This paper represents a review of the recent researches that investigate the behavior of the gas turbulent flow laden with solid particles. The significant parameters that influence the interactions between the both p...This paper represents a review of the recent researches that investigate the behavior of the gas turbulent flow laden with solid particles. The significant parameters that influence the interactions between the both phases, such as particle size, loading ratio and the gas velocity, have been extensively reviewed. Those parameters are presented in dimensionless numbers in which the applicability of studying its effect in terms of all circumstances of the gas turbulent channel flow at different condition is possible. The represented results show that the turbulence degree is proportional to the particle size. It was found that at the most flow conditions even at low mass ratio, the particle shape, density and size significantly alter the turbulence characteristics. However, the results demonstrate that the particle Reynolds number is a vital sign: the turbulence field becomes weaker if particle Reynolds number is lower than the critical limit and vies verse. The gas velocity has a strong effect on the particles settling along the channel flow and as a result, the pressure drop will be affected.展开更多
In diesel engines the fuel injection system produces the spray, which directly affects the combustion of the fuel, which in turn determines the production of pollutants. In spite of this, the details of this causal re...In diesel engines the fuel injection system produces the spray, which directly affects the combustion of the fuel, which in turn determines the production of pollutants. In spite of this, the details of this causal relationship remain unclear. There is, however, a lack of quantitative experimental data for determining and visualizing the cavitation inside real size diesel injector nozzle. The present work is devoted to analyze analytically the flow pattern inside the nozzle of a diesel engine working with hydrocarbon fuel (Diesel fuel) and to predict the relationship between the various flow parameters and occurrence of fuel cavitation in such nozzles. Basic physical parameters affecting this phenomenon are identified and quantified while the effect of nozzle geometry, fuel injection pressure, and engine cylinder temperature upon the flow pattern and occurrence of cavitation in such nozzles are assessed. In this study, a commercial computational fluid dynamics (CFD) package (FLUENT-T grid) is used while a computational grid is generated for the real geometry of diesel injector nozzle using (ANSYS). The suitability of the generated computational grid to give reliable results is examined using the suitable procedures and techniques. The results indicated that, cavitation modeling has reached a stage of maturity and it can usefully identify many of the cavitation structures present in internal nozzle flows and their dependence on nozzle design and flow conditions. The qualitative distributions and comparison of cavitation inception and distribution as well as flow parameters at the nozzle exit are also studied.展开更多
The predictive capability of two different numerical cavitation models accounting for the onset and development of cavitation inside real-sized diesel nozzle holes is assessed on the basis of the referenced experiment...The predictive capability of two different numerical cavitation models accounting for the onset and development of cavitation inside real-sized diesel nozzle holes is assessed on the basis of the referenced experimental data.The calculations performed indicate that for the same model assumptions,numerical implementation,discretization scheme,and turbulence grid resolution model,the predictions for differently applied physical cavitation submodels are phenomenologically distinct from each other.We present a comparison by applying a new criterion for the quantitative comparison between the results obtained from both cavitation models.展开更多
As the practicability of a hydrogen-fueled economy emerges, intermediate technologies would be necessary for the transition between hydrocarbon fueled internal combustion engines and hydrogen powered fuel cells. In th...As the practicability of a hydrogen-fueled economy emerges, intermediate technologies would be necessary for the transition between hydrocarbon fueled internal combustion engines and hydrogen powered fuel cells. In the present study, the hydrogen engine efficiency and the load control are the two main parameters that will be improved by using the combined operation of in-cylinder direct fuel injection (DI) and port fuel injection (PFI) strategies to obtain maximum engine power outputs with acceptable efficiency equivalent to gasoline engines. Wide open throttle (WOT) operation has been used to take advantage of the associated increase in engine efficiency, in which the loads have been regulated with mixture richness (qualitative control) instead of volumetric efficiency (quantitative control). The capabilities of a 3D-CFD code have been developed and employed to simulate the whole engine physicochemical process which includes the hydrogen injection through the intake manifold (PFI) and/or the hydrogen DI in the engine compression stroke. Conditions with simulated PFI, PFI + DI and DI have been analyzed to study the effects of mixture preparation behaviors on the hydrogen ignition and its flame propagation inside the engine combustion chamber. Numerically, the CFD code has been intensively validated against experimental engine data which provided remarkable agreement in terms of in-cylinder pressure history evaluation.展开更多
External mixture formation (PFI) of a diesel fuel aerosol has employed to investigate the diesel HCCI engine combustion and emissions characteristics. The key to the external mixture formation with diesel fuel is the ...External mixture formation (PFI) of a diesel fuel aerosol has employed to investigate the diesel HCCI engine combustion and emissions characteristics. The key to the external mixture formation with diesel fuel is the proper fuel/air mixture preparation. A proposed intake diesel fuel aerosol system mainly consists of a small chamber, in which the diesel fuel is fully vaporized by means of fuel cavitation inside the diesel injector nozzle. Nozzle cavitation is mainly affected by the injection pressure and the fuel system temperature. Results obtained reveal that the proposed method determines the possibility of producing a complete homogeneous fuel/air mixture, which can be applied to the diesel HCCI engine. With this method, the combustion and emission behavior were entirely optimized and the engine is capable of running in HCCI combustion mode with nearly ideal mixture preparation. In the present investigation, a methodology for the HCCI combustion mode of the diesel aerosol/air mixtures based on the fuel cavitation inside the injector nozzle parameters (such as the injection pressure and the fuel system temperature where fuel premixed ratio, NOx, CO, CO2, and HC emissions) have analyzed. Based on the engine performance and emissions characteristics the fuel injection pressure and the fuel system temperature have optimized to produce a suitable fuel premixed ratio and the perfect fuel/air mixture homogeneity at different engine operating conditions. The optimal injection pressure ranges between 150 - 200 bars, while the fuel system temperature lies within 175℃ - 200℃. Loops of exhaust gas recirculation (EGR) are used to extend the engine load by controlling the combustion phasing.展开更多
文摘This paper represents a review of the recent researches that investigate the behavior of the gas turbulent flow laden with solid particles. The significant parameters that influence the interactions between the both phases, such as particle size, loading ratio and the gas velocity, have been extensively reviewed. Those parameters are presented in dimensionless numbers in which the applicability of studying its effect in terms of all circumstances of the gas turbulent channel flow at different condition is possible. The represented results show that the turbulence degree is proportional to the particle size. It was found that at the most flow conditions even at low mass ratio, the particle shape, density and size significantly alter the turbulence characteristics. However, the results demonstrate that the particle Reynolds number is a vital sign: the turbulence field becomes weaker if particle Reynolds number is lower than the critical limit and vies verse. The gas velocity has a strong effect on the particles settling along the channel flow and as a result, the pressure drop will be affected.
