MEASUREMENT OF THE FRACTAL DIMENSION OF SOOT USING UV LASER-RADIATION

Accurate values were determined for the fractal dimension of soot particulates formed in a small, over-ventilated C2H4/air diffusion flame. The experiment principally entailed measurement of the near forward to backward elastic scattering of UV laser light by the soot. Mass fractal dimensions were inferred from log-log plots of scattering versus the absolute value of the momentum transfer vector in the asymptotic, large scattering angle regime. The inferred dimensions were toward the low end of the reported range for soot. The scattering data were supplemented by measurements of optical extinction at the 266-nm laser wavelength, as well as extinction versus wavelength using a conventional lamp. The laser extinction data were used in evaluating particulate albedos, while the lamp data ruled out the possible interference of polycyclic aromatic hydrocarbon UV absorptions. The role of the primary monomer size in limiting the asymptotic range over which the fractal dimension may be determined is discussed.