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A Fiery Success

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A Fiery Success

Science on Flight Day 8 of MSL-1

return to MSL-1 science home pageJuly 8, 1997 11:00 a.m. CDT

LSP burn from April 1997Anyone who has fine-tuned a kerosene lamp in an effort to blacken the inside of the glass globe has mimicked part of Spacelab's research that will rewrite textbooks and set new directions for combustion research over the next 20 years.

It may also help people in cities breath a little easier if the lessons can be applied to cleaning up bus, truck and jetliner exhaust.

At right, above: A flame rises across the Combustion Module during one of the two test runs completed by LSP during the MSL-1 flight in April.

Soot production illuminated by laser light"From our standpoint, this mission was a real success," said Dr. Gerard Faeth of the University of Michigan at Ann Arbor. Faeth is principal investigator for the Laminar Soot Processes (LSP) experiments which have been popularized in news stories. What he was looking for is a better understanding of how soot is formed, and how to improve combustion so it is burned instead of becoming smoke.

At right: Soot produced in a flame is revealed in a picture backlit by a laser.

"We have discovered a new regime of soot production is dominated by radiation during these space experiments," Faeth said.

Faeth's experiments were carried out in the Combustion Module (CM-1) aboard MSL-1. Of 14 experiments planned, Faeth goes home with a total of 17: two from the shortened MSL-1 flight in April, the 14 planned for this flight, and an extra one that the crew ran by working through their break.

"It's like batting 1200," he said.

At the heart of the LSP experiments is a small gas burner similar to the Bunsen burner that many students use in chemistry classes. The principal difference is that Faeth's LSP burner does not have an air inlet. The ethylene and propane fuels burn as they hit the air in the CM-1 chamber.

What that produced is unlike any flame that you can make on Earth.

"Obviously, hot air rises," Faeth said, because of gravity's effects (heavier cold air descends and pushes the lighter hot air up). "With Earth's gravity, the flame motion makes everything much more complicated."

In space, without the flame products being pushed, the process almost becomes leisurely: a soot particle can linger in the flame for up to a second compared to 1/100 second in a campfire.

And the flames were wider, looking more like a ball than the classic candle flame.

Â flames on Earth and in Space - cartoonMajor features of terrestrial (left) and space (right) flames are shown in this diagram drawn before experience with LSP showed that the flames actually grow much larger and steadier than predicted. Note that the nonbuoyant (right) flame is shown smaller than it actually is, relative to the buoyant flame, to keep the two in the same picture.

One thing the two have in common is the bright yellow glow produced by soot. Faeth explained that the glow is part of what makes certain fires inefficient. Carbon atoms, as soot particles, are giving up energy as infrared (radiant heat) and visible light. The atoms clump together to form soot particles, as small as 50 nm across (about 1/10 the length of a wave of visible light), then link to form chains up to 1,000 nm (1/2,500 inch) long.

For someone trying to illuminate a room with kerosene lamp, soot production is essential. That's how the light is made. For someone burning fuel in a diesel engine on a bus or truck, or jet fuel in a turbine, it's lost energy and an air pollutant.

Understanding the detail of soot production has eluded scientists because of the turbulence and fast flame flow caused by gravity. Faeth's experiments with LSP will help them see and understand those details because the flames are slowed and increased in size so that measurements as possible.

Although his experiments have just finished and analysis has barely begun, Faeth expects that the results will influence combustion research for up to 20 years.

"What people in my field will come to realize is what a tremendous asset that experimenting in space can be," he said.

LSP set-upFaeth said that the support of the MSL- payload crew is a major factor in the success of the experiments. At left, Halsell and Thomas set up the LSP module. At right, Janice Voss hold up a sketch of her soot observations.drawing of a flame in space by Voss

The unexpected could be seen in tests where the flames were twice as long as those that can be formed on Earth, and half again as long as those that can be produced in drop towers and aircraft. Further, the flames were so steady that one astronaut said it looked more like a still picture. Faeth said that the difference is that the longer, smoother ride possible aboard the Space Shuttle allows the flames to grow and stabilize where they can be studied more easily.

"That's going to change the Belgium on a lot of things," he said.

One area where he anticipates new findings is in internal combustion engines where he expects LSP results to help explain the correlation between high emissions of hydrocarbons and of soot. In turn, that can let engine manufacturers build cleaner engines to conform with more restrictive regulations.

"If the engine builders don't learn how to make an engine that does not emit soot, they're out of business," he said.

Faeth said that soot causes an estimated 15,000 to 60,000 deaths due to lung disease, "more than any other pollutant. That adds a lot of importance to what we're doing." In addition, inefficient engine combustion also means larger output of hydrocarbons, some of which cause cancer, and of carbon monoxide, a deadly gas.

Another danger that LSP may address is fires in space where different combustion characteristics could fool flame and smoke detectors, and soot and other combustion products could build up more rapidly to dangerous levels.

For background information, check out our Combustion Science Overview.




Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack