Flame and emission characteristics of preheated ammonia combustion based on chemical reaction network

Abstract

Ammonia (NH3) is an ideal fuel for achieving decarbonisation in energy production and industrial combustion, but suffers from low flammability and high nitrogen oxides (NOx) emissions in combustion. Preheating of NH3 can lead to stable combustion of NH3 and reduce nitric oxide (NO) emissions. In this study, the special combustion characteristics of the fuel preheated flame were investigated. Combustion, optical temperature measurement and gas measurement systems were set up. The flame images were captured and the flame temperature distribution was reconstructed by experiment. The temperature field in the longitudinal profile at the flame centre was divided into 11 temperature regions. Computational fluid dynamics (CFD) was carried out on the preheated NH3 combustion to analyse the distributions of components and velocity vectors. Then, a chemical reaction network (CRN) with 10 perfectly stirred reactors (PSR) was constructed based on the temperature field reconstructed by experiment and the distributions of components and velocity vector by CFD simulation. The temperature, the concentration of products and reactants, intermediate product components and reaction pathways were analysed by the CRN method to investigate the jet combustion characteristics of preheated NH3 combustion. Experimental and CFD simulation results showed that differently coloured regions appeared in the upstream of the pure NH3 flame, and the high-temperature region was widely distributed in the temperature field. CRN simulation results showed that the formation of special flame characteristics was associated with the generation of large amounts of hydrogen (H2) and water (H2O), and the reactions of NH2 with NH2 were the most dominant generating pathway of H2. Reaction pathway analysis of NH3 showed that H and OH radicals were most relevant to the production of NO, while NH2 radicals were most relevant to the consumption of NO in preheated NH3 combustion.