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The Effect of Microgravity on Flame Spread over a Thin Fuel

01 Dec 1987-
TL;DR: In this article, a flame spreading over a thermally thin cellulose fuel was studied in a quiescent microgravity environment, and two different extinction limits were found in microgravity for the two thicknesses of fuel.
Abstract: A flame spreading over a thermally thin cellulose fuel was studied in a quiescent microgravity environment. Flame spread over two different fuel thicknesses was studied in ambient oxygen-nitrogen environments from the limiting oxygen concentration to 100 percent oxygen at 1 atm pressure. Comparative normal-gravity tests were also conducted. Gravity was found to play an important role in the mechanism of flame spread. In lower oxygen environments, the buoyant flow induced in normal gravity was found to accelerate the flame spread rate as compared to the microgravity flame spread rates. It was also found to stabilize the flame in oxidizer environments, where microgravity flames in a quiescent environment extinguish. In oxygen-rich environments, however, it was determined that gravity does not play an important role in the flame spread mechanism. Fuel thickness influences the flame spread rate in both normal gravity and microgravity. The flame spread rate varies inversely with fuel thickness in both normal gravity and in an oxygen-rich microgravity environment. In lower oxygen microgravity environments, however, the inverse relationship breaks down because finite-rate kinetics and heat losses become important. Two different extinction limits were found in microgravity for the two thicknesses of fuel. This is in contrast to the normal-gravity extinction limit, which was found to be independent of fuel thickness. In microgravity the flame is quenched because of excessive thermal losses, whereas in normal gravity the flame is extinguished by blowoff.
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Journal ArticleDOI
TL;DR: In this article, a wind-aided flame spread process along a solid fuel rod under oblique forced flow is analyzed in absence of gravity or when the forced flow dominates the gravity-induced flow.

14 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated how radiation heat transfer influences downward flame spread by presenting a gas phase radiation model, described by a two dimensional P-1 approximation method, to incorporate with the combustion model of Duh and Chen.
Abstract: This work investigates how radiation heat transfer influences downward flame spread by presenting a gas phase radiation model, described by a two dimensional P-1 approximation method, to incorporate with the combustion model of Duh and Chen (1991). The parametric study is based on the variation of gravity, which changes the Damkohler number (Da) and radiation to conduction parameter (I/N∞) simultaneously. Comparing the results with the previous studies of Duh and Chen (199l) and Chen and Cheng (1994). which only considered the radiation effect in cross stream direction, the role of stream-wise radiation was identified. The stream-wise radiation contributes to reinforce the forward heat transfer rate subsequently increasing the flame spread rate. However, this model also provides more directional radiation loss than that of Chen and Cheng (I994) and, in doing so, draws more energy out from the flame to further reduce its strength. The results indicates that the effect of heat loss is greater than that of e...

14 citations

01 Mar 1993
TL;DR: In this article, the authors summarized the fire detection and suppression techniques proposed for the Space Station Freedom and discussed both the application of low-gravity combustion knowledge to improve fire protection and the critical needs for further research.
Abstract: Experiments conducted in spacecraft and drop towers show that thin-sheet materials have reduced flammability ranges and flame-spread rates under quiescent low-gravity environments (microgravity) as compared to normal gravity. Furthermore, low-gravity flames may be suppressed more easily by atmospheric dilution or decreasing atmospheric total pressure than their normal-gravity counterparts. The addition of a ventilating air flow to the low-gravity flame zone, however, can greatly enhance the flammability range and flame spread. These results, along with observations of flame and smoke characteristics useful for microgravity fire-detection 'signatures', promise to be of considerable value to spacecraft fire-safety designs. The paper summarizes the fire detection and suppression techniques proposed for the Space Station Freedom and discusses both the application of low-gravity combustion knowledge to improve fire protection and the critical needs for further research.

14 citations

01 Mar 2000
TL;DR: In this paper, the principal NASA acceptance tests described in this paper assess the flammability of materials and components under "worst-case" normal-gravity conditions of upward flame spread in controlled-oxygen atmospheres.
Abstract: Spacecraft fire-safety strategy emphasizes prevention, mostly through the selection of onboard items classified accord- ing to their fire resistance. The principal NASA acceptance tests described in this paper assess the flammability of materials and components under "worst-case" normal-gravity conditions of upward flame spread in controlled-oxygen atmospheres. Tests conducted on the ground, however, cannot duplicate the unique fire characteristics in the nonbuoyant low-gravity environment of orbiting spacecraft. Research shows that flammability an fire-spread rates in low gravity are sensitive to forced convection (ventilation flows) and atmospheric-oxygen concentration. These research results are helping to define new material-screening test methods that will better evaluate material performance in spacecraft.

14 citations


Cites background from "The Effect of Microgravity on Flame..."

  • ...Early studies on the combustion of thin-paper fuels under various oxygen concentrations in quiescent microgravity show that, for atmospheres with high oxygen concentrations, the flame-spread rate is independent of the gravity level (15)....

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Journal ArticleDOI
TL;DR: In this paper, the ignition behavior of vertically oriented cellulosic materials subjected to a radiant heat flux in a normal gravitational field was numerically investigated and the entire process was delineated into two distinct stages.
Abstract: This study numerically investigates the ignition behaviors of vertically oriented cellulosic materials subjected to a radiant heat flux in a normal gravitational field. The entire process is delineated into two distinct stages. In the heating up stage, the maximum temperature increases with time but at a decreasing rate because of the pyrolysis reaction. The flame development stage consists of ignition and transition processes. In the ignition process, the maximum temperature in gas phase increases dramatically within a short period of time because a large amount of heat is generated from chemical reaction of the accumulative, flammable mixture. The flame is in a transition from a premixed flame to a diffusion one, except for the small region around the flame front. For the effect of varying the heating duration on ignition behavior, prolonging the imposed radiative heat time leads the ignition from a transition one to a persisting ignition. The effect of varying the solid fuel thickness indicates that th...

13 citations