A Review of Ammonia Combustion and Emissions Characteristics in Spark-Ignition Engines and Future Road Map.

Ammonia (NH₃) is gaining recognition as a viable "green" transportation fuel due to its zero-carbon characteristic, its high energy density and its widespread availability. However, NH₃ has a high auto-ignition temperature, resulting in potential emissions of NO_x and unburned NH₃. Addressing combustion challenges requires innovative solutions, such as the application of combustion promoters to enhance NH₃ combustibility. This review article focuses on the compatibility of NH₃ as a fuel for spark-ignition (SI) engines, examining its combustion under various modes including pure NH₃ combustion, gasoline blends, NH₃/hydrogen (H₂) blends, and NH₃/natural gas blends in single or dual-fuel configurations. The formation of nitrogen oxides (NO_x) and slip-NH₃ is explored to understand emissions species such as NO and N₂O. Additionally, the article highlights the limitations of NH₃ as a fuel for SI combustion. The comprehensive discussion provided in this review aims to fill a critical gap in the literature regarding NH₃'s feasibility as a zero-carbon fuel for SI engines, particularly in the maritime sector. By offering insights into NH₃ combustion characteristics and emissions profiles, the article seeks to provide a roadmap for leveraging NH₃ as a suitable non-carbon fuel to decarbonize the marine sector and advance global sustainability goals. [ABSTRACT FROM AUTHOR]