Effects of Various Compression Ratios on a Direct Injection Spark Ignition Hydrogen-Fueled Engine in a Single-Cylinder Engine

The effects of compression ratio and injection timing on a direct injection spark ignition hydrogen engine under various excessive air ratios were analyzed using a 0.4-L single-cylinder engine in this study. The engine speed was set to 1500 rpm, and the excessive air ratio was changed by controlling the amount of injected hydrogen under wide-open throttle conditions. The compression ratio was changed from 10, 12, and 14 and the injection timing was varied from BTDC 200, 160, 120°CA. The results revealed that for a compression ratio 14 at a rich limit, late injection timing reduced knocking incidence by taking advantage of stratified mixtures combustion and increased indicated thermal efficiency by reducing combustion loss while producing lower NOx emissions. For compression ratio 14 at an excessive air ratio of 2.2, late injection timing increased indicated thermal efficiency by reducing both combustion and heat losses, achieving the higher indicated thermal efficiency of 42.3%. Although NOx emissions increased with the injection timing retardation, NOx emissions decreased to under 1 g/kWh under excessive air ratios above 2.5 conditions at all injection timings.