Experimental and numerical analysis of hotspot-induced pre-ignition characteristics in a direct-injection hydrogen engine

Hydrogen, as a clean, carbon-neutral energy carrier with broad application prospects in transportation and other sectors, has emerged as a pivotal enabler for achieving global carbon neutrality goals. However, its ultralow ignition energy and short quenching distance render direct-injection turbocharged hydrogen engines highly susceptible to pre-ignition, which generates destructive pressure spikes and compromises engine reliability. Given the randomness of hotspot occurrence location and triggering timing, this study performed experimental and numerical investigations based on a 2.0 L turbocharged direct-injection hydrogen engine to clarify the effects of hotspot characteristics on pre-ignition intensity (PI). The results indicate that high-frequency pre-ignition occurs within the brake mean effective pressure (BMEP) range of 15–17.5 bar, with the highest frequency (12 occurrences per 220 cycles) observed at 16.5 bar BMEP. Hotspots located on the side opposite the hydrogen injector induce the maximum PI of 1.08. Hotspot temperature exhibits a positive correlation with PI, and no pre-ignition is triggered when the temperature is below 1000 K. Earlier triggering timing leads to higher PI; in contrast, excessively early triggering timing prevents pre-ignition initiation. In the single-factor study on triggering timing, PI increases from 0.44 to 0.85 as the timing ranges from −10 °CA to −22 °CA, while no pre-ignition occurs at −24 °CA. Multifactor analysis reveals that pre-ignition location, triggering timing, and their interaction have the most significant impacts on PI, with contribution rates of 15%, 39%, and 32% respectively. These findings establish theoretical foundations and actionable strategies for pre-ignition suppression, thereby advancing the development of high-reliability hydrogen engines.