Study On Process Of Hydrogenated Catalytic Biodiesel/Gasoline RCCI Combustion Based On Optical Engine

Reaction activity controlled compression ignition(RCCI)has important engineering application value for improving engine thermal efficiency and achieving low emissions.However,the control of the RCCI combustion phase is facing severe challenges.Optical diagnosis technology can clearly and intuitively observe the combustion process in the cylinder,which is helpful to analyze the control mechanism of combustion phase.As the second generation of biodiesel,hydrogenated catalytic biodiesel(HCB)has attracted more and more attention due to its ultra-high activity.The application of HCB in high activity fuel of RCCI engine can achieve better combustion phase.In this paper,a full window optical system is built based on a diesel engine.High-speed imaging technology is used to capture the combustion process in the cylinder of the optical engine.RCCI combustion is realized by direct injection of high active fuel in the cylinder and injection of low active fuel in the intake port.After calibration of fuel injection system and cycle fluctuation test,the performance of optical engine bench was tested,and the cycle stability of optical engine was analyzed.HCB and diesel were used as high active fuel and gasoline as low active fuel respectively in the experiment.The effects of highly active fuel proportion,injection time,and intake air temperature on the RCCI combustion process and combustion phase were studied.The ignition characteristics and the control mechanism of combustion phase of RCCI were obtained.The injection time of high active fuel is-40 to-15°CA ATDC.The results show that the combustion phase of RCCI can be effectively controlled at the injection time of highly active fuel,and the combustion phase is-20°CA ATDC,the peak values of combustion pressure and heat release rate are the most,and the combustion duration is the shortest.At this time,the combustion duration of HCB/gasoline RCCI is 5.54°CA,diesel/gasoline RCCI combustion duration is6.93°CA;From-30°CA ATDC,the injection time of highly active fuel is delayed,the ignition delay period is shortened,the combustion occurs more near the top dead center,the combustion center is advanced and close to the top dead center,and the combustion duration first decreases and then increases;For the optical engine used in the test,the injection time of HCB should be later than-38°CA ATDC,too early injection will lead to combustion deterioration.The results show that the proportion of highly active fuel has a direct effect on the combustion phase of RCCI combustion.The proportion of high active fuel is 10%～50%,when the proportion of highly active fuel is 10%,HCB/gasoline RCCI has better ignition and combustion characteristics,and the ignition delay period is 20.65°CA.The RCCI of Diesel/gasoline is21.88°CA.At the same time,the maximum combustion pressure is lower than HCB/gasoline RCCI;As the proportion of highly active fuel increases,the maximum combustion pressure of RCCI increases,the peak heat release rate increases,the ignition delay period shortens,and the combustion duration shortens.Too much highly active fuel will increase the possibility of engine knock.Under the test conditions of optical engine,increasing the intake air temperature can achieve more stable RCCI ignition combustion.Because the activity of HCB is higher than diesel,the intake air temperature required for ignition is lower when the proportion of HCB is 30%,and the combustion is stable when the intake air temperature is above 50℃;The stable combustion of diesel Requires 40% ratio and the intake air temperature should be higher than 60℃.With the increase of intake air temperature,RCCI combustion load increases,the maximum combustion pressure increases,the peak heat release rate increases,the combustion phase advances,the ignition delay period shortens,and the combustion duration shortens.