Effect of ammonia and diesel fuel injection pressure on combustion characteristics of high-pressure ammonia direct injection marine dual fuel engine

Ammonia has emerged as a potential zero-carbon marine fuel owing to its compatibility with existing liquefied petroleum gas infrastructure and its potential role as a hydrogen carrier. Nevertheless, its practical application is challenged by low combustion speed, incomplete combustion, and nitrogen oxide (NO x ) emissions. This study investigated the combustion performance and emission characteristics of ammonia in a 12.5 l single-cylinder marine dual-fuel engine. The experimental configuration employed high-pressure ammonia injection and diesel micro-pilot (MP) ignition to overcome ammonia’s high self-ignition temperature and low energy density. By systematically varying ammonia and MP injection pressures and timings, the effects on thermal efficiency, combustion stability, and exhaust emissions were evaluated. The results demonstrated that higher ammonia injection pressures improved both efficiency and combustion stability, while optimized MP injection pressure enhanced diesel atomization and facilitated reliable ammonia ignition.