Ethylene Inverse Diffusion Flame Research Articles

FT-IR and 1H NMR characterization of the products of an ethylene inverse diffusion flame

Knowledge of the chemical structure of young soot and its precursors is very useful in the understanding of the paths leading to soot particle inception. This paper presents analyses of the chemical functional groups, based on FT-IR and 1H NMR spectroscopy of the products obtained in an ethylene inverse diffusion flame. The trends in the data indicate that the soluble fraction of the soot becomes progressively more aromatic and less aliphatic as the height above the burner increases. Results from 1H NMR spectra of the chloroform-soluble soot samples taken at different heights above the burner corroborate the infrared results based on proton chemical shifts (Ha, H α, H β, and H γ). The results indicate that the aliphatic β and γ hydrogens suffered the most drastic reduction, while the aromatic character increased considerably with height, particularly in the first half of the flame.

Formation of Ni-catalyzed multiwalled carbon nanotubes and nanofibers on a substrate using an ethylene inverse diffusion flame

The synthesis of Ni-catalyzed multiwalled carbon nanotubes and nanofibers on a catalytic metal substrate, using an ethylene-fueled inverse diffusion flame as a heat source, was investigated. When the approximate gas temperature was varied from 1400 to 900 K, carbon nanotubes with diameters of 20–60 nm were formed on the substrate. In the regions where the approximate gas temperature was higher than 1400 K or lower than 900 K, iron nanorods or carbon nanofibers were synthesized, respectively. Based on the quantitative analyses of many scanning electron microscope (SEM) and transmission electron microscope (TEM) images, the nanotubes formed closer to the flame had a tendency to have larger diameters. High-resolution TEM images and Raman spectra revealed that the synthesized carbon nanotubes had multiwalled structures, with some defective graphite layers at the wall. Based on the graphite mode of the Raman spectra, it was believed that the optimal synthesis could be obtained if the substrate was positioned at between 5.5 and 5.0 mm from the flame center. However, in the case of higher gas temperatures with respect to the formation of nanotubes rather than nanofibers, the graphite layers on the catalyst metal might be under relatively strong stress due to the large amount of precipitated carbon atoms on the edge. As a result of this strong compressive stress the carbon nanotubes are formed with empty or periodic compartments which are hollow on the inside.

The existence of young soot in the exhaust of inverse diffusion flames

Knowledge of the chemical and physical structure of early soot is useful in the development of sootparticle inception models. This paper examines the hypothesis that soot exiting an inverse diffusion flame is similar in chemical and morphological structure to (1) soot precursor particles and (2) soot that exits underventilated flames. Experiments in volving soot collection from the exhaust of laminar ethylene inverse diffusion flames were performed. Soot samples were analyzed for morphology using transmission electron microscopy, for carbon-to-hydrogen ratio using elemental analysis, for organic fraction using thermaloptical analysis, and for polycyclic aromatic hydrocarbon content using laser microprobe mass spectrometry and gas chromatography/mass spectrometry. Results of these analyses support the validity of the above hypothesis. This finding is significant because exhaust collection from the inverse flame provides an opportunity to gather large samples of young soot without invading the flame with an intrusive probe (a necessary task when collecting precursors low in the center of a normal diffusion flame). Larger samples can then be subjected to more detailed analysis than previously possible. An identification of specific polycyclic aromatic hydrocarbon isomers present in young soot from diffusion flames is reported. The data are available for comparison with polycyclic aromatic hydrocarbon growth, soot inception, and soot growth models.

Soot Formation In Laminar Inverse Diffusion Flames

Abstract Soot formation in laminar ethylene inverse diffusion flames has been investigated experimentally and modeled. Soot volume fraction and temperature measurements have been made and compared to numerical predictions using a soot formation model previously applied to normal diffusion flames. The inverse flame configuration serves as a good test of the applicability of the model and is relevant to practical combustor designs. Comparisons ofthe predictions and data show good agreement. The model reasonably predicts several features of the inverse flame, including flame length. the locations of soot-bearing regions of the flow, and the evolution of the soot volume fraction profile.