Combustion and heat transfer characteristics of a heavy-duty low-pressure-direct-injection hydrogen engine with a flat-roof-and-shallow-bowl combustion chamber

Hydrogen shows great potential for its use in internal combustion engines as a carbon-free fuel. Most experimental studies focus on light-duty engines, while experimental studies of heavy-duty direct-injection hydrogen engines are still rare. In this study, a dedicated low-pressure-direct-injection combustion system is designed on a 2.15 L single-cylinder hydrogen engine. Based on this, the combustion and heat transfer characteristics of the engine are investigated at IMEP 10 bar and 15 bar, with various excess air ratios (2 = 1.8-3.0) and spark timings (-16 to - 4 degrees CA ATDC), and the applicability of classical empirical heat transfer models in hydrogen engines are further examined. As the spark timing advances, the combustion phases are linearly advanced, while the combustion duration remains almost unchanged due to the high reactivity of hydrogen. The 2 range for stable combustion is 2 = 2.0-3.0 at IMEP 10 bar and 2 = 2.2-2.8 at IMEP 15 bar, relatively narrower than the reported results in light-duty engines. Knock occurs under conditions of 2 = 1.8 with IMEP 10 bar and 2 = 2.0 with IMEP 15 bar. At 2 = 3.0, combustion instability occurs at both 10 bar and 15 bar IMEP. It is noted that pre-ignition occurs alongside combustion instability at 2 = 3.0 and IMEP 15 bar. Selected heat transfer models fail to accurately predict the heat transfer laws of the engine, and the modified Shudo equation shows good performance.