Soot-particle core-shell and fractal structures from small-angle X-ray scattering measurements in a flame

We have characterized soot particles measured in situ a laminar co-flow ethylene-air diffusion flame using small-angle X-ray scattering (SAXS). The analysis includes temperature measurements made with coherent anti-Stokes Raman spectroscopy (CARS) and complements volume-fraction maturity laser-induced incandescence (LII). compared the results of fits to SAXS unified model fractal core-shell model. Power-law parameters yielded by indicate that aggregates primary are mass-fractal regime, whereas surface-fractal regime middle flame. Higher lower flame, primary-particle power-law parameter approaches 4, suggesting smooth particles. These trends consistent model, which an established structure internally homogeneous at higher heights Primary-particle size distributions derived demonstrate excellent agreement inferred from transmission electron microscopy (TEM) images second small mode appears distributions, particle fragmentation during oxidation. Surface oxidation would explain (1) aggregate (2) loss leading smoother surfaces removal carbon overlayers. much more sensitive incipient young than LII significant volume fraction low where signal is negligible.