Investigation on chemical structures of premixed toluene flames at low pressure

Chemical structures of premixed toluene/O2/Ar flames with five equivalence ratios (0.75, 1.00, 1.25, 1.50, and 1.75) were studied at low pressure (4.0 kPa). Synchrotron vacuum ultraviolet photoionization mass spectrometry was used for the isomeric detection of flame species and the measurements of their mole fractions. The global trends of the flame temperature and mole fractions of detected species with varying equivalence ratio were observed and discussed, drawing complete pictures for the chemical structures of premixed toluene flames. Based on the experimental results, a kinetic model was developed from previous models and updated with many recently studied reactions related to toluene decomposition and polycyclic aromatic hydrocarbons (PAHs) formation. The model was validated by simulating the measured mole fractions of flame species, showing good agreement in reproducing the maximum mole fractions of most observed species and their global trends with varying equivalence ratio. The rate of production analysis reveals the major formation and consumption channels of some key intermediates involved in toluene decomposition in the ϕ = 0.75 and 1.75 flames, and the major formation channels of some large aromatics and typical PAHs in the ϕ = 1.75 flame, indicating the importance of benzyl in toluene flames.