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Flame and Soot Boundaries of Laminar Jet Diffusion FlamesThe shapes (flame-sheet and luminous-flame boundaries) or steady weakly buoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue CO2 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K. ambient pressures of 4-50 kPa, jet-exit Reynolds numbers of 3-54, initial air/fuel velocity ratios of 0-9, and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at microgravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smoke-point conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smoke-point conditions. Flame-shape predictions were based on simplified analyses using the boundary-layer approximations along with empirical parameters to distinguish flame-sheet and luminous-flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 of the lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions because of the presence of luminous soot particles in the fuel-lean region of the flames.
Document ID
20030016586
Acquisition Source
Glenn Research Center
Document Type
Reprint (Version printed in journal)
Authors
Xu, F.
(Michigan Univ. Ann Arbor, MI United States)
Dai, Z.
(Michigan Univ. Ann Arbor, MI United States)
Faeth, G. M.
(Michigan Univ. Ann Arbor, MI United States)
Yuan, Z.-G.
Urban, D. L.
Yuan, Z.-G.
Date Acquired
August 21, 2013
Publication Date
December 1, 2002
Publication Information
Publication: AIAA Journal
Volume: 40
Issue: 12
ISSN: 0001-1452
Subject Category
Inorganic, Organic And Physical Chemistry
Funding Number(s)
CONTRACT_GRANT: NAG3-1878
CONTRACT_GRANT: NAG3-2048
CONTRACT_GRANT: NCC3-661
Distribution Limits
Public
Copyright
Other

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