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Microgravity combustion science: A program overview

30 Aug 2013-
TL;DR: A recent survey of results, the available set of reduced gravity facilities, and plans for experimental capabilities in the Space Station era can be found in this paper, where the authors introduce the promise of microgravity combustion research by way of a brief survey.
Abstract: The promise of microgravity combustion research is introduced by way of a brief survey of results, the available set of reduced gravity facilities, and plans for experimental capabilities in the Space Station era. The study of fundamental combustion processes in a microgravity environment is a relatively new scientific endeavor. A few simple, precursor experiments were conducted in the early 1970's. Today the advent of the U.S. space shuttle and the anticipation of the Space Station Freedom provide for scientists and engineers a special opportunity, in the form of long duration microgravity laboratories, and need, in the form of spacecraft fire safety and a variety of terrestrial applications, to pursue fresh insight into the basic physics of combustion. The microgravity environment enables a new range of experiments to be performed since buoyancy-induced flows are nearly eliminated, normally obscured forces and flows may be isolated, gravitational settling or sedimentation is nearly eliminated, and larger time or length scales in experiments become permissible. The range of experiments completed to date was not broad, but is growing. Unexpected phenomena have been observed often in microgravity combustion experiments, raising questions about the degree of accuracy and completion of our classical understanding and our ability to estimate spacecraft fire hazards. Because of the field's relative immaturity, instrumentation has been restricted primarily to high-speed photography. To better explain these findings, more sophisticated diagnostic instrumentation, similar to that evolving in terrestrial laboratories, is being developed for use on Space Station Freedom and, along the way, in existing microgravity facilities.
References
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Journal ArticleDOI
TL;DR: In this article, the role of chemical kinetics in the behavior of near-limit flames at rnicrogravity (μg) was investigated experimentally by comparison of the properties of these flames in mixtures having varying chemistry but similar diffusive transport properties.
Abstract: The role of chemical kinetics in the behavior of near-limit flames at rnicrogravity (μg) was investigated experimentally by comparison of the properties of these flames in mixtures having varying chemistry but similar diffusive transport properties. Conversely, the importance of unequal rates of diffusion of thermal energy and mass was evaluated by comparison of flames in mixtures having similar chemistry but varying Lewis numbers, It was found that the characteristics of near-limit flames at μg were affected much more by Lewis number effects than chemistry. It is concluded that there are at least three regimes of near-limit behavior at μg, depending upon the Lewis number (Le): (1) cellular flames, which are highly resistant to extinguishment, for mixtures with Le≪l, (2) self-extinguishing flames and well-defined flammability limits for mixtures with Le≃ 1, and (3) ignition energy limited flame propagation for Le ≪ 1, Gradual rather than abrupt transitions between regimes were observed.

148 citations

Journal ArticleDOI
TL;DR: In this paper, fuel-lean flammability limits and burning velocities in a closed vessel were measured for methane-air mixtures burning at earth gravity (oneg) and zero gravity (zero-g) at initial pressures of 50-1500 Torr.

124 citations

Journal ArticleDOI
TL;DR: In this article, the authors measured minimum ignition energies and flame radii as a function of time for near-limit, limit, and sub-limit fuel-lean methane air mixtures burning at one-g and zero-g.

70 citations

Journal ArticleDOI
TL;DR: In this article, the results of experiments on the burning of individual 1-2 mm decane droplets in air at room temperature and atmospheric pressure were presented, and the NASA Lewis 2.2 s drop tower was used as well as a newly designed droplet-combustion apparatus that promotes nearly spherically symmetrical combustion.

70 citations

Journal ArticleDOI
TL;DR: Theoretical and experimental research on the effects of buoyancy on gas-jet diffusion flames is described in this article, where the results show that uncertainties in the current understanding of flame structure exist and further research is required before reliable predictions of ignition, stabilization, and propagation of flames under microgravity conditions can be made.

47 citations