Study on the impacts of ammonia addition on combustion and emissions in a high compression ratio jet ignition gasoline engine

Carbon emissions have triggered severe global crises, heightening decarbonization urgency. The transportation sector, particularly internal combustion engines (ICEs) utilizing carbonaceous fuels, represents a critical domain requiring immediate emission mitigation. This study advances carbon reduction via thermal efficiency enhancement zero-carbon fuel widely adoption, employing a novel gasoline engine with 17.5 compression ratio (CR) and active pre-chamber jet ignition system. Experimental modifications enabled ammonia port injection, systematically examining ammonia energy fractions (0–60 %) and intake pressures (−44.9 to −23.6 kPa, as baseline) on: pre-chamber combustion, main-chamber knock propensity, combustion characteristics, and emissions. Ammonia addition effectively suppressed gasoline knock intensity (KI), achieving a KI reduction above 73.00 % at 40 % ammonia ratio (AR) versus pure gasoline. This advances combustion phasing, enhancing indicated mean effective pressure (IMEP) by over 2.49 % relatively and brake thermal efficiency (BTE) by over 2.85 % absolutely. Collaborative combustion retardation arises from pre-chamber/main-chamber interactions: at 40 % AR, pre-chamber jet energy degrades over 81 % while ignition delay and combustion duration in the main chamber prolong significantly. Elevated intake pressure compensates for ammonia's low laminar burning velocity and high minimum ignition energy (MIE) to achieve stable combustion, evidenced by reduced coefficient of variation (COV) over 50 % AR. Emission analysis shows NOx and N2O reductions exceeding 61 % (at 30 % AR) and 31 % (at 40 % AR) respectively versus gasoline baseline, despite substantially elevated unburned NH3 concentrations over 4000 parts per million (ppm). This study provides critical insights for optimizing ammonia-blended combustion in next-generation high-efficiency ignition engines.