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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: The major challenge to spacecraft fire extinguishment design and operations is from the micro-gravity environment, which minimizes natural convection and profoundly influences combustion and extinguishing agent effectiveness, dispersal, and post-fire cleanup.
Abstract: Fire extinguishment agents range from water and foam in early-design spacecraft (Halon 1301 in the present Shuttle) to carbon dioxide proposed for the Space Station Freedom. The major challenge to spacecraft fire extinguishment design and operations is from the micro-gravity environment, which minimizes natural convection and profoundly influences combustion and extinguishing agent effectiveness, dispersal, and post-fire cleanup. Discussed here are extinguishment in microgravity, fire-suppression problems anticipated in future spacecraft, and research needs and opportunities.

3 citations

Journal ArticleDOI
TL;DR: In this paper, an analysis of the problem of a diffusion flame embedded in a laminar boundary layer developed by a continuous moving solid fuel plate in a parallel flow of oxidizer is presented.
Abstract: An analysis of the problem of a diffusion flame embedded in a laminar boundary layer developed by a continuous moving solid fuel plate in a parallel flow of oxidizer is presented. The classical Blasius-type (BT) boundary-layer combustion, and the Sakiadis-type (ST) boundary-layer combustion where the boundary layer is developed by a continuously moving plate in a quiescent environment, are special cases of this generalized formulation. Numerical results are presented for a range of the mass transfer number and for a fixed Prandtl number of 0.7. The gas-phase chemistry is assumed to be infinitely fast and a unit Lewis number assumption is also made. The results show that the flames lie closer to the surface for the ST boundary layers compared to the BT ones. The BT boundary-layer flames are more sensitive to the relative velocity differences between the freestream and the fuel feed rate compared to the ST boundary layers. Results for local burning rate and skin friction are also presented.

2 citations

Journal ArticleDOI
TL;DR: In this article, two experiments were performed on board an aircraft flying repeated parabolic trajectories to generate free-fall conditions to investigate the way in which rate of heat release varies with gravity for a candle flame under an imposed low speed flow.
Abstract: Two experiments were performed on board an aircraft flying repeated parabolic trajectories to generate free-fall conditions. The first experiment investigates the way in which rate of heat release (RHR) varies with gravity for a candle flame under an imposed low-speed flow. In line with previous studies of flame spread rate it has been shown that rate of heat release drops significantly in microgravity. The heat loss due to radiation decreases by a larger proportion than that due to non-radiative processes indicating a lower flame temperature. The RHR from a microgravity flame is flow rate dependent, increasing for increased flow rate at air speeds under 0.03 ms -1 . For the geometry used in this experiment hypergravity caused only a small increase in RHR. The second experiment studied the ignitability of thermoplastics under an imposed radiant heat flux. The ignition test apparatus consists of a conical spiral heating element positioned horizontally above the sample, a continuous spark ignition source and a removable heat shield. Experiments were conducted in a sealed pressure chamber on samples of either PMMA (polymethylmethalcrylate) or POM (polyoxymethylmethylene), 1.5 mm thick, with a ceramic backing. There is some indication that gravity influences the time to ignition for some materials.

2 citations

Dissertation
01 Jan 2009

1 citations


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

  • ........................................................................... 53 Figure 2.10: Flame spread rates of thin paper sheets in normal gravity and microgravity (after Olson [13])....

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  • ...10: Flame spread rates of thin paper sheets in normal gravity and microgravity (after Olson [13])....

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Journal ArticleDOI
TL;DR: In this article, the authors discuss the differences between a fire on-board a spacecraft and one in a terrestrial facility that must be accounted for in any risk assessment, and discuss some of the methodology modifications, as well as several experimental results.
Abstract: Due to the closed environment of a spacecraft and the lack of egress, fire on-board may pose a significant risk. There are many differences between a fire on-board the spacecraft and one in a terrestrial facility that must be accounted for in any risk assessment. Both the risk assessment methodology and the phenomena-based models for terrestrial applications must be modified. This paper discusses some of the methodology modifications, as well as several experimental results. Multiple experiments have been conducted in terrestrial and microgravity environments in order to construct and validate models required for the assessment and management of risk on-board spacecraft. Past Shuttle experience with electrical overheating events supports the belief that these types of events may pose a serious threat to any human-crewed spacecraft andlor the crew. Experiments have been performed to simulate these events and quantify several damage modes. A preliminary set of experiments at the 2.2 second NASA Lewis Drop Tower has led to several conclusions. First, the production of damage causing elements depends on temperature. Second, the wire insulation involved can have a significant impact on the risk of the event. Third, the smoke particle size distribution is shifted towards larger sizes in microgravity, which may prove important in designing a smoke detector or selecting a sensitivity.

1 citations