Combustion analysis of ammonia and methanol fuels and their blends in an optical spark-ignition engine

In order to meet global decarbonization targets, modern internal combustion engine operations will demand the use of either carbon-neutral fuels or fuels with lower fossil hydrocarbon content. There are several potential fuels such as ammonia (NH3), hydrogen (H2), and methanol (CH3OH), which are considered potentially revolutionary fuels for advanced IC engines in terms of their being able to be made in a netzero- carbon or carbon-neutral manner. This study investigates the combustion characteristics of pure ammonia, methanol, and their blends in a spark-ignition research engine. The results showed that pure ammonia combustion produced highly unstable combustion with lower engine efficiency even at advanced spark timing (ST) due to its lower burning velocity. However, methanol combustion exhibited higher engine performance for the same operating conditions due to its higher burning speed. In addition, this study also investigated the effect of methanol usage with ammonia fuel. Adding methanol to ammonia improved the combustion characteristics significantly because it increased the reactivity of the mixture, which further raised the higher heat release rate (HRR) and in-cylinder pressure. Furthermore, a highspeed natural flame luminosity (NFL) imaging technique was used to capture the flame propagation for different ammonia/methanol blending cases. Moreover, it was also observed that increasing the methanol fraction mixture leads to higher NOx emissions because of both fuel-bound NOx from arising from the nitrogen in ammonia and thermal the NOx due to the higher in-cylinder temperature generated by the higher heat release.