Investigation On Spray,Combustion And Emission Characteristics Of GDI Gasoline Engine Under Different Injection Pressure

The increasingly severe problems of environmental degradation and energy shortage have led to more stringent fuel consumption regulations and emission standards in various countries.GDI gasoline engine has been widely studied and applied because of its strong power,good economy and rapid response.In order to explore the performance potential of GDI gasoline engine fully,researchers at home and abroad improve the GDI gasoline engine through lots of technologies.Increasing the injection pressure can optimize the formation and combustion process of the mixed gas in the cylinder,thereby it can improve the power performance,reduce the fuel consumption rate and improve the exhaust emission of GDI gasoline.This paper comprehensively studied the spray macro and micro characteristics,the formation of the mixed gas in the cylinder and the combustion and emission characteristics of GDI gasoline engine by means of the shadow photographic method,PDPA,numerical simulation and bench test to explore the effect of injection pressure on spray,combustion and emission characteristics of GDI gasoline engine.The results of the study show that:Increasing injection pressure can increase the initial speed of fuel out of the injector,speed up the diffusion of fuel,and increase the penetration and spray area,but the promotion of their increase is decreasing.The maximum and stability values of the spray cone angle increase by 1.1 degrees on each increase of the injection pressure of 5 MPa.Increasing the injection pressure can effectively improve the post injection phenomenon of the injector,promote the breakup of the post injection spray.Increasing injection pressure can increase the speed of fuel particles,promote the fragmentation and evaporation of fuel particles,significantly reduce the SMD of fuel particles and increase the number of small size particle.Increasing the injection pressure can make the distribution of fuel more uniform in the cylinder and reduce the concentration of fuel.Increasing the injection pressure can accelerate the evaporation rate of fuel droplets,increase the evaporation ratio of fuel for the same injection quantity,but the promotion effect on fuel evaporation is decreasing.Increasing the injection pressure can increase the mixing time of fuel and gas,rapidly enhance the turbulent motion of the airflow in the cylinder in a short time,intensify the mixing between fuel and air,and improve the quality of the mixture.Increasing the injection pressure increases the quality of the fuel film formed by the fuel impinging on the wall,but the quality of oil film under different injection pressure is almost consistent at ignition time.Increasing the injection pressure can accelerate the speed of flame propagation,effectively shorten the period of flame development and rapid combustion,and make the combustion of the mixture more compete and stable.Increasing the injection pressure can increase the average temperature,the pressure and the instantaneous exothermic rate of the combustion process,and make the time of their peak appear in advance.Increasing the injection pressure can reduce the production of CO and HC.Because increasing the injection pressure can increase the average temperature in the cylinder,NO_X emissions icrease.Increasing the injection pressure can effectively suppress the thermal cracking and dehydrogenation of the fuel,and reduce the production of the nuclear particles.Increasing the injection pressure can reduce the possibility of the aggregation of nuclear particles and the adsorption of volatile organic matter to form the accumulated particles,so it can reduce the overall emission of particles.