Assessment and optimization of ammonia combustion mechanisms in the temperature interval 900–1800 K

• A new ammonia combustion mechanism was developed. • The developed mechanism has accurate predictions across various conditions. • A new approach to mechanism optimization is proposed. • Ten ammonia combustion mechanisms were analyzed and optimized. • Several reactions were identified as critical for mechanism accuracy. A new mechanism is proposed for ammonia combustion under atmospheric pressure and temperatures below 1800 K. The mechanism is developed using a novel optimization approach, starting from an existing mechanism and preserving its structure. In the optimization, ten different mechanisms were used as starting point. The new mechanism significantly reduced errors in NO, NH 3 , and N 2 O predictions across lean, stoichiometric, and rich conditions and ammonia concentrations from part per million to percent range. This was achieved through changes made only to reaction rate parameters of four reactions, NH 2 + O = H + HNO, NH 2 + NO = H 2 O + N 2 , NNH + O 2 = HO 2 + N 2 and H + HNO = H 2 + NO. The investigations showed that not all mechanisms have the same potential for improvement. However, many of the mechanism could with minor changes reach similar overall accuracy in predictions. The reactions NH 2 + NO = N 2 + H 2 O, NH 2 + HO 2 = NH 3 + O 2 , and 2NH 2 = N 2 H 2 + H 2 are identified to be the main contributors to restricting mechanism improvement. Adjusting the rates of these reactions typically led to an increase in accuracy for a specific concentration range while decreased it in other ranges.