Thermal diffusive effect on the flame motion with equivalence ratio oscillation

Responses of the methane/air premixed flames in an axi-symmetric stagnation flow fields under equivalence ratio oscillations were numerically investigated. The mixture equivalence ratio oscillates at 10 Hz and 20 Hz frequencies with the mean equivalence ratio at lean and rich conditions. One step irreversible reaction mechanism was used in this study. In all cases, the flame responds to the equivalence ratio oscillation in the quasi-steady state condition. It is reasonable because the wavelength by the equivalence ratio oscillation is longer than the flame thickness. It is observed that the flame propagation speed responds to the equivalence ratio oscillation with some hysteresis. This is found due to the thermal diffusion effect. The simplified model based on integral analysis was developed to show the thermal diffusion effect on the flame propagation speed hysteresis.