scispace - formally typeset
Search or ask a question

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.
Citations
More filters
01 Jan 1988
TL;DR: In this paper, the authors discuss the application of low-gravity combustion knowledge and appropriate aircraft analogies to fire detection, fire fighting, and fire-safety decisions for eventual fire-risk management and optimization in spacecraft.
Abstract: Practical risk management for present and future spacecraft, including space stations, involves the optimization of residual risks balanced by the spacecraft operational, technological, and economic limitations. Spacecraft fire safety is approached through three strategies, in order of risk: (1) control of fire-causing elements, through exclusion of flammable materials for example; (2) response to incipient fires through detection and alarm; and (3) recovery of normal conditions through extinguishment and cleanup. Present understanding of combustion in low gravity is that, compared to normal gravity behavior, fire hazards may be reduced by the absence of buoyant gas flows yet at the same time increased by ventilation flows and hot particle expulsion. This paper discusses the application of low-gravity combustion knowledge and appropriate aircraft analogies to fire detection, fire fighting, and fire-safety decisions for eventual fire-risk management and optimization in spacecraft.

20 citations


Additional excerpts

  • ...The comparative flame-spreading tests of Andracchio and Aydelott (1970), confirmed in a different geometric configuration by Olson (1987), were performed under quiescent (no forced flow) condi- tions....

    [...]

Journal ArticleDOI
01 Jan 2015
TL;DR: In this article, the effects of gravity on pool fire characteristics were investigated under conditions of normal to low gravity; using the drop tower at Hirosaki University in Japan to obtain arbitrary low-gravity acceleration, which varied from 1G to 0.55G.
Abstract: The flame characteristics of pool fires such as their height and oscillation frequency vary depending on gravity. To improve our understanding of the effects of gravity on flame characteristics, we experimentally investigated small-scale pool fires under conditions of normal to low gravity; using the drop tower at Hirosaki University in Japan to obtain arbitrary low-gravity acceleration, which varied from 1G to 0.55G. Our experiments include analyses of the flame height and oscillation frequency of puffing phenomenon caused by buoyancy under low-gravity environments with a high-speed camera. To clarify the factor of puffing occurrence factor, experiments were performed using eleven different sizes of fuel pan and three different kinds of fuels. It emerged that the flame height and puffing frequency declined with decreasing gravity, whereas the puffing phenomenon which occurred with fuel pan size rose with decreasing gravity. The puffing phenomenon was suppressed with decreasing gravity and the puffing frequency under low-gravity environments was summarized by the relationship between the Strouhal-and Froude numbers. The occurrence of the puffing phenomenon, namely the puffing-limit, was summarized by the relation between the ( H / D ) limit and Grashof number, and found to be inversely proportional.

19 citations

Journal ArticleDOI
TL;DR: In this paper, a new concept based on the Damkohler number (Da) was proposed to describe the complete transition behavior found in a flame spread in a solid combustible tube.

18 citations

Journal ArticleDOI
TL;DR: In this article, a numerical analysis using an unsteady combustion model is presented to study the ignition and subsequent downward flame spread over a thermally thin solid fuel in a gravitational field.
Abstract: A numerical analysis using an unsteady combustion model is presented to study the ignition and subsequent downward flame spread over a thermally thin solid fuel in a gravitational field. The solid-fuel temperature rises gradually in the heat-up stage and the pyrolysis becomes more intense. Ignition, including the induction period and thermal runaway, occurs as soon as a flammable mixture is formed and the gas-phase temperature, heated by the solid fuel, becomes high enough. During the induction period, the reactivity and temperature in the gas phase are mutually supportive. The thermal runaway consists of a burning premixed flame as the flow moves with the flame front. This is followed by a transition from a premixed flame into a diffusion flame. The flame front extends along and toward the upstream virgin fuel as the diffusion flame is formed. Finally, steady flame spread takes place as burnout appears. The ignition delay time is found to be controlled mainly by the time required to form the flammable mi...

17 citations


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

  • ...Several experiments and models, such as those by Fernandez-Pello and Hirano (1983), Chen and Hou (1991), Olson (1987, 1991), and Sacksteder and T’ien (1994), indicated that the ambient oxygen concentration will alter flame behavior....

    [...]

  • ...The experiment by Olson (1987) found that Vf / Y1:18O1 for YO1 0:21....

    [...]

  • ...The corresponding exponent obtained experimentally by Olson (1987) was 1.18....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the scenario approach of risk assessment is used to identify modeling needs and, in turn, experiments that would aid in the development of models that would meet these needs.

16 citations