Enhancing combustion efficiency and reducing nitrogen oxide emissions from ammonia combustion: A comprehensive review

Ammonia is an efficient energy carrier with high hydrogen content and can be used as a clean energy source to replace traditional petroleum fuels. Compared with hydrogen, ammonia production technology is mature, and convenient for storage and transportation. However, ammonia combustion suffers from difficult ignition, low flame velocity, narrow flammability range, and high nitrogen oxide (NOx) emissions. To address these problems, this review summarizes technologies such as improving ammonia fuel activity, fuel blending and assisted combustion to enhance combustion. Blended combustion and oxygen-enriched fuels can increase the ammonia combustion rate. In addition, ammonia can be produced through various methods, including chemical synthesis, biomass conversion, and electrolysis of water. Existing research indicates that the electrochemical synthesis of ammonia is currently one of the most promising routes for ammonia synthesis. However, ammonia combustion generates a large amount of NOx emissions. Therefore, the paper also analyzes the mechanism of NOx emissions caused by ammonia combustion and explores measures to reduce NOx emissions, such as improving combustion processes and catalytic conversion technologies. Moderate or intense low-oxygen dilution (MILD) combustion technology has the potential to improve the combustion efficiency of ammonia fuel and reduce NOx emissions.