Abstract
The relationship between soot surface growth, soot nanostructure and reactant temperature (T-r) in a coflow diffusion ethylene flame was investigated with multiple experimental techniques. The T-r was raised by heating the coflow air. Three cases, with 300K, 473K, and 673K T-r, respectively, were studied. Laser-induced Incandescence revealed that increasing T-r promotes soot formation. Although soot primary particle diameter (d(p)) also increases with T-r, the increase in d(p) slows down after 473K T-r, suggesting that there is a deceleration in soot surface growth. Transmission Electron Microscopy (TEM) imaging showed that increased T-r promotes soot aggregation and yields larger and more mature primary particles. The assessment of the Selected Area Electron Diffraction (SAED) patterns indicated that, at 673K T-r, there is a growth of lattice planes. Raman spectroscopy revealed further structural details. By assessing the band intensity ratios, soot for the T-r of 673K has more curved nanostructures. The deceleration of soot surface growth may be explained by surface aging, which is characterized by an increase in curved nanostructures. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.