UC Irvine

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 size information was obtained via computer-aided image analysis. Particle morphology was observed to be similar to that found in other combustion devices (i.e., nearly spherical primary particles fused into aggregate 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 diffusion 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. Aggregate sizes were also observed to increase with cambustor axial location, and were found to be distributed in a lognormal manner during the particle inception and growth stages. Fractal dimensions for characteristic aggregate populations were determined to be around 1.8, and were 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. Comparisons with more traditional methods for soot size determination were made with moderate success.