Emission characteristics and heat release rate surrogates for ammonia premixed laminar flames

Ammonia is a carbon-free fuel that has the potential to meet increasing energy demand and to reduce CO2 emissions. In the present work, the characteristics of pollutant emissions in ammonia premixed laminar flames are investigated using one-dimensional simulations, and heat release rate (HRR) surrogates for ammonia combustion are proposed. Both atmospheric and high-pressure conditions were considered, and four representative mechanisms for ammonia combustion were employed. It is shown that the total emission of NO and NH3 achieves a minimum around an equivalence ratio (phi) of 1.1 under atmospheric conditions, and there is no noticeable emission of NO and NH3 for phi = 1.1 -1.5 under high-pressure conditions. Three HRR surrogates, [NH3][OH], [NH2][O], and [NH2][H], were proposed based on the analysis of HRR and elementary reaction profiles. The performance of HRR surrogates was found to vary with equivalence ratios. For example, with the Miller mechanism, [NH3][OH], [NH2][O], and [NH2][H] have the best performance under atmospheric conditions at phi = 1.15, 0.95 and 1.05, respectively, and under high-pressure conditions at phi = 1.11, 0.87 and 0.96, respectively. Similar conclusions can also be drawn with other mechanisms. These findings provide valuable insights into emission control and flame identification of ammonia combustion. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.