The Acoustically Excited Flame

Abstract

A premixed laminar propane-air flame burning at the exit of a nozzle, was acoustically excited upstream by a speaker-driver unit. Detailed acoustic measurements were made to show that sound amplification and attenuation can occur over the measurement frequency range from 50 Hz to 350 Hz. The effect of excitation strength and fuel-air ratio was also investigated. Two acoustic phenomena related by forced vortex hydrodynamic behavior have been identified, and were investigated by means of high speed schlieren photographic measurements. The generation of a one-half harmonic of the fundamental frequency was explored and explained in terms of vortex hydrodynamic behavior. The work contributes to the understanding of the origin of noise from acoustically excited combustors.