Stable lean co-combustion of ammonia/methane with air in a porous burner

Abstract

Ammonia is being considered as a promising zero carbon fuel due to its unique properties, while its combustion still poses challenges in term of instability and higher nitrogen oxides (NOx) emissions. In this study, the co-combustion stability of ammonia/methane with air under lean burn condition is experimentally investigated using a silicon carbide (SiC) ceramic foam burner with a two-layer structure stabilizing the flame. The influences of different operating parameters (methane fraction ω, equivalence ratio φ, and flow velocity V) on the co-combustion flame temperature and emissions are analyzed. The results indicate that the lean stable co-combustion of ammonia/methane with air can be achieved in two-layer ceramic foam burner, with its lower limit extending to φ = 0.5, even for the pure ammonia at specific operating conditions. Notably, the nitric oxide (NO) emissions decrease significantly as the equivalence ratio increases, particularly with a rise in methane fraction. The reduction can reach as low as 843 ppm with φ increasing to 0.9, further reducing to an ultra-low level of less than 150 ppm at φ = 1.3, significantly lower than those of traditional free flame burners. Carbon monoxide (CO) emissions remain at ultra-low levels, indicating the excellent co-combustion efficiency of ammonia/methane-air in the porous burner. An optimal co-combustion region with lower NO and CO emissions were conclusively identified. These findings demonstrate the effectiveness of porous media combustion in improving the co-combustion stability of ammonia/methane and reducing NO emissions, thereby helping to develop the porous burners of ammonia-based fuel and promoting its clean utilization for realizing carbon neutrality.