Experimental Study On The Effects Of Fuel Properties And Injection Strategies On Partially Premixed Combustion

Partially premixed combustion(PPC)has the potential to achieve high-efficiency and clean combustion,which is one of the hotspots in internal combustion engine research community.At high load,the large premixed combustion proportion of PPC will lead to excessive pressure rise rate(PRR),while there is still inevitable diffusion combustion,resulting in soot emissions.Therefore,the trade-off among PRR,thermal efficiency and emission is the major chanllege of PPC for high load operation.In recent years,researchers have conducted a lot of researches on the co-optimization of fuel properties and engines to realize high-efficiency and clean PPC combustion,especially the effects of octane number and sensitivity of low reactivity gasoline-like fuels on PPC combustion.Researchers found that octane number and octane sensitivity show important impact on the combustion and emission characteristics of PPC through mixture stratification,fuel components/reactivity and the following heat release process.Meanwhile,injection strategy is one of the major measures to control the in-cylinder mixture distribution,which also plays an important role for PPC combustion and emission control.Therefore,this paper systematically carried out experimental study on the effects of fuel octane number and octane sensitivity coupled with injection strategies on the combustion and emission characteristics of PPC.Firstly,the effects of fuel octane number and octane sensitivity on PPC combustion and emission were studied.The results show that with the increase of octane number,the premixed combustion ratio increases,the soot emission decreases,but the maximum pressure rise rate(MPRR)and NOx increase.High sensitivity fuels have longer ignition delay,result in larger premixed combustion,increased indicated thermal efficiency(ITE),reduced soot emission and proportion of accumulation mode particle.High sensitivity TRF95 containing toluene produces the highest NOx emission,while ERF95 produces the lowest NOx and PM.As EGR increases,ERF95 can effectively suppress soot formation and emission,but penalty in MPRR is observed.The lower viscosity and higher volatility of commercial 95#gasoline greatly affect PPC combustion,and both the MPRR and soot emission of 95#gasoline are higher than those of ERF95.In order to resolve the high PRR issue of high octane sensitivity fuels within PPC combustion,the effects of octane number and octane sensitivity coupled with double injection strategy on PPC combustion were further studied.For RON90 fuels,small pilot-main injection interval has a great influence on PRR and gas emissions,but shows limited effect on the particulate matter(PM)emissions.A proper pilot-main interval can effectively reduce MPRR while maintaining low emissions.With the increase of pilot injection ratio,MPRR firstly decreases and then increases,while NOx,PM and the ratio of accumulation mode particle decrease.The lowest PRR can be obtained with30%pilot injection ratio for all tested fuels,and ERF90 with sensitivity of 4(ERF90S4)shows previllege in MPRR,NOx,PM and ITE.For RON70 fuels,sensitivity has little effect on combustion and emission.The adjustable ranges of pilot-main injection interval and pilot injection ratio of RON70 fuels are wider than those of RON90 fuels,and both the PM and NOx emissions can be reduced with double injection.With slight penalty in PRR,lower NOx/PM emissions and higher ITE can be obtained with ERF70S4 compared to other RON70 fuels.Through the optimization of fuel properties and injection strategies,the MPRR,NOx and PM concentration of ERF90S4 at 30%pilot injection ratio are 0.65MPa/°CA,1.1g/(k W·h)and 2.31×10~7#/cm~3 respectively while maintaining the ITE of 46.1%.