's free surface is predicted using a modified VOF methodology accounting for phase-change and variable liquid properties. The surface cooling during droplet's evaporation is predicted by solving simultaneously with the fluid flow and heat transfer equations, the heat conduction equation within the solid wall. The droplet's evaporation rate is predicted using a model from the kinetic theory of gases coupled with the Spalding mass transfer model, for different initial contact angles and substrate's temperatures, which have been varied between 20-90?? and 60-100 ??C, respectively. Additionally, results from a simplified and computationally less demanding simulation methodology, accounting only for the heat transfer and vaporisation processes using a time-dependent but pre-described droplet shape while neglecting fluid flow are compared with those from the full solution. The numerical results are compared against experiments for the droplet volume regression, life time and droplet shape change, showing a good agreement. ?? 2007 Elsevier Ltd. All rights reserved.


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  A lot of effort has been put in the past years into the understanding of the delivery and development of diesel sprays in engine-like conditions as it has been proved to be a very important step for the design of better and cleaner commercial engines. Due to the bigger share of passenger cars engines over heavy duty engines, the research has been mainly focused on the investigation using small nozzles. This paper studies two nozzles with diameters representative of those that can be encountered in heavy duty engines, with the objective of corroborating the conclusions gathered for small nozzles representative of passenger car engines. The experimental data have been acquired by state-of-the-art techniques and equipment, and serves two purposes: further the understanding of the physics involved in the injection event and spray evaporation; and provide a dataset to CFD models that can accurately predict the behavior of the injection event. The tests were performed in a constant pressure flow vessel that allows to simulate engine-like conditions (1000 K and 15 Mpa) with continuous flow. The injection system tested is a novel, common-rail, solenoid-actuated injector for heavy duty applications which operates up to 220 Mpa. All experiments were performed in non-reacting conditions. The extended test matrix allowed to determine the influence of several parameters such as rail pressure, gas temperature, gas density, and nozzle geometry on the air–fuel mixing and evaporation process, by analyzing the spray penetration and spreading angle. Mie scattering and double-pass Schlieren optical configurations have been used to measure global liquid and vapor penetration, respectively. The data proves that spray penetration at low temperature can be up to 15% faster than spray penetration at high temperature conditions at the same density for the nozzles experimented, which limits the usability of low temperature experiments to infer the behavior of the injector at high temperature conditions. The data also shows that the nozzle with the biggest diameter provided the highest value of stabilized liquid length as expected. Also, when vapor phase is reached, the temperature has negligible effect on the global diesel spray morphology, and no influence on the tip penetration or on the spreading angle.


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  The improvement of spray atomization and penetration characteristics of GDI multi-hole injector sprays is a major component of the engine combustion developments, in order to achieve the fuel economy and emissions standards. Significant R&D efforts are directed towards optimization of the nozzle designs, in order to achieve optimum multi- objective spray characteristics. The Volume-of-Fluid Large-Eddy-Simulation (VOF-LES) of the injector internal flow and spray break-up processes offers a computational capability to aid development of a fundamental knowledge of the liquid jet breakup process. It is a unique simulation method capable of simultaneous analysis of the injector nozzle internal flow and the near-field jet breakup process. Hence it provides a powerful toll to investigate the influence of nozzle design parameters on the spray geometric and atomization features and, consequently, reduces reliance on hardware trial-and-tests for multi-objective spray optimizations. This publication reports investigations of a single, axisymmetric nozzle-hole, pertinent to GDi multi-hole injector nozzle geometry, with the aid of the current state-of-the-art VOF-LES method. The focus of the study is the influence of nozzle degsign and geometric features on the plume structure and its primary break-up process. Specifically, the influence of nozzle length-to-diameter ratio (l/d), counter-bore, and nozzle tapered geometry on the jet primary breakup are studied. Analysis of alternative nozzle geometries reveal the influence of marked influence of nozzle shape and l/d ratio on the nozzle flow structure, hydraulic efficiency and the jet breakup characteristics. There is marked influence of flow separation and hydraulic flip in the nozzle hole for amplification of the Kelvin-Helmholtz instabilities and the jet breakup length.


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  Calcium looping process simulation based on an advanced thermodynamic model combined with CFD analysis


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  The current study presents a new methodology for the simulation of the Calcium Looping (CaL) process based on the coupling of CFD and advanced thermodynamic models. As a first step, CFD models for the two reactors, i.e. the carbonator and the calciner, of a pilot scale Dual Fluidized Bed system are developed and validated by comparing the numerical predictions with corresponding experimental data for pressure distribution, carbonator capture efficiency and sorbents regeneration in the calciner. For the carbonator modeling, the Two-Fluid-Model (TFM) approach is combined with the advanced EMMS scheme in order to provide results with high accuracy, even for the difficult to model dense bottom zone of the riser. A similar approach is adopted for the calciner; numerical results indicate that CO2 follows an almost linear trend along the bubbling bed height, while the bubbling formations might result in a reduced efficiency for the calcination reaction due to the entrapment of CO2 bubbles inside the emulsion phase. Numerical results related mostly to the hydrodynamics of the reactors, such as the solids distribution and residence time are then used as input parameters in a kinetics-based process algorithm. Process modeling simulations reveal the importance of splitting the carbonator riser into two distinct sections, i.e. the bottom zone with dense solid phase and the upper one (freeboard) with a more dilute solid concentration. The heat balance calculation for these two regions demonstrates a big gap between the heat flux density for the bottom zone (19.26 kW/m2) and the freeboard (0.46 kW/m2), which should be taken into account for the design of an effective heat removal system for scaled-up reactors. As a final step, a sensitivity analysis is performed for the optimization of the parameters governing the operation of the whole carbonation-calcination cycle. Efficient sorbent regeneration and high looping ratio enhances the CO2 capture efficiency in the carbonator, whilst low CO2 concentration in the calciner is suggested for more effective lime regeneration.


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  Theoretical and experimental comparison of internal flow and spray characteristics between diesel and biodiesel


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  The internal flow in nozzle and macroscopic spray characteristics of diesel and biodiesel, by employing a validated numerical model and a laser-based Mie-scattering technique, are investigated. The results indicate that both the mass flow rate and the orifice exit average velocity of diesel are larger than those of biodiesel. Also, that diesel consistently produced higher cavitation intensity and turbulence kinetic energy confirms diesel can boost the naissance of cavitation and the turbulence disturbance inside the nozzle. Meanwhile, the cavitation intensity and the turbulence kinetic energy increase dramatically as the injection pressure increases; the cavitation domain is consistent with the domain of high turbulence kinetic energy. Furthermore, the radial velocity of diesel is significantly higher than biodiesel under the same injection pressure, while the radial velocities of both fuels increase as the injection pressure increase. Moreover, the spray tip penetration of biodiesel is longer than that of diesel, while the aerodynamic spray cone angle of biodiesel is narrower that of diesel under the same injection pressure. Higher surface tension and viscosity of biodiesel resulted in smaller cavitation intensity, turbulence kinetic energy and radial velocity at the nozzle exit, which in turn contribute to the narrowing of the aerodynamic spray cone angle.


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  An important first step in spray combustion simulation is an accurate determination of the fuel properties which affects the modelling of spray formation and reaction. In a practical combustion simulation, the implementation of a multicomponent model is important in capturing the relative volatility of different fuel components. A Discrete Multicomponent (DM) model is deemed to be an appropriate candidate to model a composite fuel like biodiesel which consists of four components of fatty acid methyl esters (FAME). In this paper, the DM model is compared with the traditional Continuous Thermodynamics (CTM) model for both diesel and biodiesel. The CTM model is formulated based on mixing rules that incorporate the physical and thermophysical properties of pure components into a single continuous surrogate for the composite fuel. The models are implemented within the open-source CFD code OpenFOAM, and a semi-quantitative comparison is made between the predicted spray-combustion characteristics and optical measurements of a swirl-stabilised flame of diesel and biodiesel. The DM model performs better than the CTM model in predicting a higher magnitude of heat release rate in the top flame brush region of the biodiesel flame compared to that of the diesel flame. Using both the DM and CTM models, the simulation successfully reproduces the droplet size, volume flux, and droplet density profiles of diesel and biodiesel. The DM model predicts a longer spray penetration length for biodiesel compared to that of diesel, as seen in the experimental data. Also, the DM model reproduces a segregated biodiesel fuel vapour field and spray in which the most abundant FAME component has the longest vapour penetration. In the biodiesel flame, the relative abundance of each fuel component is found to dominate over the relative volatility in terms of the vapour species distribution and vice versa in the liquid species distribution. ?? 2014 Elsevier Ltd. All rights reserved.


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  Combustion and emission performance of a split injection diesel engine in a double swirl combustion system


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  The authors developed and tested a split injection strategy in a double swirl combustion system (DSCS). Different split injection strategies with different ratios of pilot injection fuel to total fuel mass (herein defined as “pilot injection/fuel mass ratios”) and dwell times were compared with an optimized single injection strategy in terms of the break specific fuel consumption (BSFC). The in-cylinder pressure, heat release rate and in-cylinder temperature were analyzed to explore the in-cylinder combustion process. The NOx emission was also measured. With the total fuel mass being 100 mg/cycle and excess air coefficient being 2 at 2100 r/min at a 5% pilot injection/fuel mass ratio and a 10 deg dwell time, the BSFC decreased by 2.7% compared with the single injection strategy. The NOx emission increased from 940 ppm to 1140 ppm. An ‘acceleration effect' helped the DSCS when dwell time was short. A spray visualization experiment and numerical simulations were carried out to explain these phenomena. It is concluded that the split injection condition with a smaller pilot injection/fuel mass ratio and a shorter dwell time performed better than the single injection condition in terms of the thermo-atmosphere utilization, space utilization and acceleration effect.


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  Building robust chemical reaction mechanisms : next generation of automatic model construction software


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  An implementation and validation of the coupled Σ-Y ADF model is presented in this work for reacting Diesel spray CFD simulations under a RANS turbulence modeling approach. An Approximated Diffusion Flamelet (ADF) model Michel et al. (2008) implemented in the OpenFOAM CFD open-source library by Winklinger (2014) is fed with the spray description, i.e. mixing formation process, provided by the Σ-Y Eulerian atomization model Garcia-Oliver et al. (2013). In the present investigation, the Engine Combustion Network Spray A reference configuration is used for validation. Specifically, the model can provide accurate predictions of typical reacting spray metrics, such as the ignition delay and the lift-off length. Moreover, the internal structure is also fairly reproduced in terms of quasi-steady spatial distribution of formaldehyde and OH, related with low and high temperature reactions respectively. Additionally, modeling results have been compared to recent Particle image velocimetry (PIV) measurements Garcia-Oliver et al. (2017) under both inert and reacting conditions. Flow response to heat release is quantitatively predicted by the model, both in terms of local velocity increase as well as radial dilation. The model has been used to understand combustion-induced reduction in entrainment, in particular around the lift-off length location. Flow confinement does not seem to influence the global flame behaviour, even though some changes in the local flow hint can be observed when moving from an open to a closed domain.


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  Effects of multiple-injection strategies on overall spray behavior, combustion, and emissions reduction characteristics of biodiesel fuel


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  This study described the combustion and exhaust emissions characteristics of biodiesel fuel with multiple-injection strategies. Also, this investigation included the free spray characteristics and in-cylinder spray behaviors of the multiple-injection modes. Free spray and in-cylinder spray images were obtained from the spray visualization system. Combustion and exhaust emissions characteristics were analyzed using a single cylinder diesel engine with a displacement volume of 373.33cm3and a compression ratio of 17.8. The exhaust emissions were analyzed using a smoke meter and an exhaust gas analyzer. A scanning mobility particle sizer (SMPS) was utilized to measure the particle number and size distribution of the nano-sized particle matter.It revealed that the injected spray before BTDC 25° developed toward the piston bowl region, and then progressed along the piston wall. When the biodiesel spray was injected at BTDC 25°, the spray targeted the piston lib. In single-injection combustion, the combustion pressure and rate of heat release at an injection timing of BTDC 30° dramatically decreased. These characteristics influenced on the decrease of the indicated mean effective pressure (IMEP) and the increase of soot, HC, and CO emissions because of the incomplete combustion. The multiple-injection modes showed a higher IMEP than the single-injection mode. In addition, the pilot injection strategy represented a higher IMEP than the split injection mode. The analysis of exhaust emissions characteristics of the multiple-injection modes showed that a short injection interval induced a decrease in soot, HC, and CO emissions, while NO.xemission increased. On the other hand, when the multiple-injection modes applied to the diesel engine, particles with large sizes were significantly decreased compared to single-injection combustion. © 2010 Elsevier Ltd.


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  Recently, a combustion chamber of a high speed diesel engine has been downsized in order to improve fuel economy. Moreover, injection pressure of the diesel fuel tends to increase due to promotion of fuel atomization. Therefore, the diesel spray flame impinges on a cavity wall of a combustion chamber in recent diesel engines. It results that promotion of heat loss from the engine occurred due to the heat transfer between the impingement spray flame and the cavity wall. Therefore, it is necessary to understand the impingement phenomenon of the diesel spray flame for improvement of the thermal efficiency. In order to understand the impingement mechanism between the spray flame and the wall, velocity measurement of an impingement diesel spray flame is required. Moreover, the heat transfer strongly depends on the flow characteristics of the impingement spray flame. Velocity information of the impingement spray might provide heat transfer mechanism between the spray and the wall although the diesel spray was not a flame. In this study, velocity field of an impingement diesel spray was measured with time-resolved PIV. Effect of ambient gas density, injection pressure and impingement angle on flow characteristics of the impingement diesel spray was investigated. Moreover, velocity of the diesel spray just before impingement on the wall was measured in order to investigate dependence of the impinging spray velocity on the post-impingement spray velocity. As the result, averaged radial peak velocities of the post-impingement diesel spray decreased with an increase of ambient gas density. Moreover, dependence of the impinging spray velocity on the averaged peak velocities of the post-impingement spray was clarified.


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  Simultaneous applications of high-speed toluene-LIF thermometry and PIV at kHz rates were utilized to investigate the evolution of gas temperature stratification imposed from direct-injection of liquid fuel within a motored SIDI engine. Temperature imaging was based on the two-color detection method that measures the LIF signal ratio from two separated wavelength ranges to enable LIF temperature imaging within inhomogeneously mixed systems. It was observed that cold gases associated with evaporative cooling exist within the regions of dense liquid fuel droplet clouds. As droplets disperse, the cold-gas regions expand and relative temperatures as low as -50 K exist. Average temperature gradients between cold- and bulk-gases are up to 30 K/mm and gradients persist but drop in magnitude throughout compression as cold- and bulk-gases mix. Temperature stratification is greatest as the fuel disperses within the field-of-view producing large areas of cold-gases with relative temperatures as low as -50 K. Individual temperature images and 2D PDFs of identified cold-gas regions reveal that local regions of cold-gas imposed from evaporative cooling can last up to 30 CAD after fuel injection for the given operating conditions. The time-resolved imaging study show the mechanics of localized evaporative cooling and bulk-flow motion-driven mixing that over time reduces temperature gradients but does not completely homogenize the temperature fields.


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  CARS diagnostics of the burning of H 2 — O 2 and CH 4 — O 2 mixtures at high temperatures and pressures


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  2003-01-0067 Modeling of Air Fuel Mixing in a Stratified Gasoline Direct Injection Engine Using Multicomponent Fuel Representation


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  Review and Benchmarking of Alternative Fuels in Conventional and Advanced Engine Concepts with Emphasis on Efficiency, CO 2 , and Regulated Emissions


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  A flame particle tracking analysis of turbulence-chemistry interaction in hydrogen-air premixed flames


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  Interactions of turbulence, molecular transport, and energy transport, coupled with chemistry play a crucial role in the evolution of flame surface geometry, propagation, annihilation, and local extinction/re-ignition characteristics of intensely turbulent premixed flames. This study seeks to understand how these interactions affect flame surface annihilation of lean hydrogen-air premixed turbulent flames. Direct numerical simulations (DNSs) are conducted at different parametric conditions with a detailed reaction mechanism and transport properties for hydrogen-air flames. Flame particle tracking (FPT) technique is used to follow specific flame surface segments. An analytical expression for the local displacement flame speed (. Sd) of a temperature isosurface is considered, and the contributions of transport, chemistry, and kinematics on the displacement flame speed at different turbulence-flame interaction conditions are identified. In general, the displacement flame speed for the flame particles is found to increase with time for all conditions considered. This is because, eventually all flame surfaces and their resident flame particles approach annihilation by reactant island formation at the end of stretching and folding processes induced by turbulence. Statistics of principal curvature evolving in time, obtained using FPT, suggest that these islands are ellipsoidal on average enclosing fresh reactants. Further examinations show that the increase in Sd is caused by the increased negative curvature of the flame surface and eventual homogenization of temperature gradients as these reactant islands shrink due to flame propagation and turbulent mixing. Finally, the evolution of the normalized, averaged, displacement flame speed vs. stretch Karlovitz number are found to collapse on a narrow band, suggesting that a unified description of flame speed dependence on stretch rate may be possible in the Lagrangian description.


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  Investigation of Different Droplet Formation Regimes in a T-junction Microchannel Using the VOF Technique in OpenFOAM List of parameters


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  Dual-fuel biodiesel-producer gas combustion has shown potential in reducing nitric oxides and particulate emission levels compared to only diesel operation; however, engine overall efficiency is slightly penalized, while the main drawbacks are represented by the higher levels of total hydrocarbons and carbon monoxide emissions. In this work, the improvements in the combustion development deriving from the splitting of the liquid fuel injection at low loads have been assessed using a 0.51 L single-cylinder research diesel engine equipped with a high pressure common rail injection system and operated in dual-fuel mode. In this case, a synthetic producer gas was used as inducted gaseous fuel, while biodiesel was used as pilot fuel. Initially, the spray morphology was characterized in a constant-volume vessel for different values of injection duration and pressure, as well as vessel backpressure. Then, the experimental campaign, run on the engine at 1500 rpm, was divided in two sessions. During the former, only one pilot injection of constant fuel amount (11 mm3/cycle) was performed, the rail pressure was set equal to 500 or 1000 bar, the injection timing was varied in the range −50 ÷ 5 degrees crank angle after top dead center while the amount of gaseous fuel inducted in the cylinder was varied on three levels. During the latter, the pilot fuel amount, kept equal to the one pilot injection tests, was split in two smaller injections and the effect of the dwell between them – varied in the range 5 ÷ 50 degrees crank angle – was investigated as well. The results of the first set of experiments revealed that pilot injection timing and pressure both affect the combustion development. This resulted in sensible variations on thermal and combustion efficiencies, and therefore on fuel conversion efficiency, the last one exhibiting higher values with pilot injection timing slightly advanced respect to top dead center and lower injection pressure. In these conditions, total hydrocarbons and carbon monoxide are lowered, while nitric oxides are increased. The amount of gas demonstrated to have a secondary effect on combustion development and emissions levels at the exhaust. Splitting pilot injection, demonstrated to be an effective way to increase fuel conversion efficiency and to reduce the levels of all the pollutant species compared to the single pilot injection strategy. Based on the extensive experimental activity described in this paper, a dwell ranging between 10 and 30 degrees of crank angle, combined with a first injection timing ranging between 35 and 20 degrees of crank angle before top dead center guarantee the highest fuel conversion efficiency and the lowest pollutants emission levels. Injection pressure confirmed to be a significant factor in affecting the combustion development, while a secondary effect was determined by the gaseous mass inducted in the cylinder. Ultimately, pilot injection splitting demonstrated to be an effective way for improving gaseous fuel combustion in dual-fuel mode at low load (lean mixture) conditions.


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  Experimental study on the spray characteristics discharging from elliptical diesel nozzle at typical diesel engine conditions


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  The elliptical orifice diesel nozzle has potential beneficial for improving spray and air-fuel mixing quality, which has great impact on combustion and emission performances for diesel engine. This paper presents experimental studies on the macro spray characteristics and the mechanism of axis-switching for elliptical and circular orifice diesel nozzles with same cross section area, with biodiesel fuel by using shadowgraph technique, under various injection pressures (50 MPa, 70 MPa, 90 MPa) and backpressures (1MPa, 2 MPa, 3 MPa). Two CCD cameras were adopted to acquire the macro spray images at the minor and major view planes simultaneously. Macroscopic spray characteristics from different view planes of spray were processed by MATLAB. The results indicated that the spray width of the elliptical spray was greater than that of the circular spray in all the view planes. Elliptical orifice spray exhibited axis-switching phenomenon during the injection process even at high injection pressure and backpressure. The increasing of backpressure enhances the aerodynamic effects, resulting in suppressing axis-switching of elliptical spray. However, increasing the injection pressure is beneficial for improving the axis-switching frequency, because the higher spray inertia resulting from higher injection pressure can cause greater spray surface-instabilities, which are conductive to enhance the axis-switching. Moreover, the spray width at the downstream increases as the backpressure increases, and for all geometrical orifices exhibited greater spray width under the higher injection pressure. In addition, the spray tip penetration of circular orifice was longer than that of elliptical orifice during the whole injection process. This is due to the larger spray surface of elliptical spray resulting in larger aerodynamic drag. Furthermore, the spray cone angle of the circular orifice is consistently smaller than that of elliptical orifice under typical diesel engine conditions. Because the axis-switching phenomenon of elliptical spray is helpful to improve the air entrainment ratio and thus resulting in larger spray cone angle. Finally, the present experiment results indicate that elliptical sprays are conductive to increase air entrainment ratio and air–fuel mixing quality as compared to circular sprays, due to the axis-switching phenomenon, larger spray cone angle and width.


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  Visualization of combustion characteristic of diesel in premixed methanol – air mixture atmosphere of different ambient temperature in a constant volume chamber


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  Flow in the Piston-Cylinder-Ring Crevices of a Spark-Ignition Engine: Effect on Hydrocarbon Emissions, Efficiency and Power


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  Shock tube ignition delay times and methane time-histories measurements during excess CO2 diluted oxy-methane combustion


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  The combustion of methane in air results in large amounts of CO2 and NOX emissions. In order to reduce the NOX emissions, one possible solution is the oxy-methane combustion with large CO2 dilution so that the combustion products can be reduced mainly to CO2 and H2O. However, there are very few studies on the chemical kinetics of oxy-methane combustion in a CO2 diluted environment. In this study, methane time-histories, CH* emission profiles, and pressure time-histories measurements were conducted behind reflected shock waves to gain insight into the effects of CO2 dilution of the gas mixtures on the ignition of methane. The measurements were carried out for mixtures of CH4, CO2 and O2 in argon bath gas at temperatures of 1577-2144 K, pressures of 0.53-4.4 atm, equivalence ratios (Φ) of 0.5, 1, and 2, and CO2 mole fractions (XCO2) of 0, 30, and 60%. The laser absorption measurements were conducted using a continuous wave distributed feedback interband cascade laser (DFB ICL) centered at 3403.4 nm. The results showed the decrease of activation energy and the increase of ignition delay time as the amount of CO2 dilution was increased. However, the changes were minor and within the experimental uncertainties of the measurements. Also, the results were compared to the predictions of two different natural gas mechanisms: GRI 3.0 and AramcoMech 1.3 mechanisms. In general the predictions were reasonable when compared to the experimental data; however, there were discrepancies at some conditions. Three different influences of CO2 addition to the argon bath gas in regards to chemistry, collision efficiencies, and heat capacities were examined. In addition, the present study included experimentally obtained correlations for absorption cross sections of methane for its P(8) line in the v3 band in argon bath gas with and without carbon-dioxide dilutions at temperatures between 1200 \textless T \textless 2000 K and pressures between 0.7 \textless P \textless 1.2 atm.


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  Unsteady deflagration speed in an auto-ignitive DME / Air mixture at NTC conditions Computational Approach


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  Enhancement of HTPB Combustion in a Hybrid Rocket Motor Using Amorphous Ti – Al – B Nanopowder Additives


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  A new EDC approach for modeling turbulence/chemistry interaction of the gas-phase of biomass combustion


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  Small-scale grate-firing biomass combustors generate high level of pollutants as a result of poor air/fuel mixing and short residence time of combustion. Reliable gas-phase combustion modeling can play a key role in the improvement and optimization of the design of a biomass furnace. This paper proposes a new combustion model based on the framework of the well-known eddy dissipation concept (EDC) approach. The ability of EDC to incorporate detailed chemical reactions in turbulent reacting flows has made it attractive for modeling combustion. However, its application poses a challenge especially for modeling weakly turbulent reacting flow conditions, as well as reacting flows with comparable flow and chemical time scales. The newly proposed combustion scheme can reasonably describe the interaction of chemistry and turbulent flow over a wider range of turbulence conditions. To validate the model, simulations are carried out using diffusion and partially premixed jet flames covering weakly to highly turbulent flow conditions. Moreover, the capability of the new model in predicting NOx emissions, based on fuel bound nitrogen source as well as thermal NOx, is investigated. All numerical results are compared with their counterparts' experimental measurements of temperature and species concentrations. Compared to the standard EDC, the results of the new EDC approach reveal noticeable improvement in the predictions, especially for slow-forming and kinetically dominated species such as CO and NOx.


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  Nowadays, the most critical issues concerning internal combustion engines are the reduction of the pollutant emissions, in particular of CO2, and the replacement of fossil fuels with renewable sources. An interesting proposition for Diesel engines is the Dual Fuel (DF) combustion, consisting in the ignition of a premixed charge of gaseous fuel (typically natural gas) by means of a pilot injection of Diesel Fuel. Dual fuel combustion is a quite complex process to model, since it includes the injection of liquid fuel, superimposed with a premixed combustion. However, CFD simulation is fundamental to address a number of practical issues, such as the setting of the liquid injection parameters and of the gaseous fuel metering, as well as to get the maximum benefit from the DF technique. In this paper, a customized version of the KIVA-3V Computational Fluid Dynamic (CFD) code was adopted to analyze the combustion process of a 4-cylinder, 2.8 1, turbocharged HSDI Diesel engine, operating in both Diesel and DF (Diesel and Natural Gas) modes. Starting from a previously validated diesel combustion model, a natural gas combustion model was implemented and added to simulate the DF operations. Available engine test data were used for validation of the diesel-only operation regimes. Using the calibrated model, the influence of the premixed charge composition was investigated, along with the effect of the diesel injection advance angle, at a few characteristic operating conditions. An optimum setting was eventually found, allowing the DF engine to deliver the same brake power of the original Diesel unit, yielding the same maximum in-cylinder pressure. It was found that DF combustion is soot-less, yields a strong reduction of CO and CO2, but also an increase of NO. ?? 2013 The Authors.


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  A method to estimate the propagation speed of a three-dimensional ignition front in Direct Numerical Simulation (DNS) is discussed. The objective is to contribute to the design of advanced numerical tools for the study of sporadic pre-ignition kernels leading to violent pressure waves, which may for instance damage moving parts in engines. Estimating the speed of a propagating ignition front in three-dimensional DNS, before it is occurring, is not an easy task, because this speed scales as the inverse of the spatial gradient of the time left till ignition, which is a priori an unknown quantity. The proposed approach introduces, for every point of the DNS, an estimation of the time left till ignition, which is obtained from reactors dynamically parameterized from the time evolving DNS results. This provides a three-dimensional distribution of ignition delays at every instant in time of the DNS fields. The time evolution of the ignition speed is then computed from the space derivative of the ignition delay field. Only the pre-ignition phase is examined and the demonstration of the method is made with oversimplified chemistry, in order to apply it to an existing rapid compression machine, in which the mixture composition is homogeneous, whereas the temperature distribution is non-uniform due to heat-transfer at wall. The two expected distinct ignition regimes are reported. In the first, ignition propagates at the speed of sound, or even above, and occurs over a large portion of the combustion chamber, with a strong and sudden pressure increase. The second ignition regime is much more localized in space and with a propagation mechanism pertaining to a deflagration mode. A method is also discussed to delineate in the DNS between ignition influenced by either the constant pressure or the constant volume canonical behaviors.


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  There has been much recent progress in the area of surrogate fuels for diesel. In the last few years, experiments and modeling have been performed on higher molecular weight components of relevance to diesel fuel such as n-hexadecane (n-cetane) and 2,2,4,4,6,8,8-heptamethylnonane (iso-cetane). Chemical kinetic models have been developed for all the n-alkanes up to 16 carbon atoms. Also, there has been experimental and modeling work on lower molecular weight surrogate components such as n-decane and n-dodecane that are most relevant to jet fuel surrogates, but are also relevant to diesel surrogates where simulation of the full boiling point range is desired. For two-ring compounds, experimental work on decalin and tetralin recently has been published. For esters, kinetic mechanisms for compounds of lower molecular weights but similar to those found in typical biodiesel blendstocks also have been published. For multi-component surrogate fuel mixtures, recent work on modeling of these mixtures and comparisons to real diesel fuel is reviewed. Detailed chemical kinetic models for surrogate fuels are very large in size, so it is noteworthy that significant progress also has been made in improving the mechanism reduction tools that are needed to make these large models practicable in multi-dimensional reacting flow simulations of diesel combustion. Nevertheless, major research gaps remain. In the case of iso-alkanes, there are experiments and modeling work on only one of relevance to diesel: iso-cetane. Also, the iso-alkanes in diesel are lightly branched and no detailed chemical kinetic models or experimental investigations are available for such compounds. More components are needed to fill out the iso-alkane boiling point range. For the aromatic class of compounds, there has been little work for compounds in the boiling point range of diesel. Most of the new work has been on alkyl aromatics that are of the range C7-C9, below the C10-C20 range that is needed. For the chemical classes of cycloalkanes and esters, experiments and modeling on higher molecular weight components are warranted. Finally for multi-component surrogates needed to treat real diesel, the inclusion of higher molecular weight components is needed in models and experimental investigations.


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  Modeling Knock in Spark-Ignition Engines Using a G -equation Combustion Model Incorporating Detailed Chemical Kinetics


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  A UNIFAC-based Approach to Gasoline Droplet Evaporation and the Role of Oxygenates on PM Precursor Vaporization


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  NUMERICAL SIMULATION OF THE DROPLET-SURFACE IMPACT USING INTERFOAM A Thesis Presented By to Mechanical and Industrial Engineering The Department of __________________________ in partial fulfillment of the requirements for the degree of Master of Science i


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  With the increasing public interest in energy supply and the environment, attention has focused on the development of ecological and efficient combustion technologies. One of these technologies could be the use of natural gas as supplement fuel for diesel fuel in DI diesel engines. The great availability at attractive prices and the clean nature of combustion are the most important advantages of natural gas compared to conventional diesel fuel. In the present work are given theoretical and experimental results for the combustion mechanism of natural gas in a compression ignition environment, with special emphasis on the combined heat release rate of natural gas and diesel fuel, the duration of combustion and the ignition delay period. Results are also provided for the formation history of pollutants inside the combustion chamber of a DI diesel engine operating in dual fuel mode (with natural gas fuelling). The model used is a two - zone phenomenological one describing the combustion mechanisms of natural gas and diesel fuel. Natural gas is ignited from the diesel fuel and the existence of a flame front is considered to describe its combustion rate. The experimental investigation was conducted on a single cylinder DI diesel engine properly modified to operate under dual fuel conditions using natural gas as supplementary fuel. The experimental results seem to be in good agreement with the theoretical ones, obtained from the simulation model. Comparing the results under normal diesel and dual fuel operation a serious effect of the presence of natural gas on exhaust emissions and main combustion characteristics is observed. As far as the exhaust emissions are concerned, the presence of gaseous fuel affects positively (reduction) the values of NO and Soot. On the contrary dual fuel operation has a negative effect on CO emissions. Concerning the combustion analysis of dual fuel operation, heat release rate is affected seriously by the presence of natural gas in the combustion chamber.Compared to normal diesel operation, the increase of natural gas quantity results to a decrease of the percentage of heat released during premixed combustion period while ignition delay increases. Combustion duration is higher under dual fuel operation at low load, but with the increase of load the difference is decreased and it becomes even lower compared to normal diesel operation at high load.


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  The near-nozzle spray development of a typical fouled gasoline direct injection (GDI) injector was investigated. The fouled injector had been used in a stratified-charge combustion GDI engine and showed typical characteristics, such as accumulated deposits inside and around the nozzles and a reduced flow rate of 2.9–5.7%. Back-illumination and Mie-scattering methods were employed in spray experiments, in conjunction with a high speed camera and a macro lens, to assess the near-nozzle spray behaviors. The experimental results show that at all injection pressures tested, the interaction between deposits and spray led to several poor spray behaviors during the full injection evolution, including spray distortion, residual fuel storage in the nozzles and deposits layer, liquid splashing, the formation of ligament and large droplets and tip wetting/dripping. These effects all may result in high soot emissions. The after-injection stage of the fouled injector produced more liquid ligaments than that of the new injector. It was also found that high injection pressures did not improve atomization during after-injection, nor reduce the amounts of ligaments and droplet clusters beyond the main spray boundary. The plume width and projected spray area of a single nozzle in the fouled injector were decreased by 5–7% and 17–20%, respectively, due to fuel flow losses. The delays in the start of injection and end of injection were approximately 20 μs and 30–40 μs, respectively.


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  A formulation representing multicomponent-fuel (MC-fuel) composition as a probability distribution function (PDF) depending on the molar mass is used to construct a model of a large number of MC-fuel drops evaporating in a gas flow, so as to assess the extent of fuel specificity on the vapor composition. The PDF is a combination of two Gamma PDFs, which was previously shown to duplicate the behavior of a fuel composed of many species during single drop evaporation. The conservation equations are Eulerian for the flow and Lagrangian for the physical drops, all of which are individually followed. The gas conservation equations for mass, momentum, species, and energy are complemented by differential conservation equations for the first four moments of the gas-composition PDF; all coupled to the perfect gas equation of state. Source terms in all conservation equations couple the gas phase to the drops. The drop conservation equations for mass, position, momentum, and energy are complemented by differential equations for four moments of the liquid-composition PDF. The simulations are performed for a three-dimensional mixing layer whose lower stream is initially laden with drops. Initial perturbations excite the layer to promote the double pairing of its four initial spanwise vortices to an ultimate vortex. The drop temperature is initially lower than that of the surrounding gas, initiating drop heating and evaporation. The results focus on both evolution and the state of the drops and gas when layers reach a momentum-thickness maximum past the double vortex pairing; particular emphasis is on the gas composition. Comparisons between simulations with n-decane, diesel, and three kerosenes show that at same initial Reynolds number and Stokes number distribution, a single-component fuel cannot represent MC fuels. Substantial differences among the MC-fuel vapor composition indicate that fuel specificity must be captured for the prediction of combustion.


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  Reaction Mechanism Generator (RMG) constructs kinetic models composed of elementary chemical reaction steps using a general understanding of how molecules react. Species thermochemistry is estimated through Benson group additivity and reaction rate coefficients are estimated using a database of known rate rules and reaction templates. At its core, RMG relies on two fundamental data structures: graphs and trees. Graphs are used to represent chemical structures, and trees are used to represent thermodynamic and kinetic data. Models are generated using a rate-based algorithm which excludes species from the model based on reaction fluxes. RMG can generate reaction mechanisms for species involving carbon, hydrogen, oxygen, sulfur, and nitrogen. It also has capabilities for estimating transport and solvation properties, and it automatically computes pressure-dependent rate coefficients and identifies chemically-activated reaction paths. RMG is an object-oriented program written in Python, which provides a stable, robust programming architecture for developing an extensible and modular code base with a large suite of unit tests. Computationally intensive functions are cythonized for speed improvements. Program summary Program title: RMG Catalogue identifier: AEZW-v1-0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEZW-v1-0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT/X11 License No. of lines in distributed program, including test data, etc.: 958681 No. of bytes in distributed program, including test data, etc.: 9495441 Distribution format: tar.gz Programming language: Python. Computer: Windows, Ubuntu, and Mac OS computers with relevant compilers. Operating system: Unix/Linux/Windows. RAM: 1 GB minimum, 16 GB or more for larger simulations Classification: 16.12. External routines: RDKit, Open Babel, DASSL, DASPK, DQED, NumPy, SciPy Nature of problem: Automatic generation of chemical kinetic mechanisms for molecules containing C, H, O, S, and N. Solution method: Rate-based algorithm adds most important species and reactions to a model, with rate constants derived from rate rules and other parameters estimated via group additivity methods. Additional comments: The RMG software package also includes CanTherm, a tool for computing the thermodynamic properties of chemical species and both high-pressure-limit and pressure-dependent rate coefficients for chemical reactions using results from quantum chemical calculations. CanTherm is compatible with a variety of ab initio quantum chemistry software programs, including but not limited to Gaussian, MOPAC, QChem, and MOLPRO. Running time: From 30 s for the simplest molecules, to up to several weeks, depending on the size of the molecule and the conditions of the reaction system chosen.


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  Open cycle CFD investigation of SI engine fueled with hydrogen/methane blends using detailed kinetic mechanism


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  Enhanced aneurysmal flow diversion using a dynamic push-pull technique: An experimental and modeling study


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  BACKGROUND AND PURPOSE: Neurovascular flow diverters are flexible, braided stent-meshes for intracranial aneurysm treatment. We applied the dynamic push-pull technique to manipulate the flow-diverter mesh density at the aneurysm orifice to maximize flow diversion. This study investigated the hemodynamic impact of the dynamic push-pull technique on patient-specific aneurysms by using the developed high-fidelity virtual-stenting computational modeling technique combined with computational fluid dynamics. MATERIALS AND METHODS: We deployed 2 Pipeline Embolization Devices into 2 identical sidewall anterior cerebral artery aneurysm phantoms by using the dynamic push-pull technique with different delivery-wire advancements. We then numerically simulated these deployment processes and validated the simulated mesh geometry. Computational fluid dynamics analysis was performed to evaluate detailed hemodynamic changes by deployed flow diverters in the sidewall aneurysm and a fusiform basilar trunk aneurysm (deployments implemented previously). Images of manipulated flow diverter mesh from sample clinical cases were also evaluated. RESULTS: The flow diverters deployed in silico accurately replicated in vitro geometries. Increased delivery wire advancement (21 versus 11 mm) by using a dynamic push-pull technique produced a higher mesh compaction at the aneurysm orifice (50% metal coverage versus 36%), which led to more effective aneurysmal inflow reduction (62% versus 50% in the sidewall aneurysm; 57% versus 36% in the fusiform aneurysm). The dynamic push-pull technique also caused relatively lower metal coverage along the parent vessel due to elongation of the flow diverter. High and low mesh compactions were also achieved for 2 real patients by using the dynamic push-pull technique. CONCLUSIONS: The described dynamic push-pull technique increases metal coverage of pure braided flow diverters over the aneurysm orifice, thereby enhancing the intended flow diversion, while reducing metal coverage along the parent vessel to prevent flow reduction in nearby perforators.


