Experimental Study on the Effect of Ignition Strategy on Combustion and Emissions in a Direct Injection Hydrogen Engine

Hydrogen-fueled internal combustion engines (H₂ICEs) are a promising pathway toward carbon-neutral transportation, but their efficiency and emissions performance are highly sensitive to ignition control strategies. This study systematically investigates the combined effects of spark timing (−10 to −26 °CA BTDC) and spark energy (25–40 mJ) on combustion characteristics in a direct injection H₂ICE operating at a constant speed of 1400 r/min under low, medium, and high load conditions. Results show that spark timing advance produces load-dependent effects: at low load, it increases the peak heat release rate while delaying peak pressure and shortening combustion duration; at medium and high loads, it advances both peaks toward TDC with an optimal spark timing shifting closer to −14 °CA. Ignition delay was only slightly reduced at low load but significantly shortened by about 3 °CA at high load. NOx emissions increased nearly linearly with spark advance, while slight retardation effectively halved NOx at low load without compromising torque. Increasing spark energy reduced ignition delay by up to 23% and shortened combustion duration by 2–4 °CA at low load, resulting in a torque increase from 48 to 60 N·m; however, the benefits diminished with increasing load. Additionally, higher spark energy led to a moderate NOₓ rise, particularly under medium load. These findings offer valuable insights into the optimization of ignition strategies for H₂ICEs, providing a foundation for improving combustion efficiency while minimizing emissions in zero-carbon hydrogen-powered engine systems.