NASA/July 17, 1997 MSL-1 Science Wrapup - Combustion
Flame On - and on, and on Combustion Science on MSL-1
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stole much of the show with "fires in space" getting most of the
news coverage during the mission. All the combustion experiments achieved
more than their planned runs as they burned virtually every drop or whiff
of fuel available to them. Each experiment took different, complementary
approaches to studying the basics of fire.
Structures of Flameballs at Low Lewis numbers (SOFBALL; in the Combustion Module (CM-1) made the biggest news with the tiniest fires, flame balls about the size of a pinhead and glowing with 1/50th the energy of a birthday candle. To everyone's joy, the flameballs, generated by electric sparks, burned - motionless in their chamber - for 500 seconds when the experiment was designed to blow them out. These are believed to be the weakest fires ever stoked, and should lead to clues on how to design engines that burn with leaner fuel-air mixtures and thus produce less pollution. SOFBALL had 15 tests planned; 26 were completed for a total of three hours of burn time that will be studied for years, says alternate payload specialist Paul Ronney, who is also the principal investigator. SOFBALL results will affect fire safety on Earth as well as aboard spacecraft.
The Laminar Soot Processes (LSP) experiment, working like a Bunsen burner in space, produced flames twice as large as those formed on Earth and which appeared as steady as freeze-frames on TV. The laminar (smooth flow) flames formed soot, a pollutant, sooner than expected. Scientists also saw flames extinguished by energy radiating from soot, a new phenomenon that will alter studies for years to come. The results should also resolve a controversial hypotheses that will simplify how flames are modeled. Of 14 planned tests, 19 were conducted.
Droplet Combustion Experiments (DCE; above), with its own facility, released droplets of hydrocarbon fuel (less than 1/6 ounce for the entire flight) into a chamber then ignited it with heated wires. This provided "one dimensional" models of how the flame moves inward and exhaust products move outward. Each droplet is really three-dimensional, but droplets pull themselves into spheres, one dimension can describe the whole droplet, making modeling easier. DCE achieved 56 tests, 21 more than the planned 35.
Fiber Supported Droplet Combustion (FSDC-2; in the glovebox) ignited larger drops held in place on a fireproof thread (the drops were large enough that the thread is a minor factor). The payload crew became so adept at these experiments that they performed 73 tests beyond the 52 planned, including the first-ever experiments with two droplets next to each other. The drops were forced apart by their exhaust products, then pulled together as they depleted the fuel vapor between themselves. This was named the Thomas Twin Effect in honor of mission specialist Dan Thomas who performed the experiment.