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  Multidimensional Simulation of the Influence of Fuel Mixture Composition and Injection Timing in Gasoline-Diesel Dual-Fuel Applications


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  Homogeneous charge compression ignition (HCCI) combustion is considered to be an attractive alternative to traditional internal combustion engine operation because of its extremely low levels of pollutant emissions. However, there are several difficulties that must be overcome for HCCI practical use, such as difficult ignition timing controllability. Indeed, too early or too late ignition can occur with obvious drawbacks. In addition, the increase in cyclic variation caused by the ignition timing uncertainty can lead to uneven engine operation. As a way to solve the combustion phasing control problem, dual-fuel combustion has been proposed. It consists of a diesel pilot injection used to ignite a pre-mixture of gasoline (or other high octane fuel) and air. Although dual-fuel combustion is an attractive way to achieve controllable HCCI operation, few studies are available to help the understanding of its in-cylinder combustion behavior. In this paper, numerical simulations of dual-fuel combustion processes are presented. An implemented version of the multi-dimensional CFD KIVA3V code was used for the study. This version incorporates various advanced sub-models, including the G-equation flame propagation model coupled with CHEMKIN. The influence of injection timing and mixture composition on emission production, as well as on combustion pressure and on heat release rate has been analyzed with two different multi-hole injectors (six and eight holes). Four combustion strategies were compared, and pressure, heat release rate, temperature and emissions results are provided. As expected, decreasing the amount of diesel fuel injected, combustion behavior becomes closer to HCCI combustion, especially with the eight-hole injector. An effective ignition controllability has been obtained with very low percentages of injected diesel fuel for the whole set of considered injection timings.


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  Review on the Effects of Dual-Fuel Operation, Using Diesel and Gaseous Fuels, on Emissions and Performance


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  Combustion characteristics of natural gas and dimethyl ether (DME) mixture in a homogeneous charge compression ignition (HCCI) engine were studied numerically. Detailed chemical kinetics with 83 species and 360 reactions was used with an engine CFD code to simulate the combustion process. Operating conditions with different fuel compositions were simulated. Combustion, nitrogen oxides emissions and effects of fuel compositions on engine operating limits were well predicted by the present model. Chemical kinetics analysis indicated that ignition was achieved by DME oxidation which, in turn, induced combustion of natural gas. Low-temperature heat release is more pronounced as the amount of DME increases. Engine operations become unstable as the excess air ratio of natural gas is reduced near 2. The model also captures the HCCI features of low-combustion temperature and low-nitrogen oxides emissions for the alternative fuels used in this study.


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  http://www.sciencedirect.com/science/article/pii/S001623610600456X{\%}5Cnhttp://ac.els-cdn.com/S001623610600456X/1-s2.0-S001623610600456X-main.pdf?{\_}tid=a8ecf33c-1c6e-11e5-8431-00000aab0f27{\&}acdnat=1435369911{\_}ac9616da206cf9dda2b40cad92b4df83


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  A reduced chemistry model for multiple gasoline-ethanol surrogates by a Jacobian-aided DRGEP approach


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  Optimization of spray break-up CFD simulations by combining Σ-Y Eulerian atomization model with a response surface methodology under diesel engine-like conditions (ECN Spray A)


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  This work evaluates the performance of the Σ-Y Eulerian atomization model at reproducing the internal structure of a diesel spray with a special focus on Sauter Mean Diameter (SMD) predictions. Modeling results have been compared to x-ray radiography measurements [21,24,38] which provided unique data within dense spray region. The first step corresponds to accurately reproduce the large scale spray dispersion. Among different RANS turbulence models, the standard k-ϵ with the round jet corrected C1ϵvalue (1.60), has shown the best performance, as shown in [12]. Then, the study is devoted to the application and optimization of the predicted interphase surface density (Σ). In this work, a combination of CFD modeling and the statistical Design of Experiments (DOE) technique known as Response Surface Method (RSM) is applied in order to improve Sauter Mean Diameter (SMD) predictions from Σ equation compared to experimental measurements. In the investigation, two different optimizations are conducted for the three modeling parameters involved in the equation, following a Central Composite Design (CCD), leading to 15 simulations for each one. After that, both optimum sets of values are validated to assure the accuracy of the method and it is decided the best choice. Finally, different injection and ambient conditions are simulated, with those selected values, providing a remarkable improvement in the modeling performance.


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  CFD for Evaluation and Treatment Planning of Aneurysms: Review of Proposed Clinical Uses and Their Challenges


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  Computational fluid dynamics (CFD) has been used for several years to identify mechanical risk factors associated with aneurysmal evolution and rupture as well as to understand flow characteristics before and after surgical treatments in order to help the clinical decision making process. We used the keywords, "CFD" and "aneurysms" to search recent publications since about 2000, and categorized them into (i) studies of rupture risk factors and (ii) investigations of pre- and post-evaluations of surgical treatment with devices like coils and flow diverters (FD). This search enables us to examine the current status of CFD as a clinical tool and to determine if CFD can potentially become an important part of the routine clinical practice for the evaluation and treatment of aneurysms in near future. According to previous reports, it has been argued that CFD has become a quite robust non-invasive tool for the evaluation of surgical devices, especially in the early stages of device design and it has also been applied successfully to the study of rupture risk assessment. However, we find that due to the large number of pre-processing inputs further efforts of validation and reproducibility of CFD with larger clinical datasets are still essential to identify standardized mechanical risk factors. As a result, we identify the following needs to have a robust CFD tool for clinical use: (i) more reliability tests through validation studies, (ii) analyses of larger generalized clinical datasets to find converging universal risk parameters, (iii) fluid structure interaction (FSI) analyses to better understand the detailed vascular remodeling processes associated with aneurysm growth, evolution and rupture, and (iv) better coordinated and organized communications and collaborations between engineers and clinicians.


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  Experimental investigation of effects of super high injection pressure on diesel spray and induced shock waves characteristics


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  Modern diesel engines employ higher injection pressure in the common-rail injection system that utilizes high-speed fuel jet to achieve rapid fuel-air mixing for spray atomization improvement. However, the spray characteristics under super high pressure are not well understood. To provide more information on spray characteristics, both the macro- and micro-characteristics of spray have been investigated under super high pressures (up to 300 MPa) via an experimental method. The spray penetration and spray cone angle were measured using a high speed camera and the microscopic characteristic of Sauter mean diameter (SMD) was obtained via Malvern Spray Tec to analyze the influence of super high injection pressure on diesel spray atomization. Induced shock waves were captured using a Schlieren system when the spray tip velocity was greater than the local sound velocity accompanied by diesel spray. The results obtained show that higher injection pressures lead to larger spray velocities and a smaller shock wave angle if it exists, with connection between spray and shock waves, and generates a smaller SMD with less decreasing amplitude. Additionally, two different types of leading shock waves—bow and oblique shock wave appeared sequentially with increasing injection pressure.


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  Efficincy and Emission Characteristics of Partially Premixed Dual-Fuel Combustion by Co-Direct Injection of NG and Diesel Fuel (DI2)-Part 2


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  The status of direct numerical simulation of multiphase flows with phase change is discussed, with particular emphasis on the formation of microstructure during solidification, in the presence of flow, and boiling. A number of methods have recently been developed to simulate these problems, mostly using the “one-fluid” approach, where one set of governing equations is used for both phases. Results for both problems, using a combined finite volume/front tracking method are shown.


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  http://ac.els-cdn.com/S0045794904004158/1-s2.0-S0045794904004158-main.pdf?{\_}tid=626344da-166e-11e5-ae82-00000aacb35e{\&}acdnat=1434710085{\_}b111c54e7d89d6e383e4e722c66f1ba2


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  Performance, Gaseous and Particle Emissions of a Small Compression Ignition Engine Operating in Diesel/Methane Dual Fuel Mode


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  Autoignition of trans -Decalin , a Diesel Surrogate Compound : Rapid Compression Machine Experiments and Chemical Kinetic Modeling


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  An experimental and numerical investigation of premixed syngas combustion dynamics in mesoscale channels with controlled wall temperature profiles


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  The dynamics in H2/CO/O2/N2 premixed combustion was investigated experimentally and numerically in a 7-mm height mesoscale channel at atmospheric pressure, fuel-lean equivalence ratios 0.25-0.42, volumetric CO:H2 ratios 1:1 to 20:1, and wall temperatures 550-1320 K. Experiments were performed in an optically-accessible channel-flow reactor and involved high-speed (up to 1 kHz) planar laser induced fluorescence (LIF) of the OH radical and thermocouple measurements of the upper and lower channel wall temperatures. Simulations were carried out with a transient 2-D code, which included an elementary syngas reaction mechanism and detailed species transport. Demarcation of the experimentally-observed parameter space separating stationary and oscillatory combustion modes indicated that the former were favored at the higher wall temperatures and higher CO:H2 volumetric ratios, while the latter predominately appeared at the lower wall temperatures and lower CO:H2 ratios. The numerical model reproduced very well all stationary combustion modes, which included V-shaped and asymmetric (upper or lower) modes, in terms of flame shapes and flame anchoring positions. Simulations of the oscillatory flames, which appeared in the form of ignition/extinction events of varying spatial extents, were very sensitive to the specific boundary conditions and reproduced qualitatively the flame topology, the ignition sequence (including the periodic reversion from upper-asymmetric to lower-asymmetric flame propagation), and the range of measured oscillation frequencies. Predicted emissions in the stationary modes ranged from 25 to 94 ppm-mass for CO and from 0.1 to 0.3 ppm-mass for H2, while in the oscillatory modes incomplete combustion of both CO and H2 was attested during their oscillation period.


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  Effect of split fuel injection and EGR on NOx and PM emission reduction in a low temperature combustion (LTC) mode diesel engine


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  In this study, an advanced combustion concept ‘premixed charge compression ignition' (PCCI) has been explored for application in diesel engines. PCCI combustion is a single-stage combustion process, in which a large fraction of fuel burns in premixed combustion phase resulting in relatively lower in-cylinder temperatures compared to compression ignition (CI) combustion. However at high loads, PCCI combustion results in severe knocking and higher oxides of nitrogen (NOx) emissions. This limits the applicability of this combustion concept up to medium engine loads. This limitation of PCCI combustion can be resolved by altering in-cylinder pressure-temperature history at the time of fuel injection. This can also be resolved by deploying suitable split fuel injection strategy and exhaust gas recirculation (EGR), which control combustion events such as start of combustion (SoC) and combustion phasing, leading to lower knocking and NOx emissions. To investigate the effects of various split injection strategies and EGR on PCCI combustion, engine experiments were conducted at different start of main injection (SoMI) timings (12, 16, 20 and 24ï¿½ bTDC), start of pilot injection (SoPI) timings (30, 35 and 40ï¿½ bTDC) and EGR rates (0, 15 and 30%). This study also included detailed particulate characterization such as particulate number-size distribution using an engine exhaust particle sizer (EEPS) and particulate bound trace metal analysis by inductively coupled plasma-optical emission spectrophotometry (ICP-OES). PCCI combustion was found to be superior at 35ï¿½ bTDC SoPI timing and 15% EGR. At retarded SoPI timing (30ï¿½ bTDC), PCCI combustion resulted in slightly higher NOx and particulate emissions, however at too advanced SoPI timing (40ï¿½ bTDC), PCCI combustion showed relatively inferior engine performance. Application of EGR improved PCCI combustion and emission characteristics, however at high EGR, PCCI combustion resulted in inferior engine performance due to reduction in bulk in-cylinder temperatures. Overall, this study showed that PCCI combustion stability, knocking and NOx emissions can be optimized by selecting suitable combination of SoMI and SoPI timings, and EGR rate.


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  SAE TECHNICAL Rate of Heat Release Prediction for Direct Injection Diesel Engines Based on Purely Mixing Controlled Combustion


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  International Journal of Thermal Sciences Turbulent film condensation in the presence of non-condensable gases over a horizontal tube


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  Fuel spray impingement on piston surfaces is a concern because it can cause particulate exhaust emissions from gasoline direct injection (GDI) engine. Transient heat transfer plays an important role that directly influences liquid film evaporation and its lifetime. In this paper, the effects of injection temperature, injection pressure, piston temperature and impact distance on n-pentane spray impingement heat transfer were fully examined. Results showed that increasing the piston temperature could increase the rate of heat transfer with a larger surface temperature reduction and a higher heat flux, which led to a shorter liquid film lifetime on the piston surface. Increasing the fuel injection temperature helped to improve atomization of the fuel spray, reduce the penetration distance and mitigate impact, which in turn led to reduced surface cooling and less liquid film on the piston surface. A decrease in impact distance and an increase in injection pressure both caused an increase in surface temperature reduction and heat flux but a decrease in the liquid film residence time. The dimensionless heat flux in terms of Biot and Fourier numbers presented a high similarity during the rapid cooling stage. A dimensionless correlation was formed to quantify this fast time-varying heat transfer behaviour.


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  The present work is aimed at development of an experimentally verified computational model based on OpenFOAM for the simu- lations of gas-liquid boiling flows. The open source CFD code OpenFOAM was developed further to include k-E turbulence model, different inter-phase coupling forces and energy transport accompanied with phase change. The most commonly used wall heat flux partitioning model, proposed by Kurul and Podowski 1, was implemented in the OpenFOAM to simulate two-phase boiling. The predicted axial and radial vapor volume fraction distribution, liquid temperature distribution and wall temperature profiles were compared with the DEBORA measurements 2. A good agreement between the predictions and measurements was observed. The experimentally verified model was used to understand the effects of various interfacial closures e.g. lift force, turbulent dispersion force and wall force, on the vapor volume fraction distribution. The effects of bubble induced turbulence and nucleation site density on the hydrodynamics of the gas-liquid boiling flows were studied. Such an experimentally verified open source CFD code will be useful to simulate boiling under different regimes and in complex geometries.


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  Premixed flames in the thin and broken reaction zones regime exhibit strong non-linear turbulence–chemistry interactions and are hence challenging to model. In the present study, a direct numerical simulation (DNS) database for a hydrogen–air flame is used to understand the effect of turbulence–chemistry interactions on the flame speed. To this end, statistics of the local flame front displacement speed are investigated and the roles of flame stretch due to curvature and strain are analyzed. The local flame speed is found to be on average around 30% lower than the laminar burning velocity, which is shown to be a consequence of strain. Strain effects are then modeled by a recently proposed strained flamelet model, which is validated a priori against the DNS in terms of the flame speed and the reaction source term. The strained flamelet model leads to a moderate improvement of the flame speed prediction and is able to reproduce the decrease of the local flame speed. Moreover, it significantly improves the source term closure, which is demonstrated on the basis of the optimal estimator approach and, overall, describes the investigated DNS flame with very good accuracy.


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  Experimental study of dual fuel engine performance using variable LPG composition and engine parameters


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  The present work investigates experimentally the effect of LPG fuel with different composition and engine parameters on the performance of a dual compression engine. Five different blends of LPG fuels are used with Propane to Butane volume ratio of 100:0, 70:30, 55:45, 25:75, and 0:100. A single cylinder, naturally aspirated, four strokes, indirectly injected, water cooled modified Ricardo E6 engine, is used in this study. The study is carried out by measuring the cylinder pressure, engine load, engine speed, crank angle, and the fuel's flow rate. The engine performance under variable LPG fuel composition, engine load, pilot fuel injection timing, compression ratio, pilot fuel mass and engine speed, are estimated by comparing the following engine parameters: the cylinder maximum pressure, the indicated mean effective pressure, the maximum rate of pressure rise, and the thermal efficiency. The experimental data indicates that the engine parameters are playing a major role on the engine's performance. Different LPG fuel composition did not show a major effect on the engine efficiency but directly impacted the levels of generated combustion noise. ?? 2013 Elsevier Ltd. All rights reserved.


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  An experimental investigation of effect on diesel engine performance and exhaust emissions of addition at dual fuel mode of hydrogen


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  Abstract The dissociation of cyclopentane has been investigated in a diaphragmless shock tube with laser schlieren densitometry at nominal post-shock pressures, P2, of 35, 70, 150, and 300 Torr and temperatures, T2, of 1472–2074 K. These are the first experimental data reported in the high temperature fall-off regime for cyclopentane. The experimental density gradients were simulated using a chemical-kinetic model with good agreement between simulations and experiments. Rate coefficients for dissociation of cyclopentane were obtained and mechanistic details were elucidated. An {RRKM} model was developed to best fit the experimental results, and the rate coefficients calculated are: k1(35 Torr) = (7.93 ± 3.96) × 1084 T−19.815 exp(−64366/T) s−1, k1(70 Torr) = (4.79 ± 2.39) × 1077 T−17.705 exp(−62316/T) s−1, k1(150 Torr) = (2.42 ± 1.21) × 1069 T−15.295 exp(−59862/T) s−1, k1 (300 Torr) = (4.66 ± 2.33) × 1061 T−13.065 exp(−57493/T) s−1, and k1∞ = (1.69 ± 0.85) × 1016 T−0.005 exp(−42983/T). Results show that cyclopentane dissociation is similar to that of cyclohexane, and involves formation of a biradical intermediate. The high-pressure limit rates for cyclopentane dissociation are also compared with previous results in the literature and show good agreement with a study by Tsang (1978) [21].


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  The cold start issue has been a problem in diesel engines. Thus, in the present research, the diesel fuel flow and macroscopic spray characteristics over a wide fuel temperature range were investigated to provide valuable insights for solving the cold start problem. An injection system including a common-rail and a fuel supplier was designed to control the fuel temperature from 243 K to 313 K. For the fuel flow characteristics, the results showed that the injection quantity decreased by 50% as the fuel temperature decreased from 313 K to 243 K under the same energizing time. It was also confirmed that the real start of injection timing was retarded as the fuel temperature decreased. The reason is that increased fuel viscosity disturbed the injector needle motion and fuel flow in the nozzle. The spray test was performed under the simulated cold start condition using a constant-volume combustion chamber (CVCC). For the macroscopic spray characteristics, the liquid-phase fuel penetration increased and the spray angle decreased with cold fuel due to attenuated fuel evaporation process and interaction with ambient gas. These results could cause poor air-fuel mixing process under the cold starting.


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  Macroscopic spray characteristics of kerosene and diesel based on two different piezoelectric and solenoid injectors


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  In this study, the behaviours like injection momentum and spray characteristics for piezoelectric and solenoid injectors were compared. With piezoelectric injector, the macroscopic spray characteristics of kerosene and diesel were investigated. The characteristic like spray penetration, spray velocity, spray angle and air entrainment were used to understand the fuel spray behaviours. The result shows that the piezoelectric injector has the advantage of faster injection response and needle opening than the conventional solenoid injector, which will enable precise and rapid injection control and must be beneficial to air-fuel mixing before ignition in a real engine. Due to the lower value of viscosity in kerosene, the injection durations for kerosene are longer than diesel. Also longer injection intervals will be needed for kerosene to realize multiple injections. Kerosene has shorter spray penetration and lower spray velocity compared with diesel, while the spray angle of kerosene is larger than diesel. Entrained air mass is a typical trade-off result of comprehensive influence of spray penetration, spray angle and charge density. Kerosene sprays get more entrained air than diesel, which means the usage of kerosene has advantage in fuel-air mixing.


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  Experimental investigation into the effects of two-stage injection on fuel injection quantity, combustion and emissions in a high-speed optical common rail diesel engine


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  Diesel combustion and the formation of pollutants are directly influenced by the spatial and temporal distributions of the fuel within the combustion chamber of an internal combustion engine. The requirements for more efficient and responsive diesel engines have led to the introduction and implementation of multiple injection strategies. However, the effects of such injection modes on the hydraulic systems, such as the high pressure pipes and fuel injectors, must be thoroughly examined and compensated for. The objective of this study was to investigate the effects of fuel injection equipment characterisation and optimisation on diesel combustion and emissions with two-stage fuel injection. The fuel injection system was characterised and optimised through the measurement of the fuel injection rate and quantity, in particular, the interaction between the two injection events was quantified and compensated for. The effects of twin and variable split two-stage injection and dwell angle on diesel combustion and emissions were investigated in a high-speed direct injection single-cylinder optical diesel engine using heat release analysis and high-speed fuel spray and combustion visualisation technique. The results indicated that two-stage injection has the potential for simultaneous reduction of NOx and soot emissions. Nevertheless, the studied two-stage strategies resulted in higher soot emission, mainly due to the interaction between two consecutive fuel injection events, whereby the fuel sprays during the second injection were injected into burning regions, generating fuel-rich combustion. In addition, the variable two-stage strategies produced high levels of uHC emission in comparison to single and twin split injection cases. This was mainly attributed to firstly greater fuel quantity injected during the second injection and secondly poor mixing and air utilisation during the second fuel injection event. © 2013 Elsevier Ltd. All rights reserved.


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  Spark Ignited Direct Injection Natural Gas Combustion in a Heavy Duty Single Cylinder Test Engine - Start of Injection and Spark Timing Effects


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  Chemical processes in many fields of science and technology, including combustion, atmospheric chemistry, environmental modelling, process engineering, and systems biology, can be described by detailed reaction mechanisms consisting of numerous reaction steps. This book describes methods for the analysis of reaction mechanisms that are applicable in all these fields. Topics addressed include: how sensitivity and uncertainty analyses allow the calculation of the overall uncertainty of simulation results and the identification of the most important input parameters, the ways in which mechanisms can be reduced without losing important kinetic and dynamic detail, and the application of reduced models for more accurate engineering optimizations. This monograph is invaluable for researchers and engineers dealing with detailed reaction mechanisms, but is also useful for graduate students of related courses in chemistry, mechanical engineering, energy and environmental science and biology.


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  The maximum liquid phase penetration and evaporation behavior was$\backslash$ninvestigated by using simultaneous measurement for mie-scattered$\backslash$nlight images and shadowgraph ones. The objective of this study was$\backslash$nto analyze effect of variant parameters and fuel properties on evaporation$\backslash$nbehavior, and to investigate liquid phase penetration for the single-$\backslash$nand multi-component fuels. The experiments were conducted in a constant-volume$\backslash$nvessel with optical access. Fuel was injected into the vessel with$\backslash$nelectronically controlled common rail injector. It was observed that:$\backslash$nliquid phase length is influenced by fuel properties. High-boiling$\backslash$npoint fuel within the multi-component fuel controls liquid phase$\backslash$nlength. 2006 Elsevier Ltd. All rights reserved.


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  In this study, it was applied to the diesel-water emulsified (DE) fuel that carried out the experiment for the characteristic of sprat using diesel water emulsified fuel in a diesel engine, and the possibility of its application to conventional diesel engines was evaluated from the fundamental characteristics of diesel-water emulsified fuel. According to the results of the spray characteristics such as spray penetration and spray distribution were measured in the experiment, and then analyzed through digital image processing. The DEs were applied to actual diesel engines and their combustion, emission, and fuel consumption characteristics were compared with those of diesel. The results showed that the experiments were confirmed as the spray atomization characteristics at the various emulsified fuels.


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  Microscopic and macroscopic characterization of spray impingement under flash boiling conditions with the application of split injection strategy


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  Microscopic and macroscopic impingement characteristics of a single jet were investigated under various flash boiling conditions. The influences of split injection strategy and the related interaction between split injections were studied. The fuel concentration distribution during the impingement process was also quantified. It was found that non-flash boiling condition lead to large secondary droplets and ligaments, resulting in a large amount of liquid fuel deposited on the impact surface. The boosted flash boiling could effectively reduce the sizes of primary droplets and secondary droplets and the resultant deposited fuel. The employment of split injection strategy could further decrease the deposited fuel. The second split injection built up the fuel film more quickly than the first injection due to the existence of the built fuel film by the first injection, however, increasing flash boiling strength decreased the building-up rate by improving dispersion and evaporation. In addition, the concentration of the deposited fuel on the surface could effectively be reduced by enhanced flash boiling and the lifetime of dense fuel was shortened by increasing dwell interval between split injections.


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  Engine-out emissions (NOx and soot) have led to serious air pollution problems, and consequently, increasingly stringent emission norms. In order to decrease the emissions and improve the combustion performance of diesel engines, the effect of split injections with swirl (swirl rate of 0 and 1) was experimentally researched, and the mechanism of the fuel/air mixture of split injections with swirl (swirl rate of 0.5–2.5) was numerically researched in this study. The experimental research was carried out on a modified 1132Z single cylinder diesel engine, equipped with an endoscope system. A two-color method was applied to record flame temperature distribution and KL factor. The experimental results indicate that the flame observed using split injections with swirl rotated obviously. Split injections with swirl had a positive influence on improving the fuel/air mixture, accelerating combustion progress and shortening combustion duration. The combustion duration decreased at swirl rate of 1, with a reduction in the range of 19.5–25.7% at various pilot quantities. In addition, brake-specific fuel consumption (BSFC) and soot emission were reduced. BSFC was lower at swirl rate of 1 than that at swirl rate of 0, with a reduction in the range of 1.1–2.01 g/(kW h)−1. For KL factor at 12°CA ATDC, it was also observed that at 12°CA ATDC, the KL factor was lower at swirl rate of 1 than that at swirl rate of 0, with a reduction of 34.9%. Related numerical research on split injections with swirl was performed, and the results show that at a specific swirl, the main injection deviated from the pilot injection and entered the area between two sprays, enhancing the utilization of air in the chamber. In addition, the main combustion process accelerated due to the better thermal-atmosphere provided by the pilot injection, so that a better engine performance and lower soot concentration was achieved.


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  Study of air inlet preheating and EGR impacts for improving the operation of compression ignition engine running under dual fuel mode


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  One of the methods to achieve curtailment of diesel engine emissions is the conversion of conventional diesel engines to using natural gas as a supplement to normal diesel fuel. In this type of engines most of the engine power output is provided by the gaseous fuel, while a pilot amount of diesel fuel is used as ignition source of the gaseous fuel-air mixture. However dual fuel operating mode, in comparison to conventional diesel one, suffers from low brake thermal efficiency and high carbon monoxide emissions. By applying a two-zone phenomenological model, the present work studies the effect of air inlet preheating and exhaust gas recirculation on the performance and exhaust emissions of a pilot ignited dual fuel diesel engine. The main objectives are to record and comparatively evaluate the relative impact that each one of the above mentioned parameters has on the engine performance characteristics and emitted pollutants. Moreover, it deals with the determination of an optimum combination between the examined parameters, so that probable undesirable effects on engine performance characteristics are avoided. By comparing the investigation results, it is revealed that the simultaneous increase of both parameters examined could be a promising solution to improving engine efficiency (increase up to 5%) and reducing CO emissions (decrease up to 10%) from a pilot ignited dual fuel diesel engine, without imparting any serious problem to engine operational lifetime. The conclusions from the study may be proved valuable for the application of this technological solution to existing diesel engines. ?? 2013 Published by Elsevier Ltd.


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  A model is described for the prediction of the onset of autoignition and knock in compression ignition engines of the dual fuel type. The associated variations with time of performance parameters such as the energy release rate, cylinder pressure and charge temperature, power output and species concentrations can also be obtained. This is achieved through modelling in detail the chemical reaction rates of the gaseous fuel during compression and subsequently during diesel fuel pilot ignition and combustion. A comprehensive reaction scheme involving 105 reaction steps with 31 chemical species is employed for the purpose. The results are based mainly on methane or propane as the gaseous fuel while acounting for the contribution of pilot diesel fuel injection. Calculated data showed good general agreement with the corresponding experimental values.


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  Dual fuel engines are more attractive due to lower emission levels in comparison with conventional diesel engines particularly at full loads. But it is required to study dual fuel combustion process with more details at part loads due to the poor performance and high CO and UHC emissions at these conditions. In the present study, numerical modeling of OM-355 dual fuel (injection of diesel pilot fuel to premixed mixture of air and methane) engine has been performed by using KIVA-3V code at part and full loads. Sub-models of the code were modified to simulate the fuel spray atomization, combustion and pollutants emissions processes, accurately. Results indicate that in-cylinder pressure, heat release rate and exhaust emissions predictions are in good agreement with experiments at all loads. Results show that a lean premixed natural gas mixture is ignited slowly. The slow progress of combustion process at part load, leads the heat release to be drawn more toward the expansion stroke which causes incomplete combustion, and consequently high amounts of UHC and CO will be emitted. It is found that at part loads, areas that are influenced by diesel diffusion flames are ignited and premixed natural gas flame could not be propagated properly. Hence development of diesel diffusion flame is required to burn lean natural gas mixture. But at full load, in addition to the diesel diffusion flames, premixed natural gas flame could be propagated suitably. Also, at part load because of low gas temperature in the environment of diesel spray and low diesel fuel temperature, diesel liquid droplets evaporate lately which are far from injector nozzles. Hence, it causes diesel diffusion flame from spray of each injector nozzles to be developed distinctly. It can be deduced that the flame structure is affected by operating conditions. Finally the effect of increasing the diesel fuel quantity on improving methane combustion is studied. The studied strategy could help to improving natural gas combustion due to enlarge the size of diesel combustion region.


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  The Engine Combustion Network (ECN) Spray A target case corresponds to high-pressure liquid fuel injection in conditions relevant to diesel engines. Following the procedure by Wehrfritz et al. (2016), we utilize large-eddy simulation (LES) and flamelet generated manifold (FGM) methods to carry out an injection pressure sensitivity study for Spray A at 50, 100 and 150 MPa. Comparison with experiments is shown for both non-reacting and reacting conditions. Validation results in non-reacting conditions indicate relatively good agreement between the present LES and experimental data, with some deviation in mixture fraction radial profiles. In reacting conditions, the simulated flame lift-off length (FLOL) increases with injection pressure, deviating from the experiments by 4–14%. Respectively, the ignition delay time (IDT) decreases with increasing injection pressure and it is underpredicted in the simulations by 10–20%. Analysis of the underlying chemistry manifold implies that the observed discrepancies can be explained by the differences between experimental and computational mixing processes.


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  Development of an optimized chemical kinetic mechanism for homogeneous charge compression ignition combustion of a fuel blend of n -heptane and natural gas using a genetic algorithm


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  The reaction between methyl and hydroxyl radicals has been studied in reflected shock wave experiments using narrow-linewidth OH laser absorption. OH radicals were gen- erated by the rapid thermal decomposition of tert-butyl hydroperoxide. Two different species were used as CH3 radical precursors, azomethane and methyl iodide. The overall rate coeffi- cient of the CH3 + OH reaction was determined in the temperature range 1081–1426 K under conditions of chemical isolation. The experimental data are in good agreement with a recent theoretical study of the reaction. The decomposition of methanol to methyl and OH radicals was also investigated behind reflected shock waves. The current measurements are in good agreement with a recent experimental study and a master equation simulation. 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 488–495, 2008


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  A numerical model for the complete thermo-fluid-dynamic and phase-change transport processes of two-component hydrocarbon liquid droplets consisting of n-heptane, n-decane and mixture of the two in various compositions is presented and validated against experimental data. The Navier-Stokes equations are solved numerically together with the VOF methodology for tracking the droplet interface, using an adaptive local grid refinement technique. The energy and concentration equations inside the liquid and the gaseous phases for both liquid species and their vapor components are additionally solved, coupled together with a model predicting the local vaporization rate at the cells forming the interface between the liquid and the surrounding gas. The model is validated against experimental data available for droplets suspended on a small diameter pipe in a hot air environment under convective flow conditions; these refer to droplet's surface temperature and size regression with time. An extended investigation of the flow field is presented along with the temperature and concentration fields. The equilibrium position of droplets is estimated together with the deformation process of the droplet. Finally, extensive parametric studies are presented revealing the nature of multi-component droplet evaporation on the details of the flow, the temperature and concentration fields. © 2011 Elsevier Ltd All rights reserved.


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  Characteristics of non-evaporating, evaporating and burning sprays of hydrous ethanol diesel emulsified fuels


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  Utilization of hydrous ethanol in diesel engines is beneficial not only for reducing the exhaust pollutant emissions but also for improving the lifecycle fuel efficiency including both in engines and refineries. However, so far detailed investigations on spray combustion characteristics of hydrous ethanol diesel emulsified fuels are rarely reported, though this information is crucial in combustion system design for better application of these fuels in diesel engines. In this paper, emulsions of the 20 wt% water-containing ethanol and commercial diesel fuel with volume fraction of the hydrous ethanol varied from 10 to 30% were firstly developed. Then, the physicochemical properties including the mixture stability, density, kinematic viscosity, surface tension, distillation temperature, latent heat of evaporation, etc. were investigated. Finally, the characteristics of non-evaporating, evaporating and burning sprays under the various injection and ambient conditions were clarified with the common-rail fuel injection system and the high-temperature, high-pressure, constant-volume combustion vessel. The results reveal that the difference of the spray cone angle and tip penetration length under either the non-evaporating or evaporating conditions for various fuels are relatively small, while the maximum liquid penetration length in the evaporating spray increases drastically with increased addition of the hydrous ethanol in the emulsions. In the case of burning spray, the natural luminosity of the flame decreases remarkably with the hydrous ethanol increasing, indicating the soot reduction in the flame. This effect becomes more pronounced with the ambient oxygen concentration decreasing. The mechanism of the above phenomena is discussed in depth.


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  Evaluation of liquid fuel spray models for hybrid RANS/LES and DLES prediction of turbulent reactive flows


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  An evaluation of Lagrangian-based, discrete-phase models for multi-component liquid sprays encountered in the combustors of gas turbine engines is considered. In partic- ular, the spray modeling capabilities of the commercial software, ANSYS Fluent, was evaluated. Spray modeling was performed for various cold flow validation cases. These validation cases include a liquid jet in a cross-flow, an airblast atomizer, and a high shear fuel nozzle. Droplet properties including velocity and diameter were investigated and compared with previous experimental and numerical results. Different primary and secondary breakup models were evaluated in this thesis. The secondary breakup mod- els investigated include the Taylor analogy breakup (TAB) model, the wave model, the Kelvin-Helmholtz Rayleigh-Taylor model (KHRT), and the Stochastic secondary droplet (SSD) approach. The modeling of fuel sprays requires a proper treatment for the tur- bulence. Reynolds-averaged Navier-Stokes (RANS), large eddy simulation (LES), hybrid RANS/LES, and dynamic LES (DLES) were also considered for the turbulent flows in- volving sprays. The spray and turbulence models were evaluated using the available benchmark experimental data.


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  The Development and Validation of a Chemical Kinetic Model for Anisole , a Compound to Represent Biomass Pyrolysis Fuels


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  As known, the constant injection mass is a criterion for measuring the thermal efficiency of diesel engine. In this study, the effects of injection pressure on diesel free-spray characteristics have been investigated in the condition of constant injection mass. The experiment has been performed in a constant volume combustion chamber. A high pressure common-rail injector with a single-hole nozzle is used. High speed camera and Schlieren visualization set-up are used to capture the behaviors of liquid phase spray and vapor phase spray respectively. For liquid phase spray, the spray penetration length increases as injection time elapsed until the saturated liquid phase spray penetration length is reached. Higher injection pressure causes higher liquid phase spray penetration rate, but the effect of injection pressure on saturated liquid phase spray penetration length is negligible. In addition, the influence of injection pressure on liquid phase spray cone angle can be neglected. For vapor phase spray, the variation of vapor phase spray penetration length can be divided into nonlinear increase period and linear increase period. Higher injection pressure causes higher mean vapor phase spray penetration rate. And higher injection pressure causes higher value of maximum vapor phase spray cone angle. The pure vapor phase spray cone angles at the time of injection stop increase linearly as the injection pressures increase.


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  Impact of pilot diesel ignition mode on combustion and emissions characteristics of a diesel / natural gas dual fuel heavy-duty engine


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  The possibility of turbocharging into a natural gas homogeneous charge compression ignition (HCCI) engine is experimentally investigated. Experiments are performed using a naturally aspirated engine fitted with an external supercharger and a butterfly valve for back pressure control to simulate a turbocharger. The results indicate that the thermal efficiency can be improved by raising the engine compression ratio and lowering the boost pressure. At an engine compression ratio of 21 and turbocharging pressure of 0.19 MPa, the brake thermal efficiency reaches 43%, with NOx emissions of only 10 ppm or less. Finally, the performance of the engine fitted with a newly developed turbocharger is demonstrated. As a result, 43.3% brake thermal efficiency, 0.98 MPa brake mean effective pressure, and 13.8 ppm NOx emission have been realized. This value shows the possibility that a power generating efficiency of 40% at a power output of 50 kW could be achieved when applied to combined heat and power (CHP), even allowing for energy losses in the generator and the power inverter. For practical use, the ignition timing control, operation control, including how to start or load input and ensuring durability, remain to be investigated. To clarify these issues, we have initiated the endurance test for a newly developed 25 kW HCCI package, although the engine is not supercharged.


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  Near-nozzle microscopic characterization of diesel spray under cold start conditions with split injection strategy


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  Near-nozzle microscopic characteristics of diesel spray under room temperature (25 °C) and low temperature (-2 °C) were investigated by microscopic imaging technique. The primary breakup of winter diesel (WD) and rapeseed methyl ester (RME) sprays were investigated with single and split injection strategies. It was shown that increased viscosity and surface tension under low temperature lead to much poorer dispersion. Under low injection pressure with split injection strategy, the first split injection was unexpectedly severely affected by both temperature and dwell, with significant breakup characteristic differences when dwell varied. By contrast, the second split under low injection pressure tended to be affected only by temperature rather by dwell. High injection pressure considerably alleviated the breakup characteristic difference of the first split injection caused by temperature and dwell although the effects of fuel properties were still seen, leading to better fuel dispersion and more predictable spray characteristics. In addition, RME with higher viscosity and surface tension consistently presented much poorer dispersion quality compared with WD even under high injection pressure where the influence of fuel properties may be insignificant.


