The effect of hydrogen on the thermal efficiency and combustion process of the low compression ratio CI engine

In this study, it was purposed to investigate the hydrogen enrichment effect on combustion characteristics of a low compression ratio turbocharged Common-Rail CI engine. The compression ratio was lowered from 18.25 to 16.9. Tests were conducted at 40 Nm, 60 Nm, 80 Nm, 100 Nm and 120 Nm loads at a constant 1750 rpm. Compared to the test with the original compression ratio, the low compression ratio tests yielded lower maximum cylinder pressures, maximum rate of heat releases, maximum rate of pressure rises, ringing intensity. Combustion durations increased but ignition delays fluctuated with hydrogen enrichment. The cylinder pressures, the first heat release and the first pressure rise rates increased with the higher hydrogen flow rates. Besides, the second peaks of pressure rise rates and heat release rates decreased. The hydrogen enrichment firstly increased and then decreased the brake thermal efficiency of the low compression ratio engine. Ringing intensity increased with increasing engine load and hydrogen amount.