Experimental investigation of the effects of CR, hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty NGSI engine fueled with 99% methane content

In order to analyze and improve thermodynamic process of NGSI engine and achieve better energy utilization, a low CR (11.6) SI engine was modified by replacing pistons with different bowl volumes and an experimental investigation of the effects of CR (13.6 and 14.5), hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty NGSI engine fueled with 99% methane content was conducted. The results showed that the PCP, maximum HRR and in-cylinder temperature increased obviously with the increase of hydrogen contents, CR and engine speed, and the locations of PCP and maximum HRR advanced towards TDC, which led to the advance of 50% combustion position, shorter combustion duration and more output work. Secondly, with the increase of hydrogen contents and CR, the proportions of indicated work and heat transfer energy to coolant turned larger but the unaccounted losses and combustion loss became smaller. In addition, with the increase of engine speed, both indicated work and friction loss were large, which caused the decrease of BTE, besides, the percentage of friction loss and pumping loss turned up. And the hydrogen contents and CR had little effect on exhaust energy and exergy. Finally, comparing the energy and exergy of NGSI engine under operated conditions, the change trends of exergy terms were similar to their corresponding energy, however, the exergy efficiency was 7.97-9.70% lower than BTE and the percentage of exhaust energy and heat transfer energy to coolant was 2.46-2.51 and 7.09-8.09 times larger than corresponding energy, respectively.