Surface Growth and Soot Particle Reactivity

Abstract

In this paper we propose modificalions to our original model of surface growth which reconciles the empirical result that surface growth is proportional to the soot surface area in "normal" (unseeded) flames but not in flames that have been seeded. The new model proposes: (i) The controlling experimenlally measured variable determining the rate of surface growth is the amount of soot generated in the inception stage and delivered to the growth stage, (ii) Growth stops at long times because of changes in the reactivity of the soot particles, not because of depletion of gas phase growth species. (iii) Acetylene and - to a lesser extent - diacetylene are the principal growth species in all premixed flames, although PAH may dominate during particle inception, and other species may dominate in diffusion flames, (iv) Surface growth occurs on reactive sites such as defects or edges which are lost by a temperature-dependent annealing process. The number of active sites is not directly affected by coagulation, surface growth, or gas phase chemistry. The initial surface area is actually a surrogate for the number of active sites.