Polycyclic aromatic hydrocarbon formation in a flame of the alkylated aromatic trimethylbenzene compared to those of the alkane dodecane

Abstract

Abstract Over the last 50 years, several chemical mechanisms have been proposed to understand the chemistry involved in the formation of Polycyclic Aromatic Hydrocarbons (PAHs) during combustion. These mechanisms range from sequential addition of small hydrocarbon intermediates to recombination of large aromatic radicals. Flames present a multitude of complexities due to high temperature gradients, short residence time and overlapping of several chemical reactions. Detailed chemical mechanisms have been developed to unravel the complex chemical pathways involved in a flame. Although these chemical mechanisms can explain the formation of PAHs from an aliphatic fuel (n-dodecane), it fails in case of an alkylated aromatic (1,2,4-trimethylbenzene). Alkylated aromatics represent a significant portion of practical fuels. An accurate prediction for these fuels is necessary to understand the practical combustion process. This study focuses on addressing how the chemical pathways of PAH formation from 1,2,4-trimethylbenzene differs from n-dodecane. The results show that 1,2,4-trimethylbenzene decomposition involves four dominant pathways of PAH formation: recombination of fuel molecule, PAH radical recombination, Clustering of Hydrocarbons by Radical Chain Reactions (CHRCR) and hydrogenation followed by methylation. The implications of these pathways on soot growth have also been discussed. A complete dataset comprising of PAH, soot and temperature measurements have been generated for 1,2,4-trimethylbenzene and n-dodecane for future model validations.