Microscopic Structures in Turbulent Diffusion Flames.

Abstract

Microscopic structures in turbulent diffusion flames are studied by time-resolved temperature distributions measured by a laser-sheet-illuminated Rayleigh scattering (LRS) method recorded by a high-speed VTR system, and one-point LRS measurement. The microscopic structures of temperature distribution are measured by analyzing the two-dimensional LRS pictures by image processing. Coaxial turbulent diffusion flames at moderate Reynolds numbers, which exhibit typical diffusion flame structures, are formed on laboratory-scale burners. It is found that the flame can be divided into four characteristic regions based on the distributions of macroscale temperature fluctuations. These four regions are visualized by the two-dimensional LRS images. The turbulent heat-transfer mechanisms in these four regions are discussed in terms of the two-dimensional LRS and the power spectral density of temperature fluctuations measured by one-point LRS. Clusters of temperature inhomogeneity are observed by the image analyses in Regions I and III. It is found that different structures of microscopic temperature inhomogeneity exist within Taylor's dissipation length scale defined by velocity fluctuations.