Study On Fuel Spray Characteristics Of Piezo Injector And Its Impact On Combustion And Particulate Emissions In A Gasoline Direct Injection Engine

Gasoline direct injection engine has a good performance in transient response characteristics,power and economy characteristics,but it also has poor particulate emission.As a key part in combustion,spray can make a big difference in combustion characteristics and particulate emission.Compared with multi-hole injector,piezo injector has the good advantages of good spray stability,and quick response,so this paper studied the characteristics of piezo injector spay,and the characteristics of combustion and particulate emission from a GDI engine using piezo injector.Firstly,we studied spray characteristics of piezo injector.We finished drive system of piezo injector,and did some spray experiments in constant volume bomb,and the results turned out that the cone spray was formed by strings,and penetration was shorter,spray cone angle was larger,and its vortex structure and string could help improve spray quality.And the increase of ambient pressure and injection pressure contributed to fuel-air interaction,on the other hand,double injection made penetration shorter.Secondly,the effect of operating parameters such as ignition timing,injection pressure,air-fuel ratio and load on combustion process and particulate emission was studied in GDI engine with single injection.The results showed appropriate ignition timing could stabilized combustion,reduce fuel consumption rate and particulate emissions.Appropriate injection pressure could reduce fuel consumption rate and particulate emission.Lean mixture could reduce particulate emission a lot,but when mixture was too lean,combustion became unstable.The increase in load increased particulate emission,and when in medium load,nuclear mode became more relatively,while in high load,accumulation mode became more.Finally,the effects of single injection,double injection and triple injection strategies on the combustion process and particulate matter emission were studied under the same operating conditions.And the results showed that when using single injection,there were a peak number in nuclear mode and two peak numbers in accumulation mode,at the same time,there was a better start time of injection(SOI)that cooperate particulate emission and economy characteristics well.While comparing with single injection,Double injection could reduce particulate a lot,the appropriate increase in fuel amount of first injection,effects to reduced particulate became better.When using double injection and triple injection,there were two peak numbers in nuclear mode and two peak numbers in accumulation mode,and particulate emission firstly increased,then reduced with the advance of SOI3,meantime coefficient of variation became smaller.Compared with single injection,double injection and triple injection could reduce particulate by 37.8% and 48.6%,and coefficient of variation and fuel consumption rate also reduced a lot.And double injection significantly reduced the particulate in nuclear mode,but triple injection significantly reduced the particulate in accumulate mode a lot.