Determination of size and concentration of soot particles in diffusion flames by a light-scattering technique

Abstract

A light-scattering technique was used to measure the intensity of light scattered from soot particles in a diffusion flame of hydrocarbons burning in air. From a comparison of the measured ratio of the two light-scattering intensities for the perpendicular and parallel polarization components with the predictions from Mie's theory, the particle size and number density of soot particles were determined. The results obtained are as follows: (1) The diameters of the soot particles in the flames lie between 0.12 and 0.20 μ; (2) the number density of soot particles in the luminous zone range from 10 6 to 10 9 particles/cm 3 of the flame; (3) the volume fractions occupied by the soot particles in the luminous zone of the flame are 10 −9 to 10 −6 ; and (4) the concentration of CO, CO 2 , CH 4 , C 2 H 4 , and C 2 H 2 increases along the height of flame to a maximum, and then decreases toward the tip of the flame. It is seen that after the concentration maximum for these gases is reached, the soot particle density increases strikingly. A possible basis for this effect is discussed in terms of the dehydrogenation and polymerization of the hydrocarbons.