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  Spark Ignited Direct Injection Natural Gas Combustion in a Heavy Duty Single Cylinder Test Engine - AFR and EGR Dilution Effects


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  Towards improvement of natural gas-diesel dual fuel mode : An experimental investigation on performance and exhaust emissions


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  Homogeneous ignition of CH 4 / air and H 2 O and CO 2 -diluted CH 4 / O 2 mixtures over Pt ; an experimental and numerical investigation at pressures up to 16 bar


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  http://papers.sae.org/2006-01-0243/ http://scholar.google.com/scholar?q=intitle:2006-01-0243+Spark+Ignition+Engine+Combustion+Modeling+Using+a+Level+Set+Method+with+Detailed+Chemistry{\#}0


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  Two-stage split-injection strategies for partially premixed compression ignition (PPCI) combustion mode were investigated in a light duty 2.2 L four cylinder compression ignition engine fuelled with G50-Dieseline (50% ULG95 gasoline in EN590 diesel by volume). The investigation of two-stage split-injection has been focused on injection quantity-ratios and timings and it aims to achieve improved charge premixing and consequently reduce the oxides of nitrogen (NOx) and particulate matter (PM) emissions simultaneously. Other parameters affecting combustion process (e.g. compression ratio) were fixed to identify the individual effects of parameters under study on the combustion and emission characteristics by the Taguchi-DOE (design of experiment) analysis. The investigation was conducted for two load groups of 1.37 and 2.97 bar BMEP selected from the new European driving cycle (NEDC) at an engine speed of 1800 RPM. Optimum operating values of injection parameters for generating the minimum and maximum combustion and emission characteristics were identified. Furthermore, very early first injection-timings were investigated for 2.97 bar BMEP with the combustion phase of 50% accumulative heat release (AHR-50) fixed. Compared with the single-injection strategy, BSNOxwas reduced by approximately 39% to 59% through applying the two-stage split-injection. Accumulation particulate concentration as well as smoke number were reduced by approximately 90%. It is believed that with very early first-injection timings, fuel wall-impingement and over mixing may have resulted in lower combustion efficiency and thus BMEP drop. Consequently, the premixing process can reach a limit where the effect of required higher injected fuel quantity dominates combustion and emission characteristics. The two-stage split-injection developed in this study appears to be effective in improving the premixing process for PPCI combustion. © 2012 Elsevier Ltd. All rights reserved.


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  Grid-Convergent Spray Models for Internal Combustion Engine Computational Fluid Dynamics Simulations


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  Experimental and numerical investigation of the effect of H 2 enrichment on laminar methane – air flame thickness


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  Probability Density Function Modeling of Turbulence/Chemistry Interactions in Methane Flame Enrichment by Hydrogen


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  Abstract: The present investigation illustrates a computational study of the turbulent diffusion flame in a cylindrical burner that is confined by two coaxial jets (methane/hydrogen and air). This is to improve the reactive mixture, the reactants combustion and to reduce the concentration of carbon monoxide as pollutant chemical species. The coupled models LES/PDF are, hereby, used to surmount the turbulence/chemistry interaction in the transport equations of chemical species. The predicted mixture fraction, the progress variable, and the carbon monoxide mass fraction are selected to validate the coupled models with respect to the experimental references data. Furthermore, the same scalar parameters which are considered in the previous numerical validation are evaluated from different fuel compositions of the hydrogen and the methane percentage to supply the combustion chamber. The computed results are carried out by FLUENT-CFD; where, they prove that hydrogen addition reduces the carbon monoxide concentration in the combustion products and improves the reactants combustion caused by the rich mixture.


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  Impact of Cetane Number on Combustion of a Gasoline-Diesel Dual-Fuel Heavy-Duty Multi-Cylinder Engine


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  Dual-fuel combustion using liquid fuels with differing reactivity has been shown to achieve low-temperature combustion with moderate peak pressure rise rates, low soot and NOx emissions, and high indicated efficiency. Varying fractions of gasoline-type and diesel-type fuels enable operation across a range of low- and mid-load operating conditions. Expanding the operating range to cover the full operating range of a heavy-duty diesel engine, while maintaining the efficiency and emissions benefits, is a key objective. With dissimilar properties of the two utilized fuels lying at the heart of the dual-fuel concept, a tool for enabling this load range expansion is altering the properties of the two test fuels - this study focuses on altering the reactivity of the diesel fuel component. Tests were conducted on a 13L six-cylinder heavy-duty diesel engine modified to run dual-fuel combustion with port gasoline injection to supplement the direct diesel injection. A single diesel injection strategy was used across a range of operating points. Diesel fuels with varying cetane number were tested, including a ULSD certification fuel; a low cetane, low aromatics, high volatility fuel from the Fuels for Advanced Combustion Engines matrix (FACE #1); and a high cetane Fischer-Tropsch diesel fuel. Decreasing diesel fuel cetane number reduces overall mixture reactivity and extends the mixing time prior to onset of combustion, reducing soot emissions and shifting the overall operating window to a higher load range. Stable operation with high gasoline fractions across a wider load range is enabled by the high cetane fuel.


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  © 2017 Taylor & Francis. A numerical study on a high-pressure laminar counterflow diffusion flame is presented. Extinction limits are studied at pressures up to 100 atm for two cases: one with pure methane and the other for a diluted mixture of methane with 40% water vapor mass fraction. The fuel stream flows against pure oxygen on both cases. Solutions for the 1D ideal-gas model and for a real-gas model are provided with both detailed and reduced chemical kinetics, and are compared against real-gas results from the literature. Previous studies increased the strain rate by rising the inflowing velocities of the opposing streams, yielding very high speeds near extinction. Here, strain rate is increased mainly by moving the nozzles closer to each other and also by small increases in the inflow velocities until extinction occurs. When no water is present, there is good agreement in the extinction strain rate between all the cases. However, substantial differences appear in extinction temperature, which features a local minimum between 70 atm and 90 atm, which was not previously reported in the literature. Furthermore, when water vapor is mixed with the fuel, both extinction strain rate and extinction temperature behave differently with increasing pressure. Extinction strain rate increases with pressure and reaches an asymptotic value at about 50 atm, while extinction flame temperature increases from 1 atm to 20 atm, and then decreases almost linearly.


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  Modeling of Multicomponent Fuels Using Continuous Distributions with Application to Droplet Evaporation and Sprays


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  The mechanisms affecting lift-off stabilization at diesel conditions were investigated by laser-igniting a diesel fuel jet upstream of its natural lift-off position. Single-nozzle fuel sprays penetrating into an optically accessible constant-volume chamber were ignited using laser-induced plasma formation both prior to natural autoignition or after a quasi-steady lift-off length was established. Fuel sprays ignited readily, with reaction kernels growing in connected regions. After laser-ignition, the lift-off persists upstream of the natural lift-off position for a substantial period of time indicating that upstream ignition has a strong influence on lift-off stabilization. While not discounting the role of flame propagation downstream of the ignition event, these results show that upstream ignition sites can start a chain of events that effectively controls lift-off. Lift-off eventually returns to its natural position, but only after injection times that are too long for practical engines. The time of return to the natural position depends upon the relative distance of the laser-ignition site to the natural lift-off length. A theory for fuel jet lift-off stabilization based on flame propagation into pure fuel-ambient reactant streams fails to predict the long upstream stabilization away from the natural lift-off length because turbulent velocities are higher in upstream regions of the fuel jet. Likewise, upstream lift-off stabilization by autoignition of pure reactants (no mixing with combustion products) fails because of cooler temperatures and shorter residence times. A potential mechanism explaining the transient lift-off response to laser-ignition is offered based on turbulent mixing with high-temperature combustion products found at the jet edges.


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  Effect of split fuel injection on heat release and pollutant emissions in partially premixed combustion of PRF70/air/EGR mixtures


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  Two- and three-dimensional direct numerical simulations are performed to study the combustion process of PRF70/air/exhaust gas mixtures under partially premixed combustion (PPC) conditions relevant to modern low temperature internal combustion engines. The aim is to gain improved understanding of the underlining physics in PPC engines. A skeletal PRF chemical kinetic mechanism is used together with full transport properties. The 2D and 3D numerical simulations are performed on respectively a 0.614×0.614mm2domain and a 0.614×0.614×0.614mm3domain with a 1.2μm cell size. The results reveal the effects of the split of the fuel mass in different injections on the combustion and emission process in PPC engines. Increasing the amount of second fuel injection results in a retarded heat release and decreased NO emission, however, increased CO emission. While this CO/NOx tradeoff has been observed in previous PPC engine experiments the fundamental reason for this is clarified here. PPC is shown to consist of a two-stage combustion process: in the first stage the stratified fuel/air mixture auto-ignites, which results in partial oxidation of the fuel in the fuel-rich region and a mixture of radicals and hot products in the fuel-lean region. In the second stage the partially oxidized fuel/air mixture is oxidized in a thin diffusion flame where the diffusion and chemical reaction both play an important role. The split of fuel mass in different injections essentially affect the amount of fuel/air in the fuel-lean region and the fuel-rich region, thereby the relative importance of the diffusion flame. This in turn affects the emissions of NO and CO. The effects of turbulence on the heat release rate, pressure-rise-rate and emissions are a manifestation of the change of the reaction zone structures. At high turbulence intensities and large integral lengths a more homogeneous mixture is achieved, which promotes the volumetric ignition stage, speeds up the heat release rate, increases the pressure-rise-rate, and increases the NO formation and CO oxidation rates. The existence of both volumetric ignition and diffusion flame in PPC poses a great challenge for numerical simulations of PPC engines.


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  The effects of strain rate history on turbulent flames have been studied in the past decades with 1D counter flow diffusion flame (CFDF) configurations subjected to oscillating strain rates. In this work, these unsteady effects are studied for complex hydrocarbon fuel surrogates at engine relevant conditions with unsteady strain rates experienced by flamelets in a typical spray flame. Tabulated combustion models are based on a steady scalar dissipation rate (SDR) assumption and hence cannot capture these unsteady strain effects; even though they can capture the unsteady chemistry. In this work, 1D CFDF with varying strain rates are simulated using two different modeling approaches: steady SDR assumption and unsteady flamelet model. Comparative studies show that the history effects due to unsteady SDR are directly proportional to the temporal gradient of the SDR. A new equivalent SDR model based on the history of a flamelet is proposed. An averaging procedure is constructed such that the most recent histories are given higher weights. This equivalent SDR is then used with the steady SDR assumption in 1D flamelets. Results show a good agreement between tabulated flamelet solution and the unsteady flamelet results. This equivalent SDR concept is further implemented and compared against 3D spray flames (Engine Combustion Network Spray A). Tabulated models based on steady SDR assumption under-predict autoignition and flame lift-off when compared with an unsteady Representative Interactive Flamelet (RIF) model. However, equivalent SDR model coupled with the tabulated model predicted autoignition and flame lift-off very close to those reported by the RIF model. This model is further validated for a range of injection pressures for Spray A flames. The new modeling framework now enables tabulated models with significantly lower computational cost to account for unsteady history effects.


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  An unsteady flamelet/progress variable (UFPV) model has been developed for the prediction of autoignition in turbulent lifted flames. The model is a consistent extension to the steady flamelet/progress variable (SFPV) approach, and employs an unsteady flamelet formulation to describe the transient evolution of all thermochemical quantities during the flame ignition process. In this UFPV model, all thermochemical quantities are parameterized by mixture fraction, reaction progress parameter, and stoichiometric scalar dissipation rate, eliminating the explicit dependence on a flamelet time scale. An a priori study is performed to analyze critical modeling assumptions that are associated with the population of the flamelet state space.For application to LES, the UFPV model is combined with a presumed PDF closure to account for subgrid contributions of mixture fraction and reaction progress variable. The model was applied in LES of a lifted methane/air flame. Additional calculations were performed to quantify the interaction between turbulence and chemistry a posteriori. Simulation results obtained from these calculations are compared with experimental data. Compared to the SFPV results, the unsteady flamelet/progress variable model captures the autoignition process, and good agreement with measurements is obtained for mixture fraction, temperature, and species mass fractions. From the analysis of scatter data and mixture fraction-conditional results it is shown that the turbulence/chemistry interaction delays the ignition process towards lower values of scalar dissipation rate, and a significantly larger region in the flamelet state space is occupied during the ignition process. © 2010 The Combustion Institute.


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  Study on viscosity and surface tension properties of biodiesel-diesel blends and their effects on spray parameters for CI engines


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  Biodiesels, prepared from different vegetable oils, have the potential to substitute the petro-diesel fuel in engines for global sustainability. In this work, the biodiesels of castor oil, neem oil and sunflower oil, have been produced in the laboratory by transesterification process and the properties of the prepared fuels are measured and compared against those of diesel. We have focused on the fuel properties that influence the spray formation in the engine cylinder following injection, viz. viscosity and surface tension, at various temperatures. The viscosity and surface tension properties are also measured for blends of diesel and biodiesels at different temperatures and blend ratios. Different correlation functions, both from the literature and newly developed, are used to evaluate the viscosity and surface tension of pure fuels and blends. The properties of the blends predicted from the correlations are compared against the measured values. The deviations in the predicted and measured values are statistically obtained to identify the most suitable correlation for the fuels under consideration. The effects of the variation in the properties of the pure and blended fuels on the spray characteristics, like mean drop diameter and spray cone angle, for compression ignition engines are studied using suitable correlations. The results are used to determine the preheating required in the biodiesel and blended fuels to achieve the identical spray parameters in the engine cylinder as with diesel fuel following injection.


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  A Path Flux Analysis Method for the Reduction of Detailed Chemical Kinetic Mechanisms A Path Flux Analysis Method for the Reduction of Detailed Chemical Kinetic Mechanisms


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  Fuel injection and combustion study by the combination of mass flow rate and heat release rate with single and multiple injection strategies


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  The injection and combustion characteristics are complicated when split injection strategy is used due to strong interaction between splits. Various injection tests were carried out with long tube real-time fuel flow measuring instrument by employing both single and split injection strategies. Many engine tests with selected operation points (various pilot injection quantities, various injection dwells and various numbers of split injections) were also carried out with split injection strategy, enabling the combination of mass flow rate (MFR) and heat release rate (HRR) information to study combustion features. The results showed that raised injection pressure shortened the injection delay and increased the MFR. The actual injection duration was much longer than the TTL duration. More importantly, for multiple injections, the interaction between splits was dominated by the duration of the first split and injection intervals. The number of splits also exerted profound influence on the interaction. In addition, higher MFR for pilot injection near the piston TDC adversely affected the HRR and normalized combustion efficiency. Increased split injections with low MFR can effectively lower the peak HRR thus reducing the maximum temperature and NOxemissions.


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  The droplet collision algorithm of O'Rourke is currently the standard approach to calculating collisions in Lagrangian spray simulations. This algorithm has a cost proportional to the square of the number of computational particles, or “parcels”. To more efficiently calculate droplet collisions, a technique applied to gas dynamics simulations is extended for use in sprays. For this technique to work efficiently, it must be able to handle the general case where the number of droplets in each parcel varies. The present work shows how the no-time-counter (NTC) method can be extended for the general case of varying numbers of droplets per parcel. The basis of this improvement is analytically derived. The new algorithm is compared to closed-form solutions and to the algorithm of O'Rourke. The NTC method is several orders of magnitude faster and slightly more accurate than O'Rourke's method for several test cases. The second part of the paper concerns implementation of the collision algorithm into a multidimensional code that also models the gas phase behavior and spray breakup. The collision computations are performed on a special collision mesh that is optimized for both sample size and spatial resolution. The mesh is different every time step to further suppress the artifacts that are common in the method of O'Rourke. The parcels are then sorted into cells, so that a list of all the parcels in a given cell are readily available. Next, each cell is individually checked to see if it is so dense that a direct collision calculation is cheaper than the NTC method. The cheaper method is applied to that cell. The final result is a method of calculating spray droplet collisions that is both faster and more accurate than the current standard method of O'Rourke.


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  Cantera: An Object-oriented Software Toolkit for Chemical Kinetics, Thermodynamics, and Transport Processes


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  Experimental investigation of the heat transfer characteristics of spray/wall interaction in diesel selective catalytic reduction systems


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  This study presents an experimental investigation of the heat transfer characteristics of the spray/wall interaction in diesel selective catalytic reduction (SCR) systems. The work was performed with a commercial 3-Hole pressure-driven injector dosing into a flow channel under typical diesel exhaust flow conditions. Infrared thermography captured the surface temperature of the wall around the impingement area with high temporal and spatial resolution. The resulting temperatures have been used for assessing the heat extracted from the wall. Phase Doppler Anemometry (PDA) was applied to measure the droplet sizes and velocities prior to the wall impingement, providing information on the kinetic properties of the impinging droplets. Based on these, the influence of the gas flow conditions on the heat transfer characteristics is deduced. The spray impingement leads to a substantial and rapid temperature drop on the wall, resulting in a maximum heat flux of several MW/m2during the injection duration. The spray cooling effect decreases with increasing exhaust gas flow rate due to the increased entrainment of spray droplets in the flow prior to impingement. Increase in gas flow temperature affects the heat transfer by increasing the wall temperature. At lower wall temperatures, the principal spray/wall interaction regime is deposition. With increasing wall temperature, there is a shift to rebound and thermal breakup. The shorter contact times in the rebound and thermal breakup regimes result in decreased spray/wall heat transfer.


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  Macroscopic and microscopic spray characteristics of fatty acid esters on a common rail injection system


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  The composition of biodiesel is significantly influenced by the feedstock sources. This variation in biodiesel composition may cause changes in fuel physiochemical properties and further affect the engine operation processes such as the fuel injection and spray processes. In this study, the macroscopic and microscopic spray parameters of diesel fuel and three biodiesel components (methyl laurate, methyl oleate and ethyl oleate) on a diesel common rail injection system are investigated at conditions of different injection pressures and ambient pressures. The macroscopic spray parameters, including the tip penetration distance, projected spray area, spray front velocity, spray cone angle, and the maximum spray width, of different fatty acid esters are characterized and compared to those of diesel fuel. Further, the images of fuel spray development obtained by the high speed camera are converted to grayscale ones, and the grayscale values within the spray contours are extracted to evaluate the light intensity level and distribution characteristics for different fuels. Finally, the microscopic spray characteristics of test fuels measured using a split laser particle size analyzer indicated that fuel properties also play an important role in the droplet sizes, and the droplets of methyl laurate and diesel have smaller SMD than methyl oleate and ethyl oleate.


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  Characterization of Internal flow and Spray of Multihole DI Gasoline Spray using X-ray Imaging and CFD


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  Multi-hole DI injectors are being adopted in the advanced downsized DISI ICE powertrain in the automotive industry worldwide because of their robustness and cost-performance. Although their injector design and spray resembles those of DI diesel injectors, there are many basic but distinct differences due to different injection pressure and fuel properties, the sac design, lower L/D aspect ratios in the nozzle hole, closer spray-to-spray angle and hense interactions. This paper used Phase-Contrast X ray techniques to visualize the spray near a 3-hole DI gasoline research model injector exit and compared to the visible light visualization and the internal flow predictions using with multi-dimensional multi-phase CFD simulations. The results show that strong interactions of the vortex strings, cavitation, and turbulence in and near the nozzles make the multi-phase turbulent flow very complicated and dominate the near nozzle breakup mechanisms quite unlike those of diesel injections. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.


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  Effect of ambient fuel vapour concentration on the vapour penetration of evaporating n-hexane sprays


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  Ambient gas properties like pressure, temperature, density etc. play an important role in spray evaporation and hence influence the spray properties like penetration, cone angle and liquid length. The concentration of fuel vapour in the ambient gas was seen to influence the liquid length in an earlier work by the present authors. A method was also reported to study spray parameters at constant pressure, temperature and density but at different fuel vapour concentration in the ambient. In the present paper, the vapour penetration of evaporating n-hexane sprays have been studied by means of a shadowgraph technique at different mass fraction of fuel vapour in the surrounding ambient gas. The results revealed that the ambient vapour concentration has an effect on vapour penetration and cone angle at low ambient densities. But, at higher densities, this effect is absent, although the liquid length is influenced even at higher densities.


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  Laminar burning velocities at high pressure for primary reference fuels and gasoline: Experimental and numerical investigation


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  Spherical flames of n-heptane, iso-octane, PRF 87 and gasoline/air mixtures are experimentally investigated to determine laminar burning velocities and Markstein lengths under engine-relevant conditions by using the constant volume bomb method. Data are obtained for an initial temperature of 373 K, equivalence ratios varying from ϕ{symbol} = 0.7 to ϕ{symbol} = 1.2, and initial pressures from 10 to 25 bar. To track the flame front in the vessel a dark field He-Ne laser Schlieren measurement technique and digital image processing were used. The propagating speed with respect to the burned gases and the stretch rate are determined from the rate of change of the flame radius. The laminar burning velocities are obtained through a linear extrapolation to zero stretch. The experimentally determined Markstein numbers are compared to theoretical predictions. A reduced chemical kinetic mechanism for n-heptane and iso-octane was derived from the Lawrence Livermore comprehensive mechanisms. This mechanism was validated for ignition delay times and flame propagation at low and high pressures. In summary an overall good agreement with the various experimental data sets used in the validation was obtained. © 2008 The Combustion Institute.


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  Evaluation of Effect of Higher Hydrocarbons on Laminar Burning Velocity and Flame Stability of Natural gas blends


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  Multidimensional modeling of fuel composition effects on combustion and cold-starting in diesel engines


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  http://www.scopus.com/inward/record.url?eid=2-s2.0-84859302328{\&}partnerID=40{\&}md5=e11abe5f0a34d2a3e3e18cdf84256b16


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  In this study, the performance of piezoelectric and solenoid injectors were compared. With a piezoelectric injector, the spray characteristics of kerosene and G50 (gasoline/diesel blend fuel), which are kinds of WDF, were investigated and compared to diesel. The characteristics such as spray penetration, spray velocity, spray angle and air entrainment were used to understand the spray behaviour of the test fuels. The results indicate that the piezoelectric injector shows significant improvement over the conventional solenoid injector in injection response and needle opening speed, which enables precise and rapid control of injection. The trade-off effects of charge density and injection pressure on spray penetration and spray velocity are quite clear, while spray angle is almost insensitive to injection pressure. Kerosene and G50 give smaller but similar spray penetration and velocity compared to diesel. The spray angle of kerosene and G50 are larger compared to diesel. The spray volume and mass of entrained air for kerosene and G50 are higher compared to diesel, which indicates kerosene and G50 can form better fuel–air mixing, which is very important for the performance of engine when fuelled by WDF.


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  Evaluation of equilibrium and non-equilibrium evaporationnext term models for many-droplet gas-liquid flow simulations


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  A variety of liquid droplet previous termevaporationnext term models,$\backslash$nincluding both classical previous termequilibrium and non-equilibriumnext$\backslash$nterm Langmuir–Knudsen formulations, are evaluated through comparisons$\backslash$nwith experiments with particular emphasis on computationally efficient$\backslash$nprocedures for gas–liquid flow simulations. The models considered$\backslash$nare those used in droplet laden flow calculations such as direct$\backslash$nnumerical simulations for which large numbers of individual (isolated)$\backslash$ndroplet solutions are obtained. Diameter and temperature evolution$\backslash$npredictions are made for single-component droplets of benzene, decane,$\backslash$nheptane, hexane and water with relatively large initial sizes not,$\backslash$nvert, similar1 mm vaporizing in convective air flows. All of the$\backslash$nmodels perform nearly identically for low previous termevaporationnext$\backslash$nterm rates at gas temperatures significantly lower than the boiling$\backslash$ntemperature. For gas temperatures at and above the boiling point,$\backslash$nlarge deviations are found between the various model predictions.$\backslash$nThe simulated results reveal that previous termnon-equilibriumnext$\backslash$nterm effects become significant when the initial droplet diameter$\backslash$nis \textless50 μm and that these effects are enhanced with increasing slip$\backslash$nvelocity. It is additionally observed that constant properties can$\backslash$nbe used throughout each simulation if both the gas and vapor values$\backslash$nare calculated at either the wet-bulb or boiling temperature. The$\backslash$nmodels based on the Langmuir–Knudsen law and a corrected (for previous$\backslash$ntermevaporationnext term effects) analytical heat transfer expression$\backslash$nderived from the quasi-steady gas phase assumption are shown to agree$\backslash$nmost favorably with a wide variety of experimental results. Since$\backslash$nthe experimental droplet sizes are all much larger than the limit$\backslash$nfor previous termnon-equilibriumnext term effects to be important,$\backslash$nfor these conditions the most crucial aspect of the current Langmuir–Knudsen$\backslash$nmodels is the corrected analytical form for the heat transfer expression$\backslash$nas compared to empirical relations used in the remaining models.


value:
  http://www.sciencedirect.com/science?{\_}ob=ArticleURL{\&}{\_}udi=B6V45-3VGM0PD-H{\&}{\_}user=143915{\&}{\_}coverDate=09{\%}2F30{\%}2F1998{\&}{\_}alid=587976149{\&}{\_}rdoc=1{\&}{\_}fmt=full{\&}{\_}orig=search{\&}{\_}cdi=5749{\&}{\_}sort=d{\&}{\_}docanchor={\&}view=c{\&}{\_}ct=1{\&}{\_}acct=C000011799{\&}{\_}version=1{\&}{\_}urlVersion=0{\&}{\_}userid=143


value:
  Effect of turbulence – chemistry interactions on chemical pathways for turbulent hydrogen – air premixed flames R


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  Effect of Hydrogen Concentration on Engine Performance , Exhaust Emissions and Operation Range of PREMIER Combustion in a Dual Fuel Gas Engine Using Methane- Hydrogen Mixtures


value:
  The development and application of a diesel ignition and combustion model for multidimensional engine simulation


value:
  An integrated numerical model has been developed for diesel engine computations based on the KIVA-II code. The model incorporates a modified RNG k-e, turbulence model, a wave breakup spray model, the Shell ignition model, the laminar-and-turbulent characteristic-time combustion model, a crevice flow model, a spray/wall impingement model that includes rebounding and breaking-up drops, and other improved submodels in the KIVA code. The model was validated and applied to model successfully different types of diesel engines under various operating conditions. These engines include a Caterpillar engine with different injection pressures at different injection timings, a small Tacom engine at different loads, and a Cummins engine modified by Sandia for optical experiments. Good levels of agreement in cylinder pressures and heat release rate data were obtained using the same computer model for all engine cases. Predictions of engine emissions were also performed and a good quantitative agreement between measured and predicted NOx and soot emission data were obtained with the use of the present modified RNG turbulence model. The results indicate that the predicted flow structures have an important impact on the prediction of NOx formation since it is very sensitive to the local temperatures in the combustion chamber.


value:
  A computational problem solving environment for creating and testing reduced chemical kinetic mechanisms


value:
  This paper describes software called computer assisted reduced mechanism problem solving environment (CARM-PSE) that gives the engineer the ability to rapidly set up, run and examine large numbers of problems comparing detailed and reduced (approximate) chemistry. CARM-PSE integrates the automatic chemical mechanism reduction code CARM and the codes that simulate perfectly stirred reactors and plug flow reactors into a user-friendly computational environment. CARM-PSE gives the combustion engineer the ability to easily test chemical approximations over many hundreds of combinations of inputs in a multidimensional parameter space. This tool allows combustion chemistry approximations to be validated and characterized with a thoroughness that was not feasible before. The demonstration problems compare detailed and reduced chemical kinetic calculations for methane-air combustion, including nitrogen oxide (NOx) formation, in a stirred reactor and selective non-catalytic reduction of NOx in coal combustion flue gas. ?? 2002 Elsevier Science Ltd. All rights reserved.


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  Simulation and Experimental Measurement of CO2 *, OH * and CH2O * Chemiluminescence from an Optical Diesel Engine ... CO2 *, OH * and CH2O * Chemiluminescence from an Optical Diesel Engine Fueled with


value:
  Fluid-structure interaction in piping systems (FSI) consists of the$\backslash$ntransfer of momentum and forces between piping and the contained$\backslash$nliquid during unsteady flow. Excitation mechanisms may be caused$\backslash$nby rapid changes in flow and pressure or may be initiated by mechanical$\backslash$naction of the piping. The interaction is manifested in pipe vibration$\backslash$nand perturbations in velocity and pressure of the liquid. The resulting$\backslash$nloads imparted on the piping are transferred to the support mechanisms$\backslash$nsuch as hangers, thrust blocks, etc. The phenomenon has recently$\backslash$nreceived increased attention because of safety and reliability concerns$\backslash$nin power generation stations, environmental issues in pipeline delivery$\backslash$nsystems, and questions related to stringent industrial piping design$\backslash$nperformance guidelines. Furthermore, numerical advances have allowed$\backslash$npractitioners to revisit the manner in which the interaction between$\backslash$npiping and contained liquid is modeled, resulting in improved techniques$\backslash$nthat are now readily available to predict FSI. This review attempts$\backslash$nto succinctly summarize the essential mechanisms that cause FSI,$\backslash$nand present relevant data that describe the phenomenon. In addition,$\backslash$nthe various numerical and analytical methods that have been developed$\backslash$nto successfully predict FSI will be described. Several earlier reviews$\backslash$nregarding FSI in piping have been published; this review is intended$\backslash$nto update the reader on developments that have taken place over the$\backslash$nlast approximately ten years, and to enhance the understanding of$\backslash$nvarious aspects of FSI. There are 123 references cited in this review$\backslash$narticle.


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  Combustion simulations of the fuels for advanced combustion engines in a homogeneous charge compression ignition engine


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  Numerical simulations of combustion have been performed for a homogeneous charge compression ignition engine operating on multi-component reference diesel fuels. Two surrogate representation methods were used to describe the nine fuels for advanced combustion engines. The first method of surrogates, denoted as physical-surrogate components, was formulated to describe the fuel's physical properties by matching its distillation profile, specific gravity, lower heating value, hydrogen-to-carbon ratio, and cetane index with measured data. The second method of surrogates, denoted as chemical-surrogate components, was introduced to represent the chemistry of the fuel components using a new group chemistry representation model. In the model, the fuel components in the physical-surrogate components and chemical-surrogate components are related through the classification of chemical structures of the components, i.e. the component in the physical-surrogate components are grouped based on their chemical classes and the chemistry of each group is calculated using a chemical kinetics mechanism (MultiChem) that represents the combustion characteristics of its chemical class. This MultiChem mechanism includes reduced reaction mechanisms for the four main surrogate hydrocarbon chemistry components of diesel fuel, n-paraffins, iso-paraffins, naphthenes, and aromatics, with two n-paraffins to provide the ability to mimic molecular weight effects. The computations were performed using a multi-dimensional computational fluid dynamic code, KIVA-ERC-CHEMKIN, and the results show that the predictions of the present multicomponent combustion models are in good agreement with experimental measurements. The combustion characteristics of the fuels for advanced combustion engines are well represented and the present models are well suited for practical engine computations.


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  ISBN: 1468-0874
  ISSN: 14680874
  Issue: 2
  Pages: 191–208
  Publication Title: International Journal of Engine Research
  Volume: 14
  DOI: 10.1177/1468087412454066


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  Numerical simulation of non-reacting diesel fuel sprays under low temperature late injection operating condition


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  Accurate simulations on combustion and emission characteristics of direct injection diesel engines are highly dependent on detailed prediction of equivalence ratio distribution inside the combustion chamber. In this study, Open-FOAM and Lib-ICE multi-dimensional CFD frameworks were used in order to model engine flow, liquid diesel fuel spray, break-up, evaporation and mixing. Simulations were conducted on the basis of experimental data from SANDIA optical engine. Initial simulation results showed tangible discrepancy with the experimental equivalence ratio data in distribution of fuel-rich zones. Investigations on three different injection angles in three different combustion chamber bowl geometries showed that cavitation phenomenon was most probably occurred in injector nozzle during the experiments. Onset of cavitation in injector nozzle internal flow can noticeably change the spray break-up length and cause asymmetric spray angle later inside the combustion chamber. Taking cavitation effects into account, simulations were performed by corrected values of spray break-up length and injection angle based on experimental injection pressure and nozzle orifice dimensions. Final spray simulations showed better agreement with experimental results for all of three bowl geometries. This enhanced accuracy of numerical prediction without unacceptable tuning of spray sub-model parameters.


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  Optimization of Dual Fuel Diesel-Methane Operation on a Production Passenger Car Engine - Thermodynamic Analysis


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  Laminar flame speeds of acetone/air mixtures have been investigated at elevated temperature and high pressure conditions in regards to the importance of this intermediate oxygenated molecule in hydrocarbon oxidation. Experiments were performed in an elevated pressure combustion vessel specifically designed around a concept of a premixed Bunsen flame. In a first step, measurements of the laminar flame speed of gaseous CH4/air mixtures were performed with OH rad chemiluminescence and OH-PLIF methodologies and compared with literature data in order to validate the experimental setup. The effects of the preheating temperature (373–523 K), pressure (0.1–1.0 MPa) and equivalence ratio (0.6–1.3) on the laminar flame speed of acetone/air mixtures were then examined. The experiments were finally complemented and compared with numerical simulations conducted with Cosilab commercial software package using published detailed chemical kinetic mechanisms for proposing a correlation relationship of the acetone/air laminar flame speed with pressure, temperature and equivalence ratio.


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  Near-nozzle dynamics of diesel spray under varied needle lifts and its prediction using analytical model


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  Due to the lack of sufficient measurement methods, great difficulties are still present in clarifying the relationship between the nozzle internal flow and liquid-jet dynamics, especially when considering the needle motion effect. In this study, by utilizing the X-ray phase-contrast imaging (XPCI) technique, the in-nozzle needle motion characteristics and the liquid-jet dynamics in the near-nozzle field have been measured within a wide range of injection-pulse durations, based on which the needle-lift dependence of liquid-jet dynamics has been discussed in detail. The study is important for the nozzle related investigations, especially in view of the increasingly widely adopted multiple-injection strategies in the injection systems. The results indicate that, ruled by the mass flow equilibrium inside the nozzle sac, the liquid-jet flow dynamics in the near-nozzle field is closely related to the needle lift and injection pressure. Insufficient needle lift under short injection-pulse duration hurts the liquid-jet momentum that should be highly considered in the multiple-injection strategies. An analytical model has also been proposed to predict the jet axial velocity in the near-nozzle field. The model was found to have good agreement with the experimental results at different conditions.


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  Natural Gas Partially Stratified Charge Combustion : Extended Analysis of Experimental Validation and Study of Turbulence Impact on Flame Propagation


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  Implementation and Validation of a Solver for Direct Numerical Simulations of Turbulent Reacting Flows in OpenFOAM


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  © 2017 Springer Science+Business Media, LLC Reactive Al–Ni composites are of interest for combustion synthesis, for joining, and as components of energetic formulations. Mechanical milling is one of the most practical techniques used for their preparation. This study investigated the effect of ball milling at cryogenic temperatures on the reactivity and structure of Al–Ni composites. Stoichiometric mixtures of Al and Ni powders were milled both at room temperature and cooled by liquid nitrogen. Products were characterized using scanning electron microscopy, differential scanning calorimetry, and x-ray diffraction. Aluminum and nickel were mixed on a finer scale in cryogenically milled powders compared to those prepared at room temperature. DSC traces of the cryogenically milled powder showed three exothermic peaks, while only two clearly resolved peaks were observed for the powders milled at room temperature. A low-temperature reaction preceding the first peak was detected only for the cryomilled material. Apparent activation energies, obtained by model-free analysis, were consistent with previous work on nanofoils. Ignition temperatures of powders prepared at room temperature decreased with increasing structural refinement. This effect was even stronger for the cryogenically milled powder. Energetic characteristics of the prepared materials were correlated with their respective structural refinement. These correlations suggest that the cryomilled material has a narrower zone separating Al and Ni in which the elements are mixed together compared to the similar material prepared by room temperature milling.


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  The Effect of Sparkplug Design on Initial Flame Kernel Development and Sparkplug Performance Reprinted From : SI Combustion and Direct Injection SI Engine Technology


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  A multi-dimensional computer model is used to study atomization and vaporization of a liquid jet injected from a round hole into a compressed gas. Atomization is described using a new method whereby 'blobs' are injected (with sizes equal to the nozzle exit diameter), and breakup of the blobs and the resulting drops is modeled using a stability analysis for liquid jets. This method can also predict various regimes of breakup which result from the action of different combinations of liquid inertia, surface tension and aerodynamic forces on the jet. The product drops are distinguished from the parent drop by having different dropsizes (previous drop breakup models have lumped the parent and product drops together). This has a significant effect on the fuel vapor distribution in a high-pressure spray because the small product drops vaporize rapidly. Like existing models, the model accounts for drop collision and coalescence, and the effect of drops on the gas turbulence. These effects are important in high-pressure sprays where breakup of the liquid yields a core region near the nozzle containing large drops. Fuel vaporization in the core is found to depend strongly on the atomization details near the nozzle. Downstream of the core, fuel-air mixing is found to be determined by a competition between local drop breakup, coalescence and vaporization rates.


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  A single-phase free surface tracking model based on the Lattice Boltzmann Method (LBM), which has capability of simulating liquid-gas system with the assumption that the gas phase has only negligible influence on the liquid phase, is utilized to simulate the flow of a drop impacting on a liquid film. Three typical outcomes in the flows, i.e., deposition, crown and splash, which have been observed in the previous experiments, are obtained in the present three dimensional numerical simulations. The numerical results are consistent with the experimental and analytical results available.


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  Autoignition Delay Time Measurements of Methane, Ethane, and Propane Pure Fuels and Methane-Based Fuel Blends


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  Autoignition delay experiments in air have been performed in an atmospheric flow reactor using typical natural gas components, namely, methane, ethane, and propane. Autoignition delay measurements were also made for binary fuel mixtures of methane/ethane and methane/propane, and ternary mixtures of methane/ethane/propane. The effect of CO2 addition to the methane-based fuel blends on autoignition delay times was also investigated. Equivalence ratios for the experiments ranged between 0.5 and 1.25, and temperatures ranged from 930 K to 1140 K. Consistent with past studies, increasing equivalence ratio and increasing inlet temperatures over these ranges decreased autoignition delay times. Furthermore, addition of 5–10% ethane or propane decreased autoignition delay time of the binary methane-based fuel by 30–50%. Further addition of either ethane or propane showed less significant reduction of autoignition delays. Addition of 5–10% CO2 slightly decreased the autoignition delay times of methane fuel mixtures. Arrhenius correlations were used to derive activation energies for the ignition of the pure fuels and their mixtures. Results show a reduction in activation energies at the higher temperatures studied, which suggests a change in ignition chemistry at very high temperatures. Measurements show relatively good agreement with predictions from a detailed kinetics mechanism, specifically developed to model ignition chemistry of C1-C3 alkanes.


