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Experimental Observations on a Low Strain Counter-Flow Diffusion Flame: Flow and Buoyancy Effects

Diffusion flames are of great interest in fire safety and many industrial processes. The counter-flow configuration provides a constant strain flow, and therefore is ideal to study the structure of diffusion flames. Most studies have concentrated on the high velocity, high strain limit, since buoyantly induced instabilities will disintegrate the planar flame as the velocity decreases. Only recently, experimental studies in microgravity conditions have begun to explore the low strain regimes. Numerical work has shown the coupling between gas phase reaction rates, soot reaction rates, and radiation. For these programs, size, geometry and experimental conditions have been chosen to keep the flame unaffected by the physical boundaries. When the physical boundaries can not be considered infinitely far from the reaction zone discrepancies arise. A computational study that includes boundary effects and accounts for the deviations occurring when the major potential flow assumptions are relaxed was presented by Borlik et al. This development properly incorporates all heat loss terms and shows the possibility of extinction in the low strain regime.

A major constraint of studying the low strain regime is buoyancy. Buoyant instabilities have been shown to have a significant effect on the nature of reactants and heat transport, and can introduce instabilities on the flow that result in phenomena such as flickering or fingering. The counter-flow configuration has been shown to provide a flame with no symmetry disrupting instabilities for inlet velocities greater than 50 mm/s. As the velocity approaches this limit, the characteristic length of the experiment has to be reduced to a few millimetres so as to keep the Rayleigh number (RaL = (βg0L3∆T)/(𝑎v)) below 2000.

In this work, a rectangular counter-flow burner was used to study a two-dimensional counter-flow diffusion flame. Flow visualisation and Particle Image Velocimetry served to describe the nature of the stagnation plane for strain rates smaller than 100 (1/s). These experiments were conducted with a non-reacting flow. Video images of a propane air diffusion flame were used to describe the behaviour of a diffusion flame in this regime. Flame geometry and pulsation frequency are described.

Document ID
19990053986
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Authors
J. A. Sutula
(University of Maryland, College Park College Park, Maryland, United States)
J. L. Torero
(University of Maryland, College Park College Park, Maryland, United States)
O. A. Ezekoye
(The University of Texas at Austin Austin, Texas, United States)
Date Acquired
August 19, 2013
Publication Date
May 18, 1999
Publication Information
Publication: Fifth International Microgravity Combustion Workshop
Publisher: National Aeronautics and Space Administration
Volume: NASA/CP-1999-208917
Issue Publication Date: May 1, 1999
Subject Category
Inorganic And Physical Chemistry
Meeting Information
Meeting: 5th International Microgravity Combustion Workshop
Location: Cleveland, OH
Country: US
Start Date: May 18, 1999
End Date: May 20, 1999
Sponsors: Glenn Research Center
Funding Number(s)
CONTRACT_GRANT: NAG3-1960
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.
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