Combustion dynamics of an acoustically forced flame

Abstract

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 lowfrequency drivers. The response of the flame is visualized by planar laserinduced 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. The authors are especially indebted to Prof. Chris Cadou (University of Maryland) for his very considerable advice and help during the initial stages of designing the PLIF apparatus, when he was a postdoctoral scholar at Caltech. We also thank Mr. Konstantin Matveev for his help in completing this article, and Cerwin-Vega for their generous donation of the acoustic drivers.

Non-linear Response of Turbulent Premixed Flames to Imposed Inlet Velocity Oscillations of Two Frequencies

“…Recent advancements in measurement methods [2,3,18,23,27,33,39,40] and the improved understanding of various phenomena underlying this complex problem have increased the prediction capability [15,25]. However, the prediction methods greatly depend on the knowledge of the response of the flame to prescribed conditions, information that might be obtained from experiments [3,5,10,22] or modelling [1,6,15,25,31,42].…”

An experimental investigation of an acoustically excited laminar premixed flame

“…A similar approach is recently reported by Pun et al [32]. To examine the contribution of the fluctuations in the flame area to the total heat release rate fluctuations, a threshold intensity level is set in all the high-speed chemiluminescence images based on the intensity distribution in the unperturbed flame.…”

Measurements of fuel mixture fraction oscillations of a turbulent jet non-premixed flame

“…This work also examines the link between flame behavior and mixing behavior. The current effort builds on previous work [13] by focusing on the fuel-air structure upstream of the flame front. To this end, two-dimensional images of the fuel-air distribution are obtained by imaging the acetone concentration.…”

“…Culick [10,11] developed a theory that is based on the Rayleigh index. The coupled effects of acoustic forcing and combustion heat release on species concentration inside the flame zone were examined by Pun et al [12,13] using OH-PLIF and chemiluminescence. This revealed that in the flame region the response of the combustion process under acoustic excitation is strongly phase-dependent, and this dependence was quantified.…”