Ammonia diffusion combustion and emission formation characteristics in a single cylinder two stroke engine

Liquid ammonia diffusion combustion (LADC) is an effective approach to achieving high ammonia energy ratio (AER) and combustion efficiency in engines. However, there is a lack of simulation studies of LADC mode in ammonia/diesel dual direct injection engines. To address this gap, the study develops a numerical model based on an independently modified marine two-stroke engine. This model analyzes the combustion performance of ammonia in LADC mode and the pollutant generation mechanisms in LADC mode across various AER conditions. The findings indicate that in the LADC mode, the liquid phase ammonia spray exhibits a concentrated distribution area, facilitating thorough combustion of ammonia fuel. The diesel mixture and flame are entrained into the liquid phase ammonia spray, facilitating multi point ignition. This process notably enhances combustion speed, thereby reducing overall combustion duration. In comparison to pure diesel combustion, soot emissions are reduced by 99 % under the LADC mode, and CA90 advanced by 11.8 °C A. In addition, when the AER range is from 50 % to 70 %, the engine exhibits favorable combustion and emission characteristics. By appropriately adjusting the liquid ammonia injection quantity, the indicated thermal efficiency improves by 10.7 %, the equivalent indication specific fuel consumption decreases by 13.9 %, and the emission such as NOx and soot can be also reduced effectively.