Experimental Study of H2 Injection Strategies in a HD Engine: Comparison of PFI and LPDI

Stringent CO2 reduction targets and tightening emission regulations have intensified interest in hydrogen internal combustion engines (H2ICEs) as a clean and robust solution for the heavy-duty (HD) sector. This study experimentally compares port fuel injection (PFI), early low-pressure direct injection (LPDI), and late LPDI strategies on a single-cylinder HD H2ICE under steady-state medium and high loads. The injection timing and fuel pressure are varied to study the overall influences on a single-cylinder heavy-duty H2ICE. PFI and early LPDI deliver high charge homogeneity but reduced volumetric efficiency compared to late LPDI. At medium load, all three strategies achieve ~41 % gross indicated thermal efficiency (gITE). Increasing LPDI pressure from 12.8 to 20 bar enhances mixture uniformity, cutting BSNOx emissions by up to 75 %. At high load, early LPDI reaches 41.7 % gITE with low NOx (0.72 g/kWh), while late LPDI benefits from reduced heat transfer loss and compression work, achieving 42.4 % gITE. However, late injection also increases BSNOx (9.3 g/kWh), unburnt H2 (435 ppm), and pressure rise rate (19.7 bar/◦CA). These results highlight LPDI’s potential for high efficiency, with injection timing and pressure as key levers to balance emissions and performance.