Study on Combustion and Emission Characteristics of a Marine Diesel-Ignited Ammonia Engine Blended with Ammonia-Derived Hydrogen-Containing Fuel

The application of ammonia decomposition technology for hydrogen production enables hydrogen-enriched combustion in marine diesel-ignited ammonia engines. This study presents experimental and simulation investigations of a diesel-ignited ammonia engine operating with hydrogen-containing fuels derived from ammonia decomposition at various blending ratios. The combustion and emission characteristics of the engine were systematically examined, and a comparative analysis was conducted on the combustion behavior of the engine between using ammonia decomposition-derived hydrogen-containing fuel and pure hydrogen. The result shows that under constant engine output power, at 1200 rpm and 75% load, increasing the hydrogen energy rate results in largely unchanged cylinder pressure and heat release rate. The diesel substitution rate exhibits an initial increase followed by a decrease, while the energy consumption rate demonstrates the opposite trend. At 1500 rpm and 75% load, an increase in hydrogen enrichment leads to an earlier rise in cylinder pressure and heat release rate, a continuous increase in diesel substitution rate, and a consistent decrease in energy consumption rate. The early stage of in-cylinder combustion is dominated by diesel combustion, followed predominantly by the combustion of ammonia and hydrogen. Regarding the difference between using decomposition-derived hydrogen-containing fuel and pure hydrogen, within the hydrogen enrichment range of 0–20%, the discrepancies in intake composition and equivalence ratio between the two hydrogen-addition modes gradually widen but remain within 1.3%. Taking a hydrogen energy rate of 10.56% as an example, the differences in in-cylinder pressure and heat release rate between the two hydrogen-addition modes are not significant, indicating that the N2 generated from ammonia decomposition has a relatively weak influence on the engine. With increasing hydrogen enrichment, NH3 emissions gradually decrease, while NO emissions increase. For N2O, hydrogen enrichment promotes its consumption, resulting in lower emissions. Under various hydrogen enrichment conditions, equivalent greenhouse gas emissions are mainly influenced by CO2 emissions.