Experimental investigation on soot volume fraction in an ethylene diffusion flame by emission spectrometry without optically-thin assumption

Abstract

An improved soot diagnostics technique based on tomographic reconstruction of flame emission spectra has been developed for an axisymmetric laminar diffusion flame without optically-thin assumption. Emission from the flame is scanned along the horizontal lateral axis of flame at several altitudes above the burner. At each measurement position, the local line-of-sight flame emission spectra is collected by a spectrometry over a spectral range of 700-1100 nm. Inversion of these data through one-dimensional tomography using a three-point Abel inversion yields radial distributions of the soot radiation from which soot volume fraction profiles are extracted. Traditionally, this procedure was applied only in the optically-thin flames for which the self-attenuation term of emitted radiation is ignored. However, this self-attenuation term is considered by iterative calculations in the paper. The configuration of the investigation flame is similar to the flames reported in the literatures. The results by the conventional method is found to be almost twice to the results by the improved method. This discrepancy revealed that the optically-thin assumption for the flames will cause serious errors in the conventional method, and the improved method could overcome this deficiency effectively.