Research On Influence Of Fuel Injection Strategy On Reactivity Controlled Compression Ignition Combustion Mode

Reactivity controlled compression ignition(RCCI)is an advanced combustion mode.Its use two fuels with different physical and chemical properties to form a combustible mixture with active stratification.RCCI can flexibly control the combustion process by changing the concentration and activity of the combustible mixture.It can also reduce the emission of NOx and particulate matter in the engine without significantly reducing the thermal efficiency.Among various fuel combinations,methanol as an oxygen-containing fuel,has a high latent heat of vaporization,which is conducive to reducing combustion temperature and achieving low-temperature combustion.Therefore,as an ideal fuel,methanol has a strong application prospect in RCCI combustion mode.In this study,starting from the application of RCCI combustion mode in high pressure common rail diesel engine,methanol and diesel fuel are combined as a group of fuels,which are all injected into the combustion chamber by incylinder direct injection.In this study,methanol and diesel were used as reactive fuels in the combustion mode.Firstly,the influence of methanol energy ratio on combustion and emission performance of methanol/diesel RCCI engine was studied by changing fuel mixing ratio in numerical simulation software.Then,by changing the injection time of methanol and diesel,and injection strategy of ignition diesel,the trend of combustion and emission characteristics of the engine is explored and compared with that of pure diesel engine.The results show that,Compared with pure diesel engines,when the methanol energy ratio is 50%,the maximum combustion pressure in the cylinder,the peak pressure rise rate and the maximum temperature in the cylinder are increased,and HC,CO and SOOT emissions are slightly increased,NOx emissions are significantly reduced,and the trad-off relationship between NOx and SOOT emissions is weakened at this time;however,higher methanol energy ratio will lead to increased engine knock and affect the stable operation of the engine.The combustion and emission characteristics of the engine did not show a significant linearity with the change of methanol injection timing.When methanol is injected at 100°CA BTDC,the methanol premixed gas with the best activity and concentration can be formed in the combustion chamber.At this time,the maximum temperature in-cylinder is highest,the peak pressure in-cylinder and peak pressure rise rate are higher;HC emission is lowest,NOx,SOOT and CO emission are lower.With the lag of ignition diesel injection timing,the peak pressure in-cylinder and maximum temperature in-cylinder first increase and then decrease,the peak pressure rise rate gradually decreases,and the start of combustion is gradually delayed;HC emissions first decrease and then rise,NOx emissions increased first and then decreased,SOOT and CO emissions increased gradually.Therefore,the injection timing of properly igniting the diesel fuel in advance is advantageous for reducing the emission of pollutants.The use of pre-injection strategy for ignition diesel will have a significant impact on pressure in-cylinder,pressure rise rate in-cylinder and temperature profile in-cylinder.With the advance of the pre-injection time of ignition diesel,the peak pressure in-cylinder increases gradually,the peak pressure rise rate decreases gradually,and the start of combustion advances gradually,SOOT and NOx emissions are lower than those without pre-injection strategy.With the delay of the main injection timing of ignition diesel,the pressure in-cylinder shows three peaks,the peak pressure in-cylinder caused by the compression of the piston gradually becomes prominent,the emissions of HC,SOOT and CO gradually increase,and the NOx emission gradually decreases.Therefore,the pre-injection strategy of ignition diesel can appropriately delay the main spray timing,but the excessively delayed main spray timing will result in a decrease in the in-cylinder combustion efficiency and an increase in pollutant emissions.Ignition diesel uses a pre-injection strategy to reduce peak pressure rise rate in-cylinder,which can effectively reduce NOx and SOOT emissions without causing a significant reduction in engine indicated thermal efficiency.