MICROSCOPIC STRUCTURES IN TURBULENT-DIFFUSION FLAMES

Microscopic structures in turbulent diffusion flames are studied by ti me-resolved temperature distributions measured by a laser-sheet-illumi nated Rayleigh scattering (LRS) method recorded by a high-speed VTR sy stem, and one-point LRS measurement. The microscopic structures of tem perature distribution are measured by analyzing the two-dimensional LR S pictures by image processing. Coaxial turbulent diffusion flames at moderate Reynolds numbers, which exhibit typical diffusion flame struc tures, are formed on laboratory-scale burners. It is found that the fl ame can be divided into four characteristic regions based on the distr ibutions of macroscale temperature fluctuations. These four regions ar e visualized by the two-dimensional LRS images. The turbulent heat-tra nsfer mechanisms in these four regions are discussed in terms of the t wo-dimensional LRS and the power spectral density of temperature fluct uations measured by one-point LRS. Clusters of temperature inhomogenei ty are observed by the image analyses in Regions I and III. It is foun d that different structures of microscopic temperature inhomogeneity e xist within Taylor's dissipation length scale defined by velocity fluc tuations.