Traces of Preferential Diffusion Observed in Turbulent Premixed Flames(Thermal Engineering)

Abstract

Effect of the preferential diffusion between oxygen and fuel molecules is observed as the cellular flame in laminar premixed flames. When the diffusion coefficient of the deficient species is larger, the deficient species diffuses preferentially to the reaction zone to cause the local stratification of the mixture ratio along the flame. Therefore, the cellular flame is established. If the preferential diffusion should occur in propane-air turbulent premixed flames, the wrinkle scale of rich flames would be smaller than that of lean flames, consequently, the turbulent burning velocity and/or the heat release rate of the former would be larger than those of the latter. Based on these considerations, traces of the preferential diffusion are sought from experimental results of propane-air turbulent premixed flames. Comparing the radius of curvature of the flamelet of rich and lean propane-air flames with the same laminar burning velocity, the radius of curvature of the flamelet of the former are smaller than those of the latter. The gas expansion ratio across the flamelet of the former is larger than that in the latter. The magnitudes of the flamelet velocity vector of the former are larger than the latter.