Experimental Study On Combustion And Emission Characteristics Of Multicomponent Gasoline Surrogate Fuels

In recent years,the deteriorating environmental issues and energy issues have put forward higher standards on the combustion and emission performance of the engine.Computer simulation is a key method to combustion process optimization of the internal combustion engine.For computer simulation,constructing chemical kinetics model simplified and accurate enough based on surrogate fuels is necessary.In recent decades,researches about gasoline surrogate fuel through computer simulation,or fundamental experiments on rapid compression machines,flow reactors and shock tubes etc.have attracted lots of attentions.However,researches focusing on the application of gasoline surrogate fuels to actual gasoline engine are rare.After detailed analysis of the 95# gasoline components,isooctane,n-heptane,toluene,cyclohexane and diisobutylene were used to construct three kinds of gasoline surrogate fuels,namely TRF(three component),CTRF(four component),CDTRF(five component)in this paper.An experimental study about the combustion parameters and emission level of the gasoline surrogate fuels was conducted on a GDI(Gasoline Direct Injection)engine under different load,spark timing,injection pressure,injection timing and equivalence ratio,and the result were compared with that of 95# gasoline.In this paper,the combustion process and emission characteristics of TRF were studied detailed firstly.The study found that there are some differences of the physicochemical properties such as flame propagation velocity,lower heat value,viscosity and H/C ratio and chemical composition between TRF and gasoline,so although TRF can roughly simulate the combustion and emission characteristics of gasoline,there are obvious differences in terms of chemical reaction rate,combustion phase,cylinder pressure,temperature and various emissions especially NOx.methane,isopentane,isobutene,aromatic hydrocarbon and formaldehyde.On this basis,the combustion and emission characteristics of CTRF and CDTRF were studied.Moreover,combustion and emissions under different combustion controlling parameters(spark timing and equivalence ratio)and fuel injection strategy(injection pressure and injection timing)were researched.According to the results,the flame propagation velocity,lower heat value and viscosity of surrogate fuel will affact the fuel concentration,atomization and chemical reaction rate.Thus,the flame propagation velocity,lower heat value and viscosity are important parameters of surrogate fuel in terms of the combustion phase,the ignition delay and combustion duration.In addition,the H/C ratio of surrogate fuel have great influence on emissions.On the one hand,H/C ratio can directly affect CO and particulate emissions,on the other hand,it can have an impact on emissions through changing cylinder temperature.Due to the difference of the flame propagation velocity,viscosity,H/C ratio and the lower heating value between the surrogate fuels and gasoline,the in-cylinder atomization of gasoline is the best,followed by CTRF,CDTRF and TRF.Thus,the sequence of the maximum in-cylinder pressure,peak value of heat release rate and the maximum pressure rise rate under different test conditions(load,ignition strategy and fuel injection strategy)maintains gasoline > CTRF > CDTRF > TRF.The combustion phase CA10 and CA50 are also postponed in sequence of gasoline,CTRF,CDTRF,TRF.According to all the research results,among the three gasoline surrogate fuels,CTRF is the closest one to gasoline in terms of physicochemical property,while CDTRF is the most optimized one in the aspect of chemical composition,which makes the emissions of CTRF and CDTRF closer to that of gasoline than that of TRF.Specifically,in terms of NOx,methane,ethylene,propylene,isobutene and particulate emissions,CTRF is closer to gasoline.In regard to THC,acetylene,1,3-butadiene and aromatic hydrocarbon emissions,CDTRF is closer to gasoline.