Development of absolute intensity multi-angle light scattering for the determination of polydisperse soot aggregate properties

This work investigates the capability of multi-angle light scattering to determine polydisperse aggregate parameters including the size distribution and the fractal dimension. The investigation considers one laser wavelength in the visible at 527 nm and a fixed angle range from 10° to 160°. The corresponding range of the scattering wave vector limits the measured section of the overall structure factor significantly and makes an unambiguous determination of the size distribution parameters using relative multi-angle scatter intensities difficult. An interplay of the distribution width parameter and the fractal dimension is significant and impairs the possibilities for determining both properties simultaneously. The ambiguity of solutions can be overcome by including the absolute scattering intensity which is obtained via comparison with a known Rayleigh scatterer. However, additional parameters like the primary particle diameter, the soot volume fraction, the fractal prefactor, and the scattering function of the refractive index F(m) must be known with sufficient accuracy. We show how the analysis can be applied to a variety of soot sources ranging from very small aggregates in premixed flames, over intermediate aggregates in a laminar diffusion flame to large cooled soot emitted from a diffusion flame in inverted geometry.