Fuel-Rich Premixed n-Heptane/Toluene Flame: a Molecular Beam Mass Spectrometry and Chemical Kinetic Study

Abstract

The mole fraction profiles of major flame species and intermediates including PAH precursors are measured in an atmospheric premixed burner-stabilized fuel-rich (φ = 1.75) n-heptane/toluene/O2/Ar flame (n-heptane/toluene ratio is 7:3 by liquid volume). These data are simulated with a detailed, extensively validated chemical kinetic reaction mechanism for combustion of n-heptane/toluene mixture, involving the reactions of PAH formation. The mechanism is extended with cross reactions for n-heptane and toluene derivatives. A satisfactory agreement between the new experimental data on the structure of n-heptane/toluene flame and the numerical simulations is observed. The mechanism reported can be successfully used in the models of practical fuel surrogates for reproducing the formation of soot precursors. The analysis of the reaction pathways shows that in the flame of the n-heptane/toluene blend (7:3 liquid volume ratio) the reactions dominant for the formation of the first aromatic ring (benzene and phenyl) are as those typical for pure toluene flames. The discrepancies between the measured and calculated species mole fractions are detected as well. The steps for the mechanism improvements are determined on the basis of the sensitivity analysis performed. To our knowledge, the measurements of mole fraction profiles of PAH and intermediates reported here, are the first of its kind and represent an unique data set extremely important for validation of chemical kinetic mechanisms for combustion of practical fuels.

Keywords

• formation of soot precursors
• chemical kinetic mechanism
• n-heptane
• toluene
• molecular-beam
• mass spectrometry