Analysis of key intermediates in the growth of polycyclic aromatic hydrocarbons using the parameter-selected merged model

Abstract

Soot, a by-product of incomplete combustion of organic fuels, can cause engine exhaust blockage, affect engine performance, and increase fuel consumption. Regulations have been introduced to reduce soot emissions, and studying the formation and growth of polycyclic aromatic hydrocarbons (PAHs) is essential to achieve this. Having a sub-model with sufficient PAH targets and understanding the key intermediates in the growth paths of PAHs is important for constructing a comprehensive model from fuel to PAHs. This enables the fuel pyrolysis or oxidation sub-models to interface effectively with the PAHs generation. The species in the 6 basic models, which target toluene, o-xylene, xylenes, trimethylbenzenes, indene, and α-methyl-naphthalene, were represented using the IUPAC Standard InChI (InChI) and their structural features were extracted using RDKit in Python. Then, 6 merged models were created by merging the same species and reactions in the 6 basic models based on 6 different parameter selection orders, resulting in a sub-model with 1376 species that includes 11 priority PAHs. The DRGEP method was used to simplify the 6 merged models and identify the key intermediates involved in the generation of benzene, which is considered as the key aromatic compound in the growth pathway of PAHs. A total of 91 species were obtained, present in both the 6 basic models and the 6 simplified models, and the performance of the merged models was evaluated based on the peak concentration results of these species. The selected merged model was further simplified using the DRGEP method with different targets to identify the key intermediates involved in the generation of the 11 priority PAHs. Through a comprehensive analysis of species based on 6 basic models, a conclusion was drawn that 32 C2-C4 hydrocarbon species are essential intermediates in the growth pathway of 11 discussed priority PAHs.