Investigation of NO emissions and chemical reaction kinetics of ammonia/ methane flames under dual-fuel co-combustion mode at elevated air temperature conditions

Utilising ammonia, which is one of the most promising carbon-free fuels, comes with the challenge of stable combustion due to its low reactivity. Therefore, advanced strategies are needed, including blending ammonia with highly reactive fuels or implementing innovative combustion techniques. For this reason, the present study proposes an ammonia-methane dual-fuel co-firing combustion mode. The second focus is to analyse the effect of preheating the main swirl air on NO emissions and examine the chemical kinetic reactions. Experimentally, chemiluminescence imaging was conducted to analyse OH* and NH2* emissions to evaluate the flame structure and reaction zones. Numerically, simulations were performed using a chemical multi-reactor network model to examine kinetics. By comparing the fully premixed combustion to the dual-flame co-burning mode, the NO emissions decreased by 80% in the latter case at T = 473K and phi = 0.6. The NH3 reaction pathway analysis shows a significantly higher percentage reduction of NO and NH2 reactions in dual flame mode compared to premixed flames. Preheating the main air impacts NO reactions in the dual flame mode, allowing for lower NO emissions.