Soot formation in co-and counter-flow laminar diffusion flames of binary mixtures of ethylene and butane isomers and synergistic effects

Soot volume fractions of binary mixtures of butane isomers, ethylene'butane isomers, and propane'butane isomers were evaluated experimentally in diffusion flames on both co-and counter-flow burners. Soot volume fractions were measured by two-dimensional line of sight attenuation of a broadband arc lamp generated light in co-flow flames, whereas in counter-flow flames, attenuation of a small radius laser beam was used. Binary mixtures of iso-butane and n-butane did not show any synergistic effects on soot formation. On the other hand, either n-butane or iso-butane addition to ethylene caused a strong synergistic effect in both types of flames that the soot volume fractions were higher than those of the individual mixture components under the same flame conditions. Binary mixtures of propane and butane isomers, however, did not display any measurable synergistic effect on soot formation. These observations were discussed in the light of mechanisms proposed by previous investigators to explain the synergistic effects detected in the flames of binary mixtures. Current results cast doubt on the universality of the dominance of any of the mechanisms previously proposed to explain the synergistic effects observed with some binary hydrocarbon mixtures.