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 NO_X 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.