Experimental and Kinetic Study of Laminar Burning Velocities for NH 3 /CH 4 /O 2 /NO/CO 2 Premixed Flames

Ammonia, as a promising carbon-neutral fuel, has attracted growing attention for blended combustion applications from academia to industry. Low-NO x -combustion strategies such as staged combustion, oxygen-enriched combustion, and exhaust gas recirculation may lead to ammonia combustion in CO 2 -rich and NO-rich environments. In this work, the laminar burning velocities ( S L ) in NH 3 /CH 4 /O 2 /NO/CO 2 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 S L , 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 S L . 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 NH 2 + NO = NNH + OH and NNH = N 2 + H, thereby accelerating chain-branching and sustaining flame propagation.