Combined Effect Of Start Of Injection And Intake Pressure On Low Load RCCI Combustion And Emissions Characteristics

With the increasingly serious environmental pollution and energy shortage,it is urgent to develop clean and efficient combustion of engines.The high efficient and clean combustion is achieved under Reactivity controlled compression ignition(RCCI)combustion mode,which is characterized as forming fuel stratification before ignition.The characteristics of fuel stratification will be effected by the start of injection(SOI),the intake pressure(IP),the premixed ratio(PR)and the cycle energy(CE),thus affecting the combustion and emission characteristics.In this paper,the RCCI experiment was conducted in fueled with diesel and gasoline and conditions with 1000 rpm,IP=110 and 125 kPa,SOI=-5~-30° CA ATDC,PR=40% and 65%,CE= 885J/cycle?1380 J/cycle and 1700 J/cycle.In this paper,the diesel is used as high-activity fuel injected into cylinders,and the gasoline as low-activity fuel into inlet.The speed of the engine was 1000 rpm,the IP was 110 kPa and 125 kPa,the SOI was-5 ~-30° CA ATDC,the PR was 40% and 60%,the CE was 885J/cycle,1380 J/cycle and 1700 J/cycle.The experimental study was conducted on combined effect of SOI and IP on RCCI combustion and emissions characteristics with different PR or CE.The results show that:(1)Investigation on combined effect of SOI and IP on combustion and emission shows that the increasing of IP can promote the generation of low temperature cold-flame reaction and ignition.The heat release rate decreases with the inhibition of increased IP on combustion process.The earlier SOI is,the less negative effect of IP on heat release rate is.The in-cylinder temperature decreases,Due to the increase in the heat capacity caused by the increasing of IP.The primary reason of the change in HC,CO and NOx is the change in in-cylinder temperature.There are greater effects of IP on HC and CO emissions,and less on NOx with the advancement of SOI.The increasing of IP promotes the size of nucleation mode particulate matter increase,and the accumulation mode particulate matter decrease.The increase in IP promotes the number of nucleation mode and accumulation mode particulate matter increase.The mass of particulate matter increases with increasing IP.(2)The following conclusions are summarized by studying the coupling effect of SOI and IP on combustion and emission with different PR.there is more contribution of the increase in IP on cold flame reaction and ignition with lesser PR.The positive effect of increasing IP on high-temperature combustion increases with lesser PR or later SOI.With the decrease of PR and the delay of SOI,the effect of IP on HC and CO is reduce,and with the advance of SOI,the effect on NOx emissions increases.There are complex changes of the coupling effect of SOI and IP on the particulate matter with different PR.(3)As for the combined effect of SOI and IP on combustion and emission with different CE,the investigation shows that the promotion of the increase in IP on cold flame decreases with greater CE.With the increasing of CE,the effect of IP on ignition is weakened,and the effect on high-temperature combustion changes from positive to negative.With larger CE,the impact of IP on HC emissions is greatly reduced.Under later SOI,the effect of IP on CO increases with the increasing of CE,but under earlier SOI,that decreases.As CE increases,the effect of IP on NOx is enhanced.For particulate emissions,the coupling effect of SOI and IP changes complexly with different CE.