EFFECTS OF POLYDISPERSITY OF AGGREGATES AND PRIMARY PARTICLES ON RADIATIVE PROPERTIES OF SIMULATED SOOT

The effects of primary particle (particle) and cluster (aggregate) siz e distributions on absorption and scattering properties of simulated s oot were studied both computationally and theoretically. Computational methods involved the solution of the volume integral equation formula tion of Maxwell's equations using the method of moments, based on the ICP algorithm. The theoretical methods employed Rayleigh-Debye-Gans ap proximation for mass fractal-like aggregates (RDG-FA) formed by small particles. An extension of the RDG-FA formulation was proposed to acco unt for polydisperse particle sizes, based on a volume correction appr oach. Differential and total scattering as well as absorption cross se ctions were considered for morphologies representative of soot found i n flame environments. Aggregates were constructed using a sequential a lgorithm which mimics mass fractal-like structures. Log-normal and nor mal (Gaussian) probability density functions were employed to consider polydisperse populations of aggregates and particles, respectively. O ver the range of evaluation, the effects of aggregate and particle pol ydispersity were negligible for the angular scattering pattern in the power-law regime. Furthermore, absorption cross section was similarly affected by polydispersity of aggregates and particles. Finally, the R DG-FA predictions generally agreed with the ICP results within 10%, co nfirming its applicability to predict mean optical properties of polyd isperse populations of soot aggregates and particles.