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  abstract Natural gas combustion with pilot ignition has been considered to be one of the most promising ways to utilize natural gas in existing diesel engine without serious engine modification and it has been widely researched all over the world. In this study, three experiments of different loads (BMEP 0.240 MPa, 0.480 MPa and 0.767 MPa) were performed on a 2.8 L four-cylinder, natural gas manifold injection dual-fuel engine to investigate the effects of natural gas injection timing on engine combustion perfor- mance and emissions. The pilot injection parameters (pilot injection timing and pressure) and natural gas injection pressure remain constant at a speed of 1600 rpm in the experiment. The cylinder pressure, HRR, CoVimep, flame development duration, CA50 and brake thermal efficiency were analyzed. The results indicated that under low and part engine loads, the flame development duration and CA50 can be reduced by properly retarding natural gas injection timing, while the CoVimep increased with retarded natural gas injection timing. As a result, the brake thermal efficiency is increased and the combustion sta- bility slightly deteriorates. Meanwhile, under low and part engine loads, PM emissions in the dual-fuel engine is much lower than that in conventional diesel engines, furthermore, at high load, the PM emis- sions are near zero. CO and HC emissions are reduced with retarded natural gas injection timing under low and part loads, however, NOx emissions are slightly increased. Under high load, the flame develop- ment duration and CA50 are obviously prolonged with retarded natural gas injection timing companied with a deterioration of brake thermal efficiency. CO and HC emissions are not significantly varied with retarded natural gas injection timing under high load, except that NOx emissions decreased slightly.


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  Now more than ever, the increasing strictness of environmental regulation and the stronger need of higher efficiency standards are pushing for the development of cleaner and energy-efficient powertrains. HCCI engines are suitable candidates to achieve these objectives. Understanding the autoignition process and how it is affected by operating conditions is central to the development of these engines. In addition to experiments, detailed kinetic modeling represents a very effective tool for gaining deeper insight into the fundamentals of HCCI autoignition and combustion. Indeed, modeling activities are today widely used in engine design, allowing a significant reduction in prototype development costs and providing a valuable support to the improvement of control strategies.Because the amount of low-temperature heat release (LTHR) strongly affects HCCI autoignition, it is important to determine the ability of kinetic models to accurately predict the LTHR over a range of operating conditions. In this work, the combustion behavior of PRF80 (a fuel showing LTHR at the conditions studied) in a 14:1 compression ratio engine operating in HCCI mode is experimentally and computationally analyzed. A new version of the Lawrence Livermore National Laboratory (LLNL) kinetic mechanism is used. This new mechanism contains substantial changes to the low-temperature chemistry that improve its ability to predict the behavior of PRF surrogates. With these improvements, the new mechanism achieves better agreement with rapid compression machine and shock tube data over a wide range of pressures and equivalence ratios. Model results are compared with HCCI engine experiments showing the effects of equivalence the ratio and engine speed on the phasing of both the low - and high-temperature heat release. Particular emphasis is placed on the ability of the model to predict the onset of LTHR at different engine conditions.


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  Direct Numerical Simulation of Complex Fuel Combustion with Detailed Chemistry : Physical Insight and Mean Reaction Rate Modeling


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  Effect of stereoisomeric structure and bond location on the ignition and reaction pathways of hexane isomers Effect of stereoisomeric structure and bond location on the ignition and reaction pathways of hexenes


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  The current work presents new experimental autoignition and speciation data on the two cis-hexenes isomers (cis-2-hexene and cis-3-hexene). The new data


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  Influence of Spray-Wall Interaction and Fuel Films on Cold Starting in Direct Injection Diesel Engines


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  Various single and split injection schemes are studied to provide a better understanding of fuel distribution during cold starting in DI diesel engines. Improved spray-wall interaction, fuel film and multicomponent vaporization models are used to analyze the combustion processes. Better combustion characteristics are obtained for the split injection schemes than with a single injection. An analysis of the fuel impingement processes identifies the mechanisms involved in producing the differences in vaporization and combustion of the fuel. A greater amount of splashing occurred for the split injections compared to a single injection. This behavior is attributed to the decreased film thickness (less dissipation of impingement energy), the decreased impingement area (obtained by increasing the impingement Weber number), and most importantly, the reduced frequency of drop impingement. In comparison, the single injection scheme resulted in an impingement time between drops (i.e., drop frequency) that was considerably smaller than the time required for splashing. Thus, subsequent impinging drops interfered with the splashing process, resulting in a greater quantity of adhered fuel on the walls. The increased splashing for the split injection schemes reduced the overall droplet size, which further aided vaporization and combustion. The partitioning of the injected fuel and the dwell between injection pulses have shown to provide better combustion characteristics for cold starting. One common approach to improve startability is to increase the amount of fuel injected. This type of strategy was also modeled. However, the results indicate that better combustion characteristics may be achieved through the optimization of the injection scheme as an alternative to overfueling. © 1998 Society of Automotive Engineers, Inc.


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  Developing diesel surrogates that mimic the essential characteristics of target fuels such as their sooting tendency and volatility is a necessary but challenging endeavor, owing in part to the scarcity of available experimental sooting data for compounds in the appropriate high molecular weight range. To address this, in this work we demonstrate an experimental approach which provides quantitative sooting data for such compounds. Specifically, we have measured spatially resolved two-dimensional soot volume fraction distributions for three large hydrocarbons: 1,3,5-triisopropylbenzene (tipb), 1,3,5-triisopropylcyclohexane (tipcx), and perhydrophenanthrene (php), as well as benzene and n-hexane. Measurements were performed in methane/air coflowing flames whose fuel was doped separately with these compounds (dopant mass fraction 0.5%). Color-ratio pyrometry was used to measure soot temperature and soot volume fraction distributions. Sooting tendencies were tipb \textgreater benzene \textgreater php \textgreater tipcx \textgreater hexane. These data are expected to be useful in formulation of surrogates with greater fidelity to the volatility and sooting characteristics of real diesel, and in validation of numerical soot models involving such surrogates.


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  Validation of OpenFOAM 1.6.x with the German VDI guideline for obstacle resolving micro-scale models


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  The open source flow solver OpenFOAM 1.6.x is validated for the computation of the statistically steady turbulent flow around single and multiple obstacles. To that end the Reynolds Averaged Navier-Stokes equations are solved together with the standard k-ϵ turbulence model. Five cases are computed comprising a 2D beam, a wall mounted cube, a wall mounted cube rotated by 45° against the approach flow, a cuboid and an array of 21 cuboids. A block structured hexahedral, an unstructured tetrahedral and an unstructured hybrid mesh of tetrahedra and prisms are used for each case. The computed mean velocity components are compared with corresponding experimental results. From the relative or absolute difference of the results a hit rate is computed. For all cases and meshes the computed hit rate is larger than the hit rate required for successful validation if all available measurement positions are taken into account. When only positions in the near field are used for the hit rate, at least for one case and velocity component the successful validation criterion is not met, independent of the mesh. Thus only partial validation is achieved, which is consistent with published results obtained with other flow solvers. Furthermore it is shown that the metrics are not very sensitive to the choice of numerical and physical parameters, which raises the question whether the pass or fail criterion adopted by the guideline is too weak. © 2012 Elsevier Ltd.


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  Real fuels are complex mixtures of thousands of hydrocarbon compounds including linear and branched paraffins, naphthenes, olefins and aromatics. It is generally agreed that their behavior can be effectively reproduced by simpler fuel surrogates containing a limited number of components. In this work, an improved version of the kinetic model by the authors is used to analyze the combustion behavior of several components relevant to gasoline surrogate formulation. Particular attention is devoted to linear and branched saturated hydrocarbons (PRF mixtures), olefins (1-hexene) and aromatics (toluene). Model predictions for pure components, binary mixtures and multi-component gasoline surrogates are compared with recent experimental information collected in rapid compression machine, shock tube and jet stirred reactors covering a wide range of conditions pertinent to internal combustion engines (3-50 atm, 650-1200 K, stoichiometric fuel/air mixtures). Simulation results are discussed focusing attention on the mixing effects of the fuel components. © 2010 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.


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  With the emergence of stringent emissions standards and needs for fuel diversification, many countries are considering a massive use of natural gas for transportation. In this context, dual fuel diesel-CNG combustion is considered as a promising solution for highly efficient internal combustion engines. This concept offers the possibility to combine a diesel pilot injection as a high energy combustion initiation event, with an indirect injection of methane as main energy source. Low CO2 emissions can be reached thanks to the use of a conventional compression ignition engine with high compression ratio, and thanks to methane's high knocking resistance and low carbon content. Another benefit of dual fuel operation with high diesel substitution rates is the drastic reduction of PM emissions since methane is a very stable molecule containing no soot precursor. Moreover, the additional cost of the gas injection system is counterbalanced by the fuel cost reduction: indeed, CNG is cheaper than diesel fuel in most countries. Until now, dual fuel approach has been applied mainly on heavy duty engines using a basic approach of diesel fuel substitution. This paper presents an example of application based on a production Euro 6 diesel passenger car engine equipped with a modern diesel common rail injection system. A port fuel gas injection system was easily implemented to allow dual fuel functionality. The advantage of this configuration is that full diesel operation can be maintained and no major modification of engine hardware is needed, which is valuable for progressive introduction of dual fuel into the automotive market. The objective of the study was to optimize the dual fuel combustion process on the largest engine operating range and to maximize the methane to diesel fuel ratio. Optimal combustion mode between stoichiometry and lean burn was selected for several operating points taking into account the Euro 6 target for engine-out NOx emissions and the maximization of CO2 savings. A first step, not detailed in this paper, consisted in optimizing the swirl level, the combustion chamber and the compression ratio. On the optimal configuration, the boundaries of dual fuel operating range were determined at part and full load. The main limitations of the concept were identified such as pre-ignition at high load and unburned HC emissions at low load caused by fuel trapped on engine crevices and flame quenching. The optimal dual fuel settings were compared to diesel operation thanks to a split of losses approach allowed by means of an in-house dedicated tool. This methodology allows identifying precisely the gains and the losses for each contributor involved in the combustion process (e.g. heat losses, pumping losses, combustion phasing and duration, etc.). This comparison is well adapted for prospective concepts in order to unlink complex phenomena. Copyright © 2013 SAE International and Copyright © 2013 KSAE.


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  Spray Characterization of Ethanol Gasoline Blends and Comparison to a CFD Model for a Gasoline Direct Injector


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  Operation of flex fuel vehicles requires operation with a range of fuel properties. The significant differences in the heat of vaporization and energy density of E0-E100 fuels and the effect on spray development need to be fully comprehended when developing engine control strategies. Limited enthalpy for fuel vaporization needs to be accounted for when developing injection strategies for cold start, homogeneous and stratified operation. Spray imaging of multi-hole gasoline injectors with fuels ranging from E0 to E100 and environmental conditions that represent engine operating points from ambient cold start to hot conditions was performed in a spray chamber. Schlieren visualization technique was used to characterize the sprays and the results were compared with Laser Mie scattering and Back-lighting technique. Open chamber experiments were utilized to provide input and validation of a CFD model. In addition to the fuel variation and operating conditions three different injectors were investigated with differences in static flow rate and internal nozzle geometry. This empirical data was used in the initial development of a robust CFD model for predicting spray behaviors from a multi-hole gasoline direct injector. Comparisons of spray penetration were made between the optimized CFD model and the empirical results. Image processing techniques were presented for characterizing the spray images to quantify the penetration and the vapor cloud development. 3D-CFD numerical simulation is commonly used in order to make selections of engine injection in the early design period. In this article, the spray behavior was predicted by CONVERGE, The characteristics of the spray tip penetration and mass of the liquid and vapor phases were calculated under different temperature and pressure conditions, Testing was also conducted at realistic chamber operating conditions for stratified operation. In these test the piston crown geometry was included in the spray chamber to evaluate fuel impingement effects. Schlieren imaging provided insight into the effect of spray impingement resulting in spray bounce and fuel puddles.


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  Spray-induced turbulence proceeding late-injection is regarded to augment mixing, playing a primary role in controlling heat-release rates and pollutant formation in direct-injection engines. This work presents the first application of tomographic PIV (TPIV) to resolve the 3-dimensional, 3-component (3D3C) spray-induced turbulent flow in a spray-guided direct-injection spark-ignition (SG-DISI) engine. TPIV measurements were performed after a single-injection from a hollow-cone spray when particle distributions were suited for accurate particle reconstruction. High-speed PIV (HS-PIV) measurements (4.8 kHz) were combined with phase-locked TPIV measurements (3.3 Hz) to provide the time history of the 2D2C flow-field preceding TPIV. HS-PIV is also used to validate TPIV measurements within the z = 0 mm plane. TPIV uncertainties of 12% are assessed for non-injection operation. TPIV is used to spatially resolve spray-induced turbulent kinetic energy (TKE), shear (S), and vorticity ($Ømega$) distributions. The added 3D3C velocity information is capable of resolving 3D shear layers that produce spatially-coherent 3D turbulent vortical structures, which are anticipated to augment fuel-air mixing. Measurements spatially quantify the increase of these parameters from injection and quantity distributions reveal significant differences to non-injection operation. The isosurface density (ρ), defined as the volume percentage for which a flow parameter exceeds a given value, is used to identify distributions of the largest TKE, S, and $Ømega$ magnitudes. Distributions quantify the increase of TKE, S, and $Ømega$ from injection and describe the decay of spray-induced turbulence with time. At ρ values below 10%, fuel injection increases TKE, S, and $Ømega$ magnitudes in excess of 400% compared to the tumble flow without injection. Magnitudes remained 2-times larger than non-injection operation 16 crank-angle degrees (CADs) after injection. This indicates that spray-induced turbulence enhancement can remain for a significant time after injection. Measurements and analyses provide insight into spray-induced turbulence phenomena and are anticipated to support predictive model development for engine sprays.


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  Investigation of the ignition and combustion processes of a dual-fuel spray under diesel-like conditions using computational fluid dynamics (CFD) modeling


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  Recent research activities in the field of diesel engines have shown the potential to reduce pollutant emissions and improve the thermal efficiency by controlling the fuel reactivity. However, understanding the impact of blending fuels with different physical and especially chemical properties on diesel-like spray mixing and combustion processes is still a challenge. Since the experimental techniques are still far from providing detailed temporal and spatial information about local spray conditions, computational fluid dynamics (CFD) modeling tools have become the key source of information for investigating the characteristics of these dual-fuel sprays. In this frame, the present research focuses on modeling a dual-fuel spray in diesel-like conditions, comparing different gasoline and diesel blends in terms of ignition characteristics and flame structure. The results confirm the suitability of the state of the art computational CFD modeling tools for reproducing the complex phenomena associated to dual-fuel sprays. Moreover, the important benefits provided by dual-fuel blends, considering the expected reduction in pollutant emissions as a consequence of the differences observed in terms of flame structure, are confirmed. © 2011 Elsevier Ltd.


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  Evaluation of equilibrium and non-equilibrium evaporation models for many-droplet gas-liquid ¯ ow simulations


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  Performance and emissions of a heavy-duty diesel engine fuelled with diesel and LNG ( liquid natural gas )


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  Numerical study of combustion and emission characteristics of dual-fuel engines using 3D-CFD models coupled with chemical kinetics


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  Dual-fuel combustion provides a relatively easy and inexpensive alternative to conventional diesel engine combustion by drastically reducing fuel consumption with comparable performance characteristics. Accurate simulation of the dual-fuel combustion requires utilization of a detailed chemistry combined with a flow simulation code. In the present study, the combustion process within the diesel and diesel/gas dual-fuel engine is investigated by use of a coupled 3D-CFD/chemical kinetics framework. In this study, methane and n-heptane are used as representatives of the natural gas and diesel fuels. The multi-dimensional KIVA-3V code, with modified combustion and heat transfer models, incorporates a chemical kinetics mechanism for n-heptane and methane oxidation chemistry. The source terms in energy and species conservation equations due to chemical reactions are calculated by integrating the CHEMKIN chemistry solver into the KIVA code. The model is applied to simulation of a medium duty dual-fuel converted diesel engine. A chemical kinetics mechanism which consists of 42 species and 57 reactions is used for prediction of n-heptane oxidation chemistry. Simulation of dual-fuel combustion is performed using the same mechanism with addition of a series of major methane oxidation pathways. The results show that Zheng and Yao's n-heptane mechanism which had been previously validated in their work, can model the diesel and dual-fuel combustion, where fuel-rich zones are present. The predictive model of this study is validated using available published experimental data. Results show that pressure and ignition delay predictions are in good agreement with experiments. Based on constant total mixture input energy in dual-fuel combustion, increasing pilot fuel amount leads to shorter ignition delay and peak pressure increment. It is found that concentrations of NOx and CO emissions tend to increase at higher pilot fuel injection quantities. © 2012 Elsevier Ltd. All rights reserved.


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  This study was conducted to assess the effect of the composition of mixed fuels on the spray inner structure in an evaporating transient spray under various ambient conditions. The spray structure and spatial distribution of the liquid phase of the multi-component fuels (three-component mixed fuels) were investigated using thin laser sheet illumination with a pulsed Nd-YAG laser as the light source. The experiments were conducted in a constant-volume vessel with optical access. Fuel was injected into the vessel with an electronically controlled common rail injector. In low-volatility multi-component fuel, droplet clusters occur at almost regular intervals resulting from fuel properties such as high liquid density and viscosity of a fuel with a high boiling point. ?? 2007 Elsevier Ltd. All rights reserved.


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  Lower Temperature Limits for Cold Starting of Diesel Engine with a Common Rail Fuel Injection System. SAE International


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  Investigation of Low Temperature Combustion in An Optical Engine Fueled with Low Cetane Sasol IPK Fuel Using OH-PLIF and HCHO Chemiluminescence Imaging


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  © 2018 SAE International. All Rights Reserved. The present study helps to understand the local combustion characteristics of PREmixed Mixture Ignition in the End-gas Region (PREMIER) combustion mode while using increasing amount of natural gas as a diesel substitute in conventional CI engine. In order to reduce NO x emission and diesel fuel consumption micro-pilot diesel injection in premixed natural gas-air mixture is a promising technique. New strategy has been employed to simulate dual fuel combustion which uses well established combustion models. Main focus of the simulation is at detection of an end gas ignition, and creating an unified modeling approach for dual fuel combustion. In this study G-equation flame propagation model is used with detailed chemistry in order to detect end-gas ignition in overall low temperature combustion. This combustion simulation model is validated using comparison with experimental data for dual fuel engine.


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  In the dual fuel engine much of the energy release comes from the combustion of the gaseous fuel while only a small amount of diesel liquid fuel provides ignition through timed cylinder injection. Such operation with optimum conversion methods has the potential to provide operational characteristics that are comparable or superior to those of the corresponding diesel or spark ignition engines. These characteristics may be realized only if sufficiently effective measures can be ensured both for the avoidance of knock, usually at high loads, and incomplete gaseous fuel utilization at relatively light loads. An objective of this contribution is to demonstrate that the main effort needed to overcome the problems associated with the operation of gas fueled dual fuel engines is via a better control of the relatively complex processes of combustion. Both experimental and analytical modeling procedures for effecting optimum improvement to the combustion process are described.


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  We have developed a new algorithm for modeling the dynamic contact angle, in which the dynamic contact angle is a function of the instantaneous velocity of the contact line. It is emphasized that in general this velocity cannot be approximated by the velocity of any material point, even when the point is very close to the contact line. The algorithm was implemented into a two-phase flow model. The model, which is two-dimensional axisymmetric, uses the volume-of-fluid (VOF) method. The model was used to simulate the spreading of drops impacting a dry solid surface at low Weber numbers. The spread factor, the height of the drop and the dynamic contact angle obtained by the numerical simulations were compared with the experimental data. The numerical results agree well with the experimental data. © 2008 Elsevier B.V. All rights reserved.


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  Aluminum nanoparticles (Al NPs) are commonly employed as fuel supplement to increase the energy density of propellants. However, due to the highly agglomerated state of the NPs and significant pre-combustion sintering, ignition and combustion are not as facile as they could be. In this work, we employed a spray approach to generate near monodisperse microparticles of Al NP's encapsulated within ammonium perchlorate (AP) and a binder (nitrocellulose (NC)) The results show that Al/AP/NC composites have an ignition temperature (∼700 K), which is significantly lower than Al melting point (∼933 K). The reactivity of Al/AP/NC composites was also tested in a confined cell where we find that although the peak pressure for Al/AP/NC is comparable to that of physically mixed Al/CuO nanothermite, the impulse generated is more than two times higher. The measured flame temperature of Al/AP/NC composites were as high as 2800 K, which is ∼500 K higher than Al/AP composites without NC. Furthermore, the potential mechanism for the early ignition of these composites were investigated. It is proposed that gaseous acid released from AP could play an important role in weakening the protective oxide shell on Al nanoparticles which could subsequently lead to the reaction of Al in the high-pressure oxygenated environment at lower temperature.


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  Characterization and Potential of Premixed Micro Pilot Combustion in a Dual - Fuel Natural Gas / Diesel Engine


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  ISBN: 1359-7345
  ISSN: 07338619
  Issue: 1
  Pages: 99–131
  Publication Title: Neurologic Clinics
  Volume: 22
  _eprint: 1707.04192
  DOI: 10.1016/S0733-8619(03)00096-3
  PMID: 24239943


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  Computational Fluid Dynamics (CFD) is used in this investigation to determine the velocity field in the vicinity of vehicle windshield due to defroster flow. The analysis was performed using the CFD package STAR-CD. CFD results were obtained and compared to test data. Hotwire anemometry was used to experimentally determine the velocity field in the vicinity of the defroster nozzle jet flow and windshield interior surface. The experimental results were used to verify the integrity of the CFD models and validate our use of CFD modeling. The ability of the CFD models to quantify the flow field can be inferred from the present results. Based on the degree of correlation of the velocity profiles between the CFD simulations and the experimental work, it can be concluded that CFD simulation is a valid technique to investigate the air flow characteristics of vehicle defroster and windshield flow field.


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  The model for sphericosymmetric thin-flame combustion of a multicomponent fuel droplet in a dilute spray using a unit cell approach, developed in the companion paper, has been used for studying the interaction effect between droplets. The effects of droplet spacing, ambient oxidizer concentration, ambient temperature and pressure have been considered. Droplet life increases with decrease in droplet spacing, ambient temperature and ambient oxidizer concentration. However, droplet life has a weak dependence on ambient pressure. Copyright (C) 2001 John Wiley & Sons, Ltd.


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  The influence of flash boiling conditions on spray characteristics with closely coupled split injection strategy


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  The isooctane spray characteristics under various flash boiling conditions were studied with high speed imaging technique and Phase Doppler particle Analyser (PDPA) technique. The potential of closely coupled split injection strategy to alleviate fuel impingement and the corresponding spray characteristics were also investigated. It was found that flash boiling led to obvious collapse of spray and improved atomization. The increasing strength of flash boiling (excluding the transitional stage) resulted in increasing penetration and potential impingement. Stronger flash boiling caused smaller droplets and higher possibility for the droplets to further breakup. Closely coupled split injection strategy effectively reduced the overall spray penetration and the potential impingement. The flash boiling considerably weakened the collision between split injections and the interaction in liquid phase but strengthened the interaction in gas phase. The dwell interval exerted marginal effects on the penetration rate for each split injection event under flash boiling conditions due to the weakened interaction in liquid phase. By contrast, under non-flash boiling condition, the second split injection observably affected by the variation of dwell interval. Besides, split injection strategy resulted in larger droplet sizes than single injection strategy and the increasing flash boiling strength decreased the size difference between injection strategies.


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  Modelling of diesel spray flames under engine-like conditions using an accelerated Eulerian Stochastic Field method


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  This paper aims to simulate diesel spray flames across a wide range of engine-like conditions using the Eulerian Stochastic Field probability density function (ESF-PDF) model. The ESF model is coupled with the Chemistry Coordinate Mapping approach to expedite the calculation. A convergence study is carried out for a number of stochastic fields at five different conditions, covering both conventional diesel combustion and low-temperature combustion regimes. Ignition delay time, flame lift-off length as well as distributions of temperature and various combustion products are used to evaluate the performance of the model. The peak values of these properties generated using thirty-two stochastic fields are found to converge, with a maximum relative difference of 27% as compared to those from a greater number of stochastic fields. The ESF-PDF model with thirty-two stochastic fields performs reasonably well in reproducing the experimental flame development, ignition delay times and lift-off lengths. The ESF-PDF model also predicts a broader hydroxyl radical distribution which resembles the experimental observation, indicating that the turbulence–chemistry interaction is captured by the ESF-PDF model. The validated model is subsequently used to investigate the flame structures under different conditions. Analyses based on flame index and formaldehyde distribution suggest that a triple flame, which consists of a rich premixed flame, a diffusion flame and a lean premixed flame, is established in the earlier stage of the combustion. As the combustion progresses, the lean premixed flame weakens and diminishes with time. Eventually, only a double-flame structure, made up of the diffusion flame and the rich premixed flame, is observed. The analyses for various ambient temperatures show that the triple-flame structure remains for a longer period of time in cases with lower ambient temperatures. The present study shows that the ESF-PDF method is a valuable alternative to Lagrangian particle PDF methods.


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  Recent progress in the correlation of contact angles with solid surface tensions are summarized. The measurements of meaningful contact angles in terms of surface energetics are also discussed. It is shown that the controversy with respect to measurement and interpretation of contact angles are due to the fact that some (or all) of the assumptions made in all energetic approaches are violated when contact angles are measured and processed. For a large number of polar and non-polar liquids on different solid surfaces, the liquid–vapor surface tension times cosine of the contact angle, γlvcos$þeta$, is shown to depend only on the liquid–vapor surface tension γlv, and the solid–vapor surface tension γsv when the appropriate experimental techniques and procedures are used. Equations which follow these experimental patterns and which allow the determination of solid surface tensions from contact angles are discussed. Universality of these experimental contact angle patterns is illustrated; other reasons which may cause data to deviate from the patterns slightly are discussed. It is found that surface tension component approaches do not reflect physical reality. Assuming the fact that solid surface tension is constant for one and the same solid surface, experimental contact angle patterns are employed to deduce a functional relationship to be used in conjunction with Young's equation for determining solid surface tensions. The explicit form of such a relation is obtained by modifying Berthelot's rule together with experimental data; essentially constant solid surface tension values are obtained, independent of liquid surface tension and molecular structure. A new combining rule is also derived based on an expression similar to one used in molecular theory; such a combining rule should allow a better understanding of the molecular interactions between unlike solid–liquid pairs from like pairs. Existing static contact angles for 34 different types of solid surfaces from Zisman et al. are evaluated in terms of their solid surface tensions using experimental contact angle patterns. A FORTRAN computer program has been implemented to automate these procedures. It is found that literature contact angles do not have to be discarded completely; they can be used to determine solid surface tensions, with caution. The surface tensions for the 34 solid surfaces from Zisman et al. are also reported.


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  ISSN: 00018686
  Publication Title: Advances in Colloid and Interface Science
  DOI: 10.1016/S0001-8686(98)00087-6
  PMID: 19528865


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  Numerical Study of Ultra Low Solidity Airfoil Diffuser in an Automotive Turbocharger Compressor Harold Sun and Tim Schram SAE Paper No . 2009-01-1470


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  For the application of advanced clean combustion technologies, such as diesel HCCI/LTC, a compressor with high efficiency over a broad operation range is required to supply a high amount of EGR with minimum pumping loss. A compressor with high pitch of vaneless diffuser would substantially improve the flow range of the compressor, but it is at the cost of compressor efficiency, especially at low mass flow area where most of the city driving cycles resides. In present study, an ultra-low-solidity compressor vane diffuser was numerically investigated. It is well known that the flow leaving the impeller is highly distorted, unsteady and turbulent, especially at relative low mass flow rate and near the shroud side of the compressor. A conventional vaned diffuser with high stagger angle could help to improve the performance of the compressor at low end. However, adding diffuser vane to a compressor typically restricts the flow range at high end. Due to the limitation of flow range, vaned diffuser is mostly used on turbocharger compressor for large diesels where the work conditions don't vary too much; e.g., generation sets. Due to the wide operation range requirement in a light-duty automotive diesel application, a centrifugal compressor with ultra-low-solidity airfoil diffuser was designed. Calibrated CFD simulation was carried out to predict its performance. It was also compared with the performance of the compressor with the same impeller but vaneless diffuser. The preliminary results showed that the ultra-low-solidity airfoil diffuser could improve the stage efficiency while


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  The engineering and scientific community has been searching for the identification of surrogate fuels that can reasonably represent the performance and emissions behavior of jet fuels (e.g., Jet A, JP-8) in engines . Many proposals exist in the literature, but there has been no consensus of opinion. I t has been recognized that if the surrogate (or its) components were identified and agreed upon, then the research community could focus their resources on the development of chemical kinetic models for accurate representation of this surrogate . This manuscript reviews the findings and recommendations of a working group created by AFOSR, ARO and NIST t o identify a sur r o gate fuel and/or i t s compone n ts. As a par t of this study, the chemi ca l kinetica lly limited pro cesses within a g a s turbine ar e identified . In additi on , a p a lette of c o m p ou nds is presented fr om which a surrogate fuel might be construc ted. We i n it ia lly sug g e sted a simplified surroga te compo s ed of n-decane, n-butylcyclohexane and n-butylbenzene and experiments were performed and


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  http://www.stanford.edu/group/pitsch/publication/ColketJet{\_}Fuel{\_}Surrogate{\_}AIAA{\_}2007.pdf{\%}5Cnhttp://arc.aiaa.org/doi/abs/10.2514/6.2007-770


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  New and realistic pathways from cyclopentadiene ( CPD ) to naphthalene , phenanthrene , and other soot precursors


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  Laminar Flame Learn more about Laminar Flame Combustion and Flames Fuel flexibility in gas turbine systems : impact on burner design and perfor- mance


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  Effects of split injection proportion and the second injection time on the mixture formation in a GDI engine under catalyst heating mode using stratified charge strategy


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  Abstract The effects of split injection proportion and start of injection for the second injection event (SOI2) are investigated with multi-dimensional computational fluid dynamics in a gasoline direct-injection (GDI) engine under catalyst heating mode using stratified stoichiometric charge strategy. Results show that when the injection timing is fixed, the equivalence ratio in the spark plug at ignition time decreases with the decrease in the second injection proportion. The homogeneity of the overall mixtures increases at the same time. The 25%-75% case can form an ideal ignitable mixture and exhibits good combustion performance, which results in rapid catalyst light-off and low soot emissions. NO emissions are relatively high but can be addressed by a three-way catalyst. When the split injection proportion is fixed, the cases with SOI2 of 610°CA, 620°CA, 630°CA, and 660°CA can form an ideal mixture at ignition time. The cases with SOI2 of 610°CA and 620°CA produce a more homogeneous mixture and thus exhibit better combustion performance; however, the detonation tendency is obvious. The mixture of the case with SOI2 of 630°CA is more homogeneous than that of the case with SOI2 of 660°CA. The former exhibits better combustion performance and has a lower amount of soot emission. Although the NO emissions of 630°CA SOI2 are slightly high, it contributes to rapid catalyst light-off. Therefore, 630°CA is the ideal SOI2 in the present conditions.


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  Study of Combustion Development in Methane-Diesel Dual Fuel Engines, Based on the Analysis of In-Cylinder Luminance


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  The effects of several operating parameters on dual fuel combustion at light load were investigated by means of direct endoscopic observation of the process. Therefore, an intense experimental campaign was performed on a single cylinder diesel common rail research engine, converted to operate in dual fuel mode and equipped with optical accesses and variable intake configuration. Three bulk flow structures of the charge were induced inside the cylinder by activating/deactivating the two different inlet valves of the engine (i.e. swirl and tumble). Methane was injected into the inlet manifold at different pressure levels and varying the injector position. In order to obtain a stratified-like air-methane mixture, the injector was mounted very close to the inlet valve, while, to obtain a homogeneous-like one, methane was injected more upstream. By combining the different positions of the methane injector and the three possible bulk flow structures, seven different engine inlet setup were tested. Moreover, pressure and quantity of the diesel pilot injection were varied. For each acquired combustion image, the luminance plane was extracted and a luminance value, averaged over the whole frame, was calculated in order to obtain an indicator of the combustion intensity. These crank angle-based luminance curves were compared while the total integral and the peak values were calculated. From the analysis of the luminance curves it can be observed that the in-cylinder bulk flow associated with the swirl port is characterized by a more rapid development of the combustion. Especially for certain combinations of the engine operating parameters, higher peaks of luminance values can be noticed while the luminance curves fall to zero earlier with respect to the other inlet configurations. Concerning the methane injector position, some noticeable effects on the intensity and distribution of the flame during dual fuel combustion were observed. Depending on the bulk flow structure induced inside the cylinder, methane injector position can induce a certain degree of stratification of the in-cylinder charge, capable to enhance dual fuel combustion at low loads.


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  The behavior of blood cells in disturbed flow regions of arteries has significant relevance for understanding atherogenesis. However, their distribution with red blood cells (RBCs) and leukocytes is not so well studied and understood. Our three-phase computational fluid dynamics approach including plasma, RBCs, and leukocytes was used to numerically simulate the local hemodynamics in such a flow regime. This model has tracked the wall shear stress (WSS), phase distributions, and flow patterns for each phase in a concentrated suspension shear flow of blood. Unlike other computational approaches, this approach does not require dispersion coefficients as an input. The non-Newtonian viscosity model was applied to a wide physiological range of hematocrits, including low shear rates. The migration and segregation of blood cells in disturbed flow regions were computed, and the results compared favorably with available experimental data. The predicted higher leukocyte concentration was correlated with relatively low WSS near the stenosis having a high WSS. This behavior was attributed to flow-dependent interactions of the leukocytes with RBCs in pulsatile flow. This three-phase hemodynamic analysis may have application to vulnerable plaque formation in arteries with in vivo complex flow conditions. ?? 2007.


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  http://dx.doi.org/10.1016/j.combustflame.2016.09.029 https://doi.org/10.1016/j.fuel.2018.01.125 http://dx.doi.org/10.1016/j.fuel.2016.11.056 http://dx.doi.org/10.1016/j.combustflame.2010.07.015 http://dx.doi.org/10.1016/j.fuel.2015.09.020 http://dx.doi.or


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  Condensation heat transfer in a horizontal rectangular duct was experimentally and analytically investigated. To prevent the dripping of condensate on the film, the experiment was conducted inside a horizontal rectangular duct with vapor condensing only on the bottom cooled plate of the duct. R-113 and FC-72 (Fluorinert Electronic Fluid developed by the 3M Company) were used as the condensing fluids. The experimental program included measurements of film thickness, local and average heat transfer coefficients, wave length, wave speed, and a study of wave initiation. The measured film thickness was used to obtain the local heat transfer coefficient. The wave initiation was studied both with condensation and with an adiabatic air-liquid flow. The test sections used in both experiments were identical.


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  ECN Spray G external spray visualization and spray collapse description through penetration and morphology analysis


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  Inside a DISI engine, a wide range of pressure and temperature conditions are possible, and with the current evolution of the systems, many of the conditions are subject to be encountered at the moment of injection. Given the great differences between Diesel injectors and GDi fuel injectors, the effects of such conditions on the development of the fuel injected can cause phenomena like flash boiling and spray collapse that fundamentally change the behavior of sprays. In this work, the Spray G injector developed by Delphi for the Engine Combustion Network (ECN) group has been tested in a High Pressure High Temperature Constant Pressure Flow Rig (HPHT - CPFR) in a wide range of experimental conditions capturing the liquid and vapor phases of the spray by means of DBI and Schlieren imaging. The work presents the results obtained by spray visualization through comparisons of parametric variations with special focus on the collapse of the spray that occurs under high ambient temperature and density conditions. Spray collapse has been described by showing the direct increase that can cause in spray penetration and the great closing effect that can produce to the aperture of the spray (spray angle). Several contour comparisons using the raw images and the detected contours have been discussed in order to support and further explain the observed trends.


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  Reducing the Emissions and Efficiency Penalties of Low Temperature Combustion ( LTC ) through Low Heat Rejection ( LHR )


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  GDi Skew-Angled Nozzle Flow and Near-Field Spray Analysis using Optical and X-Ray Imaging and VOF-LES Computational Fluid Dynamics


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  Improvement of spray atomization and penetration characteristics$\backslash$nof the gasoline direct-injection (GDi ) multi-hole injector is a$\backslash$ncritical component of the GDi combustion developments, especially$\backslash$nin the context of engine down-sizing and turbo-charging trend that$\backslash$nis adopted in order to achieve the European target CO₂, US CAFE,$\backslash$nand concomitant stringent emissions standards. Significant R&D$\backslash$nefforts are directed towards optimization of the nozzle designs, in$\backslash$norder to improve the GDi multi-hole spray characteristics.This publication reports VOF-LES analyses of GDi single-hole$\backslash$nskew-angled nozzles, with β=30° skew (bend) angle and different$\backslash$nnozzle geometries. The objective is to extend previous works to$\backslash$ninclude the effect of nozzle-hole skew angle on the nozzle flow and$\backslash$nspray primary breakup. VOF-LES simulations of a single nozzle-hole$\backslash$nof a purpose-designed GDi multi-hole seat geometry, with three$\backslash$nidentical nozzle-holes per 120° seat segment, are performed. The$\backslash$nsimulations are complemented by comparison with the spray$\backslash$nnear-field breakup structure obtained through optical shadowgraphy$\backslash$nand phase-contrast x-ray imaging techniques.The spray shadographic and X-ray imaging data reveal the jet$\backslash$nprimary breakup in the immediate vicinity of the nozzle,$\backslash$nrepresentative of the


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  The aim of this paper is to perform an accurate analysis of the evaporation of single component and binary mixture fuels sprays in a hot weakly turbulent pipe flow by means of experimental measurement and numerical simulation. This gives a deeper insight into the relationship between fuel composition and spray evaporation. The turbulence intensity in the test section is equal to 10%, and the integral length scale is three orders of magnitude larger than the droplet size while the turbulence microscale (Kolmogorov scales) is of same order as the droplet diameter. The spray produced by means of a calibrated droplet generator was injected in a gas flow electrically preheated. N-nonane, isopropanol, and their mixtures were used in the tests. The generalized scattering imaging technique was applied to simultaneously determine size, velocity, and spatial location of the droplets carried by the turbulent flow in the quartz tube. The spray evaporation was computed using a Lagrangian particle solver coupled to a gas-phase solver. Computations of spray mean diameter and droplet size distributions at different locations along the pipe compare very favorably with the measurement results. This combined research tool enabled further investigation concerning the influencing parameters upon the evaporation process such as the turbulence, droplet internal mixing, and liquid-phase thermophysical properties. © Springer-Verlag 2011.


