Response Characteristics of Burning Velocity, Velocity Gradient, and Preheat Zone Thickness of Methane-Air Premixed Wall-stagnation Flame to Sinusoidal Oscillation of Equivalence Ratio

Abstract

This study investigated the characteristics of the response of a lean methane-air premixed flame to sinusoidal oscillation of the equivalence ratio. The oscillation frequency was varied from 5 to 50 Hz. The mean equivalence ratio and fluctuation amplitude were 0.85 and 0.05, respectively. In the low frequency range, the oscillation amplitudes of the flame position x_f, burning velocity Su, velocity gradient g, and preheat zone thickness δ_p responded quasi-steadily to the equivalence ratio oscillation. However, in the high frequency range they responded unsteadily: that is, the fluctuation amplitude of x_f became less than that of the static flame, but the oscillation amplitudes of Su, g, and δ_p exceeded those of the static flame with respect to frequency over the same equivalence ratio fluctuation range, and these values peaked at 40 Hz. The increase in oscillation amplitude of Su with respect to frequency was likely a result of the dynamic characteristics of the flame movement, mass transfer from unburned gas to the side of the flame, and the preheat time of the mixture.