Morphology of soot agglomerates produced into high pressure high temperature environment as inferred by light scattering/extinction measurements

The characterization of the particulate aggregates is a topic widely covered within the main field of aerosol and colloid science. A satisfactory description of agglomerates requires the knowledge of at least six parameters, namely the number density of clusters, the mean number of the primary particles per cluster, the mean diameter of such primary particles, the characteristic length of the aggregate depending on the shape of the aggregate, the refractive and absorption index of the primary particles. To this aim it is common in the literature to hypothesize about the dominant morphology and to think about the aggregate as constituted by identical primary particles and optical properties. As a matter of fact the scattering and extinction techniques are of common use in the literature in conjunction with the results of Mie theory in spite of the fact that such agglomerates are neither spherically shaped nor homogeneous. Alternatively the study of the agglomeration morphology can be afforded by means of Berry and Percival theory and static light scattering applied to fractals. An equivalent Mie sphere can be introduced which best simulates the data. The effective diameter of the agglomerate can be defined behind different criteria which yields often to quite different results. The objective of the present paper is to characterize the carbonaceous agglomerates produced by ethylene pyrolysis into a shock tube environment via both classical light scattering/extinction measurements and a theoretical analysis for randomly oriented aggregates. The agglomeration process is investigated in a ms time scaling. The high temporal and spatial resolution involved are expected to furnish useful information about the fundamental kinetics of the surfiace growth and coagulation process of the soot particles.