Experimental investigation of combustion and emission characteristics of a heavy-duty direct-injection hydrogen engine with active and passive jet ignition

Compared to traditional spark ignition systems, jet ignition in hydrogen-fueled engines shows strong potential for improving efficiency and reducing emissions. However, research on jet-ignited hydrogen engines remains limited, particularly regarding combustion behavior, emissions, and control parameter effects. This study experimentally investigates a heavy-duty direct-injection hydrogen engine with a jet ignition system under active and passive modes. The effects of spark timing, excess air ratio (λ), and pre-chamber fuel energy ratio are evaluated. Results indicate that spark timing primarily controls combustion phasing with minimal impact on combustion duration. At a CA50 of approximately 7 °CA ATDC, the maximum ITE reached 43.0 % in passive mode and 42.0 % in active mode. Over λ = 1.6–2.6, the combustion duration was 5.0–9.3 °CA in passive mode and 4.3–8.5 °CA in active mode. Active operation produced more advanced combustion phasing and higher peak pressure because of its greater ignition energy. ITE increased with λ, reaching 42.2 % and 41.3 % at λ = 2.6 in passive and active modes, respectively, while nitrogen oxides approached zero at λ ≥ 2.4. Two pre-ignition events occurred at λ = 2.7 under active operation. ITE remained approximately 41–42 % as the pre-chamber fuel-energy ratio increased from 0.8 % to 0.9 %, but decreased to approximately 36.5 % at 2.7 %, accompanied by increased NOx emissions. Thus, pre-chamber fueling should be limited to the minimum required for reliable ignition.