Statistical analysis of soot volume fractions, particle number densities and particle radii in a turbulent diffusion flame

A recently developed two-dimensional optical technique has been applied for measuring two-dimensional maps of soot volume fractions, particle number densities and mean particle radii in a turbulent acetylene-air diffusion flame. The technique is based on the simultaneous detection of Ravleigh-Scattering and Laser-induced Incandescence (LII) in combination with the detection of the extinction from one single laser pulse (RAYLIX-technique). Single shot experiments in the investigated flame exhibit small particles in zones of high particle number densities and vice versa. Mean values and standard deviations are obtained by averaging 1000 single laser shots. The results reveal large relative fluctuations of soot volume fractions, number densities and particle radius in the outer region of the flame due to its turbulent structure. Two-dimensional probability density functions (PDFs) of number density and particle radius are obtained, which provide a useful data basis for future modeling of turbulent flames by means of PDF-models. Finally turbulent length scales are determined from autocorrelation functions. This information is important for engineering and also modeling purposes.