Experimental Study On The Effect Of High-octane Number Fuels On Engine Performance

Fuel qualit y has a significant impact on engine performance,especiall y fuel econom y.High octane-number fuels have a certain potential in achieving efficient and clean combustion.Most domestic and international studies have focused on the effects of octane number on engines,vehicle performance and emissions under knocking-sensitive conditions,while relativel y little research has been done on the effects of combustion characteristics and fuel econom y under non-useful conditions.At the same time,the conclusions of different studies on the effects of octane number on engines are different.In this paper,we investigate the correlation between fuel components,octane number and engine operating conditions from the perspective of the effect of different octane boosters on engine performance.The main stud y includes:In the first part,common famil y components were screened as octane boosters,including ox ygenated components:ethanol,isopropanol and MTBE;cyclic h ydrocarbon components:toluene,x ylene and cyc lopentane.The blending characteristics of octane boosters and base fuel（95#alk ylated oil）were investigated.The correlation characteristics between ON value（RON and MON）,BON（blending octane number）and S（octane sensitivit y）were investigated and the experimental data were anal yzed using different blending models.The results show that:There is a nonlinear additive phenomenon（synergistic and antagonistic blending）in the blending of octane boosters with base fuel.the correlation between ON and S values is poor as evidenced b y the values of their correlation coefficients R~2（0.302,0.272 and 0.268 for RON,0.106,0.039and 0.045 for MON）.There is a strong correlation between ON and BON values.The experimental data were anal yzed using ON mixture model and ON-S mixture model.the deviation values of ON mixture model were larger（maximum deviation of RON was 10.67%and maximum deviation of MON was 8.60%）.ON-S mixture model has a better prediction of octane value of the blended fuels.Using the S-value of the blended fuels,the ON-S mixture model is able to obtain better prediction results（maximum deviation of 1.94%for RON and 3.35%for MON）.In the second part,octane boosters were blended with the base fuel at10%,20%and 30%volume ratios.First,the trend of the effects of octane boosters blending ratio on engine performance at different loads was anal yzed at 2000 r/min operating conditions（50 N?m,150 N?m and 250 N?m were selected to represent small,medium and large load operating con-ditions）.Then,a comparative anal ysis of ox ygenated and cyclic h ydro-carbon components was performed.To highlight the differences between the different components,a 30%blending ratio was selected.The effects of the different components on the engine performance were anal yzed in terms of load characteristics and speed characteristics.The results show that:The addition of cyclopentane can improve fuel econom y at all loads under common speed conditions（2000r/min）,and 30%-cyclopentane has a maximum FSR of 5.42%.Ethanol blended fuels have the highest effective fuel consumption rate（maximum FSR:-6.13%）.At small and medium loads,increasing the octane number can improve the combustion process of the blending fuels.The addition of ox ygenated components can increase the ignition delay period,which is not proportional to the octane number of the blending fuels.The addition of MTBE and cyclopentane can improve the fuel econom y,with the maximum FSR of 2.65%and 5.14%under high load condition.At medium speed（2500r/min）,the addition of ethanol and isoprop yl alcohol can improve the initial reaction rate of combustion.Isoprop yl alcohol is more stable and the aromatic blending fuels are more reactive at medium temperature.The best fuel econom y was achieved at medium and high speed condition（3000r/min）,with the maximum FSR for toluene,x ylene and cyclopentane:1.41%,2.07%and 4.03%.In the third part,the macroscopic variability in engine performance of different high-octane number fuels and the deep-seated factors leading to such differences are explored b y comparing two groups of blending fuels with RON values of 99 and 102.The results show that:Under the common speed condition（2000r/min）,the airflow movement in the cylinder plays a dominant role,and the combustion duration of alcohol components is significantl y longer than that of aromatic components.Under the medium load condition,the flame propagation speed varies greatl y with the different reaction paths,and the overall reaction rate is:ethanol>toluene>MTBE>isopropanol>x ylene.The sensitivit y of ethanol-blending fuels’combustion process to octane changes is higher.The sensitivit y of the ox ygenated components’combustion process to pressure is higher than that to temperature.The difference of combustion process between different components is most obvious in medium speed condition（2500r/min）.The blending fuels econom y is the best at medium to high speed（3000r/min）,and the maximum FSR is 3.30%for the isopropanol mixture.Under high speed condition（3500r/min-4500r/min）,the MON value can better characterize the blending fuel’s anti-knock propert y.Compared with R99（RON=99）fuels,the overall fuel consumption rate of R102（RON=102）fuels are higher,indicating that a certain degree of octane number value increase will worsen the fuel econom y instead.The effect of ox ygenated components on the deterioration of fuel econom y is more serious,where the ethanol blends have the largest reduction of 8.41%in FSR.As the octane number increases,the influence of the physical and chemical properties of the fuel blends on the combustion process is more significant.