A critical review on ammonia as a fuel for internal combustion engines: Is it a viable option?

Ammonia is considered an attractive alternative fuel for power generation in the context of global decarbonisation efforts. This study examines the advancements in ammonia combustion technology for spark ignition (SI) and compression ignition (CI) engines. An extensive analysis of the characteristics of ammonia (NH3) combustion, a fuel free of carbon, is provided in this paper. Since ammonia burns similarly to fossil fuels and emits less CO2, CO, NOx, soot, and hydrocarbon (HC) pollutants, NH3 is a desirable substitute fuel that can be stored and transported using existing commercial infrastructure. It also comes with productivity from renewable sources. However, unlike traditional hydrocarbon fuels, NH3 exhibits unique combustion characteristics, highlighting the challenges of using it as a fuel for internal combustion (IC) engines. This paper critically reviews the challenges of NH3 blended with diesel, biodiesel, dimethyl ether, and some other alternative fuels in IC engines. The literature reports mixed findings on this topic. Many studies have not demonstrated NH3 as a substitute fuel for IC engines yet. In addition, ammonia's toxicity and unusual/complex combustion characteristics hinder its use as a fuel substitute in IC engines. Further research is required to overcome challenges associated with using NH3 as a fuel for IC engines. This study identifies and discusses these challenges.