Publication

Abstract : This study presents updated comprehensive gas-phase kinetic mechanism and aerosol models to predict soot formation characteristics in ethylene-air nonpremixed flames. A main objective is to investigate the sensitivity of the soot formation rate to various chemical pathways for large polycyclic aromatic hydrocarbons (PAH). The gas-phase chemical mechanism adopted the KAUST-Aramco PAH Mech 1.0, which utilized the AramcoMech 1.3 for C0-C2 species and was extended up to benzene (C6). In addition, PAH species up to coronene (C24H12 or A7) were included to describe the detailed formation pathways of soot precursors. In this study, the detailed chemical mechanism was reduced from 397 to 99 species using directed relation graph (DRG) and sensitivity analysis. The method of moments with interpolative closure (MOMIC) was employed for the soot aerosol model. Counterflow nonpremixed flames at low strain rate sooting conditions are considered, for which the sensitivity of soot formation characteristics to different nucleation pathways is investigated. Both pure and diluted fuel stream conditions are considered, for which soot formation (SF) flames are formed such that oxidation processes have little effect on the net soot concentration profiles. Results show that higher PAH concentrations result in higher soot nucleation rate, and that the average size of the particles are in good agreement with experimental results. Subsequently, the effects of different pathways, with respect to pyrene- or coronene-based nucleation models, on the net soot formation rate are analyzed. In addition, soot formation characteristics of premixed flames represented in International sooting flame workshop (ISF) were studied. From the ISF workshop, sooting flame data of flames 2 and flame 3 were considered for comparison. The KAUST model shows an improved or comparable prediction of soot volume and diameters for flames 2 and 3 in comparison with other reported modeling results. It is found that the nucleation processes (i.e., soot inception) from higher PAH precursors; coronene in particular, is critical for accurate prediction of the overall soot formation.