Influence of large aromatic species on soot formation in turbulent non-premixed jet flames

Designing cleaner combustion devices requires more accurate predictions of the emitted soot mass. Soot yield from combustion is mostly governed by soot nucleation, which is one of the most unknown processes in the soot life cycle. Soot nucleation is believed to occur from Polycyclic Aromatic Hydrocarbons (PAH) under locally fuel rich conditions. Soot nucleation models used in current turbulent combustion simulations may involve a single or multiple nucleating PAH species. In this paper, we study the effects of large PAH on soot mass and distribution. This is examined in two non-premixed turbulent sooting jet flames using ethylene and a jet fuel surrogate (JP8) as fuels. Two Large-Eddy Simulations (LES) are performed for each flame, one considering only a single nucleating PAH (naphthalene) and the other one considering a range of nucleating PAH from naphthalene to cyclopenta[cd]pyrene. Flamelet based chemistry-tabulation is used for the major thermochemical quantities, and turbulence-chemistry interactions for PAH are accounted for using a recently developed PAH relaxation model. The effects of large PAH on soot are highlighted by comparing the PAH species concentrations, nucleation rates, and soot volume fraction distributions obtained from the two simulations of each flame. Comparison is also done against experimental measurements when available. It is found that the large aromatic species have a non-negligible impact on nucleation rates and ultimately the soot yield.