Study on combustion characteristics of hydrogen addition on ammonia flame at a porous burner

Due to the high hydrogen density and carbon-free characteristics of ammonia, porous media burners fueled by ammonia are currently attracting more and more attention in small and medium combustion/power equipment. In this study, the effects of pure ammonia combustion and hydrogen addition on ammonia combustion in a porous burner are investigated by numerical simulation and experiments to realize the practical application of ammonia as a fuel. The effects of porous burner parameters, hydrogen addition ratio, and equivalence ratio on ammonia flame characteristics, temperature distribution, and NO formation characteristics have been evaluated. The results show that stable ammonia flames can be obtained by this porous burner (phi = 0.9-1.2, u0 = 3-7 m/s). When the equivalence ratio is 1.00, the peak temperature of the ammonia flame is obtained. It is worth noting that the physical parameters of porous media have a great influence on the combustion performance. As the thermal conductivity and pore density of the porous medium increase, the peak temperature of the ammonia flame decreases and the flame position moves upstream. Furthermore, the combustion temperature of the ammonia flame rises with the increase in H2 addition ratio. When the fuel is rich, element N in the fuel is rarely converted to NO in pure ammonia and ammonia/hydrogen flames. The main N element in the fuel is converted into N2, and the conversion rate is as high as 92.35%-98.57%. When the equivalence ratio is 1.20, the NO conversion rate is ideally less than 0.009%.