A CFD study on ammonia combustion and performance of a dual-fuel marine engine

Ammonia-fuelled engines have primarily targeted light-duty automotive internal combustion engines. However, ammonia can be a potential carbon-free fuel for large-bore marine engines to decarbonise the maritime sector. In this study, a CFD model was developed and validated to assess direct ammonia injection in a large-bore marine engine. The impacts of liquid ammonia energy ratios up to 77% and injection timings on combustion, engine performance, and emissions were examined. The results showed that the highest indicated thermal efficiency of 48.3% was achieved at SOI_NH3 − 40 CAD, where the main combustion occurred at TDC and overlapped with diesel ignition, leading to a shorter combustion duration. Varying ammonia injection timing revealed that the minimum NH₃ slip of 4.1 g/kWh was at SOI − 40 CAD and increased for both earlier and later ammonia injection timings. Liquid ammonia significantly reduced NO_X emissions from 7.7 g/kWh in the diesel case to just 1.3 g/kWh due to lower combustion temperature. Moreover, advancing ammonia SOI_NH3 from − 15 to − 50 CAD significantly reduced CO emissions from 9.1 to 2.7 g/kWh. The results also showed that N₂O primarily forms in thin mid-temperature NH₃-rich layers ahead of the flame front, and earlier ammonia injection expands these zones, increasing N₂O emissions.