The core-shell internal nanostructure of soot - A criterion to model soot maturity

A novel model called Surface Shell Formation (SSF) is developed which predicts soot maturity based on the equilibrium nanostructure of poly aromatic hydrocarbons (PAHs) inside soot primary particles. The characteristic isotropic core-graphitic shell internal nanostructure of soot primary particles is used to distinguish nascent from mature soot primary particles. A new sectional soot model is developed to track particle Hydrogen to Carbon (H/C) ratio and the growth in the molecular weight of PAHs inside soot primary particles. An independent Arrhenius term describes particle dehydrogenation/carbonization. It is shown that soot maturity depends on both particle size and H/C ratio. Graphitic shell formation in mature soot particles is related to the surface PAHs that change configuration from edge on surface for nascent soot to face on surface for mature soot particles. The new model is validated against experimental data for laminar premixed, partially premixed and diffusion flames. The SSF model addresses the two major limitations of the current soot modeling approaches. First, it predicts H/C ratio of soot particles by considering soot carbonization. Second, it distinguishes nascent soot from mature soot primary particles based on the internal nanostructure of soot primary particles and the presence of the graphitic shell.