Investigation On Flash Boiling Spray Characteristics Of Multi-hole GDI Injector Under High Ambient Pressure

Compared with the traditional port fuel injection(PFI)engine,the gasoline direct injection(GDI)engines due to their flexibility in controlling the mixture formation and combustion process,and gradually becomes the mainstream.In order to meet increasingly strict emission regulations,higher requirements have been placed on the spray quality of GDI engines.Flash boiling spray has been proven to significantly improve the spray quality of GDI engines,and it is common in practical conditions.However,in actual engines,the morphology of flash boiling spray may change,and spray collapse will occur.Spray collapse will cause deterioration of emissions.Therefore,it is necessary to further study the mechanism of flash-boiling collapse to suppress the collapse behavior of flash-boiling spray.This dissertation studies the flash boiling spray morphology under high ambient pressure,the growth of bubbles inside the oil droplets and the interaction between the oil bundles,and in order to understand the collapse mechanism of the flash boiling spray.Under high ambient pressure flash boiling conditions,observation of the spray morphology of n-hexane shows that individual jet can be seen.The flash boiling spray does not collapse,and the spray width gradually widens with increasing oil temperature.Because the large amount of steam generated in the high ambient pressure flash boiling condition offsets the low pressure region caused by the high speed jet motion,and it is confirmed that the low pressure zone caused by the high speed jet motion cannot fully explain the spray collapse in the flash boiling condition.By increasing the jet pressure to increase the jet velocity,it was found that the spray had not collapsed,which further verified this conclusion.The bubble growth in the jet under high ambient pressure flash boiling condition was studied,and it was found that increasing the oil temperature would promote the bubble radius growth.However the bubble growth was suppressed with the increase of ambient pressure.It can be seen that the inhibition of bubble growth in a high ambient pressure condition is one of the reasons why n-hexane flash boiling does not collapse under high back pressure.The spray morphology of single hole under high ambient pressure flash-boiling environment was studied.The spray morphology of single hole and five hole injector was compared and the jet-to-jet interaction was analyzed.It was found that under the flashboiling environment,the degree of expansion of the oil beam near the nozzle region may have a positive correlation with the collapse of the spray,that is,the higher the expansion of the single-hole jet near the nozzle region,the stronger the degree of spray collapse.Under high ambient pressure,the radial development of the jet is hindered and will inhibit the growth of bubbles,reducing the spray width near the nozzle region and jet-to-jet interaction,and eventually the spray does not collapse.