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  Modeling droplet vaporization and combustion with the volume of fluid method at a small Reynolds number


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  Diesel engines are widely used not only for heavy-duty vehicles such as ships and trucks but also for light-duty passenger cars, with a wide range of bore diameters. Since development of a new diesel engine is usually expensive and time consuming, the ability to accurately predict engine performance from existing models can reduce the resources and time required in the engine development procedure. However, so far knowledge on scaling diesel engines is far from adequacy, particularly for spray combustion processes. In this paper, two injectors with nozzle hole diameters of 0.11 mm and 0.14 mm are adopted for scaling fuel sprays under the non-evaporating conditions based on the three similarity rules. Firstly, the existence of similarity is theoretically analyzed in diesel fuel sprays of both free injection and impinging upon a wall. Then, the similarity of diesel injection rate is experimentally verified by using the Bosch long tube method. Finally, the similarity of spray angle, tip penetration length, excess air ratio and impinging spray characteristics are investigated under various injection pressures and ambient densities in an optically accessible constant volume vessel by the high-speed shadowgraphy. The theoretical analysis and experimental results reveal that the similarity rule keeping the injection pressure constant is more preferable for scaling the spray angle, tip penetration length and excess air ratio, while the other two similarity rules with reduced injection pressure result in narrowed spray angle and increased spray tip penetration length. With respect to the post-impingement behavior, although the spray from the large-hole nozzle impinges upon the wall later than those of the small-hole nozzles with the speed rule and the lift-off rule, the rebound height of the large-hole nozzle is higher than those by the small holes with the speed and the lift-off rule. The mechanism of the above phenomena is discussed in depth.


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  Effect of heat transfer on the reduction of the detailed chemical kinetics mechanism in a homogeneous charge compression ignition combustion engine


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  Peripheral vascular disease is a frequently occurring disease and is most often caused by atherosclerosis and more rarely by anomalies of the collagen or other components of the arterial wall. Arterial stiffness problems form one of the precursor phenomena of peripheral vascular disease, and in the case of atherosclerosis represents an independent risk marker for the occurrence of cardiovascular disease. The first techniques, developed to evaluate arterial stiffness, use indirect measurements such as pulse wave velocity or the analysis of variations in pressure and volume to estimate arterial wall stiffness. Techniques based on the pulse wave lack precision because they assume that arterial stiffness is uniform throughout the path of the pulse wave, and that it is constant throughout the cardiac cycle. Moreover, measuring the velocity of the pulse wave may be less precise in certain pathological situations: metabolic syndrome, obesity, large chest, mega-dolico artery. Techniques based on the analysis of variations in pressure and in volume do not accurately measure blood pressure, which can only be taken externally. In addition, these techniques require dedicated equipment, which is not reimbursed by the French health care system, and which is cumbersome to use (especially for techniques based on variation in pressure) in clinical practice. This explains why these two techniques are not used in clinical practice. Ultrafast echography is a new ultrasound imaging method that can record up to 10,000 images per second. This high temporal resolution makes it possible tomeasure the velocity of the local pulse wave and arterial wall stiffness thanks to the remote palpation carried out by shear wave. The ease of use and the accuracy of these two techniques suggest that these diagnostic applications will play a significant role in vascular pathology in the future. It is possible in real time, using a traditional vascular ultrasound probe, to make an accurate assessment of local arterial stiffness and of its variation during the cardiac cycle. This technological breakthrough will probably improve phenotype evaluation of patients suffering from vascular diseases, to more effectively evaluate the cardiovascular risk for patients, at primary and secondary prevention level, and to carry out broad epidemiological studies on cardiovascular risks. ?? 2013 Published by Elsevier Masson SAS on behalf of the ??ditions fran??aises de radiologie.


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  A mathematical model was developed for predicting the concentration of exhaust nitric oxide, soot and other emissions in a direct injection diesel engine. In the model, it was emphasized to describe the phenomena occurring in the combustion chamber from the microscopic point of view. The prediction was based on the knowledges concerning a single droplet as well as the droplet size distribution in a fuel spray and the spatial and temporal distribution histories of fuel in a combustion chamber. The heterogeneous field of temperature and equivalence ratio, and uniform pressure in the cylinder were postulated. The heat release model gives the burning rate of injected fuel and pressure and temperature history in the cylinder. The concentration of nitric oxide and soot in the cylinder was predicted by the emission formation model. In order to confirm the validity of the theoretical analysis, the calculated results were compared with the experimental results for typical direct injection diesel engine.


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  In this work the governing equations for a single, spherical water droplet evaporating in quiescent air are derived. The governing equations are solved numerically for different exemplary conditions. By that the sensitivity of the droplet evaporation rate on ambient conditions such as air temperature can be analysed. The obtained results are compared to results from literature. In the second part of this paper a case of an evaporating liquid spray is simulated by applying an existing CFD code. The used equations and methods are presented. The results of the spray simulations are shown.


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  Numerical study on fuel physical effects on the split injection processes on a common rail injection system


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  As biodiesel can be used as an alternative fuel for diesel engines, the changed fuel physical properties are found to have influences on the injection characteristics. In this study, a one-dimensional hydraulic model was established to identify the isolated effect of fuel density, viscosity and bulk modulus of compressibility, on the injection mass and pressure propagation waves of a split injection strategy on a common rail injection system. The numerical simulation results indicated that fuel density and bulk modulus of compressibility have more prominent influences on the fuel injection mass and pressure fluctuation characteristics at the injector inlet during the main injection event, while fuel viscosity effects are modest. In addition, injection dwell time between the pilot and main injection is also a crucial parameter affecting the injection characteristics of the main injection event, because the lengths of the injection dwell time influence the initial pressures at the start of the main injection stage and the mean pressures of the main injection stage. The change in these pressures finally affects the injection mass in the main injection event. Therefore, specific effects of fuel physical properties on the main injection process are subject to the injection dwell time, i.e. the specific split injection strategy.


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  An optimized reduced mechanism of n-heptane including 42 species and 58 elementary reactions adapted to charge stratification combustion is developed first in this study. Some engine experiments and a fully coupled CFD and reduced chemical kinetics model with n-heptane as fuel are adopted to investigate the combustion processes of HCCI-like charge stratification combustion aimed at diesel HCCI application. For premixed/direct-injected stratification combustion, the low temperature reaction occurs in the regions with homogeneous fuel first and high temperature reaction begins from high fuel concentration regions involved in the spray process. With the increase of the injection ratio, the high temperature reaction occurs in advance, the pressure rise rate reduces, UHC emissions decrease and CO emissions increase. At larger injection ratio, the onset of the high temperature reaction advances and the maximum pressure rise rate decreases with the retarding of injection timing. UHC and CO emissions have relation to the fuel spray penetration at different injection timings. NOx emissions increase rapidly with the increase of the stratification degree. Crown Copyright ?? 2008.


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  Coupling of the model reduction technique with the lattice Boltzmann method for combustion simulations


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  A new framework of simulation of reactive flows is proposed based on a coupling between accurate reduced reaction mechanism and the lattice Boltzmann representation of the flow phenomena. The model reduction is developed in the setting of slow invariant manifold construction, and the simplest lattice Boltzmann equation is used in order to work out the procedure of coupling of the reduced model with the flow solver. Practical details of constructing slow invariant manifolds of a reaction system under various thermodynamic conditions are reported. The proposed method is validated with the two-dimensional simulation of a premixed counterflow flame in the hydrogen-air mixture. © 2010 The Combustion Institute.


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  Major advances have been made in the development of bagasse combustion technologies and understanding the many processes involved in bagasse combustion and steam generation. CFD modeling has come to form an integral and critical part of this progression. The experience with CFD in the sugar industry through Sugar Research Institute has encompassed the full range of applications from fundamental code development, through the generation and commercialization of new ideas and technologies, to the resolution of practical plant problems. The paper summarises the numerous applications where SRI has achieved successful results utilizing CFD. It is demonstrated that the full benefits of CFD in the delivery of commercial outcomes, for new technologies and the solution of operating plant problems, are achieved through the close interaction between the code development and validation via full scale plant simulation. This two-way interaction enhances the code fundamentals by focusing on practical issues and similarly increases the confidence in the capabilities and accuracy of the CFD predictions, to an extent that justifies firm engineering decisions on commercial plant based solely on the characteristics predicted by the code. © 2004 Elsevier Ltd. All rights reserved.


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  Evaluation of a Hybrid Chemistry Approach for Combustion of Blended Petroleum and Bio-derived Jet Fuels


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  In this work, axisymmetric computations of drop impingement on dry walls are presented. The two-phase model employed is an axisymmetric lattice-Boltzmann model. Computations are performed in the parametric range of Weber number We of 7 to 8770, Ohnesorge number Oh of 0.02 to 0.137, and drop-wall equilibrium contact angle ??eq of 35?? to 150??. Deposition and rebound outcomes are reported. In deposition, the different stages of drop evolution including spread, recoil and equilibration are reproduced and studied. Comparisons made with experimentally reported data of temporal evolution of the spread factor and the dynamic evolution of the contact angle show good agreement. Rebound is observed on non-wetting surfaces. The transition between deposition and rebound is shown to be influenced by the impact We, Oh, and advancing and receding static contact angles. Apart from impingement outcomes, the influence of We and Oh on the dynamic contact angle is investigated. ?? 2007 Elsevier Inc. All rights reserved.


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  Methods have been assembled permitting the simultaneous recording of intra-arterial pressure and arterial diameter with sufficient accuracy so that the mechanical properties of arteries in vivo, under physiologic conditions, can be derived. The analysis necessitates finding the relationships between 5 simultaneous variables; hence the data were recorded on magnetic tape and processed by analog and digital computer technics. Analysis of the data established the fact that the mechanical properties of arteries can be described by a linear, first-order differential equation whose coefficients can be defined as the moduli of elasticity and viscosity. Furthermore, the magnitudes of the coefficients were evaluated. The strain which the arteries undergo as a result of arterial pulse pressure variations is normally between 0.01 and 0.04, i.e., between 1 and 4 per cent change in circumference. The total strain associated with marked constriction and dilation does not usually exceed 10 per cent. Therefore, it is established that the circumferential motion of arteries may be characterized as small strain. The fact that the strain is effectively small is confirmed by analytical consideration, i.e., stress-strain relationships can be linearized under physiologic conditions without introducing significant error. The mass of the artery wall does not play a significant role in determining the mechanical behavior of the arteries and can therefore be neglected in any such considerations. The harmonic content, i.e., the frequency spectrum, comprising the pressure and diameter pulsations associated with the cardiac cycle have been evaluated by Fourier analysis. The magnitudes of the coefficients relating pressure and strain are: elastic (Ep) varies from 1,000 to 6,000 Gm./cm.2 (with the exception of a value of 500 in the thoracic aorta of a 12-week-old puppy), viscous (Rp) from 10 to 150, and mass (Mp) from 0.0002 to 0.005. The magnitudes of the coefficients vary from individual to individual, from one site to another within the vascular tree and temporally in response to vasoactive factors. The effects of epinephrine, norepinephrine, acetylcholine and autonomic nerve stimulation on the mechanical properties and behavior of arteries are discussed. The differences between the pressure-strain relationships and the wall tension-strain relationships are discussed, since the mechanical properties of the wall material itself is not given directly by the pressure-strain relationships, i.e., radius and wall thickness must be considered. An analytical discussion is developed and mathematical equations are derived which relate pressure, wall tension, radius, strain, elasticity, viscosity and inertia in a tube which has been shown to be a reliable model of the living artery. It is concluded that the concept that the arteries function as a "peripheral heart," i.e., rhythmically contract in synchrony with the heart, is not justified. Probable relationships of these properties to the structure and functions of the arterial system are discussed.


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  An ignition delay and kinetic modeling study of methane, dimethyl ether, and their mixtures at high pressures


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  © 2014 The Combustion Institute. The development of accurate chemical kinetic models capable of predicting the combustion of methane and dimethyl ether in common combustion environments such as compression ignition engines and gas turbines is important as it provides valuable data and understanding of these fuels under conditions that are difficult and expensive to study in the real combustors. In this work, both experimental and chemical kinetic model-predicted ignition delay time data are provided covering a range of conditions relevant to gas turbine environments (T=600-1600K, p=7-41atm, ϕ=0.3, 0.5, 1.0, and 2.0 in 'air' mixtures). The detailed chemical kinetic model (Mech_56.54) is capable of accurately predicting this wide range of data, and it is the first mechanism to incorporate high-level rate constant measurements and calculations where available for the reactions of DME. This mechanism is also the first to apply a pressure-dependent treatment to the low-temperature reactions of DME. It has been validated using available literature data including flow reactor, jet-stirred reactor, shock-tube ignition delay times, shock-tube speciation, flame speed, and flame speciation data. New ignition delay time measurements are presented for methane, dimethyl ether, and their mixtures; these data were obtained using three different shock tubes and a rapid compression machine. In addition to the DME/CH4 blends, high-pressure data for pure DME and pure methane were also obtained. Where possible, the new data were compared with existing data from the literature, with good agreement.


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  ISSN: 15562921 00102180
  Issue: 2
  Pages: 315–330
  Publication Title: Combustion and Flame
  Volume: 162
  DOI: 10.1016/j.combustflame.2014.08.014


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  A vaporization model for multi-component fuel sprays is described. The discrete multi-component (DMC) fuel approach was used to model the properties and composition of gasoline and diesel model fuels. Unsteady vaporization of single and multi-component fuel droplets and sprays was considered for both normal and flash-boiling evaporation conditions. An unsteady internal heat flux model and a model for the determination of the droplet surface temperature were formulated. An approximate solution to the quasi-steady energy equation was used to derive an explicit expression for the heat flux from the surrounding gas to the droplet-gas interface, with inter-diffusion of fuel vapor and the surrounding gas taken into account. The density change of the drop as a function of temperature was also considered. In order to treat phase change under trans-critical conditions, a characteristic length was defined to determine the amount of vaporized fuel as a function of time. The present vaporization models were implemented into a multi-dimensional CFD code and applied to calculate evaporation processes of single and multi-component fuel droplets and sprays for various ambient temperatures and droplet temperatures. Differences between representing model fuels using the single and multi-component fuel descriptions are discussed. ?? 2008 Elsevier Ltd. All rights reserved.


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  In this study CFD simulations of both sessile droplets resting upon a vapour cushion and droplets bouncing off a hot solid surface are presented. As a droplet approaches a hot surface the vapour layer formed by evaporation from the droplet acts like a cushion and can prevent contact between the liquid and the hot surface. Rather than hitting and wetting the surface, the droplet can rebound from the vapour film. For the tracking of the interface between the two fluids a one-fluid Level Set method is used, embodied in the TransAT?? finite-volume two-phase flow computational code. Inter alia, this incorporates a full Navier-Stokes solution in the region of the thin film. The method is used to analyse the experiments conducted by Wachters et al. [L.H.J. Wachters, H. Bonne, H.J. Van Nouhuis, The heat transfer from a horizontal plate to sessile water drops in the spheroidal state, Chemical Engineering Science 21 (1966) 923-936] and Biance et al. [A.-L. Biance, F. Checy, C. Clanet, G. Lagubeau, D. Quere, On the elasticity of an inertial liquid shock, Journal of Fluid Mechanics 554 (2006) 47-66]. Good agreement with the experimental observations is obtained. ?? 2008 Elsevier Ltd. All rights reserved.


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  Developing detailed kinetic models of syngas production from bio-oil gasification using Reaction Mechanism Generator (RMG)


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  Detailed kinetic models for the conversion of bio-oil to syngas through gasification were developed automatically using the open source software package Reaction Mechanism Generator (RMG). The influences of process operating conditions and of RMG parameters on the performance of models were investigated. Both temperature and pressure alter the product yields, although including pressure-dependent (chemically activated and fall-off) kinetics have minimal impact on these predictions. The model size is important, although currently constrained by available RAM, motivating development of improved memory-management algorithms in RMG. To validate the RMG-built mechanisms, simulations performed with Cantera were compared with experimental data from the literature. Agreements and disagreements between RMG-built models and literature show that the automated mechanism generation approach is promising, but reveal some families of reactions involving heteroatomic cycles that require improved estimates for bio-mass derived fuels. Research in this area would be greatly helped by more quantitative experimental data, ideally showing intermediate species profiles. These findings motivate extra studies and guide further RMG development.


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  Complex chemistry DNS of n -heptane spray autoignition at high pressure and intermediate temperature conditions


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  A CFD Study of Water Condensation Inside the Tubes of an Automotive Compact Charge Air Cooler Using Large Eddy Simulation Approach


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  The usage of compressed air generated by supercharger or turbocharger by automotive Original Equipment Manufacturers (OEM) is growing with the aim to increase engine performance by increasing the density of the air charge being drawn into the cylinder. Denser air coupled with more fuel pulled into the combustion chamber results in increased engine performance. The inlet air is heated during compression which can cause pre-ignition, which leads to reduced engine functionality. The charge air cooler (CAC) is a heat exchanger introduced to extract heat created during the compression process. Previous research developed a 3-D Computational Fluid Dynamics (CFD) model using the k-epsilon turbulent model with near wall treatment to resolve turbulence in the small channels of the CAC. [1] The present research uses a refined computational scheme with a Large Eddy Simulation (LES) model to solve local data as a function of time and location and correlates the result to the experimental measurements, as well as compare to the k-epsilon approach. Using LES resulted in the ability to correlate any portion of the experimental data and take a closer look at local heat transfer between the outside surface of the tube and the cooling air. Large Eddy Simulation for heat transfer gave more information required for design of CACs which is difficult to collect for various operating conditions by experiment. The overall benefit presented is a validated simulation methodology that predicts condensation, which is then used to evaluate and design CACs that function outside the condensate formation zone during various vehicle operation modes.


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  Temperature Sensitivity and High-Pressure Characteristics of Nano-Sized Additives in AP / HTPB-Composite Propellants


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  Computations of Physical and Electronic Structure of Stacks of Polynuclear Aromatic Hydrocarbons of Varying Topologies


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  Computational Study of Reactivity Controlled Compression Ignition (RCCI) Combustion in a Heavy-Duty Diesel Engine Using Natural Gas


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  Reactivity controlled compression ignition (RCCI) combustion employs two fuels with a large difference in auto-ignition properties that are injected at different times to generate a spatial gradient of fuel-air mixtures and reactivity. Researchers have shown that RCCI offers improved fuel efficiency and lower NOx and Soot exhaust emissions when compared to conventional diesel diffusion combustion. The majority of previous research work has been focused on premixed gasoline or ethanol for the low reactivity fuel and diesel for the high reactivity fuel.The increased availability of natural gas (NG) in the U.S. has renewed interest in the application of compressed natural gas (CNG) to heavy-duty (HD) diesel engines in order to realize fuel cost savings and reduce pollutant emissions, while increasing fuel economy. Thus, RCCI using CNG and diesel fuel warrants consideration. A computational study was performed on a 15L HD diesel engine to examine trade-offs of pollutant emissions, fuel consumption, peak cylinder pressure and maximum cylinder pressure rise rate. The results from the model indicated that an RCCI combustion strategy had the potential of 17.5% NOx reduction, 78% soot reduction and a 24% decrease in fuel consumption when compared to a conventional diesel combustion strategy using the same air-fuel ratio (AFR) and exhaust gas recirculation (EGR) rate, at the rated power operating condition. This was attained while meeting peak cylinder pressure and maximum cylinder pressure rise rate constraints.


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  http://scholar.google.com/scholar?q=intitle:2006-01-0243+Spark+Ignition+Engine+Combustion+Modeling+Using+a+Level+Set+Method+with+Detailed+Chemistry{\#}0


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  The upcoming emission legislation for sea-going vessels issued by the international marine organization requires drastic reduction in nitric oxides. A well-known approach for meeting these requirements is to reduce the in-cylinder temperature prior to combustion by using the so-called Miller cycle. However, the mere use of this technique presents the actual limits due to long ignition delay, which occurs when the compression temperature is very low. As a consequence, premixed combustion develops quickly, increasing the local temperature in the combustion chamber and favoring NOx formation. Splitting the fuel injection into a small pilot and a main injection can reduce the magnitude of the premixed combustion and the local in-cylinder temperatures. The work presented here is divided in two parts and is novel by being the first systematic study of split injection combined with Miller cycle in large-bore engines. In its first stage, an extensive study of the injection dwell with two intake valve closings and three timings of the main injection are analyzed. In the second stage, both injection events are shifted later in the power stroke with fixed injection dwell. Overall, the pilot injection reduced the ignition delay but dropped the peak of the premixed combustion only with the most advanced intake valve closing. This improved fuel economy, but provided no advantages as far as emissions are concerned. In addition, while increasing injection dwell reduced NOx emissions, it also increased fuel consumption. The highest achieved NOx reduction was close to 60%, with a small drawback in fuel economy.


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  Effects of primary breakup modeling on spray and combustion characteristics of compression ignition engines


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  Injector flow dynamics and primary breakup processes are known to play a pivotal role in determining combustion and emissions in diesel engines. In the present study, we examine the effects of primary breakup modeling on the spray and combustion characteristics under diesel engine conditions. The commonly used KH model, which considers the aerodynamically induced breakup based on the Kelvin-Helmholtz instability, is modified to include the effects of cavitation and turbulence generated inside the injector. The KH model and the new (KH-ACT) model are extensively evaluated by performing 3-D time-dependent simulations with detailed chemistry under diesel engine conditions. Results indicate that the inclusion of cavitation and turbulence enhances primary breakup, leading to smaller droplet sizes, decrease in liquid penetration, and increase in the radial dispersion of spray. Predictions are compared with measurements for non-evaporating and evaporating sprays, as well as with flame measurements. While both the models are able to reproduce the experimentally observed global spray and combustion characteristics, predictions using the KH-ACT model exhibit closer agreement with measurements in terms of liquid penetration, cone angle, spray axial velocity, and liquid mass distribution for non-evaporating sprays. Similarly, the KH-ACT model leads to better agreement with respect to the liquid length and vapor penetration distance for evaporating sprays, and with respect to the flame lift-off location for combusting sprays. The improved agreement is attributed to the ability of the new model to account for the effects of turbulence and cavitation generated inside the injector, which enhance the primary breakup. Results further indicate that the combustion under diesel engine conditions is characterized by a double-flame structure with a rich premixed reaction zone near the flame stabilization region and a non-premixed reaction zone further downstream. This flame structure is consistent with the Dec's model for diesel engine combustion (Dec, 1997) [1], and well captured by a newly developed flame index based on the scalar product of CO and O2 mass fraction gradients. ?? 2010 The Combustion Institute.


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  In this work, an Euler-Euler multiphase computational fluid dynamics (CFD) model, which couples a biomass particle pyrolysis model with a multi-fluid hydrodynamics model for gas-particle flow, is used to describe a biomass pyrolysis process, and model predictions are compared to experimental data produced in a lab-scale fluidized-bed reactor. A parametric study of operating conditions was also performed. The kinetic model is based on superimposed hemicellulose, cellulose, and lignin reactions. General biomass feedstock can be represented through the initial mass composition with respect to the three components. The gas-particle flow is modeled with a multi-fluid description (gas, sand, biomass) derived from the kinetic theory of granular flows. The predicted product yields at the reactor outlet are presented and compared with the experimental measurements for both pure cellulose and red oak pyrolysis, and encouraging quantitative agreement is achieved. The model is then applied to investigate the effect of various operating conditions on the pyrolysis product yields in the reactor. Results indicate that biomass particle size and superficial gas velocity influence tar yield and residence time considerably with a fixed bed height. For the range of operating temperature studied, the model captures the trend of biomass decomposition versus temperature and shows an optimal temperature of about 500??C for bio-oil production as reported in the literature. Different biomass feedstocks are also simulated and model shortcomings are discussed. ?? 2012 Elsevier Ltd. All rights reserved.


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  Development of a Five-Step Global Methane Oxidation-NO Formation Mechanism for Lean-Premixed Gas Turbine Combustion


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  It is known that many of the previously published global methane$\backslash$noxidation mechanisms used in conjunction with computational fluid$\backslash$ndynamics (CFD) codes do not accurately predict CH4 and CO concentrations$\backslash$nunder typical lean-premixed combustion turbine operating conditions. In$\backslash$nan effort to improve the accuracy of the global oxidation mechanism$\backslash$nunder these conditions, an optimization method for selectively adjusting$\backslash$nthe reaction rate parameters of the global mechanisms (e.g.,$\backslash$npre-exponential factor, activation temperature, and species$\backslash$nconcentration exponents) using chemical reactor modeling is developed$\backslash$nherein. Traditional global mechanisms involve only hydrocarbon$\backslash$noxidation: that is, they do not allow for the prediction of NO directly$\backslash$nfrom the kinetic mechanism. In this work, a two-step global mechanism$\backslash$nfor NO formation is proposed to be used in combination with a three-step$\backslash$noxidation directly from the kinetic mechanism. In this work, a two-step$\backslash$nglobal mechanism for mechanism. The resulting five-step global mechanism$\backslash$ncan be used with CFD codes to predict CO, CO2, and NO emission directly.$\backslash$nResults of the global mechanism optimization method are shown for a$\backslash$npressure of 1 atmosphere and for pressures of interest for gas turbine$\backslash$nengines. CFD results showing predicted CO and NO emissions using the$\backslash$nfive-step global mechanism developed for elevated pressures are$\backslash$npresented and compared to measured data.


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  Volume of fluid-based numerical modeling of condensation heat transfer and fluid flow characteristics in microchannels


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  The present work proposes a numerical model for the simulation of condensation heat transfer and fluid flow characteristics in a single microchannel. The model was based on the volume of fluid approach, which governed the hydrodynamics of the two-phase flow. The condensation characteristics were governed by the physics of the phenomena and did not include any empirical expressions in the formulation. The conventional governing equations for conservation of volume fraction and energy were modified to include source terms that accounted for the mass transfer at the liquid-vapor interface and the associated release of latent heat, respectively. A microchannel having characteristic dimension of 100 μm was modeled using a two-dimensional computational domain. The working fluid was R134a and the vapor mass flux at the channel inlet ranged from 245 to 615 kg/m2 s. The channel wall was maintained at a constant heat flux ranging from 200 to 800 kW/m2. The predictive accuracy of the numerical model was assessed by comparing the two-phase frictional pressure drop and Nusselt number with available empirical correlations in the literature. A reasonably good agreement was obtained for both parameters with a mean absolute error of 8.1% for two-phase frictional pressure drop against a recent universal predictive approach, and 16.6% for Nusselt number against an available correlation. Further, a qualitative comparison of various flow patterns against experimental visualization data also indicated a favorable agreement. © 2013 Elsevier Ltd. All rights reserved.


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  Soot formation is compared in turbulent diffusion flames burning a commercial Diesel and two Diesel surrogates containing n-decane and α-methylnaphthalene. A burner equipped with a high-efficiency atomisation system has been specially designed and allows the stabilisation of liquid fuels flames with similar hydrodynamics conditions. The initial surrogate composition (70% n-decane, 30% α-methylnaphthalene) was previously used in the literature to simulate combustion in Diesel engines. In this work, a direct comparison of Diesel and surrogates soot tendencies is undertaken and relies on soot and fluorescent species mappings obtained respectively by Laser-Induced Incandescence (LII) at 1064 nm and Laser-Induced Fluorescence at 532 nm. LIF was assigned to soot precursors and mainly to high-number ring Polycyclic Aromatic Hydrocarbons (PAH). The initial surrogate was found to form 40% more soot than the tested Diesel. Consequently, a second surrogate containing a lower α-methylnaphthalene concentration (20%) has been formulated. That composition which presents a Threshold Soot Index (TSI) very close to Diesel one is also consistent with our Diesel composition that indicates a relatively low PAH content. The spatially resolved measurements of soot and fluorescent soot precursors are quite identical (in shape and intensity) in the Diesel and in the second surrogate flames. Furthermore the concordance of the LII temporal decays suggests that a similar growth of the primary soot particles has occurred for Diesel and surrogates. In addition, the comparison of the LII fluence curves indicates that physical/optical properties of soot contained in the different flames might be similar. The chemical composition present at the surface of soot particles collected in Diesel and surrogate flames has been obtained by laser-desorption ionisation time-of-flight mass spectrometry. An important difference is found between Diesel and surrogate samples indicating the influence of the fuel composition on soot content. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.


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  Cold spraying is a promising approach for the processing of refractory metals. A powder material is accelerated and heated in the gas flow of a supersonic nozzle to velocities that are sufficient to obtain cohesion of the particles to a substrate due to plastic deformation. The cohesion behavior of the particles is mainly determined by their velocity and temperature. These are controlled by the pressure and temperature of the gas at the nozzle entrance. A correlation of the process parameters gas pressure and temperature with the particle velocity and temperature is possible based upon numerical simulations. In this contribution a CFDEM simulation model for particle heating and acceleration based on OpenFOAM and LIGGGHTS is presented. CFDEMcoupling combines computational fluid dynamic (CFD) calculation of the gas flow based on the finite volume method with a description of the particles based on the discrete element method (DEM). The predictions of the simulation model are verified based on an analytical description of the cold spray nozzle and validated by experimentally measured particle velocities. Based on this experimental validation the drag model of Koch and Hill appears best suited for a CFDEM modelling of cold spraying.


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  Inverse Livengood-Wu integration method for analyzing ignition delay times in reactors with varying conditions


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  Development and use of a spray combustion modeling to predict diesel engine efficiency and pollutant emissions


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  A numerical study of the effects of pressure fluctuations inside injection nozzle on high-pressure and evaporating diesel spray characteristics


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  Effects of injection pressure fluctuations on high-pressure and evaporating spray behaviour, especially under the representative modern diesel engine injection conditions, were carefully evaluated by using a well validated two-stage modelling approach. The numerical results indicate that as the injection pressure fluctuates more drastically both liquid and gas phase motions in the spray field will be more intensively disturbed. Furthermore, the injection pressure fluctuations have strong potential to enhance fuel/gas mixing processes inside high-pressure and evaporating diesel spray field.


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  Experimental and Computational Analysis of Impact of Self Recirculation Casing Treatment on Turbocharger Compressor


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  Experimental Investigation on Fuel Film Formation by Spray Impingement on Flat Walls with Different Surface Roughness


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  The Chemkin Thermodynamic database contains polynomial fits to specific heats, standard state enthalpies, and standard state entropies. These fits are used by the Chemkin Collection, a generalpurpose chemical kinetics software package. The fourteen coefficients for each species are in the same form as used in the NASA Complex Chemical Equilibrium Program.2 This manual provides details on the compilation of the data that is currently part of the Chemkin Collection, including graphical representations of the fits to experimental (or calculated) data points. Also included is a description of a fitting utility program called Fitdat. Fitdat can be used to generate the Chemkincompatible fitting coefficients from tables of specific heats, entropies, and enthalpies vs. temperature, as well as from vibrational-frequency values.


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  Octane rating effects of direct injection fuels on dual fuel HCCI-DI strati fi ed combustion mode with port injection of n -heptane


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  The present work deals with computational modeling of the fluid flow and heat transfer taking place in the process of impact of a cold liquid drop (Td=20-25??C) onto a dry heated substrate characterized by different thermophysical properties. The computational model, based on the volume-of-fluid method for the free-surface capturing, is validated by simulating the configurations accounting for the conjugate heat transfer. The simulations were performed in a range of impact Reynolds numbers (Re=2000-4500), Weber numbers (We=27-110) and substrate temperatures (Ts=100-120??C). The considered temperature range of the drop-surface, i.e. liquid-solid system does not account for the phase change, that is boiling and evaporation. The model performances are assessed by contrasting the results to the reference database originating from the experimental and complementary numerical investigations by Pasandideh-Fard et al. [Pasandideh-Fard, M., Aziz, S., Chandra, S., Mostaghimi, J., 2001. Cooling effectiveness of a water drop impinging on a hot surface. International Journal of Heat and Fluid Flow, 22, 201-210] and Healy et al. [Healy, W., Hartley, J., Abdel-Khalik, S., 2001. On the validity of the adiabatic spreading assumption in droplet impact cooling. International Journal of Heat and Mass Transfer, 44, 3869-3881]. In addition, the thermal field obtained is analyzed along with the corresponding asymptotic analytical solution proposed by Roisman [Roisman, I.V., 2010. Fast forced liquid film spreading on a substrate: flow, heat transfer and phase transition. Journal of Fluid Mechanics, 656, 189-204]. Contrary to some previous numerical studies, the present computational model accounts for the air flow surrounding the liquid drop. This model feature enables a small air bubble to be resolved in the region of the impact point. The reported results agree reasonably well with experimental and theoretical findings with respect to the drop spreading pattern and associated heat flux and temperature distribution. ?? 2011 Elsevier Inc.


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  The transients of the early stage evolution of high pressure diesel sprays from a clean and a deposit rich injector were explored using high speed imaging at 24.4 kiloframes per second (kfps). Fuel was injected into a liquid that offered high density ambient conditions and, for comparison, fuel was also injected into air at less dense ambient conditions. By comparison of the evolving fuel spray from a new fuel injector to those of an injector rich in carbonaceous deposits at/in the nozzle, anomalous spray behaviour resulting from the presence of deposits becomes apparent. The fuel spray cone angle from a deposit rich injector increased by 10-140% compared to the fuel spray cone angle from a new injector. The accompanying spread in the measured angle was from 100% to 200% greater for the deposit rich case. The presence of deposits significantly affected the early stages of spray evolution, the reproducibility of the spray shape from a deposit rich injector being very low. The observed occurrence of transient radial bulging has the potential to reduce the axial momentum and reduce the combustion performance in diesel engines.


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  Fluid-solid interaction simulation of flow and stress pattern in thoracoabdominal aneurysms: A patient-specific study


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  Thoracoabdominal aneurysm (TA) is a pathology that involves the enlargement of the aortic diameter in the inferior descending thoracic aorta and has risk factors including aortic dissection, aortitis or connective tissue disorders. Abnormal flow patterns and haemodynamic stress on the diseased aortic wall are thought to play an important role in the development of this pathology and the internal wall stress has proved to be more reliable as a predictor of rupture than the maximum diameter for abdominal aortic aneurysms; but this assumption has not been validated yet for aneurysms involving the thoracic aorta. In the present study, three patients with TAs of different maximum diameters were scanned using magnetic resonance imaging (MRI) techniques. Realistic models of the aneurysms were reconstructed from the in vivo MRI data acquired from the patients, and subject-specific flow conditions were applied as boundary conditions. The wall and thrombus were modelled as hyperelastic materials and their properties were derived from the literature. A normal descending aorta was also simulated to provide data for comparison. Fully coupled fluid-solid interaction (FSI) simulations as well as solid static simulations were performed using ADINA 8.2. The results show that the wall stress distribution and its magnitude are strongly dependent on the 3-D shape of the aneurysm and the distribution of thrombus. Maximum wall stresses in all TA models are higher than in the normal aorta, and values of maximum wall stress are not directly related to the maximum aneurysm diameter. Comparisons between the FSI and solid static simulation results showed no significant difference in maximum wall stress, supporting those previous studies which found that FSI simulations were not necessary for wall stress prediction. © 2007 Elsevier Ltd. All rights reserved.


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  Autoignition of Liquid Hydrocarbon Droplets in Lean , High Pressure Natural Gas Mixtures in a Rapid Compression Machine


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  Natural gas is a promising alternative fuel as it is affordable, available worldwide, has high knock resistance and low carbon content. This study focuses on the combustion visualization of spark ignition combustion in an optical single cylinder engine using natural gas at several air to fuel ratios and speed-load operating points. In addition, Turbulent Jet Ignition optical images are compared to the baseline spark ignition images at the world-wide mapping point (1500 rev/min, 3.3 bar IMEPn) in order to provide insight into the relatively unknown phenomenon of Turbulent Jet Ignition combustion. Turbulent Jet Ignition is an advanced spark initiated pre-chamber combustion system for otherwise standard spark ignition engines found in current passenger vehicles. This next generation pre-chamber design simply replaces the spark plug in a conventional spark ignition engine. Turbulent Jet Ignition enables very fast burn rates due to the ignition system producing multiple, widely distributed ignition sites, which consume the main charge rapidly. This high energy ignition results from the partially combusted (reacting) pre-chamber products initiating combustion in the main chamber. The distributed ignition sites enable relatively small flame travel distances enabling short combustion durations and high burn rates. Multiple benefits include extending the knock limit and initiating combustion in very dilute mixtures (excess air and/or EGR), with dilution levels being comparable to other low temperature combustion technologies (HCCI), without the complex control drawbacks. Copyright © 2012 SAE International.


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  Experimental investigation on performance and emissions of a spark-ignition engine fuelled with natural gas–hydrogen blends combined with EGR


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  An experimental investigation on the influence of different hydrogen fractions and EGR rates on the performance and emissions of a spark-ignition engine was conducted. The results show that large EGR introduction decreases the engine power output. However, hydrogen addition can increase the power output at large EGR operation. Effective thermal efficiency shows an increasing trend at small EGR rate and a decreasing trend with further increase of EGR rate. In the case of small EGR rate, effective thermal efficiency is decreased with the increase of hydrogen fraction; while in the case of large EGR rate, thermal efficiency is increased with increasing of hydrogen fraction. For a specified hydrogen fraction, NOx concentration is decreased with the increase of EGR rate and this effectiveness becomes more obviously at high hydrogen fraction. HC emission is increased with the increase of EGR rate and it decreases with the increase of hydrogen fraction. CO and CO2 emissions show little variations with EGR rate, but they decrease with the increase of hydrogen fraction. The study shows that natural gas–hydrogen blend combining with EGR can realize high-efficiency and low-emission spark-ignition engine.


