Noise Characteristics of Turbulent Diffusion Flames with Coherent Structure

Abstract

In order to elucidate the interrelationship between flame structure and noise characteristics and to obtain those properties which are easily measurable and understandable, and are strongly correlated with the acoustic pressure perturbation, three kinds of flames with different structure are first formed in a plane shear layer by varying the flow and turbulence conditions: a flame within which organized eddies are clearly observed, a flame which has a rather complicated appearance and a higher eddy-formation frequency than the first due to the increased mean convection velocity, and a flame without any organized eddy, which is stabilized under the same flow conditions as the first flame, but has increased turbulence levels. Simultaneous measurements and FFT-analyses of the fluctuations of sound pressure, ion current, temperature, and CH-emission are made on these three flames. The results are shown concerning not only clear properties of the correlations between flame structure and sound intensity, but also the directionality and spectral characteristics of the combustion noise.