Abstract

Abstract Ammonia is a promising carbon-neutral fuel for internal combustion engines. However, its widespread application requires accurate ammonia kinetic models for numerical simulations used in engine development. Current development of ammonia kinetics mainly focuses on predicting fundamental combustion parameters such as ignition delay and laminar flame speed. Yet, significant discrepancies remain among different kinetics in predicting nitrogen-based pollutants (such as NOx and N2O). To improve the immature ammonia kinetics, especially for nitrogen-based pollutant chemistry, this study applies the Reaction Mechanism Generator (RMG) tool to enhance existing kinetics from the literature. Additionally, the kinetics is further optimized by incorporating advanced theoretical calculations of key reaction rates from the latest literature. The results show that the RMG-derived models excel in predicting species concentrations, ignition delay times, and laminar flame speeds. Moreover, the RMG-improved kinetics significantly enhances model robustness and applicability by automatically generating and expanding chemical reaction networks and iteratively adding new reactions and species that are essential according to the flux analysis. Further, kinetic analysis reveals the presence of an important species, HN2O, missing in the chemical mechanism from existing literature, which shows high sensitivity in the ammonia oxidation pathway. Overall, these findings highlight the need for more fundamental studies to improve immature ammonia oxidation kinetics by identifying new oxidation pathways and key species under a wider range of conditions representative of engine in-cylinder conditions, which is vital for predicting ammonia engine nitrogen-based emissions and finding strategies to control them.