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  This paper reports a theory investigation focusing on liquid penetration of diesel spray. A one-dimensional model on liquid length is developed for the prediction of liquid length, based on the momentum flux and fuel mass flux conservation along the sprays' axis, and energy conservation on the control volume. The heterogeneous distribution of velocity and fuel concentration over the cross-section of spray is taken into consideration. A Gaussian radial profile is assumed for the velocity and fuel volume fraction distribution, and a distribution factor (β) is introduced to describe the distribution profile of axial velocity and fuel volume fraction. The model derived in this research was validated by the measured data from Siebers' experiment over a wide ambient gas temperature and density. This comparison indicates that the velocity and fuel concentration profiles are critical and cannot be neglected in the derivation of liquid length. The distribution factor is confirmed from the best fit of the calculated liquid lengths to the measured data, and should be set as 1.8 for the best fit. The model is further validated by the measured data over a wide orifice pressure drop, orifice diameter, and fuel temperature range. Based on the validated model, liquid length of diesel spray under different gas composition is calculated, and effect of ambient gas composition on liquid length is discussed.


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  The effects of difference in fuel components on the droplet evaporation and combustion are numerically investigated. Jet-A is used as liquid fuel, and one (n-decane)-, two (n-decane and 1,2,4-trimethyl-benzene)- and three (n-dodecane, iso-octane and toluene)-component fuels are used as the surrogate fuels of Jet-A. The results show that the evaporation of the three-component surrogate fuel becomes faster and slower than those of the one- and two-component surrogate fuels in the initial and subsequent evaporating periods, respectively. The differences in the gas temperature evolution among these three different surrogate fuels are remarkable right after the ignition, but become small with time. © 2014 Elsevier Ltd. All rights reserved.


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  In this work non-reacting spray simulations are performed using two Computational Fluid Dynamic (CFD) codes, KIVA and OpenFoam. The metric used is the liquid tip penetration which is compared with experimental data from the Engine Combustion Network at Sandia National Laboratories. Some important spray sub-models, available in KIVA, are implemented in OpenFOAM so that the two codes have more common models. In addition, model coefficients and computations cells used in the simulations are the same in both codes. The differences in spray source terms formulations and other spray sub models between the codes and their effect on liquid penetration are discussed.


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  This study assesses the feasibility of an intraperitoneal (IP) implantable closed-loop insulin delivery device in rats, that delivers insulin via a glucose-sensitive material such that blood glucose (BG) levels are adjusted automatically to within normal tolerances. A gateway layer of this gel governs the output of insulin from an insulin reservoir device for IP implant. The performance of the system was compared over time in diabetic rats with a control system using oral glucose challenges and daily assessments of BG and body weight. The automated response of the active system was quantified using IP multiple dose injection (MDI) results in the same rat model. Successful control was found for the device containing active gel when assessed daily and when challenged with large glucose doses. This was not found when comparing an inactive gel analog as a control. The regimen was quantified by comparison with the informative MDI study. The device was well tolerated and might operate to further advantage when vascular omentum grows into the perforated front of the device. The successful device must have been outputting approximately 0.5 U/kg/h basal with 2 U/kg boosts in order to match the demand of the challenges. However, the device eventually exhausts and a refill mechanism needs to be devised in future models.


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  This work focuses on the construction of a 2D dynamic model, taking into consideration the turbulent flux combustion reactions of syngas inside a combustion chamber and its displacement through the cylinder of a diesel engine model OM 447 LA converted to Otto cycle operation. The engine has a multi-spark ignition system. The geometry of both the chamber and cylinder is symmetric to a radius of 0.064 m and to a length of 0.17595 m. The simulation is carried out on only half of the system, with a premixed supply of the syngas and air. The supply temperature of the mixture is 336 K. The supply relation air/syngas ratio is 1.1:1, and the supply pressure of the mixture is 1 bar. The gaseous phase is modeled as a multi-component mixture comprised of carbon monoxide (CO), hydrogen (H2), methane (CH4), nitrogen (N2), carbon dioxide (CO2) and oxygen (O2). The study describes a Computational Fluid Dynamic (CFD) numerical model, in which the conservation of matter, motion and energy equations are solved; in addition, sub-models are used to represent the turbulence intensity and the multiple reactions. The model predicts the profiles of syngas speed, temperature, chemical composition, pressure, and turbulence intensity for the gases when the working parameters and the supply characteristics are modified (air-syngas ratio, initial temperature of the mixture, initial pressure, compression ratio, and engine speed). The equation formulation is elliptic staggered. The result is a simple nonlinear map that resolves combustion time sequences using the commercial code CFD in PHOENICS. © 2009 Elsevier Ltd. All rights reserved.


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  Investigation of Substitution Limits and Emissions of an In-Line Six Cylinder Diesel-Natural Gas Dual Fuel Engine


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  CFD simulations using the TDAC method to model iso-octane combustion for a large range of ozone seeding and temperature conditions in a single cylinder HCCI engine


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  While HCCI engines have many advantages such as better efficiency and lower emissions, the control of these engines is still complex. In this context, cycle-to-cycle control using oxidizing species such as ozone (O3) presents a good potential. Only 1 ppm of O3 has already a significant impact on the ignition. Predicting this effect as well as the low temperature combustion and ignition generally requires a detailed mechanism. Using CFD simulations with the Tabulation of Dynamic Adaptive Chemistry (TDAC) method and a mechanism including more than 1000 chemical species, we have predicted the effect of ozone seeding on the combustion of iso-octane in a HCCI engine. This paper presents the validation of the CFD simulations with a large range of ozone concentration and initial temperature. It shows that the TDAC method is able to reproduce accurately such complex chemical phenomena accounting for heat transfer and chemical reactions in a real geometry. ?? 2014 Elsevier Ltd. All rights reserved.


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  In the present study, optimization of engine operating conditions was performed to reduce fuel consumption for stoichiometric diesel combustion. Microgenetic algorithms were used, and variations of injection strategy, spray included angle, and initial conditions (such as temperature and pressure) were evaluated. The KIVA code, coupled with the Chemkin chemistry solver, was used for three-dimensional CFD modeling, and the ignition and combustion processes were modeled using a reduced n-heptane mechanism. The KIVA code in use was verified against pressure histories and emissions for stoichiometric diesel combustion obtained experimentally. Optimized engine operating conditions for minimum fuel consumption were found at the 43rd generation. The optimized case includes 50-50% split injection, reduced spray included for reduction of unburned HC in crevices, and lower oxygen concentration to retard combustion phasing. This optimization yielded an 11.8% improvement in fuel consumption, along with simultaneous reductions of soot, NOx, CO, and HC. © 2011 Elsevier Ltd. All rights reserved.


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  A Compuational and Experimental Study on Combustion Processes in Natural Gas/Diesel Dual Fuel Engines


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  In honor of the fiftieth anniversary of the Combustion Institute, we are asked to assess accomplishments of theory in combustion over the past fifty years and prospects for the future. The title of our article is chosen to emphasize that development of theory necessarily goes hand-in-hand with specification of a model. Good conceptual models underlie successful mathematical theories. Models and theories are discussed here for deflagrations, detonations, diffusion flames, ignition, propellant combustion, and turbulent combustion. In many of these areas, the genesis of mathematical theories occurred during the past fifty years, and in all of them significant advances are anticipated in the future. Increasing interaction between theory and computation will aid this progress. We hope that, although certainly not complete in topical coverage or reference citation, the presentation may suggest useful directions for future research in combustion theory.


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  Controlling autoignition timing over a wide range of speeds and loads is challenging. Overcoming this challenge in practical HCCI engines requires an improved understanding of the in-cylinder processes and how these processes can be favorably altered by various control techniques. In the current study, a zero-dimensional thermodynamic model that contains a simple heat release sub-model and an autoignition model was used in a predictive fashion to better understand the in-cylinder processes and the efficiency potential of a natural gas engine in the HCCI mode. The model was also used for parametric studies to evaluate HCCI control strategies that can be tested on the research engine. The results indicated that if the initial conditions of the mixture are known precisely at intake valve closing, the autoignition timing is controllable. A thermal efficiency close to 0.45 is possible with an IMEP range from 4 to 5 bar for the described engine, also.


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  A Level Set Based Flamelet Model for the Prediction of Combustion in Spark Ignition Engines Unsteady Premixed Combustion Model


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  A Flamelet Model based on the Level Set approach for turbulent premixed combustion is presented. The original model [11, 12] is enhanced in order to consistently model the evolution of the premixed flame from laminar into a fully developed turbulent flame. This is accomplished by establishing a linear relationship between the thickness of the turbulent flame brush and the turbulent burning velocity. Starting from there a model for the initial flame propagation of a spherical spark kernel immediately after ignition and for the flame propagation in 3D space is derived. In contrast to other models, the same physical modeling assumptions are employed for the phase initially after spark ignition and for the later phases of flame propagation. The model is applied to a test case in an homogeneous charge Spark Ignition (SI) engine.


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  In this study, we present the numerical investigations on the effect of finite velocity modulations imposed on an otherwise unperturbed cylindrical liquid jet issuing into stagnant gas. Sinusoidal velocity fluctuations of finite frequency and amplitude are imposed at the liquid jet inlet and the resulting liquid jet surface deformation is captured using a volume of fluid (VOF) methodology, utilizing compressive interface capturing scheme for arbitrary meshes (CICSAM) scheme. Variation of the simulation parameters, comprising of the mean liquid jet velocity, modulation amplitude and frequency grouped together using a set of non-dimensional parameters, leads to the formation of a wide gamut of reproducible liquid structures such as waves, upstream/downstream directed bells, chains of droplets similar to those observed in experiments. Elaborate tests on the effect of injection velocity and inlet jet diameter are investigated to characterize the breakup process. The computations efficiently capture the diverse flow structures generated by the evolving modulated liquid jet inclusive of several non-linear dynamics such as growth of surface waves, ligament interaction with shear vortices and its subsequent thinning process. The simulations identify the deterministic behavior of modulated liquid jets to predict liquid disintegration modes under given set of non-dimensional parameters. ?? 2011 Elsevier Inc.


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  The problem of blood flow in a narrow catheterized artery has been investigated using a two-phase macroscopic model of blood (i.e., a suspension of red cells in plasma). It is found that the effective viscosity and the frictional resistance increase with hematocrit. Flow characteristics assume lower magnitudes in catheterized artery as compared to uncatheterized artery for any given set of parameters. Numerical results reveal that the effective viscosity and the increased frictional resistance assume their minimal magnitude and consequently the volumetric flow rate assumes its maximal magnitude during the artery catheterization at the catheter size approximately fifty percent of the artery size. © 2009 Elsevier Ltd. All rights reserved.


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  Large-eddy simulation analysis of the influence of the needle lift on the cavitation in diesel injector nozzles


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  © IMechE 2014. The cavitation phenomenon has a strong influence on the internal flow and spray development in diesel injector nozzles. Despite its importance, there are many aspects which still remain unclear, especially for partial needle lifts when the injector is in the opening and closing phases. For that reason, the current paper is focused on the influence of the needle lift on the internal flow in a diesel nozzle. This study was carried out with three-dimensional simulations at a high injection pressure (160 MPa) using a homogeneous equilibrium model implemented in OpenFOAM to model the cavitation phenomenon. The nozzle was simulated with large-eddy simulation methods at six different needle lifts (10 μm, 30 μm, 50 μm, 75 μm, 100 μm and 250 μm), providing relevant information about the evolution of the internal flow, the turbulence development (the vorticity, the turbulence-cavitation interaction and the turbulent structures) and the flow characteristics in the nozzle outlet (the mass flow, the momentum flux and the effective velocity) with the needle position.


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  The phenomenon of drop spreading is important to several process engineering applications. In the present work, numerical simulations of the dynamics of drop impact and spreading on horizontal and inclined surfaces were carried out using the volume of fluid (VOF) method. For the horizontal surfaces, the dynamics of impact and spreading of glycerin drops on wax and glass surfaces was investigated for which the experimental measurements were available [??ikalo, ??., Tropea, C., Ganic, E.N., 2005a. Dynamic wetting angle of a spreading droplet. Experimental Thermal and Fluid Science 29, 795-802; ??ikalo, ??., Tropea, C., Ganic, E.N., 2005b. Impact of droplets onto inclined surfaces. Journal of Colloid and Interface Science 286, 661-669]. The influence of surface wetting characteristics was investigated by using static contact angle (SCA) and dynamic contact angle (DCA) models. The dynamics of drop impact and spreading on inclined surfaces and the different regimes of drop impact and spreading process were also investigated. In particular, the effects of surface inclination, surface wetting characteristics, liquid properties and impact velocity on the dynamics of drop impact and spreading were investigated numerically and the results were verified experimentally. It was found that the SCA model can predict the drop impact and spreading behavior in quantitative agreement with the experiments for less wettable surfaces (SCA \textgreater 90 {ring operator}). However, for more wettable surfaces (SCA \textless 90 {ring operator}), the DCA observed at initial contact times were order of magnitude higher than SCA values and therefore the DCA model is needed for the accurate prediction of the spreading behavior. ?? 2007 Elsevier Ltd. All rights reserved.


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  Ignition delay times for jet and diesel fuels: Constant volume spray and gas-phase shock tube measurements


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  Ignition delay times for conventional and alternative jet and diesel fuels were measured in a constant volume spray combustion chamber and a shock tube in homogenous gas-phase reflected shock experiments. Experiments were performed in the spray environment for injection of liquid fuel sprays into hot air at 1.0, 2.14, and 4.0 MPa and 620–830 K. Shock tube experiments were performed for homogenous stoichiometric fuel/air mixtures at pressures around 2, 4, and 8 MPa and for 660–1310 K. These experiments characterize relative fuel reactivity, the dependence of reactivity on temperature and pressure, and allow for correlation of reactivity under spray and homogenous gas-phase conditions. Important results include the observation of three temperature regimes for reactivity in the shock tube experiments: high- and low-temperature regimes with positive overall activation energy connected by a negative-temperature-coefficient (NTC) regime. While increasing pressure was shown to result in decreasing ignition delay in all regimes, pressure was shown to have an appreciably larger influence in the NTC regime. Spray ignition experiments exhibited decreasing temperature dependence with increasing temperature from the low-temperature regime towards the entrance to the NTC. Fuel reactivity trends from spray ignition experiments, quantified using the derived cetane number (DCN), were found to correlate via a power law relationship with ignition delay times measured in the shock tube at NTC conditions, suggesting that DCN is primarily sensitive to NTC gas-phase chemical kinetic reactivity. The extensive experimental database reported here for jet and diesel fuels at high-pressure engine-like combustion conditions should be valuable for the future development of real fuel chemical kinetic modeling.


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  A model for the three-dimensional direct numerical simulation of evaporating, deforming droplets in incompressible flow is presented. It is based on the volume-of-fluid method and is therefore capable of capturing very strong deformations. The evaporation rate is computed based on the vapour mass fraction and the PLIC reconstruction of the surface. Emphasis is put on the correct calculation of the velocities of the gaseous and liquid phase at the interface which is very important for cases with high mass transfer rates and thus high Stefan flow. It is accomplished by the use of an iterative algorithm that enforces a divergence constraint in cells containing the interface. Validation comprises a 1D test case for interfacial mass transfer, droplet collisions and oscillations as well as calculation of Sherwood numbers for two different cases of evaporating droplets where low and high mass transfer rates occur. Comparison with data from the literature shows good agreement of the obtained results. The simulation of a strongly deformed water droplet in a flow at a high Reynolds and Weber number is used to demonstrate the capabilities of the presented method. The emerging flow field in the wake of the droplet is very complex and three-dimensional. ?? 2008 Elsevier Inc. All rights reserved.


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  A reduced chemical kinetic mechanism of the n-butanol/biodiesel blend was developed for dual fuel engine simulations. The reaction flow analysis reduction method was adopted to lump and remove the unimportant species and the related reactions. The reduced mechanism of n-butanol contains 71 species and 349 reactions. The reduced mechanism of n-butanol was merged into a reduced mechanism of biodiesel to construct a combined mechanism of n-butanol/biodiesel with 171 species and 765 reactions. The combined mechanism was validated against the n-butanol experimental data including ignition delays in shock tubes and the mole fractions of species in a jet-stirred reactor. The n-butanol/biodiesel mechanism was further validated against the engine experiments fuelled with the n-butanol/biodiesel dual fuel under multiple operating conditions. The predicted pressure and the heat release rate profiles, as well as CO, HC, NOx, and soot emissions under various conditions agreed well with the experimental data. Analysis of the interaction of n-butanol/biodiesel during the ignition process shows that the biodiesel produces OH radicals at the low in-cylinder temperature, and the produced OH radicals are consumed by n-butanol to produce HO2 radicals after a consecutive reaction. HO2 radicals are then transformed to H2O2, which dissociate to OH radicals at higher in-cylinder temperature. OH radicals in turn facilitate further consumption of n-butanol/biodiesel dual fuel. Analysis of the evolution of oxygen contained in the fuel molecules indicates that the O atom in the n-butanol molecule ends up in CH2O, which is turned into CO and the O atoms in the biodiesel may also give rise to CO2 directly.


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  A millimeter-scale flow reactor consisting of a cylindrical tube with a controlled tem-perature profile is studied through numerical simulations. Stable flames are observed at high and low velocity regimes and non-stationary dynamic flames (with repetitive extinction and ignition) are observed at moderate velocity regimes. The focus is placed on the dynamic flames since the cyclic ignition/extinction behavior is expected to be sensitive to both chemical kinetics and transport. A fast, one-dimensional, unsteady flame solver designed to handle large chemical mechanisms and different transport models is used. Computations are performed to compare four different transport models of varying complexity and computational cost: constant Lewis numbers, mixture-averaged diffusion coefficients excluding thermal diffusion, mixture-averaged diffusion coefficients including thermal diffusion, and multi-component species diffusion including thermal diffusion. The simula-tions are compared to recent experimental results for varying flow velocities and different gaseous fuels.


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  Potential Natural Gas Impact on Cost Efficient Capacity Planning for Automakers and Electricity Generators in a Carbon Constrained World


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  Development and Validation of Power Performance Prediction Chart for Conversion of Diesel Engine to Dual Fuel Engine


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  Mixed-mode homogeneous charge compression ignition-direct injection combustion on common rail diesel engines: An experimental characterization


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  In recent years, increasing attention has been given to the study of homogeneous charge compression ignition (HCCI) for automotive diesel engines, due to its potential to lower NOx and particulate matter (PM) emissions. However, controlling the combustion process and engineering a mixture preparation method that does not require significant modifications to the engine hardware are still significant barriers to a vehicle implementation. In this scenario, external mixture formation, performed through a diesel fuel atomizer, is a simple and reliable method to obtain a truly homogeneous charge, resulting in ultra-low NOxand negligible PM formation. This technology does not require any modification to the engine compression ratio or to the fuel direct injection (DI) system. The possibility of combining two separate fuelling systems allows for mixed-mode HCCI-DI combustion, where a diesel-type combustion is induced during HCCI operations, increasing the IMEP and the output engine torque. This would allow for a seamless transition from HCCI to conventional DI mode at high load, while retaining the HCCI combustion benefits on emissions at part-load engine operating conditions. Building on preliminary experimental results proving the feasibility and benefits of the HCCI combustion with external mixture preparation on a high-speed common rail diesel engine, the proposed work aims at extending the HCCI combustion characterization, in order to define an engine operating region for its application. Then, mixed-mode HCCI-DI operations were investigated as a strategy to overcome the IMEP limitations of pure HCCI combustion. The analysis of HCCI-DI combustion aims at studying the effect of important control parameters, such as EGR ratio and direct injection timing, on combustion and emissions, showing the effects of partial HCCI combustion at higher engine loads. © 2009 IMechE.


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  Experimental limitations for certain nuclear reactor safety applications have pushed forward the demand for high fidelity DNS reference solutions for complex geometric configurations such as a T-junction or a spherical pebble bed. The application of traditional high-order DNS codes is limited to simple flow domains such as a periodic box or channel. As a possibility to create reference DNS solutions for more complex geometries, we have assessed the (quasi-)DNS capabilities of the OpenFOAM finite volume CFD solver for both structured hexahedral meshes and arbitrary polyhedral meshes. The feasibility of (quasi-)DNS analyses on polyhedral grids is of main interest, since this may offer the possibility to significantly expand the availability of (quasi-)DNS-quality data on arbitrarily complex geometries. In order to have a basis for the considered assessment, the mutual differences between generally recognized reference DNS data bases for turbulent channel and pipe flows are determined first. Subsequently, the differences between these reference DNS solutions and the present OpenFOAM (quasi-)DNS solutions are quantified for the considered mesh types. We use an existing finite volume CFD method and well known turbulent channel and pipe flow DNS reference cases for the assessments in this paper. New in this paper are the application of this CFD method to (quasi-)DNS analyses using arbitrary polyhedral meshes, and the quantification of respectively the mutual differences between generally recognized reference DNS data bases and the differences between the obtained OpenFOAM (quasi-)DNS data and these reference DNS data bases.Based on the presented assessment, it is observed that the differences between the OpenFOAM solutions and the considered reference DNS solutions are practically the same as the mutual differences between these reference DNS solutions when structured hexahedral meshes are used. Furthermore, it is observed that the differences as obtained by OpenFOAM on extruded polyhedral meshes are practically the same as those obtained for the structured hexahedral meshes. In contrast, the full polyhedral mesh shows somewhat larger differences near the peaks in the rms velocity profiles, whereas the differences in the bulk flow are again practically the same as those for the hexahedral grids. ?? 2014 Elsevier Ltd.


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  Experimental investigation concerning the effect of natural gas percentage on performance and emissions of a DI dual fuel diesel engine


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  During the last years a great effort has been made to reduce pollutant emissions from direct injection (DI) diesel engines. Towards this, engineers have proposed various solutions, one of which is the use of gaseous fuels as a supplement for liquid diesel fuel. These engines, which use conventional diesel fuel and gaseous fuel, are referred to as dual fuel engines. The main aspiration from the usage of dual fuel (liquid and gaseous one) combustion systems is mainly to reduce particulate emissions and nitrogen oxides. One of the gaseous fuels used is natural gas, which has a relatively high auto ignition temperature and moreover is an economical and clean burning fuel. The high auto ignition temperature of natural gas is a serious advantage against other gaseous fuels since the compression ratio of most conventional DI diesel engines can be maintained. Moreover the combustion of natural gas produces practically no particulates since natural gas contains less dissolved impurities (e.g. sulfur compounds). The present contribution is mainly concerned, with an experimental investigation of the characteristics of dual fuel operation when liquid diesel is partially replaced with natural gas under ambient intake temperature in a DI diesel engine. Results are given revealing the effect of liquid fuel percentage replacement by natural gas on engine performance and emissions. ?? 2002 Elsevier Science Ltd. All rights reserved.


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  Effect of EGR on combustion and exhaust emissions in supercharged dual-fuel natural gas engine ignited with diesel fuel


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  The combustion and exhaust emissions characteristics of a supercharged dual-fuel natural gas engine with a single cylinder were analyzed. We focused on EGR (Exhaust Gas Recirculation) to achieve higher thermal efficiency and lower exhaust emissions. The combustion of diesel fuel (gas oil) as ignition sources was visualized using a high-speed video camera from the bottom of a quartz piston. The luminous intensity and flame decreased as the EGR rate increased. Furthermore, the ignition delay became longer due to the EGR. Characteristics of the combustion and exhaust emissions were investigated with changing EGR rates under supercharged conditions. The indicated mean effective pressure and thermal efficiency decreased with increasing EGR rate. In addition, NOx emissions decreased due to the EGR. In this study two-stage combustion was observed. When two-stage combustion occurred, it was supposed that auto-ignition of compressed natural gas and air mixture occurred during the flame development. However, knocking did not occur. Two-stage combustion occurred under the condition of low EGR rate and advanced injection timing. The indicated mean effective pressure and thermal efficiency increased, during two-stage combustion; however, NOx emissions also increased by a large amount compared to normal combustion. High indicated mean effective pressure, high thermal efficiency, and low NOx emissions were achieved just before the occurrence of two-stage combustion by changing EGR rate and injection timing of diesel fuel. Copyright © 2009 SAE International.


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  http://linkinghub.elsevier.com/retrieve/pii/S1877042812030376{\%}5Cnhttp://papers.sae.org/2009-01-1832/


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  Fuel reactivity effects on the efficiency and operational window of dual-fuel compression ignition engines


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  An experimental engine efficiency study was conducted that explores the effects of direct injected fuel properties on gross thermal efficiency and operational authority as functions of intake pressure and temperature, and equivalence ratios (premixed and global) using the Reactivity Controlled Compression Ignition (RCCI) combustion strategy. The experiments were conducted in a heavy-duty single-cylinder engine at constant net IMEP of 8.45 bar, 1300 rev/min engine speed, with 0% EGR, and a CA50 combustion phasing of 0.5 CA ATDC. The engine was port fueled with E85 for the low reactivity fuel and direct injected with either #2 ULSD or 3% 2-ethylhexyl nitrate doped into 91 Anti-Knock Index (AKI) gasoline for the high reactivity fuel. The reactivity of the EHN enhanced fuel has been correlated to an AKI of approximately 56 and a cetane number of approximately 28. Intake pressure and temperature were swept independently of each other while combustion phasing and load were maintained by adjusting the global fuel reactivity and DI fuel timing as needed. The results demonstrate that for fixed cycle thermodynamics, sources of engine inefficiency are functions of the premixed and global equivalence ratios. At extremes in either, excessive losses occur, decreasing the gross thermal efficiency. The study's findings demonstrate that losses can be minimized through proper balancing of the intake pressure and temperature, which are affected by fuel reactivity differences. Specifically, when the reactivity difference between the high and low reactivity fuel streams is reduced, with the EHN + Gas/E85 strategy, the control and effectiveness of the DI fuel is reduced, making combustion more abrupt. To reduce the peak pressure rise rate, leaner conditions were required, and the peak gross thermal efficiency increased. The results demonstrate that through proper optimization of both engine conditions, and fuels, increases in engine efficiency are possible with RCCI. ?? 2013 Elsevier Ltd. All rights reserved.


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  n-Butanol pyrolysis in a flow reactor was investigated at the pressures of 5, 30, 80, 200, and 760 Torr. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used for the identification of pyrolysis species and the measurement of their mole fractions. A detailed kinetic model consisting of 121 species and 658 reactions was developed to simulate the n-butanol pyrolysis. To enhance the accuracy of the model, the rate constants of unimolecular reactions of n-butanol and β-scission reactions of four n-butanol radicals (C4H8OH) were calculated with the variable reaction coordinate–transition-state theory (VRC–TST) and the Rice–Ramsperger–Kassel–Marcus (RRKM) theory coupled with the master equation method. These rates are very sensitive to the mole fractions of pyrolysis species and have been well-validated by the pyrolysis experiment. The model was further validated by the low-pressure premixed flames at different equivalence ratios, oxidation data from the jet-stirred reactor, and ignition del...


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  One dimensional numerical simulation for steady annular condensation flow in rectangular microchannels


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  The dynamic contact angle is required as a boundary condition for modelling problems in capillary hydrodynamics, including certain stages of the droplet impact problem. The dynamic contact angle differs appreciably from the static advancing or receding values, even at low velocities. This paper presents experimental results of the dynamic contact angle of spreading droplets after impacting on horizontal and inclined surfaces. Droplets of an 85% (vol.) glycerin/water solution (D = 2.45 mm) and water (D = 2.7 mm) were used in the study. Two surfaces, wax (low wettable) and glass (high wettable) are used, to study the effect of surface wettability (static contact angle). The results include the dynamic contact angle of droplets together with the contact line velocity and the dimensionless spread factor as a function of time. © 2005 Elsevier Inc. All rights reserved.


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  Combustion Characteristics of Hydrocarbon Droplets Induced by Photoignition of Aluminum Nanoparticles


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  In case of coil embolization of a giant or a multilobular aneurysm, it is difficult to fill an aneurysm sac completely with coils, therefore, partial blocking of an aneurysm sac is inevitable. Blood flow characteristics, which may influence embolization process of an aneurysm, are affected by the locations of coils for partially blocked aneurysms. Blood flow fields inside an aneurysm are also influenced by the geometry of a parent vessel. In order to suggest the coil locations effective for aneurysm embolization, the blood flow fields of lateral aneurysm models were analyzed for different coil locations and parent vessel geometries. Flow rate into an aneurysm sac from a parent vessel (inflow rate) and wall shear stress were also calculated. Inflow rates were smaller and low wall shear regions were larger in the distal neck blocked model comparing to the dome blocked models. In the distal neck blocked model, inflow volume was smaller by 31% (straight parent vessel model) and 34% (curved parent vessel model) comparing to other models. The time averaged values of normalized low wall shear regions were 4% and 12% greater in the distal neck blocked models with a straight and a curved parent vessel, respectively. Since smaller inflow and low wall shear stress provide hemodynamic environment promoting thrombus embolization, distal neck should be the effective coil location for aneurysm embolization.


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  Spray performance and steadiness of an effervescent atomizer and an air- core-liquid-ring atomizer for application in spray drying processes of highly concentrated feeds


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  The formation of engine pollutants directly relates to the local composition of air/fuel mixture within the combustion chamber. The evaporation of wall film, formed by spray/wall impingement, is much slower than free droplets and has strong effects on engine emission. A finite diffusion wall film evaporation model using continuous thermodynamics is developed for multi-dimensional engine modeling, accounting the multi-component nature of practical fuels, which is essentially a complicated liquid mixture. The vaporization rate is evaluated using the turbulent boundary-layer assumption and a quasi-steady approximation. Third-order polynomials are used to model the fuel composition and the temperature profiles within the liquid phase for accurate predictions of surface properties, which are important for evaluating the mass fraction, moments and heat flux. The governing equations for the film are then reduced to a set of ordinary differential equations and significantly reduce the computational cost while retaining adequate accuracy in the solution. The model is verified against high precision numerical solutions obtained with the finite difference method that solves the governing partial differential equations using a fine grid over the same computational domain. Good agreement is obtained for the evaporation of a film on a flat plate under various conditions. The boiling point of a practical fuel is found to increase steadily with evaporation and may surpass the wall temperature. The evaporation process can therefore be reverted to non-boiling evaporation. This phenomenon is unique to multi-component liquids and not observed during the evaporation process of single component liquids. The presented model, with improved computational efficiency and adequate accuracy, is applicable in multi-dimensional engine simulations. Finally, the model is used for a spray/wall impingement simulation. The results show that the multi-component nature of a practical fuel can have significant implications on the distributions of fuel concentration and composition during the spray/wall interaction. ?? 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.


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  Development of a Phenomenological Dual-Fuel Natural Gas Diesel Engine Simulation and Its Use for Analysis of Transient Operations


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  Detailed characterization of diesel-ignited propane and methane dual-fuel combustion in a turbocharged direct-injection diesel engine


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  This paper presents an experimental analysis of dual-fuel combustion based on the performance, emissions, and in-cylinder combustion measurements with gaseous propane or gaseous methane as the primary fuel and diesel as the pilot fuel. Two different sets of experiments were performed on a 1.9 litre four-cylinder engine at a constant engine speed of 1800 r/min: first, constant-pilot-quantity experiments, allowing the primary fuel concentration and the brake mean effective pressure to vary; second, constant-brake-mean- effective-pressure experiments, allowing the percentage energy substitution of the primary fuel and the pilot quantity to vary. In the constant-pilot-quantity experiments, the apparent heat release rate profiles showed the influence of the preignition chemistry and gaseous fuel burn rates on the dual-fuel combustion phasing and duration, the fuel conversion efficiency, and the engine-out emissions. With a fixed pilot quantity, the nitrogen oxide emissions were either reduced or unaffected while the smoke levels were increased or unaffected with increasing primary fuel concentration. The carbon monoxide and total unburned hydrocarbon emissions decreased and the fuel conversion efficiency increased as the pilot quantity or the primary fuel concentration was increased. Overall, diesel-propane combustion yielded higher carbon monoxide emissions, lower total unburned hydrocarbon emissions, and slightly higher fuel conversion efficiencies than diesel-methane combustion did. In the constant-brake-mean-effective- pressure experiments, at a brake mean effective pressure of 2.5 bar, diesel-propane and diesel-methane combustion behaved very similarly, the primary differences being in the preignition chemistry and the ignition delay trends. At a brake mean effective pressure of 2.5 bar, the nitrogen oxide and smoke emissions were simultaneously reduced while the carbon monoxide and total unburned hydrocarbon emissions were increased. At a brake mean effective pressure of 10 bar (a baseline diesel fuel conversion efficiency of 38%), diesel-propane fueling was prone to rapid earlier combustion while diesel-methane combustion was slower. For diesel-methane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency decreased to 37.1% as the percentage energy substitution was increased to 51%. For diesel-propane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency increased to 39% as the percentage energy substitution was increased to 46%. At high-brake-mean-effective-pressure-high-percentage- energy-substitution and large-pilot-quantity-high-equivalence-ratio conditions, diesel-propane combustion showed an apparent departure from the classical three-phase dual-fuel combustion to a distributed volumetric combustion process that resembled a "diesel-regulated homogenous-charge-compression-ignition- like" combustion process. © 2013 IMechE.


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  The liquid feedstock or suspension as a different mixture of liquid fuel ethanol and water is numerically studied in high-velocity suspension flame spray (HVSFS) process, and the results are compared for homogenous liquid feedstock of ethanol and water. The effects of mixture on droplet aerodynamic breakup, evaporation, combustion, and gas dynamics of HVSFS process are thoroughly investigated. The exact location where the particle heating is initiated (above the carrier liquid boiling point) can be controlled by increasing the water content in the mixture. In this way, the particle inflight time in the high-temperature gas regions can be adjusted avoiding adverse effects from surface chemical transformations. The mixture is modeled as a multicomponent droplet, and a convection/diffusion model, which takes into account the convective flow of evaporating material from droplet surface, is used to simulate the suspension evaporation. The model consists of several sub-models that include premixed combustion of propane-oxygen, non-premixed ethanol-oxygen combustion, modeling of multicomponent droplet breakup and evaporation, as well as heat and mass transfer between liquid droplets and gas phase. © 2014 ASM International.


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  A Multi-Dimensional CFD-Chemical Kinetics Approach in Detection and Reduction of Knocking Combustion in Diesel-Natural Gas Dual-Fuel Engines Using Local Heat Release Analysis


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  Dual-fuel diesel-natural gas (NG) engine exhibits higher power density and lower specific emissions compared to dedicated diesel engines. However, high intake temperatures, high compression ratios, combined with high engine loads may lead to engine knock. This is potentially a limiting factor on engine downsizing and getting higher power. In the present study, the combustion process under knocking conditions has been investigated in a dual-fuel diesel-NG engine. A comprehensive multi-dimensional simulation framework was generated by integrating the CHEMKIN chemistry solver into the KIVA-3V code. A detailed chemical kinetics mechanism was used for n-heptane and methane as diesel and NG surrogates. Combination of detailed chemical kinetics and detailed fluid dynamics calculation enabled the model to take into account the characteristics of most pronounced knock type in dual-fuel engines, so called end-gas knock. Within the CFD computational domain, eight regions that are the representatives of the dual-fuel heat release patterns have been selected to extract local properties. Using local knock identification factors, end-gas knock was observed in abnormal combustion cases. A new Knock Intensity factor (K.I) was introduced based on local heat release rate. Using developed knock prediction method, results showed knock could be mitigated by using EGR. Moreover, effect of premixed methane equivalence ratio on knocking combustion was investigated. © 2013 SAE International.


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  Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions


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  Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.


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  An experimental study of injection and spray characteristics of diesel and gasoline blends on a common rail injection system


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  The injection and spray characteristics of diesel and gasoline blends are investigated on a common rail injection system. The injection rate, fuel spray evolution process (tip penetration distance, spray cone angle, projected spray area and relative brightness intensity contour) and microscopic droplet features are analyzed. The results show that diesel and gasoline blends have higher volumetric injection rates, earlier starts of injection and shorter injection delays, but little variances are observed in the mass injection rates for different test fuels. Increased gasoline proportion in the test blends causes slightly decreased spray tip penetration distance but increased spray cone angle. Also, more smaller-size droplets are observed in the fuel jet of the diesel and gasoline blends, indicating that the spray breakup and atomization processes are promoted.


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  The brake thermal efficiency and exhaust emission issues are still not fully-resolved to diesel/natural gas dual fuel engines. To better understand the effect of pilot diesel ignition mode on combustion and emissions characteristics of dual fuel engines, a detailed study concerned with diesel injection timing was conducted. The testing work was operated on a 6-cylinder turbocharged intercooler diesel/natural gas dual fuel heavy-duty engine at light load operations, and diesel injection timing was controlled over a very wide range. The investigated results show that the diesel injection timing (Tinj) has an obvious effect on pilot diesel ignition mode. A significant advancing Tinj leads to pilot diesel ignition mode differs from traditional diesel engine compression ignition mode in the sense that it does not occur at a specific place in the spray, which is a two-stage autoignition mode. With advancing Tinj, engine combustion and emissions characteristics, including cylinder pressure, cylinder temperature, heat release rate, start of combustion (SOC), ignition delay, combustion duration, crank angle of 50% heat release (CA50), nitrogen oxides (NOx) and total hydrocarbon (THC), show completely different variation trends in different ignition modes. Overall, higher thermal efficiency and lower emissions can be achieved simultaneously in two-stage autoignition mode. Satisfactory results can be obtained with higher brake thermal efficiency (35%), lower NOx (60ppm) and THC (0.4%) emissions, when Tinj is 42.5°CA BTDC.


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  International Journal of Heat and Mass Transfer Condensation heat transfer in rectangular microscale geometries


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  Interactions of Multi-hole DI Sprays with Charge Motion and their Implications to Flexible Valve-trained Engine Performance


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  Stability of rich laminar hydrogen-air flames in a model with detailed transport and kinetic mechanisms


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  Spark assisted compression ignition (SACI) is a practical mode for controlling the heat release rate of low temperature combustion (LTC). While flames are key phenomena in the SACI combustion process, they may not always be effective or viable under the mildly stratified and highly dilute low burned gas temperature conditions of LTC. To better understand the limits of flammability or flame effectiveness, this work explores combustion within a single cylinder direct injection engine near the high load limit of the HCCI combustion regime, where spark induced flame propagation has been seen to affect combustion phasing and heat release rate. Flame limiting conditions were identified using progressively more advanced spark timing, up to 120 before top dead center, for differing levels of air and EGR dilution while holding the chemical energy content of the charge constant. Under air dilute conditions, the measured combustion phasing advanced from 8 to 0 after top dead center with spark advance, while almost no effect was seen under EGR dilute conditions. Estimates of the experimental global and local state conditions were made at the time of spark using heat release analysis and a KIVA-3V engine model, respectively, and the flammability for each case was evaluated using the Karlovitz criterion. The results show that fuel rich stratification near the spark plug was likely responsible for the observed variations in the SACI flame behavior.


