Simulation Study On Combustion Process Of DI Diesel Engine

In recent years, the proportion of direct injection diesel engine and its application fieldrised year by year. The reason is that compared to the separation type combustion systems,the direct injection diesel engine can reduce the fuel comsumption rate by10%to15%aswell as CO2emission. However, its major problems are higher emissions of NOx and Soot.The cylinder mixture formation of direct injection diesel engine determines its combustionquality and its emission performance, which was decided by injector parameters. Atpresent, besides experimental method, the calculation of numerical simulation provides anew way to study the combustion process.In this article, the auther built the mathematical and ite physical model. Themathematical model includes Dokowicz evaporation model, Wave break-up model,Walljet1interaction model, Enable turbulent dispersion model, EBU turbulent combustionmodel, auto ignition model, Zeldovic NOx model, Kennedy-Hiroyasu-Magnussen Sootmodel. To solve the mathematical equations and the numerical simulation, we used thefinite volume method and the SIMPLE algorithm. Finally compared with experimentalresults, the calculation models are proved to be reasonable. So we used AVL-FIREsoftware to analysis the original diesel engine and obtained the mean cylinder pressure andtemperature, NO, Soot concentration at different crank angle.To study the influence of combustion process and emission performance, we usedvariable parameters method to analysis the injector parameters including nozzle diameterand spray angle.The simulation results shows that with the decrease of nozzle diameter, the cylindermaximum pressure and temperature increased, on the other hand, with the decrease ofspray angle, the cylinder maximum temperature decreased and the pressure do not changea lot; The value of NO concentration increased with the nozzle diameter decreased, butcontrary to the spray angle and it will freeze at the post-phase; The value of Soot concentration increased with the nozzle diameter and spray angle decreased, and part ofthem will be oxidized at the post-combustion stage.From different nozzle diameter and spray angle of cloud diagram shows that thevelocity field of nozzle diameter was mainly influnced by the formation of the mixture, butthe velocity field of spray angle was mainly influnced by the changing of air movement incombustion chamber; From the temperature field we know that the key of reducing NO isto control the combustion chamber temberature at the late temperature field. From the NOconcentration field of different nozzle diameter and spray angle, we know that the key ofreducing NO is to control the production of the bottom of the combustion chamber, theclearance and the injector area; From the Soot concentration field, we know that the key ofreducing Soot is to control the production of the bottom of the combustion chamber andthe clearance.