Study of soot growth in a plug flow reactor using a moving sectional model

Abstract

Combustion in a plug flow reactor (PFR) is similar to that occurring in the postflame region of laminar flames, and hence provides a well-defined environment to study those soot formation processes at a relatively larger residence time, which are identified as simultaneously occurring surface growth (typically by HACA mechanism) and PAH surface condensation together with the particle coagulation. The roles of HACA mechanism and PAH condensation are of great interest in recent research. A moving sectional aerosol dynamics model is implemented in this study for prediction of soot formation in a PFR. Coupled with the detailed gas phase chemistry, the soot model provides reasonable predictions of the molar concentrations of major species, PAHs and radicals, soot mass concentration, soot mean particle diameter, and the particle size distribution. The predicted size distribution shows the evolution of its shape from the power law to a bi-modal distribution. The study of the soot growth rate shows that both HACA surface growth and PAH surface condensation are important in the modeling of soot formation in the PFR. All available PAH radical species are included in surface condensation, which results in good prediction of mass growth rate without excessive depletion of the PAH species. However, the use of a single incipient species, pyrene, results in its concentration being underpredicted. This new soot model provides a solid approach to investigate further the soot formation in combustion with simultaneous particle nucleation, surface growth, PAH condensation, and coagulation.