A detailed kinetic model for aromatics formation from small hydrocarbon and gasoline surrogate fuel combustion

This work develops a detailed chemical kinetic model for Polycyclic Aromatic Hydrocarbon (PAH) chemistry that builds on a chemical model for gasoline surrogates by Cai et al. [Proc. Combust. Inst. 37 (2019) 639-647]. Informed by ab-initio and experimental studies, the model development emphasizes the prediction of soot precursors starting from C3H4 isomers up to the size of acepyrene. The proposed model was validated against experimental measurements from 79 publications, including ignition delay times, laminar burning velocities, and speciation data for several fuels in various conditions. A validation against measured peak mole fractions from 31 counterflow flames demonstrates an average prediction error of aromatic species up to the size of acenaphthalene below a factor of three. Additionally, the effects of experimental uncertainty are quantitatively discussed by computing confidence intervals for the true model prediction error. The formation of two-ring aromatic species is often still considered poorly understood. Accordingly, special attention is given to the formation of indene and naphthalene. Reaction flux analyses based on rigorously defined species selection criteria reveal that indene formation pathways are initiated by reactions of phenyl and benzyl and described by the reaction kinetics from theoretical calculations. In contrast, naphthalene formation is dominated by more uncertain pathways relying on estimated rates that are initiated by reactions of benzene and fulvenallenyl. Five-member rings on the periphery of PAH species and soot particles play a crucial role in recent experimental and theoretical studies. Therefore, this work investigates acenaphthene and other C12H8 isomers. The most abundant C12H8 isomers are acenaphthene, 1-ethynylnaphthalene, and 2-ethynylnaphthalene, and their respective concentrations are predicted to be similar in many flames. Furthermore, reaction flux analyses show that their formation is dominated by HACA routes starting from naphthalene.(c) 2022 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Automated summary

This work develops a detailed chemical kinetic model for Polycyclic Aromatic Hydrocarbon (PAH) chemistry and focuses on the prediction of soot precursors. The model was validated against experimental measurements and analyzed the effects of experimental uncertainty. The study also investigates the formation mechanisms of indene and naphthalene, as well as the role of five-member rings in PAH species and soot particles.