Optimization of EGR and split injection strategy for light vehicle diesel low temperature combustion

Low temperature combustion was developed using a four-cylinder light vehicle diesel engine. Operating conditions considered were 1600 rpm, 1bar and 3bar IMEP. Both EGR and split injection strategy were optimized in order to obtain the lowest BSFC accompanied with a low level of emissions. It was found that a late injection strategy with high levels of EGR rate was required for simultaneous reduction of NOx and soot. However, the fuel consumption remains higher than the conventional combustion regime. Thus, the optimization study of injection parameters to improve the trade-off between NOx and soot emissions while maintaining good fuel efficiency was performed. Several injection pressures were tested. The results showed that as injection pressure increased, NOx emissions increased slightly, soot initially decreased sharply, but further increase of injection pressure on soot was not obvious at low temperature atmosphere, and might lead to increased BSFC. Next, split injection strategy was adopted, optimized pilot injection conditions for minimizing fuel consumption were found at late pilot injection timing with big injection quantity, but little amount of pilot injection could make better comprehensive performance of diesel engine. Through multi-parameter collaborative optimization, the emission reduction path was proposed at operating condition of partial load. Low NOx and soot emissions could be obtained with slightly increase of fuel consumption.