Microscopic Structure of Turbulent Diffusion Flames.

Abstract

Microscopic structure of turbulent diffusion flames is studied by a time-resolved planar video picture system obtained by a laser Rayleigh scattering (LRS) method and a single-point LRS measurement. The microscopic temperature is measured by using a two-dimensional LRS signal and 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 typical regions characterized by the distribution of macroscale of temperature fluctuations. These four regions are visualized by the two-dimensional LRS pictures. 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, in terms of one-point LRS. A cluster of temperature inhomogeneity is observed by cluster analysis in Regions I and III. It is found that different structures of microscopic inhomogeneity in the mixing region of Taylor's dissipation length scale appear, corresponding to the characteristics of mixing and combustion mechanisms in each region.