Abstract
High-efficiency, low-emission ammonia-hydrogen engines with low hydrogen energy share (XH2) help promote a carbon-neutral transition in heavy-duty, long-distance transportation. In this study, numerical investigations were carried out on a hydrogen jet ignition (HJI) ammonia engine to study the effects of ammonia port fuel injection (PFI) and ammonia direct injection (ADI) on the engine performance, including combustion and emission characteristics, at XH2 = 3 % with varied spark timing (ST). The results show that the ADI mode has higher volumetric efficiency, lower in-cylinder temperature, and lower heat transfer loss compared with the PFI mode, and more retarded injection can further increase the volumetric efficiency and reduce the temperature. ADI mode results in a more inhomogeneous fuel distribution and a lower local equivalence ratio, with hydrogen consumed earlier than ammonia, potentially resulting in more rapid early-stage combustion. ADI mode with multiple injections is more conducive to engine performance than single injection and can achieve the higher indicated mean effective pressure (IMEP) and indicated thermal efficiency (ITE) than PFI mode. By further optimizing ST, the ADI mode improves ITE by 2.8 % and reduces NO emission by 70 % compared with the PFI mode under acceptable NH3 and N2O emission conditions.
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