A sectional PAH model with reversible PAH chemistry for CFD soot simulations

A novel sectional approach for the modeling of polycyclic aromatic hydrocarbons (PAHs) is presented. The PAH model includes PAH radicals and is based on a reversible PAH growth mechanism. Combustion of species up to benzene and toluene is treated by finite-rate chemistry. The soot particle size distribution (PSD) is discretized by a sectional approach. Soot, PAHs, and the thermo-chemical state of the gas phase are fully coupled by a simultaneous solution of all governing equations. The new PAH model has been validated for a series of combustion configurations and shows significant improvements compared to irreversible PAH models at basically no increase in computational cost. Compared to irreversible PAH models, soot nucleation is significantly slower, yielding a better agreement to measured soot volume fractions in a series of laminar premixed flames. Moreover, the model developments led to correct predictions of the temperature dependency of the soot yield in ethylene pyrolysis after reflected shock waves. Finally, it will be shown that the new model describes the influence of the equivalence ratio on soot PSD functions correctly.