A comprehensive chemical kinetic modeling and experimental study of NH₃₋methanol/ethanol combustion towards net-zero CO₂ emissions

Ammonia is gaining attention as a green fuel with the potential to reduce carbon emissions. Its versatility allows it to be used directly in combustion engines, fuel cells, and as a hydrogen carrier, making it a key candidate for sustainable energy applications. This study provides a comprehensive analysis of the oxidation kinetics of ammonia (NH₃) blends with methanol (CH₃OH) and ethanol (C₂H₅OH) under diverse conditions. We measured laminar flame speeds of different NH₃-alcohol blends — varying CH₃OH/C₂H₅OH ratios (0–100 %) — using a constant volume combustion chamber across temperatures from 503 to 645 K and pressures of 2–11.3 bar. We also obtained the ignition delay times for NH₃/C₂H₅OH blends with 10 % and 30 % (by mole) C₂H₅OH using a shock tube at pressures of 1, 10, and 20 bar and temperatures of 1100–1500 K. Our results show that incorporating CH₃OH and C₂H₅OH into NH₃ increases the laminar flame speed, with C₂H₅OH being a more effective promoter than CH₃OH due to its higher contribution to the formation of reactive radicals (OH, H, and O). Our model suggests that at high temperatures, both CH₃OH and C₂H₅OH contribute to increased NO formation, with C₂H₅OH being more effective in reducing N₂O emissions than CH₃OH. In shock tube experiments, adding C₂H₅OH significantly shortens ignition delay times of NH₃. At low temperatures (in the rapid compression machine case), the sensitivity to ignition delay times decreases when the CH₃OH/C₂H₅OH content exceeds 5 % in NH₃-alcohol blends. C₂H₅OH is a more effective combustion promoter, enhancing NH₃ reactivity and reducing NOx emission more efficiently than CH₃OH. We developed a detailed kinetic model, building on our previous work, and validated it against new experimental and literature data. Our model accurately predicts the combustion behavior of neat NH₃ and NH₃ fuel blends and serves as a base for future research on NH₃ blended with higher hydrocarbons and/or oxygenated blends.