Combustion and emission characteristics of ammonia-hydrogen fueled SI engine with high compression ratio

Ammonia combustion offers the advantage of zero carbon emissions. However, its high ignition energy requirement and slow flame propagation limit its use as an engine fuel. Employing a technological approach that combines a high compression ratio with spark ignition can be beneficial for enhancing ammonia combustion, and this approach warrants further in-depth research. This study investigates the combustion of ammonia within a spark-ignition engine with a compression ratio of 15:1. It enhances combustion by introducing hydrogen as a reactivity-enhancing fuel. Both ammonia and hydrogen are introduced into the engine's intake port. The findings suggest that efficient pure ammonia combustion occurs at low engine speeds (1000 r/min) and high brake mean effective pressure (BMEP exceeding 0.6 MPa). Pure ammonia combustion achieves a brake thermal efficiency of 33.7% at a BMEP of 0.94 MPa. Introducing hydrogen at an energy ratio of 2-16% expands the engine's load range. With hydrogen blending, the efficiency rises to 35.8% at a BMEP of 0.63 MPa. The research on NOx emissions reveals that, under specific operating conditions, there is a reduction reaction between unburned ammonia and NOx, leading to a decrease in NOx emissions as BMEP increases. This study can offer support for the application of ammonia engines.