SOOT MORPHOLOGY IN A LIQUID-FUELED, SWIRL-STABILIZED COMBUSTOR

The morphology of particulate soot formed in a liquid-fueled, complex- flow (i.e., turbulent, recirculating) combustor has been studied using thermophoretic sampling and transmission electron microscopy. Soot si ze information was obtained via computer-aided image analysis. Particl e morphology was observed to be similar to that found in other combust ion devices (i.e., nearly spherical primary particles fused into aggre gate chains and clusters). Axial regions where soot nucleation, growth , agglomeration, and oxidation occur were identified. Primary particle size was observed to increase with combustor height, but the largest primary size reached is small compared to that observed in laminar dif fusion flames. From calculated estimates of the specific soot surface growth and oxidation rates, the growth rate was found to be lower and the oxidation rate comparable to those for laminar diffusion flames. A ggregate sizes were also observed to increase with combustor axial loc ation, and were found to be distributed in a lognormal manner during t he particle inception and growth stages. Fractal dimensions for charac teristic aggregate populations were determined to be around 1.8, and w ere independent of combustor axial location. The results suggest that cluster-to-cluster aggregation-and not surface growth-is the dominant soot aggregate growth mechanism in the complex-flow reactor. Compariso ns with more traditional methods for soot size determination were made with moderate success. (C) 1998 by The Combustion Institute.