Experimental study on the effects of EGR on combustion and emission of an SI engine with gasoline port injection plus ethanol direct injection

Abstract Ethanol has shown substantial capacity for improving the emission and combustion. EGR can effectively and significantly reduce emissions. Based on the open-loop control system, the performance of GPI + EDI four-cylinder SI engine under different EDIr and EGR was studied under the operating conditions of λ = 1, speed = 1500rmp, DIT = 120° CA BTDC. The results show that, with the increase of EGR, IMEP first increases and then decreases, NOx keeps decreasing, BSFC, CO and HC first decreases and then increases, CoVPmax, CA 0–10 and CA 10–90 all increase. When EGR = 12%, EDIr = 15%, IMEP reaches the highest value of 0.417 MPa, which is about 10.74% higher than the original engine level. At this working point, BSFC reaches 307.22 g/(kW·h), which is about 10.49% lower than the original engine level. Until EGR = 12%, CoVPmax is always lower than baseline. And it has the largest average decrease of 31.49% at EDIr = 15%. When EGR = 12%, NOx can decrease about 164 ppm with an average increase of 1% EGR. At this time HC also drops to the lowest point, with an average drop of 39.80%. And the lowest value of CO is 0.32 vol% at EGR = 12%, EDIr = 45%. In summary, ethanol has a higher oxygen content and LFS is faster. EGR can not only reduce pumping losses and throttling losses, but also effectively accelerate the positive effects of ethanol on combustion and emissions. EGR + EDI + GPI can obviously increase the engine power performance, improve fuel economy and decline the gaseous emissions. 12%EGR + 15%EDI provides an innovative and optimal solution for ethanol/gasoline dual fuel SI engine coupled EGR.