Hydrogen engines are a promising decarbonization pathway for the transport
sector; however, their performance is constrained by the abnormal combustion
phenomenon of pre-ignition (PI). While hydrogen PI shares similarities with the
extensively studied “low-speed PI” observed in boosted gasoline engines, it
exhibits distinct characteristics, notably higher frequency and lower individual
cycle intensity. These differences arise from the thermochemical properties of
hydrogen and differing operating strategies, most notably lean versus
stoichiometric combustion.
This study investigates the mechanisms of hydrogen PI, broadly divided into
hotspot vs oil-induced pathways, in a heavy-duty, lean-burn, port fuel–injected,
spark-ignition (SI) hydrogen engine. Experimental data at three combustion
phasing conditions are analyzed to understand the dominant mechanisms. Retarding
ignition timing increased PI frequency from under 5% to over 20% by extending
the pre-spark window during which PI triggers could initiate combustion. Oil
droplet autoignition is believed to be the primary PI mechanism under the tested
conditions. For quantitative assessment of PI frequency, a median-based
statistical approach is proposed to identify events based on early combustion
onset and/or elevated peak pressure. This approach addresses limitations of
conventional standard deviation–based outlier detection methods (like the
Grubbs’ method), which are prone to statistical masking at the high-PI
frequencies observed.
