LIGHT-SCATTERING MEASUREMENTS OF MONOMER SIZE, MONOMERS PER AGGREGATE, AND FRACTAL DIMENSION FOR SOOT AGGREGATES IN FLAMES

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.