Numerical study on the thermal characteristics and emission analysis of traditional combustion and MILD in NH3/H2

• The changes of ammonia oxidation reaction zones under different conditions are discussed. • The effects of ammonia hydrogen combustion under different combustion modes were analyzed. • Compare NO x and N 2 O emissions under different conditions. Ammonia and hydrogen have attracted global attention as zero-carbon energy carriers. Hydrogen can enhance the combustion efficiency of ammonia, while ammonia can serve as a hydrogen transport carrier. However, the combustion of both fuels results in considerable NO x emissions. Therefore, identifying effective strategies to suppress and reduce NO x emissions generated from NH 3 /H 2 combustion has become a key research focus. This paper mainly conducts a numerical study on the two distinct combustion modes (traditional combustion and MILD combustion) of NH 3 /H 2 , exploring the effects of varying H 2 mole fractions (ranging from 0 to 50%) on the flow field distribution, thermal characteristics and pollutant emissions. The results indicate that increasing hydrogen fraction improves the combustion performance of ammonia. MILD combustion can generate the entrainment and recirculation effects of the surrounding high-temperature flue gas. Under the hydrogen content increases from 0% to 50%, for traditional combustion, the maximum temperature rise reaches 230 K, while the average temperature rise is 15 K; for MILD combustion, the maximum temperature rise is 83 K, with an average increase of 20 K. Owing to the uniform and low-temperature characteristics of MILD combustion, the concentration of the intermediate product HNO remains relatively high, which indicates high activity of its reaction network. This promotes the conversion of nitrogen in ammonia combustion to N 2 rather than NO. In contrast, the high-temperature oxidation reaction zone in traditional combustion (TC) is insufficient to facilitate the conversion of HNO to N 2 , thus leading to the generation of higher concentrations of NO x . At a 20% hydrogen blending ratio, the reaction zone volume of MILD combustion reaches its maximum, and the NO x emission achieves the lowest value of 837 ppm.