Low temperature oxidation of toluene in an n-heptane/toluene mixture

Abstract

As an important component of transportation fuels, toluene has little reactivity in the low temperature regime. However, the low temperature reactivity of toluene may be enhanced by the reaction of other reactive components (e.g., n-heptane) in fuel mixtures. This work examines low temperature oxidation of toluene in jet stirred reactor oxidation of an n-heptane/toluene mixture (1:1 in mole, 500–800 K, ϕ=0.5, τ=2.0 s, p = 1 bar). Two measurement techniques, time of flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet radiation as the photon ionization source and gas chromatography mass spectrometry, were applied to identify and measure 32 species, including four polycyclic aromatic hydrocarbons (PAH) and oxygenated PAH (OPAH). Numerical simulations using the latest kinetic model from Lawrence Livermore National Laboratory predicted the mole fractions of fuel molecules and small intermediates well, but under-predicted the mole fractions of oxygenated aromatics (phenol, benzyl alcohol, and cresol). The identification of benzyl peroxide–an important intermediate–supported the proposed formation pathways for the identified aromatics. Model analysis highlighted the influence of H-atom abstraction, OH/H radical ipso substitution, and OH addition reactions of toluene on the formation of phenol, benzyl alcohol, and cresol, which may further grow to OPAH molecules by the addition of benzyl radical from H-atom abstraction of toluene.