Experimental investigation of the structure of a sooting premixed benzene/oxygen/argon flame burning at low pressure

The structure of a one-dimensional premixed benzene-oxygen-argon flame burning at 50 mbar with a fuel equivalence ratio (phi) of 2.0 has been determined experimentally. Mole fraction profiles of species up to C22H12 have been measured by using molecular beam mass spectrometry and the temperature profile by a Pt/PtRh10% thermocouple. Large maximum mole fractions (> 10(-3)) have been measured for acetylene, diacetylene, cyclopentadiene, and vinylacetylene. Linear acetylenic intermediates remain in the burned gases significantly longer than olefinic and aromatic compounds. Also, at a given carbon content in a hydrocarbon intermediate, its maximum concentration shifts downstream when the hydrogen content decreases. The comparison with a leaner flame (phi = 1.8) studied by Bittner and Howard has shown a substantial increase in the maximum concentration of aromatics (PAH) and therefore the detection of larger intermediates as a consequence of the equivalence ratio effect. The comparison with an ethylene flame (phi = 2.5) investigated by Renard et al. has illustrated the strong impact of benzene as the initial fuel which enhances the formation of cyclopentadiene and heavier hydrocarbons. Light species (< C-5) occur in similar maximum quantities in all discussed flames. Some discrepancies with the results issuing from a model validated in rich ethylene flames have illustrated the importance of the C-4 route compared to the C-3 path in the oxidation and degradation mechanism of benzene in flames. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved