Sustainable ammonia is one of the leading candidates in the search for alternative clean fuels for marine applications. This paper aims to build a simulation model of a six-cylinder, four-stroke diesel engine to investigate the effects of increasing the ammonia proportion in methanol–ammonia fuel blends on engine performance and emissions. In the present study, the conditions of different speeds and different proportions of ammonia in fuel blends are investigated. The results show that the average effective pressure, brake power, and brake torque increase by about 5% with an increased ammonia substitution ratio. In terms of economic performance, the changes under medium and low speed conditions are not obvious. However, the change in high speed conditions is significant. The brake specific fuel consumption (BSFC) is reduced by 6.6%, and the brake thermal efficiency (BTE) is increased by 4%. It is found that the performance of the engine is best at medium speed. The best performance is achieved with higher efficiency and lower emissions. The present results can provide guidance for the optimization of ammonia–methanol blends and their applications in engines.

The combustion of diesel fuel in internal combustion engines faces challenges associated with excessive emissions of pollutants. A direct solution to this issue is the incorporation of cleaner energy sources. In this study, a numerical model was constructed to investigate the characteristics of ammonia–diesel dual-fuel application in a medium-speed diesel engine. Effects of ammonia–diesel blending ratios on engine performance and emissions were investigated. The results indicate that for this engine model, the optimal diesel energy ratio is about 22%. When the diesel energy ratio is less than 22%, the engine’s output performance is significantly affected by the diesel energy ratio, while above 22%, the influence of the intake becomes more pronounced. When the diesel energy ratio is below 16%, the cylinder cannot reach combustion conditions. Diesel energy ratios below 22% can cause ammonia leakage. With increasing diesel energy ratio, the final emissions of carbon oxides increase. With a higher diesel energy ratio, NO emissions become lower. When the diesel fuel energy ratio exceeds 22%, the N₂O emissions can be almost neglected, while below 22%, with poor combustion conditions inside the cylinder, the N₂O emissions will increase.