SYNERGISTIC EFFECT OF ETHYLENE-PROPANE MIXTURE ON SOOT FORMATION IN LAMINAR DIFFUSION FLAMES

Sooting characteristics in laminar diffusion flames have been studied experimentally for ethylene-propane mixtures, and a synergistic effect from mixture fuels has been observed. Soot volume fraction and polycy clic aromatic hydrocarbon (PAH) concentration are increased when a sma ll amount of propane is added to ethylene diffusion flames. Considerin g C2H2 concentrations and adiabatic flame temperatures, the experiment al results indicate that H-abstraction-C2H2-addition (HACA) reaction a lone is insufficient to explain soot inception and growth processes in diffusion flames of ethylene-propane mixtures. The synergistic effect of fuel mixture is discussed, emphasizing the importance of C-3 recom bination reaction during the initial ring formation process for incipi ent PAHs. The results of soot number density and particle size in low- temperature soot growth region also support continuous soot inception via PAH agglomeration. Therefore, it is suggested that PAHs are direct ly involved in the soot particle inception processes. The synergistic effect is less significant for ethylene-ethane mixtures compared to et hylene-propane mixtures. (C) 1998 by The Combustion Institute.