Numerical Study on Formation Mechanism and Reduction Methods of NO in Methane/Oxygen-Enriched Air Diffusion Flame

In this study, a methane/oxygen-enriched air counterflow diffusion flame was analyzed numerically using detailed chemical kinetics, on the condition that the oxygen mass fraction in the oxidizer stream varied from 21% to 99%. The obtained results show that as the oxygen concentration in air increases, the maximum temperature increases; the region of combustion reaction is gradually divided into two parts, and the total NO production rate and especially the thermal NO production rate increase greatly. With consideration of the possibility of gas recirculation to minimize NOx in the industrial combustor, the usefulness of NOx reduction in combustion was analyzed numerically when the methane stream was diluted with the inert gases N-2 or CO2. The obtained results show that the flame structure and dominant mechanism of NO formation change greatly with the concentration of diluents in fuel; the emission index of NO decreases gradually when the concentration of diluent CO2 increases.