Detailed kinetic modeling of soot particle formation in laminar premixed hydrocarbon flames.

摘要

The formation and growth of incipient soot particles in laminar premixed hydrocarbon flames has been studied theoretically. A detailed kinetic model has been developed, which is based on the classical picture of soot nucleation in flames. The model describes (1) the pyrolysis and oxidation chemistry of small hydrocarbons including methane, ethylene and acetylene, (2) the formation and growth of polycyclic aromatic hydrocarbons (PAHs) and (3) the nucleation and growth of soot particles.;The enthalpies of formation of polycyclic aromatic hydrocarbons were examined using a method combining semi-empirical quantum mechanical calculations with group equivalent corrections. The rate coefficients of the reactions of acetylene with a number of vinylic and aryl radicals were studied using the RRKM theory. A predictive reaction model was developed for describing the oxidation of acetylene and ethylene and the formation and growth of PAHs in burner-stabilized flames.;The results of computer simulations for a number of premixed flames indicate that the growth of PAH molecules can be quantitatively accounted for by the hydrogen-abstraction-acetylene-addition mechanism, and that the characteristic decay of PAH concentrations in the post-flame zone appears to be caused by the thermal decomposition of PAH radicals.;The simulation of incipient soot particle formation has been performed for a laminar premixed acetylene-oxygen-argon flame. Using the algorithm developed for calculating the light absorption and scattering properties from the moments of particle size distributions, the computational results are directly compared to experimental measurements. The inception of soot particles is primarily determined by PAH coagulation, initiated and controlled by PAH coalescence into dimers. The surface growth of soot is primarily determined by two processes: acetylene addition via the hydrogen-abstraction-acetylene-addition mechanism and PAH condensation onto the particle surface. The oxidation of soot particles by OH and O