COMBUSTION DYNAMICS OF AN ACOUSTICALLY FORCED FLAME

摘要

A technique has been devised that can provide information about the local dynamic response of a flame to an acoustic field. In the experiments, a flame in an acoustic chamber is subjected to pressure oscillations by a pair of low-frequency drivers. The response of the flame is visualized by planar laser-induced fluorescence of the hydroxyl radical, which is used as a qualitative indicator for heat release in the flame. The resulting images are phase-resolved and averaged to yield a qualitative picture of the fluctuation of the heat release. This is correlated with the output of a pressure transducer near the flame. The tendency to cause instability can then be evaluated using Rayleigh's criterion. Results indicate that the forcing frequency and burner configuration have pronounced effects on the response of the flame. Forcing frequencies ranging from 22 to 55 Hz are applied to the jet-mixed burner supplied with a premixed 50/50 mixture of methane and carbon dioxide at a Reynolds number of 20,000. The burner is operated in two configurations: with an aerodynamically stabilized flame, and with a flame stabilized by two protruding bluff-bodies. Results indicate that, in general, the bluff-body stabilized flame is less sensitive to chamber acoustic excitation.