Optimizing low-temperature combustion in a dual-fuel marine engine with hydrogen-rich reformer gas and micro-injection strategies

This study investigates low-temperature combustion (LTC) in a dual-fuel heavy-duty marine engine using hydrogen-rich reformer gas (75% hydrogen, 25% carbon monoxide by volume) and diesel micro-injection. A validated CFD model evaluates the effects of gradually replacing methane with reformer gas while maintaining constant energy input. As reformer gas concentration increases from 0% to 75%, combustion becomes more reactive. Peak in-cylinder pressure rises from 11.92 MPa to 16.03 MPa, and the combustion duration shortens from 37.4° to 19.8° CA. Efficiency improves, but nitrogen oxides emissions more than double at 45% reformer gas. In contrast, hydrocarbon and carbon monoxide emissions drop sharply, by over 99% and 50%, respectively. To balance efficiency and emissions, advanced diesel injection strategies are explored at 45% reformer gas. The injection timing is advanced from 20° to 70° CA before top dead center, using both single and multiple injections. Earlier injections improve combustion phasing, increase work output by 9%, and reduce knock intensity. Among multiple injection cases, one strategy reduces nitrogen oxides by 49% while maintaining acceptable indicated mean effective pressure and minimizing hydrocarbon and carbon monoxide emissions. These findings show that combining moderate reformer gas ratios (40–45%) with optimized injection strategies enables efficient and cleaner LTC operation. The approach supports the transition to low-emission marine propulsion systems using hydrogen-rich fuels.