Flame broadening and its impact on the apparent Lewis number in premixed turbulent reacting flows

The effect of turbulent scales smaller than the laminar flame thickness on the laminar flame structure for flames with Lewis number (Le) different from the unity is considered. It is recognized that in this case the apparent Lewis number (Le*) in the reaction zone differs from its laminar value. This is due to spatial seperation between temperature and deficient reactant concentration profiles inherent in the laminar flames with Le ≠ 1. Small turbulent vortices are shown to further move these profiles apart in the broadened reaction zone. This results in further deviation of the Lewis number from unity. The apparent Lewis number is shown to be dependent also on the ratio between the laminar flame thickness and the Kolmogorov length scale, i.e. Le* = Le* (Le, δ/η).