Ammonia is a promising alternative to conventional fossil fuels for internal combustion engines, especially in the maritime industry, because it does not emit carbon dioxide. Since redundancy is important in marine engines, a dual fuel system with diesel oil is currently widely applied to use alternative fuels such as liquefied natural gas, and a similar system is expected for ammonia-fueled ships. However, ammonia has low ignitability and low burning speed, hence improvement of combustion efficiency is major challenge. In addition, the emission of N2O which has a high global warming effect is also problematic as well as emission of NOX as air pollutant. To overcome these challenges, a mixing with hydrogen, which has high ignitability and high burning speed, can be effective. Therefore, in this study, combustion and emission characteristics of tri-fuel combustion engines, in which ammonia and hydrogen-air mixture is ignited by μ-pilot injection of diesel oil, were investigated. Numerical analysis showed that the increase in combustion temperature due to mixing with hydrogen and reduction in excess air ratio were effective in reducing unburned NH3 and N2O emissions. Experimental results showed that the higher the hydrogen mixing ratio, the shorter the combustion duration. At the same time, unburned NH3 and N2O emissions decreased simultaneously. These results indicate that hydrogen blending is effective in improving combustion efficiency and reducing GHG emissions derived from N2O, while NOX, which increases with increasing combustion temperature, has a trade-off relationship with N2O.
