Lean co-combustion and emissions of ammonia/methane with air staging in a porous burner

Ammonia is gaining attention as a potential zero-carbon fuel. However, its combustion still faces critical challenges, particularly instability and high NOx emissions. In this study, overall lean co-combustion and emissions of ammonia/methane with air staging were experimentally investigated in a two-layer ceramic foam burner. Combustion performance in staged and unstaged modes was compared to demonstrate the effectiveness of staged combustion in reducing NO emissions. A detailed analysis on staged combustion was conducted, focusing on axial temperature profiles, flame positions, and CO/NO emissions. The influences of key operating parameters, including methane mixing ratio, primary equivalence ratio, secondary air ratio, and secondary air inlet heights, were systematically examined. The results show that integrating air staging with porous media combustion not only enhances flame stability but also significantly reduces NO emissions. NO emissions from air-staged combustion are generally maintained below 200 ppm, even dropped to below 50 ppm under specific conditions. Optimal air-staged co-combustion regions with ultra-low NO and CO emissions were conclusively identified for primary equivalence ratios, methane mixing fractions, and secondary air ratios. These findings confirm the effectiveness of air-staged combustion in porous burner for reducing NO emissions to ultra-low levels, supporting the utilization of ammonia-based fuel.