Reduced Mechanisms for Prediction of $NO2$ Formation and Ignition Delay in Methane-Air Combustion

Two new 14-step and 16-step reduced mechanisms for methane-air combustion were systematically developed by assuming the quasisteady state for 26–28 species in the starting mechanism. A series of comparison between the reduced mechanisms and the starting mechanism was carried out with the emphasis on their capabilities in predicting $NO2$ formation and ignition delay. The two reduced mechanisms successfully capture the complex behaviors of $NO2$ formation, which depends on the characteristic mixing time, pressure, and the contamination of hydrocarbon in air. The flame structure and $NOx$ formation in diffusion flame were well predicted by the 16-step mechanism, while the 14-step showed less satisfactory performance on predicting prompt NO formation. The 16-step mechanism was shown accurate in predicting ignition delay over a wide range of equivalence ratio, temperature and pressure. The necessity of including $CH2O,$$C2H6,$$C2H4,$ and $HO2$ in the reduced mechanisms was discussed.