PNNL

Abstract

Previous studies suggest that soot formed in premixed flat flames can contain a substantial amount of aliphatic compounds. Presence of these compounds may affect the kinetics of soot mass growth and oxidation in a way that is currently not understood. Using an infrared spectrometer coupled to a microscope (micro-FTIR), we examined the composition of soot sampled from a set of ethylene-argon-oxygen flames recently characterized (Abid, A.D. et al. Combust. Flame, 2008, 154, 775-788), all with an equivalence ratio 0 = 2.07 but varying in maximum flame temperatures. Soot was sampled at three distances above the burner surface using a probe sampling technique and deposited on silicon nitride thin film substrates using a cascade impactor. Spectra were taken and analyses performed for samples collected on the lowest five impactor stages with the cut-off sizes of D50 = 10, 18, 32, 56 and 100 nm. The micro-FTIR spectra revealed the presence of aliphatic C-H, aromatic C-H and various oxygenated functional groups, including carbonyl (C=O), C-O-C and C-OH groups. Spectral analyses were made to examine variations of these functional groups with flame temperature, sampling position and particle size. Results indicate that increases in flame temperature leads to higher contents of non-aromatic functionalities. Functional group concentration was found to be ordered as follows: [C=O]