Insights into the Decomposition and Oxidation Chemistry of p-Xylene in Laminar Premixed Flames.

This work reports an experimental and kinetic modeling investigation on laminar premixed flame of p-xylene at 0.04 atm and equivalence ratios of 0.75, 1.0, and 1.79. Intermediates such as the p-xylyl radical, p-xylylene, and styrene, as well as polycyclic aromatic hydrocarbons (PAHs), were detected by using synchrotron vacuum ultraviolet photoionization mass spectrometry. Based on our previous aromatic kinetic model, a detailed kinetic model of p-xylene combustion was developed, and the model was validated against the present flame structure data. Model analysis work was also performed in order to reveal the important reactions in p-xylene decomposition and oxidation. The H-abstraction reactions leading to the p-xylyl radical are found to control the consumption of p-xylene in all the three flames. In the rich flame, p-xylyl mainly suffers the H-elimination and isomerization reactions, which produce p-xylylene and the o-xylyl radical, respectively. The further decomposition reactions of the o-xylyl radical contribute to the production of styrene, which is another important C8 intermediate observed in the rich flame. In the stoichiometric and lean flames, p-xylyl mainly suffers the oxidation reactions by O, which give p-methylbenzaldehyde as major product. The growth pathways of PAHs in the rich flame were also investigated in this work. Indenyl, indene, naphthalene, and phenanthrene were observed as the abundantly produced bicyclic and tricyclic PAHs due to the existence of direct formation pathways from the decomposition of p-xylyl radical.