Experimental and Kinetic Study of Laminar Burning Velocities for NH3/CH4/O2/NO/CO2 Premixed Flames

Ammonia, as a promising carbon-neutral fuel, has attracted growing attention for blended combustion applications from academia to industry. Low-NOx-combustion strategies such as staged combustion, oxygen-enriched combustion, and exhaust gas recirculation may lead to ammonia combustion in CO2-rich and NO-rich environments. In this work, the laminar burning velocities (SL) in NH3/CH4/O2/NO/CO2 flames with various ammonia blended ratios under atmospheric pressure were investigated using the heat flux method. The addition of NO to the oxidizer significantly enhances SL, with the enhancement factor ξ proportional to the NO fraction in the oxidizer and strongly dependent on the fuel composition. Chemical effects rather than thermal-diffusion effects dominate the enhancement of SL. Kinetic analysis shows that NO actively participates in the reaction network during the early flame stage, promoting the formation of key radicals such as H and OH through pathways like NH2 + NO = NNH + OH and NNH = N2 + H, thereby accelerating chain-branching and sustaining flame propagation.