Investigation on the combustion of ammonia using direct high/medium-pressure-Otto injection approach in a diesel two-stroke marine slow speed engine

The urgent need to reduce exhaust gas emissions has led to increased research activities on the potential of using ammonia as fuel in marine engines. Various researchers have already investigated the combustion of ammonia specifically in two-stroke, slow-speed marine engines, and obtained promising results. In the available literature, both high-pressure direct injection-Diesel (HPDF) and low-pressure direct injection dual fuel - Otto (LPDF) two-stroke engines have been well-researched. This study numerically investigates the potential of using a direct high/medium pressure (Otto) ammonia injection strategy on a marine two-stroke engine. A diesel-fueled engine was retrofitted with ammonia injectors on the cylinder head. The effects of ammonia injection direction, timing, and injection pressure on the combustion efficiency, engine performance, and exhaust gas emissions were investigated to ensure optimum injection parameters. Ammonia substitution rate (ASR) ranging from 40 to 80 % was used in this study. The investigated injection strategy revealed flexibility in achieving the original pure diesel engine power over a wide range of injection pressures (700-200 bar). At 80 %, ASR CO₂ emissions were reduced up to 80 % while NOx emissions attained Tier II emission limits. The results of this study are helpful in the development process of ammonia dual-fuel marine two-stroke engines.