Numerical Study On The Effect Of Fuel Injection Strategy On Combustion And Emission Characteristics Of Methanol/Dimethyl-ether RCCI Engine

Building a resource-saving and environment-friendly society has been our country’s long-term development goal,and the energy conservation and the emission reduction are the greatest challenges for the internal combustion engine.The combination of alternative fuels and advanced Reactivity Controlled Compression Ignition(RCCI)methods offers the possibility to solve the problems of traditional internal combustion engines.However,there are still some problems in the application of RCCI engines,especially the incomplete combustion at low load.In this paper,a reactive controlled compression ignition(RCCI)combustion mode is constructed by methanol and dimethyl-ether(DME),and the numerical study of the effect of fuel injection strategy on the combustion and emission characteristics of the methanol/DME RCCI engine is realized by using KIVA-3V program,and the engine is operated under low load(IMEP≈0.49 MPa).The injection strategy for realizing efficient and clean combustion of the RCCI engine is clarified.Firstly,the combustion and emission characteristics of methanol/DME RCCI engines under single direct injection and dual direct injection strategies are compared and analyzed.Comparing with the single direct injection,the dual direct injection is able to extend the distribution of the high-reactivity DME,and the sufficient combustion of the premixed methanol near the piston and cylinder wall can be realized.The reduction of equivalent indicated fuel consumption rate(EISFC)is able to achieve 0.79-5.65 g/k Wh,and the HC,CO and NO_x emissions can be efficiently reduced.Secondly,the combustion and emission characteristics of the methanol/DME RCCI engine under different initial temperatures,pressures and premix ratios are investigated.With the initial temperature is 390 K and the initial pressure is 1.2 bar,the efficient and clean combustion can be realized under 65%premix ratio.At this time,the EISFC of the engine is 162.1 g/k Wh,and the NO_x emissions is below 0.4 g/k Wh.Finally,the study is focus on the effects of the injection timing and the injection ratio of pilot injection and main injection.The pilot injection timing plays a significant role on the combustion characteristics,and the early pilot injection timing and the higher injection ratio are suggested for improving the combustion efficiency.The ESFIC is able to reach 160.5 g/k Wh and the NO_x is near zero emissions,when the pilot injection timing is-90°CA ATDC,the main injection timing is-10°CA ATDC,and the injection ratio is 7:3.