Sound emission from a turbulent flame

Abstract

The objective of this paper is to obtain knowledge of the relationship between combustion sound and the heat release rate in turbulent flames. Using an ion probe and a light emission detector, the correlation between the field sound pressure and the local fluctuating intensity of ion current or OH radical light emission in a turbulent Bunsen burner flame was studied. Based on the observations, the following three mechanisms of sound emission from the flame were proposed: (1) “local combustion roar” generated locally in the flame due to the combustion of turbulent eddies and the resultant thermal expansion. (2) “flame tip combustion roar” caused by the fluctuation of heat release rate at the flame tip which is enhanced by the propagated disturbance originated in the upstream flame element and (3) “jet sound” due to the turbulence at the jet boundaries. The turbulent combustion in a flame element emits a “local combustion roar” and generates a flame disturbance simultaneously which propagates and enhances the “flame tip combustion roar”. This investigation has suggested that both the light emission of OH radicals and the ion current correspond well to the local heat release rate.