Effect of ammonia jet strategy and intake air temperature on mixing characteristics in ammonia/diesel dual-fuel marine engine

The ammonia-diesel dual-fuel strategy is one of the promising methods to achieve near zero carbon emissions from marine engines. For low-pressure premixed ammonia/diesel dual-fuel engine, there is still a lack of research on the characteristics of the ammonia slip and ammonia/air mixing. The injection strategy to reduce ammonia slip was studied by numerical simulation using the single-cylinder engine model firstly, and then the effects of ammonia jet valve number, ammonia jet angle and intake air temperature on the ammonia/air mixing characteristics were studied under the condition of ultra-low ammonia slip. The results show that retarding the ammonia jet timing as well as using a relatively smaller valve outlet diameter of the jet valve could significantly reduce ammonia slip. Compared with two jet valves, the mixing with four ammonia jet valves is relatively inhomogeneous due to momentum loss and concentration superposition of the ammonia jets. When jet angle rotates excessively to cylinder liner results in layered distribution of "top lean, bottom rich", the jet angle rotates excessively to cylinder center results in a layered distribution of "inner lean, outer rich" during the compression process due to different flow velocity distributions. Optimal mixing quality of ammonia/ air could be obtained by adjusting the jet angle to utilize the air around cylinder center and cylinder liner together. With higher intake air temperature, the higher flow velocity due to larger pressure difference will promote the diffusion of ammonia as well as mixing.