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  Flame Kernel Development and its Effects on Engine Performance with Various Spark Plug Electrode Configurations


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  Numerical investigation of the spray-mesh-turbulence interactions for high-pressure, evaporating sprays at engine conditions


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  This work presents a numerical methodology to simulate evaporating, high pressure Diesel sprays using the Eulerian-Lagrangian approach. Specific sub-models were developed to describe the liquid spray injection and breakup, and the influence of the liquid jet on the turbulence viscosity in the vicinity of the nozzle. To reduce the computational time and easily solve the problem of the grid dependency, the possibility to dynamically refine the grid where the fuel-air mixing process takes place was also included. The validity of the proposed approach was firstly verified simulating an evaporating spray in a constant-volume vessel at non-reacting conditions. The availability of a large quantity of experimental data allowed us to investigate in detail the effects of grid size, ambient diffusivity and used spray sub-models. In this way, different guidelines were derived for a successful simulation of the fuel-air mixture formation process. Finally, fuel injection and evaporation were simulated in an optical engine geometry and computed mixture fraction distributions were compared with experimental data. © 2010 Elsevier Inc.


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  Experimental and Numerical Characterization of Gasoline-Ethanol Blends from a GDI Multi-Hole Injector by Means of Multi-Component Approach


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  This paper reports an experimental and numerical investigation of the spray structure development for pure gasoline fuel and two different ethanol-gasoline blends (10% and 85% ethanol). A numerical methodology has been developed to improve the prediction of the pure and blends fuel spray. The fuel sprays have been simulated by means of a 3D-CFD code, adopting a multi-component approach for the fuel simulations. The vaporization behavior of the real fuel has been improved testing blends of 7 hydrocarbons and a reduced multi- component model has been defined in order to reduce the computational cost of the CFD simulations. Particular care has been also dedicated to the modeling of the atomization and secondary breakup processes occurring to the GDI sprays. The multi-hole jets have been simulated by means of a new atomization approach combined with the Kelvin- Helmholtz/Rayleigh-Taylor hybrid model. At the nozzle hole exit an initial distribution of atomized droplets has been predicted by the numerical approach taking into account cavitation phenomena and turbulent effects. Sprays have been investigated using a 6-hole gasoline direct- injection (GDI) injector and injecting fuel into an optically- accessible constant volume vessel at 5.0, 10.0, and 15.0 MPa of injection pressure, at ambient back pressure. Mie- scattering images have been performed using a high-speed camera and a pulsed-wave flash system which is able to track liquid phase in order to estimate the spray development, morphology and cone angle. Moreover fuel injection rates measurements have been carried out using a meter working on the Bosch tube principle to characterize the injected mass. The liquid fuel penetration registered highest values for gasoline fuel with respect to its blends with ethanol at different percentages.


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  Theoretical and experimental studies dealing with the spray ignition phenomena are reviewed. Two major topics covered are external-source ignition of liquid fuel sprays and spontaneous spray ignition. Experimental and theoretical investigations of external-source ignition of sprays employing different configurations are discussed first. Three major topics included here are: (i) ignition of quiescent and flowing fuel sprays; (ii) ignition of monodisperse and polydisperse sprays; and (iii) ignition of single-component and multicomponent fuel sprays. Then, experimental studies of autoignition of sprays employing constant-volume enclosures, injection in a uniform air flow, and shock tube techniques, are discussed. Theoretical investigations dealing with spray autoignition phenomena range from phenomenological models to one-dimensional numerical models using global one-step as well as detailed multistep chemistry, and to multidimensional simulations with reduced mechanisms. These models are also discussed in the review. Finally, some advanced topics which are common to both external-source ignition and spontaneous ignition are identified and discussed. An attempt is made to provide a common link between the three dominant ignition modes in sprays, namely individual droplet ignition, droplet cluster ignition, and spray ignition. In a similar manner, common features of external-source ignition and spontaneous ignition of sprays are identified. A general spray ignition model along with important numerical and physical issues are presented. The effect of pressure on spray ignition processes is also discussed. Potential topics for further research are suggested.


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  Curve matching , a generalized framework for models / experiments comparison : An application to n- heptane combustion kinetic mechanisms


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  In the present study a reduced chemical reaction mechanism for biodiesel surrogate fuel was developed and validated for multi-dimensional engine combustion simulations. An existing detailed methyl butanoate mechanism that contained 264 species and 1219 reactions was chosen to represent the oxygenated portion of the fuel. The reduction process included flux analysis, ignition sensitivity analysis, and optimization of reaction rate constants under constant volume conditions. The current reduced mechanism consists of 41 species and 150 reactions and gives predictions in excellent agreement with those of the comprehensive mechanism.In order to validate the mechanism under biodiesel-fueled engine conditions, it was combined with another skeletal mechanism for n-heptane oxidation. This combined reaction mechanism can be used to adjust the energy content of the fuel, and account for diesel/biodiesel blend engine simulations. The combined mechanism, ERC-bio, contains 53 species and 156 reactions. Biodiesel-fueled engine operation was successfully simulated using the ERC-bio mechanism.


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  In order to improve the accuracy of the WAVE breakup model for an evaporating spray, it was calibrated using a series of diesel spray experiments with different orifice diameters, injection pressures, background gas densities and temperatures. The calibration focused on liquid length and spray (vapor) penetration. Based on the calibration results, it is concluded that the standard WAVE model with a constant C2, which is an adjustment parameter for breakup time, accurately predicts liquid length and spray penetration with a variety of orifice diameters, injection pressures and background gas densities. However, the same cannot be said for background temperature. Background temperature strongly affects the C2 value. Particularly, the C2 decreases with an increase in background temperature. Interestingly, the relationship between the C2 value and the background temperature seems to be of approximate inverse proportion. Therefore, due to this relationship between the C2 value and background temperature, and in order to obtain greater simulation accuracy, the proposed WAVE model with a variable C2 was developed and used to simulate a single-cylinder diesel engine. It was found that there is a significant decrease in liquid length alongside the development of the in-cylinder spray and combustion process. This is reasonable because liquid droplets break-up and evaporate faster in a higher temperature environment. Moreover, the result is in accordance with images from optical diesel engine experiments captured and performed by others.


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  With the increasing concern regarding diesel engine emissions, including nitrogen oxides (NOX) and particulate matter (PM), and the rising of energy demand as well, the utilization of alternative fuels in diesel engine has been found to be an attractive solution. Natural gas is a very promising and highly attractive fuel because of its domestic availability, widespread distribution infrastructure, low cost, and clean-burning qualities to be used as a transportation fuel. Natural gas/diesel dual fuel is an operation mode in which natural gas is introduced into the intake air upstream of the manifold and then ignited by the direct injected diesel in the cylinder. The aim of this paper is to identify the potential use of natural gas/diesel dual fuel on diesel engine. In this literature review, the combustion, emission and performance characteristics of natural gas/diesel dual fuel combustion-mode published mainly in scientific journals have been collected and critically analyzed. A wide range of natural gas mass ratio which represents the mass fraction of natural gas in the total fuel and different types of engines were involved. It has been found that dual fuel mode has a lower compression pressure and a longer ignition delay compared with normal diesel mode. The application of dual fuel mode significantly decreases the NOX, carbon dioxide (CO2) and PM emissions. However, the hydrocarbon (HC) and carbon monoxide (CO) emissions may increase by several times or even more than 100 times in comparison to normal diesel combustion. And there appears a trade-off relationship between NOX and HC emissions with dual fuel mode. The engine power is decreased up to 2.1% at dual fuel mode, but the power loss can be reduced or recovered by changing some of the operating parameters. The brake thermal efficiency (BTE) of dual fuel mode is lower at low and intermediate loads, while under high engine load conditions it is similar or a little higher when compared with normal diesel mode, and the maximum increase is about 3%. The COVIMEP seems to be generally higher than normal diesel mode and it decreases with the increasing engine load.


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  Emulsified fuel remains a potential solution to meet the increasingly stringent emission regulations for internal combustion engines due to its capability of simultaneously reducing NOx and particular matter (PM). In this study, emulsified diesels with 10% and 20% water by volume were studied. The stability of the water emulsified diesel was first investigated in terms of the hydrophilic-lipophilic-balance (HLB) value. Based on the stability test, a suitable surfactant composition for the diesel/water interfacial condition was given and the separation tendency of the fuel with different water volumetric ratio was analyzed. The emulsions were later injected and combusted in a pre-burn type constant volume chamber, which is able to provide high ambient temperature and pressure to mimic real engine operation conditions. High speed imaging was used to capture the spray and combustion process under various conditions. Results show longer initial liquid penetration for emulsified diesel under low ambient temperatures. Longer ignition delay of emulsified diesel also provided more air/fuel mixing time, thus significantly lowering the soot luminosity. Although droplet micro-explosion has been intensively studied, its behavior in a burning spray is much less reported. This study in particular focused on micro-explosion in a burning spray. Broadband natural flame images were recorded with intentional overall over-exposure such that the central lift-off region could be illuminated by soot incandescence. Puffing and disruptive droplet combustion was consistently observed at high ambient temperature in the central lift-off region with emulsified diesel indicating the occurrence of micro-explosion in a burning spray flame. It is demonstrated that micro-explosion is not only able to enhance the secondary breakup, but also affect the primary breakup under certain conditions, which to the author's awareness has not been reported in any previous literature. Lower injection pressure and higher ambient temperature favor the occurrence of micro-explosion before primary breakup as a competition between the micro explosion delay time and the primary breakup time. ?? 2014 Elsevier Ltd.


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  Kinetic Study of Low Temperature Oxidation of N-pentane with Nitric Oxide Addition in a Jet Stirred Reactor.


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  The effect of noncondensable gas on condensation heat transfer inside horizontal tubes was investigated experimentally. Air was used as the noncondensable gas. The effects of inlet noncondensable gas mass fraction, inlet gas mixture mass flux and inlet pressure on overall heat transfer performance were analyzed. Moreover, local heat transfer performance was investigated by comparing centerline temperatures and local heat transfer coefficients. The results showed that the overall heat transfer coefficient decreased as inlet noncondensable gas fraction increased. Increasing inlet mass flux could enhance the heat transfer rate and overall heat transfer coefficient. Furthermore, the heat transfer rate showed an increasing trend, whereas the overall heat transfer coefficient decreased with increase of inlet pressure. The local heat transfer coefficient decreased along the condenser tube due to the decrease of gas mixture Reynolds number and the increase of liquid film thickness and local air fraction. For stratified flow, the local heat transfer coefficient at the top part was higher than that at the bottom owing to the asymmetrical liquid film. However, this gap gradually decreased along the tube, especially at higher inlet noncondensable gas fraction. Finally, two correlations respectively for stratified flow and annular flow regimes were developed, using the modified Froude number as the indicator of transition from stratified to annular flow. © 2014 Elsevier Inc.


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  An experimental and modelling study of the combustion and emission characteristics for gasoline-diesel dual-fuel engines


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  In this study, the combustion and emissions characteristics of gasolinediesel dual-fuel operation were investigated both experimentally and numerically. Gasoline fuel was injected through an intake port, and diesel fuel was injected directly into the combustion chamber to trigger combustion. The tested concentrations of diesel fuel were 30percent and 40percent, and it was found that a smaller amount of diesel fuel forms a more homogeneous mixture. Numerical calculations were performed for selected injection timings (i.e. 20 crank angle (CA) after top dead centre) for increased understanding of the combustion regime of dual-fuel combustion using the KIVA code coupled with the primary reference fuels mechanism. The injection timings of the diesel fuel were swept from 40 to +3 CA.The results showed that gasolinediesel dual-fuel operation exhibited significant reductions in soot and nitrogen oxide emissions by suppressing the formation of locally rich mixtures or high-temperature regions. However, the carbon monoxide and hydrocarbon emissions were increased for a wide range of injection timings.


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  Impact of Biodiesel Emission Products from a Multi-Cylinder Direct Injection Diesel Engine on Particulate Filter Performance


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  Computationally Efficient Simulation of Multicomponent Fuel Combustion Using a Sparse Analytical Jacobian Chemistry Solver and High-Dimensional Clustering


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  The need for more efficient and environmentally sustainable internal combustion engines is driving research towards the need to consider more realistic models for both fuel physics and chemistry. As far as compression ignition engines are concerned, phenomenological or lumped fuel models are unreliable to capture spray and combustion strategies outside of their validation domains - typically, high-pressure injection and high-temperature combustion. Furthermore, the development of variable-reactivity combustion strategies also creates the need to model comprehensively different hydrocarbon families even in single fuel surrogates. From the computational point of view, challenges to achieving practical simulation times arise from the dimensions of the reaction mechanism, which can be of hundreds species even if hydrocarbon families are lumped into representative compounds and, thus, modeled with nonelementary, skeletal reaction pathways. In this case, it is also impossible to pursue further mechanism reductions to lower dimensions. central processing unit (CPU) times for integrating chemical kinetics in internal combustion engine simulations ultimately scale with the number of cells in the grid and with the cube number of species in the reaction mechanism. In the present work, two approaches to reduce the demands of engine simulations with detailed chemistry are presented. The first one addresses the demands due to the solution of the chemistry ordinary differential equation (ODE) system, and features the adoption of SpeedCHEM, a newly developed chemistry package that solves chemical kinetics using sparse analytical Jacobians. The second one aims to reduce the number of chemistry calculations by binning the computational fluid dynamics (CFD) cells of the engine grid into a subset of clusters, where chemistry is solved and then mapped back to the original domain. In particular, a high-dimensional representation of the chemical state space is adopted for keeping track of the different fuel components, and a newly developed bounding-box- constrained k-means algorithm is used to subdivide the cells into reactively homogeneous clusters. The approaches have been tested on a number of simulations featuring multicomponent diesel fuel surrogates and different engine grids. The results show that significant CPU time reductions, of about 1 order of magnitude, can be achieved without loss of accuracy in both engine performance and emissions predictions, prompting for their applicability to more refined or full-sized engine grids. Copyright © 2014 by ASME.


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  The influence of pilot-main injection matching on DI diesel engine combustion using an endoscopic visualization system


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  Several studies have found that pilot injection enhances the mixture and combustion of the main injection fuel, which effectively improves performance and reduces emission. However, only a few investigations have focused on remediating the negative effect of pilot injection, which is that it restricts the advancement of the split injection. Therefore we study the influence of pilot-main injection matching on the combustion of diesel engines. The experiment was conducted using a single-cylinder direct injection diesel engine equipped with a high-pressure common rail system and an endoscopic visualization system. Through the endoscopic visualization method, the effect of pilot injection on mixing, combustion characteristics, and soot formation of the main injection fuel was investigated. The results show that the thermos atmosphere of a pilot injection with the correct parameters (a small pilot ratio and short dwell time) improves the mixture and combustion of the main injection fuel, which shortens the combustion duration. Compared with single injection as well as with split injections with longer dwell times or larger pilot injections, the pilot injection with a small pilot ratio and short dwell time obtained higher thermal efficiency. Also flame temperature peak and soot concentration decreased. For spilt injection with longer dwell time, the TA by pilot injection traversed far away from the main injection, thus not to promote evaporation, mixing, and ignition of the main injection fuel; for spilt injection with larger pilot injection, the TA by pilot injection will constraint the combustion of the main injection fuel, deteriorating mixing and combustion.


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  Blood flow in intracranial aneurysms treated with Pipeline embolization devices: computational simulation and verification with Doppler ultrasonography on phantom models.


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  PURPOSE The aim of this study was to validate a computational fluid dynamics (CFD) simulation of flow-diverter treatment through Doppler ultrasonography measurements in patient-specific models of intracranial bifurcation and side-wall aneurysms. METHODS Computational and physical models of patient-specific bifurcation and sidewall aneurysms were constructed from computed tomography angiography with use of stereolithography, a three-dimensional printing technology. Flow dynamics parameters before and after flow-diverter treatment were measured with pulse-wave and color Doppler ultrasonography, and then compared with CFD simulations. RESULTS CFD simulations showed drastic flow reduction after flow-diverter treatment in both aneurysms. The mean volume flow rate decreased by 90% and 85% for the bifurcation aneurysm and the side-wall aneurysm, respectively. Velocity contour plots from computer simulations before and after flow diversion closely resembled the patterns obtained by color Doppler ultrasonography. CONCLUSION The CFD estimation of flow reduction in aneurysms treated with a flow-diverting stent was verified by Doppler ultrasonography in patient-specific phantom models of bifurcation and side-wall aneurysms. The combination of CFD and ultrasonography may constitute a feasible and reliable technique in studying the treatment of intracranial aneurysms with flow-diverting stents.


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  http://www.ncbi.nlm.nih.gov/pubmed/25754367{\%}5Cnhttp://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=PMC4372715


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  Impact of Thermal Expansion and Lewis Number on Premixed Flame Propagation in Channels with Adiabatic and Isothermal , Nonslip Walls


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  A multicomponent droplet vaporization model including both gas and$\backslash$nliquid phase transport processes was developed for multidimensional$\backslash$nspray computations. This paper focuses on two effects altering vaporization$\backslash$nin a high-pressure and high-temperature environment. One effect is$\backslash$non droplet surface regression caused by a higher vaporization rate.$\backslash$nThis effect is well characterized by the Lewis number and the Peclet$\backslash$nnumber with the regression velocity. Formulas based on the two numbers$\backslash$nwere included to improve model accuracy. The other effect is on the$\backslash$nnonideal behavior and was covered in the model by using the Peng-Robinson$\backslash$nequation of state to determine phase equilibrium at the droplet surface.$\backslash$nThe model was validated by the results from an accurate simplified$\backslash$nvortex model and experimental measurements, and excellent agreements$\backslash$nwere demonstrated. Further comparisons against the model without$\backslash$nthe two effects and an infinite diffusion model show that significant$\backslash$nimprovement was achieved by the model for single-droplet and spray$\backslash$ncomputations.


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  Two idealized models for the preheat stage of liquid droplets are analyzed theoretically. These models contain the effects of transient heat conduction and evaporation. It is assumed that the droplet surface area decreases linearly with time. This assumption necessitates the solution of moving boundary problems . These models, however, do not consider gas-phase mass transport . In the finite-gradient model, the temperatures of both the droplet and surrounding hot gases vary spatially and temporally. In the zero-gradient model the gas temperature varies spatially and temporally but the droplet temperature varies only temporally, i.e., the droplet temperature is spatially uniform. Numerical examples, which require extensive calculations of confuent hypergeometric functions, are presented for typical values of the droplet latent heat and evaporation rate constant. The temperature profiles given by the finite-gradient and zero-gradient models agree to within 20 percent of each other for all cases examined.


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  Copyright © 2017 ASME. Autoignition behavior of jet fuel relevant pure hydrocarbon components have been investigated using a rapid compression machine and validated with chemical kinetics simulations. Employment of alternative energy sources can alleviate the energy crisis that this generation confronts. Alternative fuels can be obtained from diverse feedstocks through a variety of pathways. Due to this diversity, numerous alternative fuels have unique compositions which are distinct from conventional fuels. Evaluating differences in combustion behavior of these fuels is a pivotal and initial task of drop-in fuel applications. Hydrocarbon species in conventional and alternative fuels can be broadly classified into four major groups: normal alkanes, isoalkanes, cyclic alkanes, and aromatics. The focus of this study are normal and isoalkanes, where three isomers of dodecane have been selected and tested to evaluate the contribution of chemical structure in autoignition behavior. Ndodecane, which is a straight chain of twelve carbons, and two isododecanes with different degrees of branching are tested in heated rapid compression machine (RCM) at University of Illinois, Urbana-Champaign. Measurements were made at compressed pressures (Pc) of 10 and 20 bar, with fuel and oxidizer (dry air) mixture of equivalence ratio (?) at unity, 0.5 and 0.25. Compressed temperatures (Tc) of the tests are in low to intermediate range (620 K \textless T \textless 710 K) where NTC behavior has been observed for heavily branched isododecane. The direct test chamber method is used for precise and reliable measurements. Ignition delay times of n-dodecane are the shortest among tested fuels, as expected. Extremely low reactivity of the pentamethylheptane, heavily branched isododecane has been observed. The results have also compared to JP-8 as a reference. For several conditions where first and second stage ignition are distinguishable, it is shown that temperature dependency is greater for first stage ignition delay than second stage.


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  Multidimensional Numerical Investigation of NO x Formation in a Burner Coupled Flow Tube Configuration : NO x Kinetics in Post , Pre and Flame Locations


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  Experimental study on combustion characteristics of a spark-ignition engine fueled with natural gas–hydrogen blends combining with EGR


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  An experimental study on the effect of hydrogen fraction and EGR rate on the combustion characteristics of a spark-ignition engine fueled with natural gas–hydrogen blends was investigated. The results show that flame development duration, rapid combustion duration and total combustion duration are increased with the increase of EGR rate and decreased with the increase of hydrogen fraction in the blends. Hydrogen addition shows larger influence on flame development duration than that on rapid combustion duration. The coefficient of variation of the indicated mean effective pressure increases with the increase of EGR rate. And hydrogen addition into natural gas decreases the coefficient of variation of the indicated mean effective pressure, and this effectiveness becomes more obviously at high EGR rate. Engine fueled with natural gas–hydrogen blends combining with proper EGR rate can realize the stable low temperature combustion in gas engine.


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  As a result of recent focus on the control of Low Temperature Combustion (LTC) modes, dual-fuel combustion strategies such as Reactivity Controlled Compression Ignition (RCCI) have been developed. Reactivity stratification of the auto-igniting mixture is thought to be responsible for the increase in allowable engine load compared to other LTC combustion modes such as Homogenous Charge Compression Ignition (HCCI). The current study investigates the effect of ethanol intake fuel injection on in-cylinder formaldehyde formation and stratification within an optically accessible engine operated with n-heptane direct injection using optical measurements and zero-dimensional chemical kinetic models. Images obtained by Planar Laser Induced Fluorescence (PLIF) of formaldehyde using the third harmonic of a pulsed Nd:YAG laser indicate an increase in formaldehyde heterogeneity as measured by the fluorescence signal standard deviation. The experimental observations are complemented by a discussion regarding definitions of “reactivity”.


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  Combustion Kinetics of Conventional and Alternative Jet Fuels using a Hybrid Chemistry (HyChem) Approach


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  https://www.researchgate.net/profile/Kun{\_}Wang42/publication/316582611{\_}Combustion{\_}Kinetics{\_}of{\_}Conventional{\_}and{\_}Alternative{\_}Jet{\_}Fuels{\_}using{\_}a{\_}Hybrid{\_}Chemistry{\_}HyChem{\_}Approach/links/5904eedd4585152d2e945903/Combustion-Kinetics-of-Conventional-and-Alternative


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  Multidimensional Simulation of PCCI Combustion Using Gasoline and Dual-Fuel Direct Injection with Detailed Chemical Kinetics


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  Homogeneous or partially premixed charge compression ignition combustion is considered to be an attractive alternative to traditional internal combustion engine operation because of its extremely low levels of pollutant emissions. However, since it is difficult to control the start of combustion timing, direct injection of fuel into the combustion chamber is often used for combustion phasing control, as well as charge preparation. In this paper, numerical simulations of compression ignition processes using gasoline fuel directly injected using a low pressure, hollow cone injector are presented. The multi-dimensional CFD code, KIVA3V, that incorporates various advanced sub-models and is coupled with CHEMKIN for modeling detailed chemistry, was used for the study. Simulation results of the spray behavior at various injection conditions were validated with available experimental data. Then predictions of gasoline HCCI operations using detailed chemical kinetics were compared with experimental measurements for various charge equivalence ratios and injection timings. The results show good agreement with the experimental data in terms of pressure, apparent heat release profile and emissions. Further, the numerical code was modified to be able to simulate the combustion of gasoline pre-mixtures with ignition by diesel fuel direct injection and simulation results of the dual-fuel combustion are presented.


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  The limitations of an existing characteristic-time combustion (CTC) model are explored and a new combustion model is developed and applied to simulate combustion in dual-fuel engines in which the premixed natural gas is ignited by the combustion flame initiated by a diesel spray. The model consists of a diesel auto-ignition model and a flame propagation model. A G-equation-based model previously developed to simulate SI engine combustion was incorporated with an auto-ignition model to simulate the flame propagation process in partially premixed environments. The computer code is based on the KIVA-3V code and consists of updated sub-models to simulate more accurately the fuel spray atomization, auto-ignition, combustion, and emissions processes. Modifications were made to implement the level set G-equation approach and to track the location of the flame as a function of the turbulent flame speed, flame curvature, flow velocity, and the movement of the computational mesh in the engine environment. Good agreement with engine experiments was obtained by using the present model.


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  Effects of B20 Fuel and Catalyst Entrance Section Length on the Performance of UREA SCR in a Light-Duty Diesel Engine


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  A combustion model for multi-component fuels using a physical surrogate group chemistry representation (PSGCR)


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  A combustion model to simulate the oxidation of multi-component fuels has been developed and applied to model autoignition combustion processes. The model is called the Physical Surrogate Group Chemistry Representation (PSGCR) method, which combines a multi-component fuel model to describe the physical properties of the fuel with reduced reaction mechanisms to represent the chemistry of the fuel components. A group of physical surrogate (PS) components are used to describe the fuel's physical properties, such as the distillation profile, specific gravity, lower heating value and hydrogen-to-carbon (H/C) ratio. The oxidation processes of the fuel are modeled using skeletal reaction mechanisms for a group of chemical surrogate (CS) components that employ generic reactions as well as detailed reaction kinetics. The generic reactions were built to model unavailable reaction pathways from physical surrogates to the base CS components or their intermediate species. The model includes the 6 major chemical classes of typical hydrocarbon fuels, i.e., n-paraffins, iso-paraffins, olefins, naphthenes, aromatics and oxygenates, and 65 representative hydrocarbon components are included in a data base for the physical surrogate components and 43 chemical surrogate components are considered for the group chemistry representation. Six types of generic reaction sets are proposed to model the oxidation of 15 physical surrogate components that are called extended-CS (chemical surrogate) components. The present generic reactions are modeled such that the major characteristics of the oxidation process of the fuel components are included in a consistent manner. The final version of the PSGCR reaction mechanism consists of 264 species and 1292 reactions. Validation of the reaction mechanisms was performed by comparing predicted ignition delay times with experimental measurements and/or predictions from comprehensive mechanisms available in the literature. The model was also validated against HCCI experimental data of the FACE fuels. Then the model was applied to simulate practical diesel fuel (F76) spray combustion in a constant volume chamber, and the predicted ignition delay times of the surrogate model fuel were compared with measured values. The results show that the present PSGCR method captures the combustion characteristics of complex multi-component fuels, giving reliable performance for combustion predictions, as well as computational efficiency improvements for multi-dimensional CFD simulations through the use of reduced mechanisms.


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  In the effort to reduce pollutant emissions from diesel engines various solutions have been proposed, one of which is the use of natural gas as supplement to liquid diesel fuel, with these engines referred to as fumigated, dual fuel, compression ignition engines. One of the main purposes of using natural gas in dual fuel (liquid and gaseous one) combustion systems is to reduce particulate emissions and nitrogen oxides. Natural gas is a clean burning fuel; it possesses a relatively high auto-ignition temperature, which is a serious advantage over other gaseous fuels since then the compression ratio of most conventional direct injection (DI) diesel engines can be maintained high. In the present work, an experimental investigation has been conducted to examine the effects of the total air–fuel ratio on the efficiency and pollutant emissions of a high speed, compression ignition engine located at the authors' laboratory, where liquid diesel fuel is partially substituted by natural gas in various proportions, with the natural gas fumigated into the intake air. The experimental results disclose the effect of these parameters on brake thermal efficiency, exhaust gas temperature, nitric oxide, carbon monoxide, unburned hydrocarbons and soot emissions, with the beneficial effect of the presence of natural gas being revealed. Given that the experimental measurements cover a wide range of liquid diesel supplementary ratios without any appearance of knocking phenomena, the belief is strengthened that the findings of the present work can be very valuable if opted to apply this technology on existing DI diesel engines.


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  This paper presents an experimental and modeling study of the oxidation of large linear akanes (from C10) representative from diesel fuel from low to intermediate temperature (550-1100 K) including the negative temperature coefficient (NTC) zone. The experimental study has been performed in a jet-stirred reactor at atmospheric pressure for n-decane and a n-decane/n-hexadecane blend. Detailed kinetic mechanisms have been developed using computer-aided generation (EXGAS) with improved rules for writing reactions of primary products. These mechanisms have allowed a correct simulation of the experimental results obtained. Data from the literature for the oxidation of n-decane, in a jet-stirred reactor at 10 bar and in shock tubes, and of n-dodecane in a pressurized flow reactor have also been correctly modeled. A considerable improvement of the prediction of the formation of products is obtained compared to our previous models. Flow rates and sensitivity analyses have been performed in order to better understand the influence of reactions of primary products. A modeling comparison between linear alkanes for C8 to C16 in terms of ignition delay times and the formation of light products is also discussed.


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  3D DNS of MILD combustion: A detailed analysis of heat loss effects, preferential diffusion, and flame formation mechanisms


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  Abstract Moderate or intense low oxygen dilution (MILD) combustion is a relatively new technology which combines low emissions with high efficiency. As the name suggests, it requires high degrees of dilution in addition to preheating of the reactants using the combustion products. It has been applied to industrial burners for some time, but the complex physical mechanisms are yet to be resolved to extend the application to other areas. In this study, our aim is to analyze MILD combustion conditions to reveal the mentioned physical phenomena and their interactions. To this end, direct numerical simulations (DNS) in the form of autoigniting mixing layers are conducted, and the results are thoroughly analyzed. Conditions used in the simulations are taken from the jet in hot coflow experiments, which are designed to mimic MILD conditions. Detailed chemistry and transport models are employed in the numerical tools to fully understand the interactions of turbulence, molecular diffusion and chemical reactions. In addition, temperature variations due to heat loss effects in the experiments are taken into account. We have found that the heat loss and preferential diffusion effects are crucial in predicting not only the ignition delay, but also the flame structures and heat release rates. In addition, it is found that the flame formation is initiated by autoignition with different ignition delays along the most reactive mixture fraction, instead of a flame propagation following an initial autoignition spot. The findings of this study will broaden the knowledge on MILD combustion, and provide useful insight in developing reduced turbulence and chemistry models in the future.


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  This study focuses on the in-nozzle flow characteristics and the primary spray breakup of diesel at the near-nozzle region under atmospheric conditions. A long working distance microscope and a Canon EOS 700D CCD Camera were employed to study the cavitation flow in the nozzle and the spray structure at near-nozzle region via photographic technique with backlighting. Images were obtained with short exposure time and sufficiently high spatial and temporal resolutions which allowed a detailed observation of the early phase of fuel injection from the nozzle orifice to near nozzle region. The images revealed that the formation of a variety of complex two-phase flow regimes. Stagnant bubbles were present inside the nozzle at the start of injection. The stagnant bubbles may have originated from the last injection because they have not been evacuated from the nozzle or sucked into the nozzle orifice as the needle valve opened. During the opening and closing stages of the needle valve, the cavitation occurred in the valve seat area. Subsequently, free cavitation was observed at the inlet orifice followed by film cavitation, cloud cavitation and string cavitation in the orifice. A dimensionless number S derived from the images of transparent nozzles was adopted to evaluate the cavitation intensity, which increased monotonically with the increase of injection pressure. In addition, mushroom shaped spray head was also found at the nozzle exit. A close inspection revealed that the stagnant bubbles or the fuel trapped in the injector orifice at the end of injection had an appreciable impact on the near nozzle spray structures. The spray angle, penetration length and the spray area also increased for every 10 MPa rise by about 20%, 10% and 15% respectively.


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  Large-eddy simulation of a jet-in-hot-coflow burner operating in the oxygen-diluted combustion regime


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  Three-dimensional direct numerical simulation (DNS) of exhaust gas recirculation (EGR)-type turbulent combustion operated in moderate and intense low-oxygen dilution (MILD) condition has been carried out to study the flame structure and flame interaction. In order to achieve adequate EGR-type initial/inlet mixture fields, partially premixed mixture fields which are correlated with the turbulence are carefully preprocessed. The chemical kinetics is modelled using a skeletal mechanism for methane-air combustion. The results suggest that the flame fronts have thin flame structure and the direct link between the mean reaction rate and scalar dissipation rate remains valid in the EGR-type combustion with MILD condition. However, the commonly used canonical flamelet is not fully representative for MILD combustion. During the flame-flame interactions, the heat release rate increases higher than the maximum laminar flame value, while the gradient of progress variable becomes smaller than laminar value. It is also proposed that the reaction rate and the scalar gradient can be used as a marker for the flame interaction. ?? 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.


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  Numerical investigation on the combustion and emission characteristics of a hydrogen assisted biodiesel combustion in a diesel engine


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  The present study aims to bridge the gap on hydrogen assisted biodiesel combustion, and to investigate its impacts on the engine performance, combustion and emission characteristics. Simulations were conducted on a diesel engine fueled by biodiesel with supplementary hydrogen inductions of 0.5%, 1%, 2% and 3% vol of H2 in air. A skeletal reaction mechanism was developed to include the reaction kinetics of biodiesel and hydrogen, with the CO, NO x and soot formation mechanisms embedded. The developed reaction mechanism was validated by performing the ignition delay calculations against the detailed biodiesel reaction mechanism, as well as the 3D numerical simulations against the experimental results. Good agreements in terms of ignition delay, cylinder pressure and heat release rate predictions were obtained. Key simulation results review that with the increase of hydrogen induction, a substantial increase in the peak cylinder pressure and heat release rate can be obtained under 50% and 100% load conditions, indicating an improved performance. But a reduced performance is observed at light load (10% loads) conditions due to the poor ignition and combustion processes. In terms of emissions, a general decreased trend is observed for both CO and soot emissions at all the engine speeds and loads, and a more remarkable reduction is found at 100% engine load conditions. Furthermore, due to the enhanced combustion, NOx emissions are increased slightly at 50% and 100% engine loads. © 2013 Elsevier Ltd. All rights reserved.


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  In this study, the effect of nozzle inlet rounding on diesel spray formation and combustion is investigated. In order to take into account nozzle geometry, two different nozzle geometries (sharp inlet and rounded inlet) were used in the experiments. Diesel spray injected into a constant volume combustion chamber was modeled by using KIVA3V R2 code. One dimensional nozzle flow model was used in numerical simulations. This model calculates nozzle discharge coefficient and updates the initial droplet radius and droplet velocities according to nozzle inlet geometry. Diesel fuel is represented by diesel oil surrogate mechanism which consists of 71 species and 323 reactions. The numerical spray results were validated with macroscopic spray characterization data obtained by constant volume experiments. Results showed that inlet rounding increases discharge coefficient. At high ambient pressure conditions, sharp and rounded nozzles have similar spray internal structure. However, it is observed that sharp inlet nozzle produces smaller droplets that shorten spray tip penetration and autoignition delay period due to low discharge coefficient. Comparing spray combustion of rounded and sharp inlet nozzles, it is showed that rounded inlet nozzle has lower combustion temperature, less NO and soot concentration than sharp inlet nozzle.


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  This paper presents a statistical analysis of edge flames in a turbulent lifted flame using direct numerical simulation (DNS). To investigate the dynamics of edge flames, a theoretical framework describing the edge-flame propagation velocity as a function of propagation velocities of mixture-fraction and product-mass fraction iso-surfaces at the flame base is used. The correlations between these propagation velocities and several other variables are then studied, including iso-surface curvatures, iso-surface orientations, strain rates, scalar dissipation rate and gradients of product mass fraction. The contribution of these parameters to the overall behaviour of the edge flame is also investigated using conditional averaging on two-dimensional spatial locations at the flame base. The analysis reveals that the tangential and normal strain rates in addition to the curvatures and scalar dissipation rates have significant contributions to the overall behaviour of the edge flame. The elliptical motion of the flame base described in our earlier study [1] is extended to provide a clearer picture of how these various parameters affect the large fluctuations of edge-flame velocity observed at the flame base.


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  Abstract The single condensing bubble behavior in subcooled flow has been numerical investigated using the open source code OpenFOAM. A coupled Level Set (LS) and Volume of Fluid (VOF) method (CLSVOF) model with a phase change model for condensation was developed and implemented in the code. The simulated results were firstly compared with the experimental results, they were in great agreements, and thus the simulation model was validated. The validated numerical model was then used to analyze the condensing bubble deformation, bubble lifetime, bubble size history, condensate Nusselt number and other interesting parameters with different variables in subcooled flow. The numerical results indicated that the initial bubble size, subcooling of liquid and system pressure play an important role to influence the condensing bubble behaviors significantly and bubble will be pierced when the subcooling and initial diameter reach a certain value at the later condensing stage. The bubble diameter history and condensate Nusselt number were found in good agreement with the empirical correlation. The drag force coefficient was predicted well by introducing a reduced drag coefficient.


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  An analysis is presented for multicomponent-liquid-fuel vaporization in a general geometrical situation, e.g., a dense spray. Variable transport properties and only Stefan flow are considered. The problem is separated, using a mass-flux potential function, into a one-dimensional problem for the quasi-steady, gas-phase scalar properties and a three-dimensional problem for the mass-flux potential. The theory predicts scalar gas-phase profiles and vaporization rates for any value of the Lewis number. Transient heat- and mass-diffusion in the liquid interiors is considered with special attention given to the fast- and slow-diffusion limits. Eight droplets in a cubic array are considered in the calculations with a blended liquid mixture of heptane, octane, and decane. Comparisons are made amongst the results for the various liquid-diffusion models: transient behavior, the fast-vaporization limit, and the slow-vaporization limit. © 2008 Elsevier Ltd. All rights reserved.


