Kinetic Monte Carlo simulations of soot particle aggregation
Soot particles formed in flames and practical combustion devices can be described as fractal-like aggregates comprised of spheroidal primary particles. The size of primary particles is known to exceed that of particles incepted from the gas phase. It is therefore often argued that particle aggregation is preceded by a period of coalescent growth.1 It has been argued that transition from coalescent to aggregate growth is a result of simultaneous coagulation and surface growth.2 Mitchell and Frenklach3,4 investigated the mechanism of transition from coalescent to aggregate growth by calculating trajectories of individual collector particles using a dynamic Monte-Carlo method, where collector particles allowed to grow through collisions with the surrounding monodispersed candidate particles and simultaneous surface growth. These authors concluded that the morphology of aggregating particles is intimately related to both the surface deposition and particle nucleation rates. Extending this study, Balthasar and Frenklach5 conducted similar simulations using a realistic size distribution for selecting candidate particles. The simulation results provided further support to the notion that particle nucleation and the presence of small particles influence the morphology of primary particles and the location of transition. In the both studies, however, aggregate-aggregate formation was not taken into account. While the aggregation kinetics was recently modeled using a method of moments,6 the morphology of the forming aggregates could not be examined with this approach. In the present study, we extend the Monte-Carlo method to enable numerical simulations of the entire particle ensemble with aggregate-aggregate collisions included. The new approach is applied to the formation of soot particles in laminar premixed flames.