Scavenging of hydrocarbon radicals from flames with dimethyl‐disulfide II. Hydrocarbon radicals in fuel‐rich low‐pressure flames of acetylene, ethylene, 1,3‐butadiene and methane with oxygen

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Abstract
The new technique of free‐jet condensation/scavenging with dimethyl‐disulfide has been applied for the quantitative analysis of hydrocarbon radicals and carbenes in flat premixed hydrocarbon/oxygen flames burning with fuel‐rich mixtures at 27 mbar. The results are reported as profiles of mole fractions of the radicals. The limit of detectability was about 1·10−7 mole fraction. Qualitatively the radicals are very similar with the four fuels, but there are large differences in their quantities. While in the methane flame only C1 and C2 radicals were present in detectable concentration, higher radicals up to naphthyl could be detected with the unsaturated fuels. Although methyl could not be determined quantitatively, it was found to be the major hydrocarbon radical in all flames. Methoxy radical was only found in the methane flame. Whereas, for example, C2, C3H2 and C3H are typical high‐temperature species, C2H is surprisingly formed at the beginning of the oxidation zone at relatively low temperature. Vinyl and the vinyl‐type radicals C2nH3 (n = 1 to 4) are in equilibrium with acetylene and the polyynes (C2nH2) at maximum flame temperature and in the burned gas. Since phenyl peaks always after benzene, it is concluded that it is mainly a degradation product from benzene and other lower aromatics. The mechanism of formation of C2H and C2, the equilibria of the C2nH3 and the relation between aliphatic and aromatic radicals are discussed.