Matching Study Of Combustion Chamber Geometry Parameters And Spray Characteristics Of DI Diesel Engine

In the traditional internal combustion engine,The diesel engine is extensively used in transportation,engineering,agricultural machinery,and other fields because of its high thermal efficiency and good power performance,and economy.But the spray characteristics of fuel and its mixing process with air in the combustion chamber are the key factors that restrict the combustion process of diesel engines and thus affect the economy and emission characteristics of diesel engines.The shape of a combustion chamber and its matching with injection parameters are the important factors that affect the mixture formation and combustion in the cylinder,the structure parameters directly affect the flow characteristics in the cylinder.To clarify the influence mechanism of combustor structural parameters on gas flow and mixture formation,it is necessary to conduct in-depth research on the influence of combustor parameters on airflow characteristics in the cylinder,and adjust the spray model,which is of great significance to optimizing the matching with the optimization of combustor structure.In this study,the matching of combustion chamber geometry parameters and spray characteristics of direct injection diesel engine is studied by means of numerical simulation.To establish a parametric analysis method for different combustion chamber structures,The shape of the combustion chamber is parameterized by 8 parameters,and the relationship between parameters is found.The combustion chamber shapes are designed for the reentrant parameters（G1/G2）,the shape parameters（G6）,and the boss top radius parameters（G4）.Based on the verified simulation model,different combustion chamber schemes are simulated and analyzed.By analyzing the three-dimensional physical field distribution,and combining with the pressure curve,heat release rate curve,NO generation curve,and SOOT generation curve,the influences of different combustion chamber structures parameters on the flow field,mixture formation,combustion process,and emission characteristics are analyzed.The results show that when the combustor reentrant ratio is 0.88,the shape parameter is concave and the radius of the convex top is 0mm,the flow movement is strong,and it can effectively organize the mixture formation and combustion process,and reduce NO and SOOT emission.On this basis,aiming at the difficulty of machining nozzle hole diameter of the high-pressure common-rail injection system,and to further explore the influence of injection law,spray characteristics,and combustion chamber space matching on the combustion process,an axial needle injector is adopted.Because its structure has the characteristics of strong self-cleaning ability,and the diameter of the nozzle is large and easy to process,it can reduce the intake vortex,which is conducive to improving the inflation efficiency and making full use of the combustion chamber space.By designing the axial needle injector reasonably,adjusting the spray shape,matching it with the combustion chamber,and analyzing its influence on the combustion process,the conical spray characteristics are improved,and the optimal parameters of the conical spray system are finally determined.The results show that when the cone angle is150° and the main injection timing is 7.8°CA,the combustion process can be reasonably organized,the thermal efficiency can be improved,and the CO generation can be reduced.