Effect of premixed ratio on combustion and emission characteristics in a spark ignition engine with hydrogen-ammonia direct injection

s: Direct injection coupled with lean burn technology represents a pivotal advancement in effectively addressing combustion and emission control in hydrogen engines. Additionally, incorporating ammonia in specific proportions enhances the indicated effective pressure and thermal efficiency of the engines. This study employs a numerical simulation approach to build a three-dimensional spark ignition engine model using hydrogenammonia premixed fuel with direct injection, subsequently, validating its accuracy. The influence of the hydrogen-ammonia premixed mass ratio (Ra) and the equivalence ratio (4b) on the mixture formation, combustion process, and emission of in-cylinder under direct injection and lean burn conditions are studied. The results indicate that the addition of ammonia facilitates a more uniform distribution of hydrogen within the cylinder. Notably, in cases where 4b >= 0.45, a small percentage of ammonia (Ra <= 30 %) can shorten the hydrogen combustion duration by 1 to 3 crank angle degrees. Conversely, in cases with 4b <= 0.40, ammonia inclusion exhibits a suppressive effect on hydrogen combustion, with the impact becoming more pronounced at a lower equivalence ratio. On the emissions side, heightened nitrogen oxide emissions concentration correlates with increased ammonia. In all cases, evaluating overall engine performance reveals that a 4b of 0.40 with a Ra of 10 % emerges as the optimal program, achieving an indicated thermal efficiency of 47.1 % and oxide emissions of 9.34 g/kWh.