Extinction of Premixed Methane-Air Flames with Reduced Reaction Mechanism

We examine the extinction characteristics of premixed methane-air flames subject to volumetric heat loss with a reduced reaction mechanism. A combination of rate-ratio and large activation energy asymptotics is employed to resolve the multi-layered flame structure, and an expression for the non-adiabatic burning rate is obtained. Extinction turning points are reproduced and extinction conditions are found explicitly as a function of the various kinetic parameters. In particular the flame is found to extinguish when the burning rate (scaled by its adiabatic value) is reduced to a nearly constant value, roughly 0.6, over the entire range of system parameters, in agreement with previous asymptotic and numerical studies. The reduction in flame temperature at extinction is found to be less than that predicted by one-step models.