Research On The Influence Of Fuel Activity Control On Engine Performance In Gasoline Compression Ignition Mode

The research of low-temperature premixed combustion has gone through the process from HCCI to PCCI and then to RCCI.Among them,HCCI/PCCI has the disadvantages of uncontrollable combustion phase and heat release rate,and poor load adaptability.In order to expand its load adaptability and improve the controllability of combustion phase,Rolf.D Retiz of Wisconsin Engine Research Center proposed a reactive controlled compression ignition（RCCI:Reactivity Controlled Compression Ignition）combustion mode,which has become an international research hotspot in recent years.The realization of the RCCI combustion process must first explore the changing laws of related influencing factors and comprehensively analyze the combustion mechanism.Therefore,based on the experimental and simulation research of RCCI combustion,this article explores the influence of fuel activity control on engine performance in gasoline compression ignition mode..In this paper,based on the existing four-ring CA4D28C5 diesel engine in the laboratory,the experimental platform built by adding the port injection system to study the fuel activity control in the gasoline compression ignition mode on combustion and performance of RCCI engine（including diesel primary and secondary injection timing,diesel first injection ratio and external EGR rate）.The research results found that:SOI1,SOI2,diesel first injection ratio,EGR rate will have a greater impact on it.With the advancement of SOI1,the starting point of combustion and the backward shift of the combustion center of gravity combustion rate decrease,and its dynamic and economy are slightly deteriorated,CO and UHC emissions slightly increase,and NO_Xemissions decrease.With the advancement of SOI2,its CO and UHC emissions also have a changing inflection point,and the overall trend is first to rise and then to fall.With the increase in the proportion of DI one injection,under25%and 50%load,the dynamic and economical trends are opposite and NO_Xemissions have increased,while CO and UHC have slightly decreased.As the EGR rate increases,its dynamics,economy,CO and UHC emissions also have an turning inflection point.The overall trend is to increase first and then decrease,and NO_Xemissions gradually decrease.Secondly,a brief introduction to the RCCI combustion mechanism and combustion process and stages,combined with the mechanism,analyzes the chemical kinetic process of RCCI combustion under a certain working condition,and roughly divides it into a low temperature stage,a medium temperature stage and a high temperature stage,CH₂O and OH represent the low-temperature combustion and high-temperature combustion stages respectively,and n-heptane and isooctane are consumed in stages.The low-temperature reaction starts at almost the same time but the proportions of consumption are different.The concentration of n-heptane is reduced to about 1/5 of the initial value,The isooctane is reduced to about 1/2 of the initial value.Finally,with the help of CONVERGE simulation calculation and Ensight three-dimensional dynamic analysis,based on the active stratification of mixed gas and equivalent ratio stratified combustion,from the perspective of chemical reaction kinetics,Study the influence of gasoline and diesel ratio on the RCCI combustion process and the change of the concentration field representing the key components of combustion.（n-heptane,isooctane,H₂O₂,CH₂O,CO,OH）.The study found that n-heptane and isooctane reacted quickly at the edge of the combustion chamber pit first,and the consumption starting point was earlier as the ratio of n-heptane increased;a large amount of OH was produced at the edge of the combustion chamber pit in the high temperature stage,and then expand to the periphery gradually,and the higher the proportion of n-heptane,the larger the expansion area;the CH₂O consumption part and the CO production part are exactly the same,and they are concentrated on the edge of the combustion chamber pit,and CO is rapidly generated in the late stage of the medium temperature reaction.CH₂O is produced slowly,which is actually caused by the continuous conversion of CH₂O to CO.