The Candle Flames in Microgravity (CFM) experiment was designed
to study how long candle flames can be sustained in microgravity,
how the flames behave prior to extinction, and the how two closely
spaced candle flames behave. The scientists hope that one day
the results will help resolve age-old questions regarding the
effects of gravity on certain types of flames (low momentum diffusion
flames, or candle flames) and their ability to burn without the
presence of gravity. This information will provide a better understanding
of fires on spacecraft and could lead to advances in fire detection
and extinction techniques.
Microgravity provides a nonconvecting, purely diffusive environment
for this experiment. Under Earth's gravity, buoyant convection
develops when hot, less-dense combustion products rise. The resulting
flow draws oxygen into the flame and carries the combustion products
(carbon dioxide and water vapor) away from the flame. This flow
is the dominant transport mechanism in the flame. In microgravity,
however, the process is not the same; there is no buoyant convection.
Instead, the transport of combustion products and oxygen occurs
by the much slower process of molecular diffusion that results
when there is a concentration gradient in the candle flame zone.
When there is a high concentration of combustion products and
a low concentration of oxygen close to the flame, and there is
a low concentration of combustion products and a high concentration
of oxygen further away from the flame, the combustion products
migrate away from the flame and oxygen migrates towards the flame.
The diffusive transport rates in microgravity are much lower than
the transport rates due to natural convection in normal gravity.
The CFM experiment was developed at the NASA Lewis Research Center
to be used with the Microgravity Glovebox Facility in the Priroda
Module of the Russian Space Station Mir. The experiment was launched
aboard a Russian Proton rocket on April 23, 1996.
Astronaut Shannon Lucid began CFM operations aboard Mir on July
1. Dr. Lucid said that the data collected point to long-term flame
survivability (which was anticipated by the investigators, but
commonly postulated in the literature to be impossible) and show
evidence of spontaneous and prolonged flame oscillations near
extinction. Testing on Mir, which included 79 candle burns, was
completed on July 26. The experiment hardware performed successfully,
and data were returned to the investigators in October 1996, including
photographs, video, temperature data, oxygen concentration data,
gas samples, and radiometric data.
This project was designed, built, and tested by a team of civil
servants from NASA Lewis, the contractors from Aerospace Design
& Fabrication, Inc. (ADF), and university personnel. The principal
investigator is Daniel Dietrich of Lewis and the co-investigators
are Howard Ross of Lewis and Professor James T'ien of Case Western
Reserve University. The project was managed by David Frate of
Lewis.
For more information, visit the CFM homepage.
Previous articleLast updated April 30, 1997
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