Effect of gasoline injection pressure and CO2 dilution on the hydrogen knock limit extension in a Hydrogen–Gasoline dual-fuel engine

This study explores the combined effects of gasoline injection pressure (GIP) and carbon dioxide (CO2) dilution on hydrogen knock limit extension in a hydrogen–gasoline dual-fuel engine. GIPs of 80, 110, and 140 bar are tested alongside CO2 dilution rates of 2, 4, and 6 L/min (LPM). Hydrogen is introduced into the intake manifold in 2-LPM steps until knock onset is observed. Increases in GIP and CO2 dilution lead to reductions in brake mean effective pressure and brake thermal efficiency. The in-cylinder pressure drops from 28.26 bar to 26.11 and 25.18 bar at a GIP of 140 bar and CO2 dilution rate of 6 LPM, respectively. High hydrogen flow rates improve combustion and performance characteristics. While NOX emissions decrease at high GIP and CO2 dilution levels, they increase after hydrogen addition. GIP and CO2 dilution extend the hydrogen knock limit to a flow rate of 20 LPM. Notably, cyclic variations increase significantly with increasing GIP and CO2 dilution levels but decrease with hydrogen addition.