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Title: The effect of temperature on soot properties in premixed methane flames

Abstract

The effect of flame temperature on soot properties was studied in premixed methane/oxygen flames burning at a constant mixture composition (C/O = 0.60, {phi} = 2.4) and different cold-gas flow velocities (4 and 5 cm s{sup -1}). Temperature and concentration profiles of stable gases and condensed phases combustion products were measured along the flame axis. It was found that the high flame temperature conditions cause a larger decomposition of methane into hydrogen and C{sub 2}-C{sub 4} hydrocarbons, thereby reducing the formation of benzene and condensed phases including condensed species and soot. Soot properties were studied by UV-Visible absorption spectroscopy, thermogravimetry and H/C elemental analysis. A description of soot nanostructural organization was also performed by means of high-resolution transmission electron microscopy. Different properties and nanostructures were found to develop in the soot, depending on the temperature and on soot aging associated. Soot dehydrogenation occurred to a larger extent in the high flame temperature conditions. As soot dehydrogenates the mass absorption coefficients of soot exhibited an increasing trend along the flame axis. However, mature soot retained a relatively high H/C ratio and low absorption coefficients with respect to other less hydrogenated fuels even in high temperature conditions. This indicates that the aromatization/dehydrogenationmore » of soot in premixed flames is more dependent on the fuel characteristics rather than on the flame temperature. Generally, it was assessed that mature soot produced from diverse hydrocarbon fuels with similar flame temperatures and flame types possess a different chemical composition and structure. To this regard the H/C atomic ratio and mass absorption coefficients appeared to be signatures of soot properties and structural evolution. (author)« less

Authors:
; ; ;  [1];  [2]
  1. Istituto di Ricerche sulla Combustione, C.N.R., Napoli (Italy)
  2. Laboratoire de Geologie, Ecole Normale Superieure, UMR CNRS 8538, 24 Rue Lhomond, 75231 Paris Cedex 05 (France)
Publication Date:
OSTI Identifier:
21350372
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 157; Journal Issue: 10; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METHANE; SOOT; FLAMES; ABSORPTION; COMBUSTION PROPERTIES; DEHYDROGENATION; COMBUSTION KINETICS; TEMPERATURE RANGE 1000-4000 K; FUELS; HYDROGEN; OXYGEN; GAS FLOW; AROMATIZATION; DECOMPOSITION; GASES; MASS; MIXTURES; NANOSTRUCTURES; CHEMICAL COMPOSITION; EVOLUTION; VELOCITY; TEMPERATURE DEPENDENCE; TEMPERATURE DISTRIBUTION; Premixed flames

Citation Formats

Alfe, M., Apicella, B., Tregrossi, A., Ciajolo, A., and Rouzaud, J.-N. The effect of temperature on soot properties in premixed methane flames. United States: N. p., 2010. Web. doi:10.1016/J.COMBUSTFLAME.2010.02.007.
Alfe, M., Apicella, B., Tregrossi, A., Ciajolo, A., & Rouzaud, J.-N. The effect of temperature on soot properties in premixed methane flames. United States. doi:10.1016/J.COMBUSTFLAME.2010.02.007.
Alfe, M., Apicella, B., Tregrossi, A., Ciajolo, A., and Rouzaud, J.-N. 2010. "The effect of temperature on soot properties in premixed methane flames". United States. doi:10.1016/J.COMBUSTFLAME.2010.02.007.
@article{osti_21350372,
title = {The effect of temperature on soot properties in premixed methane flames},
author = {Alfe, M. and Apicella, B. and Tregrossi, A. and Ciajolo, A. and Rouzaud, J.-N.},
abstractNote = {The effect of flame temperature on soot properties was studied in premixed methane/oxygen flames burning at a constant mixture composition (C/O = 0.60, {phi} = 2.4) and different cold-gas flow velocities (4 and 5 cm s{sup -1}). Temperature and concentration profiles of stable gases and condensed phases combustion products were measured along the flame axis. It was found that the high flame temperature conditions cause a larger decomposition of methane into hydrogen and C{sub 2}-C{sub 4} hydrocarbons, thereby reducing the formation of benzene and condensed phases including condensed species and soot. Soot properties were studied by UV-Visible absorption spectroscopy, thermogravimetry and H/C elemental analysis. A description of soot nanostructural organization was also performed by means of high-resolution transmission electron microscopy. Different properties and nanostructures were found to develop in the soot, depending on the temperature and on soot aging associated. Soot dehydrogenation occurred to a larger extent in the high flame temperature conditions. As soot dehydrogenates the mass absorption coefficients of soot exhibited an increasing trend along the flame axis. However, mature soot retained a relatively high H/C ratio and low absorption coefficients with respect to other less hydrogenated fuels even in high temperature conditions. This indicates that the aromatization/dehydrogenation of soot in premixed flames is more dependent on the fuel characteristics rather than on the flame temperature. Generally, it was assessed that mature soot produced from diverse hydrocarbon fuels with similar flame temperatures and flame types possess a different chemical composition and structure. To this regard the H/C atomic ratio and mass absorption coefficients appeared to be signatures of soot properties and structural evolution. (author)},
doi = {10.1016/J.COMBUSTFLAME.2010.02.007},
journal = {Combustion and Flame},
number = 10,
volume = 157,
place = {United States},
year = 2010,
month =
}
  • Non-premixed oxy-fuel combustion of natural gas is used in industrial applications where high-intensity heat is required, such as glass manufacturing and metal forging and shaping. In these applications, the high flame temperatures achieved by oxy-fuel combustion increase radiative heat transfer to the surfaces of interest and soot formation within the flame is desired for further augmentation of radiation. However, the high cost of cryogenic air separation has limited the penetration of oxy-fuel combustion technologies. New approaches to air separation are being developed that may reduce oxygen production costs, but only for intermediate levels of oxygen enrichment of air. To determinemore » the influence of oxygen enrichment on soot formation and radiation, we developed a non-premixed coannular burner in which oxygen concentrations and oxidizer flow rates can be independently varied, to distinguish the effects of turbulent mixing intensity from oxygen enrichment on soot formation and flame radiation. Local radiation intensities, soot concentrations, and soot temperatures have been measured using a thin-film thermopile, planar laser-induced incandescence (LII), and two-color imaging pyrometry, respectively. The measurements show that soot formation increases as the oxygen concentration decreases from 100% to 50%, helping to moderate a decrease in overall flame radiation. An increase in turbulence intensity has a marked effect on flame height, soot formation and thermal radiation, leading to decreases in all of these. The soot temperature decreases with a decrease in the oxygen concentration and increases with an increase in turbulent mixing intensity. Altogether, the results suggest that properly designed oxygen-enriched burners that enhance soot formation for intermediate levels of oxygen purity may be able to achieve thermal radiation intensities as high as 85% of traditional oxy-fuel burners utilizing high-purity oxygen.« less
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