Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA.
Phys Chem Chem Phys. 2010;12(20):5206-18. doi: 10.1039/b924344e.
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 (A. D. Abid, et al. Combust. Flame, 2008, 154, 775-788), all with an equivalence ratio Φ=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 D(50)=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 concentrations were found to be ordered as follows: [C=O]<[C–O]<[aliphatic C–H]. Aliphatic C–H was found to exist in significant quantities, with very little oxygenated groups present. The ratio of these chemical functionalities to aromatic C–H remains constant for particle sizes spanning 10-100 nm. The results confirm a previous experimental finding: a significant amount of aliphatic compounds is present in nascent soot formed in the flames studied, especially towards larger distances above the burner surface.
先前的研究表明，预混平面火焰中形成的烟灰可能含有大量脂肪族化合物。这些化合物的存在可能会以目前尚未理解的方式影响烟灰质量增长和氧化的动力学。我们使用与显微镜耦合的红外光谱仪（微傅里叶变换红外光谱仪），研究了最近经过特征描述的一组乙烯-氩-氧火焰（A. D. Abid 等人，《燃烧火焰》，2008，154，775-788）中采样的烟灰的组成，所有这些火焰的当量比均为 2.07，但最大火焰温度不同。使用探针采样技术在距燃烧器表面三个不同位置采集烟灰，并使用级联冲击器将其沉积在氮化硅薄膜基底上。对收集在最低五个冲击器级别的样品进行光谱采集和分析，其截止尺寸为 D(50)=10、18、32、56 和 100nm。微傅里叶变换红外光谱显示存在脂肪族 C-H、芳香族 C-H 和各种含氧官能团，包括羰基（C=O）、C-O-C 和 C-OH 基团。光谱分析用于检查这些官能团随火焰温度、采样位置和粒径的变化。结果表明，火焰温度的升高导致非芳香族官能团的含量增加。官能团浓度的顺序如下：[C=O]<[C-O]<[脂肪族 C-H]。发现脂肪族 C-H 大量存在，而含氧基团很少。对于粒径在 10-100nm 范围内的颗粒，这些化学官能团与芳香族 C-H 的比值保持不变。结果证实了先前的实验发现：在所研究的火焰中形成的初生烟灰中存在大量的脂肪族化合物，尤其是在距燃烧器表面较大的距离处。
