Kinetic Modeling Study of Polycyclic Aromatic Hydrocarbon Formation and Oxidation for Oxygenated Fuels including Methanol, n-Butanol, Methyl Butanoate, and Dimethyl Ether

Oxygenated fuels are usually employed as alternative or additive fuels to gasoline and diesel fuels in order to reduce soot emissions. By involving the most recent reaction channels of polycyclic aromatic hydrocarbon (PAH) formation and oxidation, a reduced PAH mechanism was developed using the global sensitivity analysis for representative oxygenated fuels including methanol, n-butanol, methyl butanoate, and dimethyl ether. The new reduced chemical mechanism was constructed including 140 species and 448 reactions. The characteristics of PAH formation for different oxygenated fuels were reproduced by considering the variations of small radical and the formation and growth of PAHs with the fuel distinctive chemical structures. The present mechanism was used to predict the ignition delay times and the concentrations of primary species, A(1), and large PAHs for a single component and their blended fuels. The calculated results indicate that the new mechanism can well describe the PAH formation for oxygenated fuels and reproduce the influence of the addition of oxygenated fuels on PAH formation in their blended fuels. Finally, the pathway analysis of A(1) formation and PAH growth was performed to understand the reaction pathways and tendencies of PAH formation for different oxygenated fuels. It is found that the discrepancies in the rates of production of the important routes of the formation and growth of PAHs for the test oxygenated fuels are apparent. The tendency of PAH formation is mainly affected by the length of the carbon chain available for producing PAHs. The impact of the oxygen content in oxygenated fuels on hindering PAH formation is minor since most oxygen in oxygenated fuels is converted into different small molecule oxygenated products.