The effect of ignition energy on the lean combustion limitation in high compression ratio engines

Abstract

This study examined the impact of ignition energy for various loads on extending the limitations of lean combustion (LLC) and enhancing thermal efficiency using a high compression ratio (CR = 17) engine. It combined high compression ratio design、lean burn and high ignition energy to achieve more than 50 % indicated thermal efficiency. The findings indicated that a 424 mJ ignition energy proved helpful in reducing the ignition delay (CA0-10), widening the LLC to λ = 2.1, and achieving the highest thermal efficiency of 50.3 % at λ = 1.9 with lower exhaust loss and heat transfer loss when IMEP raised from 8.5 bar to 10 bar. Nevertheless, due to the high coefficient of variation of indicated mean effective pressure (COVIMEP), the constraints of lean combustion only reached λ = 1.45 and λ = 1.3 under IMEP = 12 bar and 13 bar, and its corresponding thermal efficiency was 45.1 % and 43.0 %, respectively. In terms of emissions, NOx was more sensitive to a bigger rise in ignition energy than other gases, and the variation of CO, THC, and NOx did not connect to a slight increase in ignition energy. The CO, THC, and NOx also tended to stay unchanged in ultra-lean conditions, remaining at about 900 ppm, 2797 ppm, and 38 ppm, respectively.