Experimental Study of Multiple Injections and Coupling Effects of Multi-Injection and EGR in a HD Diesel Engine

Diesel engines have to reduce emissions to satisfy future emission legislations. The purpose of this paper is to investigate the effect of multiple injections and the combined effects of multi-injection and EGR on HD diesel engine emissions and performance. A common rail fuel injection system and high pressure EGR system based on variable geometry turbocharger (VGT) were used. Injection parameters (injection dwell and mass) were adjusted with different injection strategies (pilot-main, pilot-pilot-main, main-post and pilot-main-post) to find out the influence of these parameters on combustion and emissions. Secondly the coupling effects of multi-injection and EGR were evaluated at both high and low loads. Finally, while keeping NOx at 2.0 g/kW.h by adjusting EGR rate, the influence of injection parameters and EGR were tested to highlight their influence on smoke and BSFC. Results show that, pilot injection can reduce NOx, CO and BSFC at low load but has no obvious influence at high load; Double pilot injection can enhance air-fuel mixing; Post injection can accelerate the mixing and oxidation processes during late combustion period and can effectively reduce smoke and CO; Optimized injection parameters coupled with EGR can significantly reduce NOx and smoke while causing no serious penalty on BSFC.