Experimental And Numeracal Study Of Different Branched Length Alkylbenzene Diesel Surrogate Fuels In Low Temperature Combution

In order to achieve near-zero emissions and ultra-high efficiency of internal combustion engine,it is urgent for scholars to master the combustion performance and emission characteristics of diesel engine in low-temperature combustion?LTC?.However,due to diesel is a complex mixture with hundreds of components,it is challenging to conduct a comprehensive study on the components of diesel.Based on the real diesel physical and chemical properties,inthis study,n-heptane was chosen as the representative composition in the alkane through detailed analysis of real diesel composition.The toluene,n-butylbenzene and1,2,4-trimethylbenzene werechosen as the representative composition in the aromatics.The density,cetane number,low heating value and hydrogen to carbon ratio of test fuels were accurately calculated and compared.The sevenblends were pure diesel?denoted as D100?,mixtures of toluene with blending ratios of 20%and 30%in n-heptane?denoted as T20 and T30?,mixtures of n-butylbenzene with blending ratios of 20%and 30%in n-heptane?denoted as BBZ20 and BBZ30?and mixtures of 1,2,4-trimethylbenzene with blending ratios of 20%and 30%in n-heptane?denoted as TMB20 and TMB30?.In order to investagate the effects of different branched length alkybenzene diesel surrogate fuelson engine combustion and emission characteristics of LTC,an experiment were conducted in a four-cylinder turbocharged diesel engine.The results showed that with increasing of EGR rate,the peaks of in-cylinder pressure and heat release rate of test fuels decreased,CA50 was delayed and the ignition delay was prolonged.The addition of alkybenzene to n-heptane resulted in an increase in the peak of in-cylinder pressure,the CA50was advanced,and the ignition delay was prolonged.Under the all operating conditions,the in-cylinder pressure,heat release rate,ignition delay and CA50 of BBZ20 were in the best agreement with D100.In terms of regular emissions,as the EGR rate increased,the soot,THC and CO emissions increased,while the NO_X emissions decreased.Compared with D100,the soot emissions ofalkybenzene blended fuels decreased,but the NO_X,CO and THC emissions increased.At medium-small EGR rates?EGR<20%?,the NO_X emissions were almost the same as that of D100 when addtingn-butylbenzene and1,2,4-trimethylbenzene to n-heptane with the gap of 2.6%.Under the all operating conditions,compared with toluene and 1,2,4-trimethylbenzene,the soot emission wasclosest to that of D100 when adding 20%n-butylbenzene to n-heptane.In addition,the CO emission of T30 was closest to that of D100.In terms of particulate matter?PM?,as the EGR rate increased,the peaks of nucleation mode particle?NMP?concentrations andaccumulation mode particle?AMP?concentrations increased,the total PM number and mass concentrations increased,and the geometric mean diameter?GMD?increased.Compared with D100,the peaks of NMP,AMP,total PM numberconcentrations,total PM massconcentrations and GMD of alkybenzene blended fuelsdecreased.Under the all operating conditions,the NMPconcentrations of alkybenzene blends were closed to that of D100,especially the particle size was less than 25nm.When EGR<30%,the ratio of particle size less than 25nmfor BBZ30 was the closest to that of D100.When EGR>30%,the ratio of particle size less than 25nmfor BBZ20 was the closest to that of D100.Based on the engine experiment,it can be concluded that n-butylbenzene was better than toluene and 1,2,4-trimethylbenzene as the representative of monocyclic aromatic hydrocarbons in diesel fuel to simulate the engine combustion process and emissions generation.In order to investigate the effects of different n-butylbenzene blending ratios on engine combustion process and emissions,especiallytheformationmechanismof soot,an-heptane/n-butylbenzene reduced mechanism coupled with CONVERGEnumerical study was conducted.The results showed that the mole fractions of C₂H₂,A₁ and A₄ increased with the increasing of EGR rate.Under test conditions,the NO spatial distributions of three fuels?D100?n-heptane?,BBZ20 and BBZ30?were almost the same.The COspatial distributions of three fuels were almost the same without EGR.However,the gap of COspatial distributions was large for three fuels as the EGR rate increased.In addition,the temperature,equivalent ratio,OH group,soot and NO emission spatial distributions of BBZ20 were closest to that of D100.