文摘In diesel engines the fuel injection system produces the spray, which directly affects the combustion of the fuel, which in turn determines the production of pollutants. In spite of this, the details of this causal relationship remain unclear. There is, however, a lack of quantitative experimental data for determining and visualizing the cavitation inside real size diesel injector nozzle. The present work is devoted to analyze analytically the flow pattern inside the nozzle of a diesel engine working with hydrocarbon fuel (Diesel fuel) and to predict the relationship between the various flow parameters and occurrence of fuel cavitation in such nozzles. Basic physical parameters affecting this phenomenon are identified and quantified while the effect of nozzle geometry, fuel injection pressure, and engine cylinder temperature upon the flow pattern and occurrence of cavitation in such nozzles are assessed. In this study, a commercial computational fluid dynamics (CFD) package (FLUENT-T grid) is used while a computational grid is generated for the real geometry of diesel injector nozzle using (ANSYS). The suitability of the generated computational grid to give reliable results is examined using the suitable procedures and techniques. The results indicated that, cavitation modeling has reached a stage of maturity and it can usefully identify many of the cavitation structures present in internal nozzle flows and their dependence on nozzle design and flow conditions. The qualitative distributions and comparison of cavitation inception and distribution as well as flow parameters at the nozzle exit are also studied.
基金Supported by the National Natural Science Foundation of China(51176057)the Specialized Research Fund for the Doctoral Program of Higher Education of China(20100142110081).
文摘The predictive capability of two different numerical cavitation models accounting for the onset and development of cavitation inside real-sized diesel nozzle holes is assessed on the basis of the referenced experimental data.The calculations performed indicate that for the same model assumptions,numerical implementation,discretization scheme,and turbulence grid resolution model,the predictions for differently applied physical cavitation submodels are phenomenologically distinct from each other.We present a comparison by applying a new criterion for the quantitative comparison between the results obtained from both cavitation models.
文摘As the practicability of a hydrogen-fueled economy emerges, intermediate technologies would be necessary for the transition between hydrocarbon fueled internal combustion engines and hydrogen powered fuel cells. In the present study, the hydrogen engine efficiency and the load control are the two main parameters that will be improved by using the combined operation of in-cylinder direct fuel injection (DI) and port fuel injection (PFI) strategies to obtain maximum engine power outputs with acceptable efficiency equivalent to gasoline engines. Wide open throttle (WOT) operation has been used to take advantage of the associated increase in engine efficiency, in which the loads have been regulated with mixture richness (qualitative control) instead of volumetric efficiency (quantitative control). The capabilities of a 3D-CFD code have been developed and employed to simulate the whole engine physicochemical process which includes the hydrogen injection through the intake manifold (PFI) and/or the hydrogen DI in the engine compression stroke. Conditions with simulated PFI, PFI + DI and DI have been analyzed to study the effects of mixture preparation behaviors on the hydrogen ignition and its flame propagation inside the engine combustion chamber. Numerically, the CFD code has been intensively validated against experimental engine data which provided remarkable agreement in terms of in-cylinder pressure history evaluation.
文摘External mixture formation (PFI) of a diesel fuel aerosol has employed to investigate the diesel HCCI engine combustion and emissions characteristics. The key to the external mixture formation with diesel fuel is the proper fuel/air mixture preparation. A proposed intake diesel fuel aerosol system mainly consists of a small chamber, in which the diesel fuel is fully vaporized by means of fuel cavitation inside the diesel injector nozzle. Nozzle cavitation is mainly affected by the injection pressure and the fuel system temperature. Results obtained reveal that the proposed method determines the possibility of producing a complete homogeneous fuel/air mixture, which can be applied to the diesel HCCI engine. With this method, the combustion and emission behavior were entirely optimized and the engine is capable of running in HCCI combustion mode with nearly ideal mixture preparation. In the present investigation, a methodology for the HCCI combustion mode of the diesel aerosol/air mixtures based on the fuel cavitation inside the injector nozzle parameters (such as the injection pressure and the fuel system temperature where fuel premixed ratio, NOx, CO, CO2, and HC emissions) have analyzed. Based on the engine performance and emissions characteristics the fuel injection pressure and the fuel system temperature have optimized to produce a suitable fuel premixed ratio and the perfect fuel/air mixture homogeneity at different engine operating conditions. The optimal injection pressure ranges between 150 - 200 bars, while the fuel system temperature lies within 175℃ - 200℃. Loops of exhaust gas recirculation (EGR) are used to extend the engine load by controlling the combustion phasing.
