SOOT ZONE STRUCTURE AND SOOTING LIMIT IN-DIFFUSION FLAMES - COMPARISON OF COUNTERFLOW AND CO-FLOW FLAMES

Soot zone structures of counterflow and co-flow diffusion flames have been studied experimentally using the soot extinction-scattering, poly cyclic aromatic hydrocarbon fluorescence, and laser Doppler velocimetr y measurements. The counterflow flame has been numerically modelled wi th detailed chemistry. Results show that two different categories of s ooting flame structures can be classified depending on the relative tr ansport of soot particles to flames. These are the soot formation-oxid ation flame and the soot formation flame. The soot formation-oxidation flame characteristics are observed in counterflow flames when located on the fuel side and in normal co-flow flames. In this case, soot par ticles are transported toward the high temperature region or the flame and experience soot inception, coagulation-growth, and oxidation. The soot formation flame characteristics are observed in counterflow flam es when located on the oxidizer side and in inverse co-flow flames. In this case, soot particles are transported away from the flame without experiencing oxidation and finally leak through the stagnation plane in counterflow flames or leave the flame in inverse co-flow flames. So oting limit measurements in both flames also substantiate the two diff erent sooting flame structures and their characteristics. (C) 1997 by The Combustion Institute.