Experimental Study On Concentration Of Super/Transcritical Fuel Injection Characteristics Of GDI Fuel Injectors

The dependence of foreign oil,which has been rising year by year,poses a great threat to China's energy security.The pollution of the exhaust gas to the environment and the harm to people's health are becoming more and more serious.For the current GDI gasoline engine,the fuel is injected into the cylinder in the form of supercritical fluid.The mixed combustion has the potential to break the thermal efficiency limit brought by the compression ratio,reduce the particulate emissions,and achieve efficient and clean combustion.According to the domestic and international research status of GDI injector supercritical and transcritical fuel injection,the supercritical and transcritical spray characteristics of GDI injectors are experimentally studied under constant environmental conditions under different environmental conditions.Supercritical spray platform was built to achieve high temperature and supercritical spray.The high-speed lithographic method was used to study the transcritical and supercritical spray characteristics of porous injector and single-hole injector gasoline and isooctane.Based on the temperature of common operating point in the intake phase of GDI engine,the jet characteristics of high temperature gasoline fuel injected into normal temperature and negative pressure environment were studied.The results show that the morphology of the low-subcritical porous spray of the macroscopic morphology of the gasoline fuel spray of the porous injector is kept well;the subcritical state has obvious collapse and convergence phenomenon;the supercritical state has the phenomenon of gas turbulent diffusion.The single-hole jet has a clearer boundary with a lower sub-criticality;the subcritical jet exit begins to show a more pronounced expansion,and the entire shape of the spray exhibits a plume-like structure;the supercritical jet shape exhibits a cloud-like structure.Through the analysis of the penetration distance under different threshold conditions,it can be seen that as the temperature increases,the density gradient of the hydrocarbon mixture decreases and the mixing is more uniform.Based on the temperature and pressure in the cylinder of GDI engine,the jet characteristics of high temperature gasoline and isooctane fuel injected into high temperature and low pressure environment were studied.The results show that the gasoline jet has a significant collapse and convergence phenomenon,while the isooctane jet does not.In the subcritical stage,the thermal motion of the fuel molecules and the internal turbulence of the jet,the interaction of the jet with the high temperature environment for heat exchange and momentum exchange will contribute to the increase of the projected area of the jet;in the supercritical phase,the thermal motion of the fuel molecules The dominant diffusion effect will cause the jet projection area to change regularly.It is predicted that the future GDI engine will break through the temperature and pressure in the cylinder after the limitation of the compression ratio,and the spray characteristics of the high-temperature gasoline fuel injected into the supercritical environment are studied.The results show that at the same injection time,the spray penetration distance of the single-hole injector increases first,then decreases steadily,but it rises in the supercritical state.As the injection temperature increases,the spray penetration distance of the porous injector rises steadily and then rapidly drops below the initial value.