Light-scattering measurements of monomer size, monomers per aggregate, and fractal dimension for soot aggregates in flames

Abstract

A new method for the in situ optical determination of the soot-cluster monomer particle radius a, the number of monomers per cluster N, and the fractal dimension D is presented. The method makes use of a comparison of the volume-equivalent sphere radius determined from scattering–extinction measurements R_SE and the radius of gyration R_g, which is determined from the optical structure factor. The combination of these data with the measured turbidity permits for a novel measurement of D. The parameters a and N are obtained from a graphical network-analysis scheme that compares R_SE and R_g. Corrections for cluster polydispersity are presented. The effects of uncertainty in various input parameters and assumptions are discussed. The method is illustrated by an application to data obtained from a premixed methane–oxygen flame, and reasonable values of a, N, and D are obtained.