Detailed Kinetic Modeling of Carbonaceous Nanoparticle Inception and Surface Growth during the Pyrolysis of C₆H₆ behind Shock Waves

Soot formation in combustion processes is of significant interest due to its influences on both environmental emissions and material synthesis (i.e., the synthesis of fullerences and carbon nanotubes). However, the inception process of the youngest carbonaceous nanoparticles from the gaseous phase is the most poorly understood phenomenon in the study of soot kinetics at the current stage. Recently, researchers have found experimentally the existence of transparent or semi-transparent carbonaceous particles (Krestinin, A. V. Combust. Flame 2000, 121, 513−524) or nanoorganic carbon particles (D'Anna, A.; Rolando, A.; Allouis, C.; Minutolo, P.; D'Alessio, A. Proc. Combust. Inst. 2004, 30, 1449−1456) during soot nucleation, which have not been successfully explained by traditional polycyclic aromatic hydrocarbon (PAH) nucleation mechanisms. Most recently, a more detailed soot kinetic model (Vlasov, P. A.; Warnatz, J. Proc. Combust. Inst. 2002, 29, 2335−2341; Part 2) has been implemented to predict soot formation behind shock waves and to describe the soot nucleation as a combined process of the fast polymerization of supersaturated polyyne vapor and the PAH growth. The lack of a detailed description of fractal particle structures in their aerosol dynamics model, however, restricted the model's accuracy in predicting the particle coagulation rates and, hence, the particle sizes. In the current study, a new comprehensive kinetic model has been developed to describe soot chemical processes in a heterogeneous phase. The nucleation process is described by the formation of the soot precursors and the transformation from those precursors to solid soot particles. The precursors are represented by six sectional bins, which are formed through the detailed PAH nucleation mechanism and polyyne pathways, respectively. The gaseous reaction mechanism has been validated against measurements of polyynes and the C/C 2 /C 3 carbon radicals. Finally, the aforementioned soot kinetic model has been implemented in an advanced aerosol dynamics model to predict the main parameters of soot particle formation in the pyrolysis of C 6 H 6 /Ar mixture. This aerosol dynamics model includes the detailed description of the agglomerate structure of soot particles and calculates the particle coagulation rates according to their sizes and structures. The numerical simulation shows that, during the fuel pyrolysis behind shock waves, both PAH growth and polyynes polymerization play an important role during the soot nucleation process. And the polyynes surface growth model alone is able to predict soot yield as well as averaged particle diameter during the earlier stage of soot formation.

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