A Diffusional-Thermal Theory of near-Stoichiometric Premixed Flames

In this paper we present a diffusional-thermal theory of premixed flames for near-stoichiometric conditions. Our theory exhibits an explicit dependence on the equivalence ratio as well as on two distinct Lewis numbers which correspond to the fuel and the oxidizer. Normally, the deficient component in the mixture is totally depleted in the reaction zone. However, for curved or strained flames, it is possible for the initially excess reactant to be consumed at the reaction zone if it is the less mobile of the two species, while the initially deficient species leaks through. The form of the derived jump conditions for temperature and enthalpy gradients across the reaction sheet depends on which of the two species is consumed. This can have important implications on predicted flame dynamics. For example, we show that, as a result of preferential diffusion, portions of a corrugated flame may burn rich while neighboring regions burn lean. This results in leakage of fuel and oxidizer through the premixed flame which are then consumed downstream by trailing diffusion flame tongues. Furthermore, the extinction characteristics of strained flames are found to depend on whether fuel or oxidizer is ultimately depleted.