The effect of CO addition on extinction limits and NOx formation in lean counterflow CH4/air premixed flames

The effect of CO addition on flame extinction and NOX formation in counterflow lean premixed CH4/air flames was investigated by numerical simulation. Detailed chemistry and complex thermal and transport properties were employed. The results revel that the addition of certain amount of CO can increases the stretch extinction limits and reduces the radiation extinction limits. As a result, the lean flammability limit of CH4/air premixed flame is extended to the leaner side by the addition of CO. The formation of NO in a flame is increased with the addition of certain amount of CO at a constant equivalence ratio. For an ultra-lean flame, the increase in the formation of NO is mainly because of the increase in the contribution from the NNH intermediate route, while this increase is mainly due to the rise in the contribution from the thermal route for a near stoichiometric flame. With the fraction of added CO being gradually increased, the formation of NO2 in a flame first decreases, and then increases at a given equivalence ratio. The addition of certain amount of CO reduces the formation N2O in an ultra-lean flame, while affects little on the formation of N2O in a near stoichiometric flame.NRC publication: Ye