Assessment of Directions in Microgravity and Physical Sciences Research at NASA (2003) / Chapter Skim
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3. Combustion Research Program
3. Combustion Research Program
Pages 28-39
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From page 28... ...
34) INTRODUCTION The NASA microgravity combustion research program has always been driven by two objectives: a desire to understand the physical phenomena thought to be relevant for spacecraft fire safety and a wish to deepen our knowledge of fundamental combustion processes on Earth (Sacksteder, 1990; Ross, 1993; Urban and King, 1999; Faeth, 2001~.
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From page 29... ...
For example, the flame balls observed in space shuttle experiments became unstable when low-power steering rockets fired and changed acceleration levels from 10 - to 10-3 times Earth gravity (Ronney, 1998~. Finally, studies of turbulent combustion phenomena require that the experiment be repeated often enough to draw statistical inferences (Cheng et al., 1999~.
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From page 30... ...
and 6 flight experiment candidacy awards (Ross, 1993~. Moreover, 4 space experiments had been completed, and a total of 24 microgravity combustion and spacecraft fire safety projects were being supported.
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From page 31... ...
Whether this is a temporary setback or the beginning of the end of the microgravity combustion program remains to be seen. IMPACT OF NASA COMBUSTION RESEARCH The topics that have received extensive coverage in NASA's microgravity combustion research program include the following: · Flame spread on thin and thick solids, · Smoldering combustion, · Jet flame lengths and shapes, · Turbulent flames, · Soot and radiation, · Flame balls, and · Droplet combustion and chemical kinetics.
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From page 32... ...
The engineers responsible for fire safety on the space shuttle and the ISS at the Johnson Space Center recognize that the microgravity combustion research program has shown many counterintuitive fire behaviors. They also recognize that the margin of safety based on normal gravity material testing is significantly greater than that in microgravity.
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From page 33... ...
Other fundamental contributions have been made as a result of experimental studies involving the first-ever stabilization of flame balls, which are relatively stable spherical surfaces across which reactants become products (Ronney, 1998~. This phenomenon, which was only theoretically predicted before the microgravity experiments, is novel in that unlike propagating spherical flames, the flame ball surface remains stationary, separating reactants and products for as long as the experiment could be
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From page 34... ...
To remedy the paucity of knowledge about fire safety on the ISS, the combustion research necessary for completing the risk assessment project to satisfaction must receive the highest priority at all levels. A major fire in space resulting in any type of loss of mission will not be excused by the public and will lead to decades of setback for all kinds of space research and space applications.
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From page 35... ...
The recommended directions for fire safety research for the ISS and other space habitats are summarized below. Development of Computer Simulation of Fire Dynamics on Spacecraft The development of fire simulation computer codes based on computational fluid dynamics (CFD)
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From page 36... ...
Basic Combustion Research Soot and Radiation While combustion has been studied for hundreds of years, the limits of clean combustion technology are illustrated by large black billows of carbon particles leaving smokestacks and rigs pulling out of truck stops. The inhalation of such particles has been shown to significantly increase levels of morbidity in polluted areas.
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From page 37... ...
Radiation heat transfer has many implications for the fire safety problem discussed above, including the effects of a highly absorbing carbon dioxide fire suppressant deployed on the ISS, flame spread by preheating, and transition from smoldering to flaming. Turbulent Combustion Most industrial combustion devices and natural fires involve turbulent combustion.
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From page 38... ...
1998. Experimental study on flame spread over wire insulation in microgravity.
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