Experimental study of H2 injection strategies in a HD engine: Comparison of PFI and LPDI

Stringent CO 2 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 BSNO x emissions by up to 75 %. At high load, early LPDI reaches 41.7 % gITE with low NO x (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 BSNO x (9.3 g/kWh), unburnt H 2 (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. • PFI vs LPDI compared on HD H2ICE engine. • Early LPDI cuts NOx by 75 % at 20 bar fuel pressure. • Early LPDI matches PFI in volumetric efficiency. • Late LPDI reaches 42.4 % gITE at high load.