Quantitative investigation of the effects of EGR strategies on performance, cycle-to-cycle variations and emissions characteristics of a higher compression ratio and heavy-duty NGSI engine fueled with 99% methane content

Abstract

In this study, an experimental investigation was conducted on the effects of EGR strategies on performance, cycle-to-cycle variations and emissions characteristics of a higher CR and heavy-duty NGSI engine fueled with 99% methane content. The results show that firstly, with the increase of EGR rate for two engine speeds, both the PCP and the maximum HRR decrease, the positions of those are delayed and stay away from the TDC, resulting in longer combustion duration, retarded the 50% combustion position and lower EER, EEE, and BTE. The EER and EEE is decreased by 8.04% and 3.87% respectively, and BSFC increases from 198.9 g/kW.h to 200.0 g/kW.h between the EGR of 0 and 20%. Secondly, in terms of cycle-to-cycle variations, the mean value of IMEP decreases with the increased EGR rate but the COVIMEP shows a slight increasing trend. Meanwhile, the change trends of PCP and COVPCP are similar to the IMEP and COVIMEP, but the value of COVPCP reaches up to 6% and more than COVIMEP. The MRPR decreases and its position is closer to the TDC with the increase of EGR rate. The PCP decreases with the extension of 50% combustion position, position of PCP and 10–90% combustion duration, and there exists a good linear correlation between the PCP and those parameters. Finally, the HC, CO and CO2 emissions increase but the NOx emissions decrease with the increase of EGR rate, and NOx emission is sharply reduced with the increased engine speed due to the shorter reaction time.