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

Abstract

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 (NH 3 ) blends with methanol (CH 3 OH) and ethanol (C 2 H 5 OH) under diverse conditions. We measured laminar flame speeds of different NH 3 -alcohol blends — varying CH 3 OH/C 2 H 5 OH 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 NH 3 /C 2 H 5 OH blends with 10 % and 30 % (by mole) C 2 H 5 OH using a shock tube at pressures of 1, 10, and 20 bar and temperatures of 1100–1500 K. Our results show that incorporating CH 3 OH and C 2 H 5 OH into NH 3 increases the laminar flame speed, with C 2 H 5 OH being a more effective promoter than CH 3 OH due to its higher contribution to the formation of reactive radicals (OH, H, and O). Our model suggests that at high temperatures, both CH 3 OH and C 2 H 5 OH contribute to increased NO formation, with C 2 H 5 OH being more effective in reducing N 2 O emissions than CH 3 OH. In shock tube experiments, adding C 2 H 5 OH significantly shortens ignition delay times of NH 3 . At low temperatures (in the rapid compression machine case), the sensitivity to ignition delay times decreases when the CH 3 OH/C 2 H 5 OH content exceeds 5 % in NH 3 -alcohol blends. C 2 H 5 OH is a more effective combustion promoter, enhancing NH 3 reactivity and reducing NOx emission more efficiently than CH 3 OH. 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 NH 3 and NH 3 fuel blends and serves as a base for future research on NH 3 blended with higher hydrocarbons and/or oxygenated blends.