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  International Journal of Heat and Mass Transfer Analytical modeling of water condensation in condensing heat exchanger


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  A novel jet-stirred reactor (JSR) is proposed to study combustion processes at low Damköhler number (Da, ratio of residence time within the reactor to the time scale of the chemical reaction) for the purpose of measuring rates of chemical reactions relevant to combustion processes. The goal of this work is to identify an optimal configuration of multiple sets of impinging jets and outlet ports for JSRs. With this motivation, ANSYS-FLUENT computational fluid dynamics computations using the RANS - Reynolds Stress Model were performed to simulate mixing and reaction in such geometries. The performance of the new JSRs was compared to the classical JSR introduced by Matras and Villermaux (1973) and Dagaut et al. (1986), which we have termed "4 Jets In Plus (+) Pattern" (4JIPP). Initial computations were conducted using a simple one-step reaction of the form A + B -→ C + D with zero heat release and zero activation energy. Results showed that a configuration of 8 jets, each surrounded by a concentric annular outlet, termed the Concentric Inlet And Outlet (CIAO) design, at the corners of an imaginary cube circumscribed by a spherical chamber provided far more uniform composition and temperature and thereby more nearly match the idealizations assumed in Perfectly-Stirred Reactor (PSR) theory, even at values of Da higher than those accessible to other JSRs. Moreover, the CIAO design yielded inferred reaction rate constants that were much closer to the ideal values (i.e., PSR predictions) than the classical 4JIPP design. Subsequent simulations were performed in CIAO and 4JIPP reactors using detailed H2-O2 chemistry. Results were compared with PSR model predictions. Again it was found that CIAO more nearly matches PSR predictions than does the 4JIPP reactor. Moreover, in the 4JIPP reactor the predicted compositions were quite different between local and volume-averaged values whereas in CIAO the composition was much more uniform over the chamber volume. To assess the viability of the CIAO design experimentally, a 3D printed chamber was built and tested in cold-flow mixing experiments using fluorescein + water solutions and Laser Induced Fluorescence imaging to quantify the mixing levels. Consistent with the computational predictions, the initial experimental results indicate much more uniform mixing than 4JIPP type chambers.


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  A quasi-discrete model for heating and evaporation of complex multicomponent hydrocarbon fuel droplets


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  A quasi-discrete model for heating and evaporation of complex multicomponent hydrocarbon fuel droplets is suggested and tested in Diesel engine-like conditions. The model is based on the assumption that properties of components are weak functions of the number of carbon atoms in the components (n). The components with relatively close n are replaced by the quasi-components with properties calculated as average properties of the a priori defined groups of actual components. Thus the analysis of heating and evaporation of droplets consisting of many components is replaced by the analysis of heating and evaporation of droplets consisting of relatively few quasi-components. In contrast to previously suggested approaches to modelling the heating and evaporation of droplets consisting of many components, the effects of temperature gradient and quasi-component diffusion inside droplets are taken into account. The model is applied to Diesel fuel droplets, approximated as a mixture of 21 components CnH2n+2 for 5 ??? n ??? 25, which correspond to a maximum of 20 quasi-components with average properties for n = nj and n = nj+1, where j varies from 5 to 24. It is pointed out that droplet surface temperatures and radii, predicted by a rigorous model taking into account the effect of all 20 quasi-components, are very close to those predicted by the model, using just five quasi-components. Errors due to the assumptions that the droplet thermal conductivity and species diffusivities are infinitely large cannot be ignored in the general case. ?? 2011 Elsevier Ltd. All rights reserved.


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  A novel method is presented for solving the forced transient diffusion flame in the exit region of a coflow burner. Streamwise diffusion is eliminated, which produces the Burke–Schumann model. A mathematical transformation renders the transient, forced convection problem equivalent to a steady-state convection problem. The transformation differs from previous approaches because its use does not require a priori restriction to small perturbations. For this reason, flow fluctuations that are large fractions of the initial flow field may be described exactly and features of nonlinear response can be examined without recourse to detailed numerical simulation. The method is applied to study flame evolution and oscillation for two physically separated coflow slot burner flames as they merge.


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  This paper first summarizes a new theoretical description that quantifies the effects of real-fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical engine operating conditions. It then focuses on the implications this has on modeling such flows with emphasis on application of the Large Eddy Simulation (LES) technique. The theory explains and quantifies the major differences that occur in the jet dynamics compared to that described by classical spray theory in a manner consistent with experimental observations. In particular, the classical view of spray atomization as an appropriate model at some engine operating conditions is questionable. Instead, non-ideal real-fluid behavior must be taken into account using a multicomponent formulation that applies to hydrocarbon mixtures at high-pressure supercritical conditions. To highlight the implications and needs related to modeling, we present a series of studies using LES that focus on experiments being conducted in the high-pressure combustion vessel at Sandia National Laboratories. We extend LES studies performed previously to the Engine Combustion Network (www.sandia.gov/ECN) Spray-H and Spray-A injectors using n-heptane and n-dodecane as the respective fuels. The accompanying analysis reveals the structural characteristics associated with the inherent scalar mixing processes at conditions directly relevant to advanced Diesel engines. © 2014 SAE International.


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  Atherosclerosis is a slow vascular degeneration. It thickens the internal walls of a blood vessel locally depositing an atherosclerotic plaque. Such reduced lumen increases the resistance to blood flow. Plaques can be punctual (eccentric, here considered) or circumferential (symmetrical). Stenoses do not have a typical shape: we hypothesised here a reference geometry (trapezium) with its possible evolutions (semi-ellipse, triangle). Two criteria (Equivalent Area and Equivalent Dimensions) were then defined to compare the results among the 35 case studies numerically analysed with a Computational Fluid Dynamics code (Comsol Multiphysics 3.3). Blood was considered a Cassonian fluid with modified viscosity equation. The artery was cylindrical, rigid and straight, interested by a pulsatile blood flow. Among the variables: shape and dimensions of the stenoses; number of stenoses (single or coupled pathologies); mutual locations (3 possibilities). The main results were that the length of the consequent flow disturbance is due to the stenotic shape and height; blood flow recirculation, downstream of the pathology, is due to the slope of the stenotic walls; and the peak velocities depend on the shape and height of stenosis. The differences from case to case diminish in diastole. ?? 2008 Elsevier Ltd. All rights reserved.


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  Laminar burning velocities of hydrogen/air mixtures can show discrepancies up to 30%, making chemical mechanism validation and improvement difficult. The source of uncertainties may come from different factors influencing at each processing and post-processing steps the final value. Considering a spherically expanding flame configuration, reflection on the accuracy of the formulations, used to derive the desired quantity, is proposed. Starting from the exact definition of the laminar burning velocity, two formulations - direct and indirect flame speeds formulations - are derived for spherical flames. Each single source of uncertainty involved in the formulations is pointed out. The emphasis is focused on a specific mixture at an equivalence ratio of 0.50, atmospheric pressure, and an initial temperature of 300 K. This point represents the best tradeoff between low ratio of flame velocity and recording sampling rate and the occurrence of cellular flames (Le \textless 1). An extensive experimental and numerical study (1D spherically expanding flames) of this mixture is carried out. As a result, the experimental laminar burning velocities determined by using the direct flame speed or the indirect flame speed formulae depict different values. However, when numerically determined, both formulae yield the same value. This paves the way to understand and identify the experimental error sources. Stretch and Lewis numbers effects (super-adiabatic temperatures) as well as radiation processes (burned gas motion) are studied. Nonetheless, they do not show to be the main source of uncertainty. The extrapolation procedure (linear or non-linear) according to the limited number of experimental points (rapid apparition of cellular structure) appears as the main factor influencing the discrepancy in laminar burning velocities.


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  Experimental study on stoichiometric laminar flame velocities and Markstein lengths of methane and PRF95 dual fuels


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  Numerical simulation and extended validation of two-phase compressible flow in diesel injector nozzles


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  In this paper, the ability of a computational fluid dynamics code to reproduce cavitation phenomena accurately is checked by comparing data acquired by numerical simulations against those obtained from different experiments involving the mass flow, the momentum flux, and the effective injection velocity. Cavitation is modelled using a single-phase cavitation model based on a barotropic equation of state together with a homogeneous equilibrium assumption. In the research reported in this paper, the ability to use the code for actual diesel injector nozzle geometries and conditions has been checked and validated. The main contribution of the present investigation and what makes it different from previous work in the literature is the consideration of extended experimental data for validation purposes: the mass flow, the momentum flux at the nozzle exit, and the effective injection velocity. These are unique features in contrast with other publications, which normally take into account at the most, if at all, the cavitation morphology or the mass flow. The results obtained and their comparison with available experimental data show how the model is able to predict the behaviour of the fluid in such conditions with a high level of confidence. © 2011 Authors.


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  Study of ignition chemistry on turbulent premixed flames of n-heptane/air by using a reactor assisted turbulent slot burner


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  The changes in flame structure and burning velocity of premixed n-heptane/air flames associated with ignition chemistry have been investigated in a reactor-assisted turbulent slot (RATS) burner. Two distinct turbulent flame regimes are identified by varying the flow residence time and reactor temperature. A chemically frozen (CF) regime is observed at a reactor temperature of 450K and a low-temperature ignition (LTI) regime is identified at 650K. At a reactor temperature of 450K, the measured turbulent burning velocities (ST) exhibit a monotonic trend, proportional only to the turbulent intensity and laminar flame speed (SL) calculated with the initial fuel/air mixture. At a reactor temperature of 650K, ST initially decreases with increasing flow residence times (decreasing turbulent intensity) but then increases once the reactor flow residence time exceeds the LTI delay. Furthermore, ST in the LTI regime exhibits a strong correlation with the extent of low-temperature reactivity (defined by CH2O concentration). The species distributions at the exit of the RATS burner after the onset of LTI are quantified by gas sampling-chromatography and used to compute the changes in SL and mixture Lewis number (Le), which are shown to substantially change after the onset of LTI. Damköhler's scaling analysis indicates that the increase in ST in the LTI regime originates from an increase in SL, a decrease in Le, and an increase in turbulence intensity due to the heat release from the low-temperature chemistry. To examine the role of ignition chemistry on flame stability, flame flashback measurements have been performed by varying mean jet velocities and n-heptane/air mixture equivalence ratios for reactor temperatures of 450 and 650K. Measurements at 650K imply the strong influence of high-temperature ignition on flame stability phenomena.


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  The validity of the commonly used flame marker for heat release rate (HRR) visualization, namely the rate of the reaction OH+CH2O↔HCO+H2O is re-examined. This is done both for methane-air and multi-component fuel-air mixtures for lean and stoichiometric conditions. Two different methods are used to identify HRR correlations, and it is found that HRR correlations vary strongly with stoichiometry. For the methane mixture there exist alternative HRR markers, while for the multi-component fuel flame the above correlation is found to be inadequate. Alternative markers for the HRR visualization are thus proposed and their performance under turbulent conditions is evaluated using DNS data.


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  Effects of Fuel Cell Material Properties on Water Management Using CFD Simulation and Neutron Imaging


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  The purpose of this paper is to present a consistent theoretical concept that can explain the various physical phenomena associated with the effect of droplet size on contact angle for droplets on solid surfaces, and with the geometry of the liquid/gas/solid contact line in general. Two droplet geometries have been considered: uniformly elongated droplets and axisymmetric droplets. It has been shown that the contact angle for elongated droplets is size-independent and, thus, satisfies the Young equation for constant material and interfacial properties. On the other hand, whereas the contact angle for axisymmetric droplets is size-dependent and does not satisfy the original Young equation, it is shown that this contact angle can still be predicted for any combination of droplet and substrate materials, and a given mass of the droplet. The theoretical work has been combined with the development of numerical schemes of solving the Laplace-Young equation for various droplet geometries. The proposed approach has been applied to different material/substrate combinations and validated against several sets of experimental data. As a result, a method has been developed for predicting the contact angle of both long and axisymmetric sessile droplets of arbitrary sizes for given liquid/solid/gas properties. ?? 2005 Elsevier B.V. All rights reserved.


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  Large eddy simulations of the flow field and temperature separation in the Ranque-Hilsch vortex tube


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  A computational fluid dynamic model is used to predict the flow fields and the associated temperature separation within a Ranque-Hilsch vortex tube. The large eddy simulation (LES) technique was employed for predicting the flow and temperature fields in the vortex tube. A vortex tube with a circumferential inlet stream and an axial (cold) outlet stream and a circumferential (hot) outlet stream was considered. The temporal evolutions of the axial, radial and azimuthal components of the velocity along with the temperature, pressure and density fields within the vortex tube are simulated. Performance curves (temperature separation versus cold outlet mass fraction) were obtained for a specific vortex tube with a given inlet mass flow rate. Simulations were carried out for varying amounts of cold outlet mass flow rates. Predictions from the present large eddy simulations compare favorably with available experimental measurements. ?? 2007 Elsevier Ltd. All rights reserved.


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  Combustion characteristics of compressed natural gas / diesel dual-fuel turbocharged compressed ignition engine


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  © 2017 Elsevier Ltd In this work, a universal methodology for ignition delay time (IDT) correlation of multicomponent fuel mixtures is reported. The method is applicable over wide ranges of temperatures, pressures, and equivalence ratios. n-Heptane, iso-octane, toluene, ethanol and their blends are investigated in this study because of their relevance to gasoline surrogate formulation. The proposed methodology combines benefits from the Livengood-Wu integral, the cool flame characteristics and the Arrhenius behavior of the high-temperature ignition delay time to suggest a simple and comprehensive formulation for correlating the ignition delay times of pure components and blends. The IDTs of fuel blends usually have complex dependences on temperature, pressure, equivalence ratio and composition of the blend. The Livengood-Wu integral is applied here to relate the NTC region and the cool flame phenomenon. The integral is further extended to obtain a relation between the IDTs of fuel blends and pure components. Ignition delay times calculated using the proposed methodology are in excellent agreement with those simulated using a detailed chemical kinetic model for n-heptane, iso-octane, toluene, ethanol and blends of these components. Finally, very good agreement is also observed for combustion phasing in homogeneous charge compression ignition (HCCI) predictions between simulations performed with detailed chemistry and calculations using the developed ignition delay correlation.


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  Numerical research on micro diesel spray characteristics under ultra-high injection pressure by Large Eddy Simulation (LES)


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  The Large Eddy Simulation model was introduced to study the micro spray characteristics under ultra-high injection pressure (\textgreater220 MPa). EFS8400 spray test platform was set up to verify the accuracy of the numerical model. The mechanisms of micro spray characteristics were studied intensively under different injection pressures (180 MPa, 240 MPa) and nozzle diameters (0.1 mm, 0.16 mm). The results indicated that the micro turbulence vortex structures can be captured, especially in the liquid spray core area. Large Eddy Simulation model combined with the small grid size of 0.25 mm show a huge advantage in studying the micro spray characteristics under ultra-high injection pressure; The turbulence vorticity and spray velocity for injection pressure of 240 MPa are more intensive than that of 180 MPa, and also the ultra-high injection pressure can contribute to strong turbulence disturbance between spray and surrounding air, which is helpful to improve the quality of spray; The spray velocity field extended wider for the diameter of 0.16 mm, and also the values of velocity in the spray center is higher than that of the diameter of 0.1 mm; The entrainment vortex appeared at the edge of the large velocity gradient between spray and surrounding air, and the higher velocity gradient for ultra-high injection pressure (240 MPa) between the spray and air is easier to increase the generation of entrainment vortex in the downstream of the spray, which can significantly increase the quality of spray and atomization.


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  Multiple-injection has shown significant benefits in the reduction of combustion emissions and soot formation. However, there is a need to understand the secondary flow-induced air-fuel mixture formation and subsequent combustion mechanism under multiple-injection. An experiment was performed by changing the dwell time between the pilot and main injections under the conditions of 23 kg/m3ambient density with 0% O2(non-combusting) and 15% O2(combusting) ambient conditions, at an injection pressure of 120 MPa. The mass ratios of pilot and main injections in the study were 15/85% and 20/80%. A hybrid shadowgraph and Mie scattering imaging technique in a nearly simultaneous mode along the same line of sight was used to visualize the spray and flame luminosity. Pilot-main spray flame properties including ignition delay, ignition location, and lift-off length were characterized from experimental images. CFD simulation of pilot-main spray combustion was performed under the same experimental conditions to provide additional insights into the combustion process. The air-fuel mixing field and ignition process followed by main injection flame structure are significantly altered at different dwells. The spray-to-flame interaction mechanism model has been established for the development of an optimal multiple-injection scheme for, possibly, low soot formation and emissions.


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  Reactivity controlled compression ignition (RCCI) has been shown to be capable of providing improved engine efficiencies coupled with the benefit of low emissions via in-cylinder fuel blending. Much of the previous body of work has studied the use of gasoline as the premixed low-reactivity fuel. However, there is interest in exploring the use of al-ternative fuels in advanced combustion strategies. Due to the strong market growth of natural gas as a fuel in both mobile and stationary applications, a study on the use of methane for RCCI combustion was performed. Single cylinder heavy-duty engine experi-ments were undertaken to examine the operating range of the RCCI combustion strategy with methane/diesel fueling and were compared against gasoline/diesel RCCI operation. The experimental results show a significant load extension of RCCI engine operation with methane/diesel fueling compared to gasoline/diesel fueling. For gasoline/diesel fuel-ing, a maximum load of 6.9 bar gross indicated mean effective pressure (IMEP g) at CA50 ¼ 0 deg aTDC (after top dead center) and 7.0 bar IMEP g at CA50 ¼ 4 deg aTDC was obtained without use of exhaust gas recirculation (EGR). For methane/diesel fueling, a maximum load of 15.4 bar IMEP g at CA50 ¼ 0 deg aTDC and 17.3 bar IMEP g at CA50 ¼ 4 deg aTDC was achieved, showing the effectiveness of the use of methane in extending the load limit for RCCI engine operation.


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  Charge Motion Benefits of Valve Deactivation to Reduce Fuel Consumption and Emissions in a GDi, VVA Engine


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  Requirements for reduced fuel consumption with simultaneous reductions in regulated emissions require more efficient operation of Spark Ignited (SI) engines. An advanced valvetrain coupled with Gasoline Direct injection (GDi) provide an opportunity to simultaneously reduce fuel consumption and emissions. Work on a flex fuel GDi engine has identified significant potential to reduce throttling by using Early Intake Valve Closing (EIVC) and Late Intake Valve Closing (LIVC) strategies to control knock and load. High loads were problematic when operating on gasoline for particulate emissions, and low loads were not able to fully minimize throttling due to poor charge motion for the EIVC strategy. The use of valve deactivation was successful at reducing high load particulate emissions without a significant airflow penalty below 3000 RPM. Valve deactivation did increase the knocking tendency for knock limited fuels, due to increased heat transfer that increased charge temperature. Valve deactivation also extended the near un-throttled operation to lower loads (2 bar BMEP) by reducing burn durations and allowing higher levels of dilution. Results are presented showing the improvements in emissions and reduction in fuel consumption. Results from an optical engine and Computational Fluid Dynamics (CFD) at representative points are also presented to quantify the in-cylinder sprays and flow structures.


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  A model for unsteady droplet vaporization is presented that considers$\backslash$nthe droplet temperature range from flash-boiling conditions to normal$\backslash$nevaporation. The theory of continuous thermodynamics was used to model$\backslash$nthe properties and compositions of multicomponent fuels such as$\backslash$ngasoline. In order to model the change of evaporation rate from normal$\backslash$nto boiling conditions more realistically, an unsteady internal heat$\backslash$nflux model and a new model for the determination of the droplet surface$\backslash$ntemperature is proposed. An explicit form of the equation to determine$\backslash$nthe heat flux from the surrounding gas mixture to the droplet-gas$\backslash$ninterface was obtained from an approximate solution of the quasi-steady$\backslash$nenergy equation for the surrounding gas mixture, with the$\backslash$ninter-diffusion of fuel vapor and the surrounding gas taken into$\backslash$naccount. The model was applied to calculate evaporation processes of$\backslash$ndroplets for various ambient temperatures and droplet temperatures.


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  Mechanistic Analysis of n -Propylcyclohexane and n -Butylcyclohexane Oxidation in Low Temperature Regime


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  The recent advent of highly effective drilling and extraction technologies has decreased the price of natural gas and renewed interest in its use for transportation. Of particular interest is the conversion of dedicated diesel engines to operate on dual-fuel with natural gas injected into the intake manifold. Dual-fuel systems with natural gas injected into the intake manifold replace a significant portion of diesel fuel energy with natural gas (generally 50% or more by energy content), and produce lower operating costs than diesel-only operation. Diesel-natural gas engines have a high compression ratio and a homogeneous mixture of natural gas and air in the cylinder end gases. These conditions are very favorable for knock at high loads. In the present study, knock prediction concepts that utilize a single step Arrhenius function for diesel-natural gas dual-fuel engines are evaluated. A heavy duty diesel engine with the capability of running both natural gas and diesel is operated at points where knock occurs and the cylinder pressure traces are recorded. Constants of the Arrhenius function for dual-fuel operation are determined empirically based on the cylinder pressure and temperature histories. Several methods for knock prediction and coefficient fitting are evaluated, and their accuracy is compared. Results indicate that Arrhenius integral methods can determine if a cycle will knock with accuracy up to 72% using coefficients similar to those for methane. Introduction


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  A simplified model on carbon monoxide yield in burning of polymeric solids containing flame retardants


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  Recent advances in Microscale Combustion Calorimetry (MCC) allow polymeric solids to be pyrolyzed and oxidized separately at the milligram scale, and the combustion gases, O2, CO, and CO2to be measured using in-line gas analyzers. A simplified two-step reaction mechanism, which involves a CO generation step and a CO oxidation step, was developed to better describe the chemical reaction scheme that generates/oxidizes these products within the premixed combustor. Different incomplete combustion conditions were attained by varying the MCC combustor temperature and a numerical model of the combustor was developed to simulate the species evolution. Kinetics parameters were found by minimizing the errors in fitting the simulated results with the experiments. The two-step method was employed to examine halogen- and phosphorous-containing polymers of known compositions. The halogen additives were found to decrease gas phase reaction rate, whereas the phosphorous additives do not show significant effect. In cone calorimeter fire tests, both additives inhibit combustion efficiency by promoting soot formation.


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  When performing chemical kinetics experiments behind reflected shock waves at conditions of lower temperature (\textless 1,000 K), longer test times on the order of 10-20 ms may be required. The integrity of the test temperature during such experiments may be in question, because heat loss to the tube walls may play a larger role than is generally seen in shock-tube kinetics experiments that are over within a millisecond or two. A series of detailed calculations was performed to estimate the effect of longer test times on the temperature uniformity of the post-shock test gas. Assuming the main mode of heat transfer is conduction between the high-temperature gas and the colder shock-tube walls, a comprehensive set of calculations covering a range of conditions including test temperatures between 800 and 1,800 K, pressures between 1 and 50 atm, driven-tube inner diameters between 3 and 16.2 cm, and test gases of N(2) and Ar was performed. Based on the results, heat loss to the tube walls does not significantly reduce the area-averaged temperature behind the reflected shock wave for test conditions that are likely to be used in shock-tube studies for test times up to 20 ms (and higher), provided the shock-tube inner diameter is sufficiently large (\textgreater 8cm). Smaller diameters on the order of 3 cm or less can experience significant temperature loss near the reflected-shock region. Although the area-averaged gas temperature decreases due to the heat loss, the main core region remains spatially uniform so that the zone of temperature change is limited to only the thermal layer adjacent to the walls. Although the heat conduction model assumes the gas and wall to behave as solid bodies, resulting in a core gas temperature that remains constant at the initial temperature, a two-zone gas model that accounts for density loss from the core to the colder thermal layer indicates that the core temperature and gas pressure both decrease slightly with time. A full CFD solution of the shock-tube flow field and heat transfer at long test times was also performed for one typical condition (800 K, 1 atm, Ar), the results of which indicate that the simpler analytical conduction model is realistic but somewhat conservative in that it over predicts the mean temperature loss by a few Kelvins. This paper presents the first comprehensive study on the effects of long test times on the average test gas temperature behind the reflected shock wave for conditions representative of chemical kinetics experiments.


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  Near-Nozzle Structure of Diesel Sprays Affected by Internal Geometry of Injector Nozzle: Visualized by Single-Shot X-ray Imaging


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  By taking advantage of high-intensity and high-brilliance x-ray beams available at the Advanced Photon Source (APS), ultrafast (150 ps) propagation-based phase-enhanced imaging was developed to visualize high-pressure high-speed diesel sprays in the optically dense near-nozzle region. The sub-ns temporal and μm spatial resolution allows us to capture the morphology of the high-speed fuel sprays traveling at 500 m/s with a negligible motion blur. Both quality and quantitative information about the spray feature can be readily obtained. In the experiment, two types of single-hole nozzles have been used, one with a hydroground orifice inlet and the other with a sharp one. Within 3 mm from the nozzle, the sprays from these nozzles behave differently, ranging from laminar flow with surface instability waves to turbulent flow. The sprays are correlated with the nozzle internal geometry, which provides practical information for both nozzle design and supporting numerical simulation models. The nozzle internal structure is also imaged by the x-ray phase-contrast method. The measured nozzle internal geometry was used to predict cavitation inside the orifice through a numerical simulation. The simulation demonstrates that cavitation generated at the sharp inlet is responsible for the cavitating spray from the nozzle.


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  The initial (t = 0) temperature distribution in a reacting mixture enables one to calculate the induction period ti to the adiabatic explosion in each particle of the mixture. Isosurfaces ti(x,y,z) = t give the location of the explosion front at the moment ti if no physical interaction of adjacent layers occurs; the inverse gradient of the induction period | grad ti |−1 determines the propagation velocity of the intensive reaction zone. The comparison of this rate with the rate of normal flame propagation and the Chapman-Jouguet detonation speed enables conclusions to be drawn about the effects of heat conductivity or substance movement on chemical reaction under given initial conditions.


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  Characterization of thermal degradation behavior for polymers containing reactive flame retardants : Application to glass fiber reinforced polyamide 66 blended with red phosphorous


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  This paper presents a comparison between the performance predicted by a computational fluid dynamic (CFD) model and experimental measurements taken using a commercially available vortex tube. Specifically, the measured exit temperatures into and out of the vortex tube are compared with the CFD model. The data and the model are both verified using global mass and energy balances. The CFD model is a two-dimensional (2D) steady axisymmetric model (with swirl) that utilizes both the standard and renormalization group (RNG) k-epsilon turbulence models. While CFD has been used previously to understand the fluid behavior internal to the vortex tube, it has not been applied as a predictive model of the vortex tube in order to develop a design tool that can be used with confidence over a range of operating conditions and geometries. The objective of this paper is the demonstration of the successful use of CFD in this regard, thereby providing a powerful tool that can be used to optimize vortex tube design as well as assess its utility in the context of new applications. © 2005 Elsevier Ltd and IIR. All rights reserved.


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  Experimental and kinetic modeling study of trans- methyl 2- octenoate oxidation using reaction rate rules from alkanes


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  Self-ignition scenarios after rapid compression of a turbulent mixture weakly-stratified in temperature


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  Turbulence and combustion inside a compression machine, experimentally studied by Guibert et al. [Flow Turbulence and Combust. 84(1): 79-85, 2010], are simulated to get some insight on flow-physics and ignition scenarios of a reactive-gas mixture pushed by a piston through a turbulence-grid, to be compressed in a 55 cubic-centimeter volume. Large Eddy Simulation (LES) with a structured-mesh solver and immersed boundaries are first performed for an inert mixture undergoing the compression, to validate the simulation procedure against experimental results. Then, keeping the flow admission-sequence the same, but downsizing its geometry, a Direct Numerical Simulation (DNS) analysis of the compression/ignition sequence is reported. Simulation parameters are varied for ignition to occur in mixtures featuring various temperature stratification patterns, due to wall cooling and turbulence characteristics. As previously discussed in the literature, conditions favoring spotty- or homogeneous-ignition are evidenced. Depending on characteristic times (coherent structure residence time, flow engulfment and mixing times) ignition may occur within localized compression zones, between vortical structures leading to spotty-ignition, or more homogeneously within large scale flow structures. Very small differences in local temperature and flow topology appear to lead to different routes toward successful auto-ignition. The underlying mechanisms are analyzed from an internal energy budget expressed as a temperature balance equation, to delineate between the contribution of the global adiabatic compression and localized flow divergence induced by turbulence velocity fluctuations. After primary ignition, the propagation phase of ignition is strongly influenced by the acoustic field and the specific temperature scalar dissipation-rate patterns. It is also shown that three-dimensional vortex stretching plays a crucial role, hence two and three-dimensional DNS lead to different ignition scenarios under similar chemical and turbulence intensity conditions. ?? 2012 The Combustion Institute.


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  Abstract: This paper focuses on the effect of diesel injection timing, intake boost pressure, and diesel injection pressure on diesel-methane dual-fuel combustion performed in a single-cylinder research engine. The engine was operated at a constant speed of 1,500 revolutions per minute (rpm) while percentage of methane energy substitution (PES) and load were maintained at 80% and 5.1 bar net indicated mean effective pressure (IMEP), respectively. The start of injection (SOI) of diesel was varied from 250 crank angle degrees (CAD) to 350 CAD while keeping the injection pressure at 500 bar and intake boost pressure at 1.5 bar. Advancing SOI from 330° to 300° reduced indicated specific NOx (ISNOx) emissions from 11.9 g=kW · h to less than 0.02 g=kW · h; further advancement of SOI did not yield any significant ISNOx reduction. Net indicated fuel conversion efficiency (IFCE) increases from 29.4% at 350 CAD SOI to 40.5% at 300 CAD SOI. Combustion efficiency trends are consistent with unburned hydrocarbon (HC) and carbon monoxide (CO) emission trends. Moreover, smoke emissions were lower than 0.1 filter smoke number (FSN) for all SOIs. A diesel injection pressure sweep from 200 to 1,300 bar at 300 CAD SOI showed that very low injection pressures lead to apparently more heterogeneous combustion and higher ISNOx, indicated specific CO (ISCO), and indicated specific HC (ISHC) emissions, whereas smoke, IFCE, and combustion efficiency remained unaffected. An injection pressure of approximately 500 bar appeared to be optimal for early SOIs. Finally, an intake boost pressure sweep from 1.1 to 1.8 bar at 300 CAD SOI and 500 bar injection pressure showed that ISNOx and smoke remained fairly low at all conditions (ISNOx \textless 0.15 g=kW · h; smoke \textless 0.1 FSN); however, increasing boost pressure resulted in an increase in both ISHC and ISCO emissions while combustion efficiency and IFCE were reduced. DOI: 10.1061/(ASCE)EY.1943-7897.0000235. © 2014 American Society of Civil Engineers.


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  To address the need of increasing fuel economy requirements, automotive Original Equipment Manufacturers (OEMs) are increasing the number of turbocharged engines in their powertrain line-ups. The turbine-driven technology uses a forced induction device, which increases engine performance by increasing the density of the air charge being drawn into the cylinder. Denser air allows more fuel to be introduced into the combustion chamber, thus increasing engine performance. During the inlet air compression process, the air is heated to temperatures that can result in pre- ignition resulting and reduced engine functionality. The introduction of the charge air cooler (CAC) is therefore, necessary to extract heat created during the compression process. The present research describes the physics and develops the optimized simulation method that defines the process and gives insight into the development of CACs. The present research develops a 3-D computational model using ANSYS® Fluent of the CAC internal flow with condensate and validates the predictions of the 3-D model using measurements from experimental data. Finally, the research presents a correlation that provides an approach for designing heat exchangers for practical applications that encounter moisture in the intake air stream. The overall benefit presented is an experimentally validated simulation methodology to evaluate and design CACs that function outside the condensate formation zone during vehicle operation modes


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  Structure of evaporating single- and multicomponent fuel sprays for 2nd generation gasoline direct injection


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  In the present paper the effect of fuel properties on spray formation and evaporation was investigated for a hollow-cone spray of a piezoelectric injector for Direct Injection Spark Ignition (DISI) engines. Late injection timing in a high-pressure atmosphere (1.5 MPa, 200 ??C) was simulated in an injection chamber. Liquid and vapor phase structure of the hollow-cone spray were studied with 2D-Mie scattering, laser-induced fluorescence (LIF) as well as phase-Doppler anemometry (PDA). The spray structure was investigated for several alkanes with high and low volatility (n-hexane, n-heptane, iso-octane, n-decane) and a three-component mixture of the n-alkanes with similar fuel properties like a multicomponent gasoline fuel. It is found that the rapid evaporation of high volatility fuels can lead to spray destabilization, whereas low volatility single-component fuels overestimate radial spray propagation and vortex formation. For iso-octane the droplet size distribution is shifted to smaller droplets and the spray appeared to be less dense compared to n-heptane despite almost identical boiling behavior. However, the much higher viscosity of iso-octane determines the internal nozzle flow which results in a reduced injected fuel mass and changed atomization. A well defined three-component fuel models the global spray characteristics as well as the droplet size, droplet momentum distribution and evaporation behavior of the used multicomponent gasoline fuel very precisely. Small amounts of low volatility fractions delay the droplet evaporation and support the overall spray stability also for multicomponent mixtures. This leads to an increased spray width as well as larger droplet sizes and momenta. The evaporation characteristic of multicomponent fuels at increased ambient pressure is complex. At the studied injection conditions it is situated between the two limiting cases of distillation-like behavior and coevaporation of the components. Moreover, the results in comparison with theoretical estimations indicate a demixing of light and heavy boiling fractions in the three-component and multicomponent fuel under conditions which are typical for DISI strategies with late injection. ?? 2010 Elsevier Ltd. All rights reserved.


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  Research for new combustion concepts for internal combustion engines has been made possible in recent years by the adoption of CFD codes which are capable of computing complete reaction mechanisms, as current pollutant regulations are leading to an increasing need for accurate predictions of the spatial distribution and time evolution of species within the combustion chamber. However, the adoption of full or detailed reaction mechanisms in multi-dimensional studies is still too computationally demanding, and the development of accurate reduced mechanisms is of fundamental importance for mantaining the predictive capabilities of the simulations. In this context, research is urged by the need for finding adequate substitutes to petroleum-based fuels for the transportation sector of the near future. Biofuels, such as bioethanol, biobutanol, biodiesel currently seem to be suitable for gradually being introduced as additives to traditional hydrocarbon fuels, and then to fully substitute them, to contribute to a viable and environmentally sustainable alternative to oil. The present work introduces a novel approach for the automatic development of reduced reaction mechanisms for biofuels' combustion, with the aim of generating reaction mechanisms which can be efficiently adopted for engine simulations with detailed chemistry. $\backslash$$\backslash$ First of all, efforts have been devoted to the development of a new computer code for the computationally efficient solution of detailed chemistry in the simulation of combustion systems. The software has been coded as a package for the estimation of finite-rate chemical kinetics in zero dimensional batch reactors and internal combustion engines. All the routines have been developed in a fully vectorized fashion, for maximum computational efficiency. The performance of the code has been compared adopting different ODE solvers, showing robustness and computational efficiency. Finally, the code has been coupled with KIVA-4, well-known CFD tool for the simulation of internal combustion engines, and parallelised adopting a shared memory paradigm. $\backslash$$\backslash$ Performance of the solution of the chemistry ODE system has then been improved through the study of a novel explicit ODE solver, exploiting time scale separation. The solution of the reacting environment is carried out according to the assumption that, if the time integration interval is small enough, a linear analysis can yield accurate predictions of the characteristic times of each species, and thus the evolution of each of them can be stopped after its estimated expiration time. This method thus significantly reduces the stiffness of the ODE system, and allows a significant reduction in total computational times, if compared to the more commonly used implicit integration approach, which cannot exploit its potential if bounded by strict integration timesteps (as happening during CFD simulations, where the fluid-dynamic timestep usually rules over the chemistry source terms).$\backslash$$\backslash$ Once that all the numerical tools have been validated and tested, the mechanism reduction procedure has been set up as an iterative algorithm, with the aim of gradually reducing the number of species involved in the mechanism, while still mantaining its predictiveness in terms of not only ignition delay times, but also the time evolution of important species. In particular, a global error function is defined taking into account a set of ignition delay calculations at different, engine-relevant, initial mixture compositions, temperatures and pressures. The choice of the species to be deleted is performed exploiting the element flux analysis method; when a global error function of the reduced mechanism exceeds the required accuracy, the collision frequencies and activation energies of selected reactions are corrected by means of a GA-based code. The results show that significantly smaller, accurate reaction mechanisms can be automatically generated and applicated to internal combustion engine simulations. Further research needs to be devoted to the development of skeletal, multi-component reaction mechanisms for allowing new combustion concepts such as multi-fuel combustion and reactivity-controlled combustion to be explored.


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  Microscopic investigation of the atomization and mixing processes of diesel sprays injected into high pressure and temperature environments


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  Atomization and mixing of sprays are key parameters to successfully describe and predict combustion in direct-injection engines. Understanding these processes at the conditions most relevant to engines (high pressures and temperatures) is of primary interest. The present work investigates the atomization and mixing processes of sprays injected into environments with progressively higher pressure and temperature. An Engine Combustion Network Spray A single-hole injector is used to inject n-dodecane fuel into an optically accessible combustion chamber. High-speed imaging is performed using long-distance microscopy and diffused back-illumination to resolve ligament structures and droplets in the near-nozzle region. A unique aspect of this study is the application of high-speed imaging of sprays in the near-field under realistic diesel conditions, particularly those near top-dead-center. Imaging showed droplet and ligament dynamics at low pressure and temperature, but not at high pressure and temperature typical of engine operation, indicating diminished effects of surface tension. Relating the ambient conditions to the fuel critical pressure and temperature showed that when the ambient conditions are slightly above the critical point of the fuel, surface tension remains in effect at gas-liquid interfaces. However, for higher pressure and temperature conditions, the surface tension appears to diminish significantly as expected for supercritical fuel-air mixtures. © 2014 Published by Elsevier Ltd.


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  Effect of Multiple Injection Strategies on Combustion and Emission Characteristics in a Diesel Engine


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  From the analysis of the experimental results, it was revealed that, when the injection pressure was increased without changing the injection timing in split injection, indicated mean effective pressure (IMEP) and brake mean effective pressure (BMEP) decreased and brake specific fuel consumption (BSFC) deteriorated, owing to the increase of dwell duration. The increase of injection interval induced deterioration of BSFC and caused an increase in NOx and HC emissions with significant reduction in CO and soot emissions. On the other hand, the retardation of injection timing with a fixed injection interval caused an improvement of the BSFC, and a decrease in NOx, CO, and HC emissions. However, soot emission increased. According to the analysis, a short injection interval and injection timing around top dead center (TDC), with not too high injection pressure, improve the BSFC and emission characteristics in split-injection diesel combustion.


