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Fire’s Weird Behavior in Space

Fenella SaundersApr 13, 2016

In the microgravity environment of outer space, flames burn very differently than they do on Earth. Understanding those differences not only helps researchers grasp the properties of combustion and burning, but is also crucial for outer-space missions. Testing how materials ignite and smolder in microgravity is essential for choosing everything from windowpanes to wire insulation for the Space Station and potentially longer-term space missions to Mars or other destinations. A recent project on the Space Station, called BASS II (for Burning and Suppression of Solids), used the assistance of astronauts on the station to conduct controlled, contained experiments on a variety of flammable materials. Sandra L. Olson, the principal investigator of the mission at NASA Glenn Research Center in Cleveland, provided imagery of some of the results. Olson also co-authored a recent feature in American Scientist on a particular type of insidious slow-growing flame in microgravity called flamelets. She and her coauthors also participated in an American Scientist hangout on the research.

Videos and images courtesy of Sandra L. Olson and NASA.

(Use the button on the right to enter 'full screen mode' to view the images and captions at the same time.)

A rod made from clear acrylic burns like a candle in a low-oxygen environment; it is shown here from its ignition until it goes out, which is known as blowoff. The small flame after ignition grows to a long flame. The airflow is then increased and the tip of the flame blows downstream. The astronaut controlling the experiment quickly turns the airflow back down, which allows the flame to stabilize and form what is called a stagnation flame at the tip of the rod. The astronaut then turns the flow back up, and once again the flame is blown downstream, but this time just a bit farther. And when the astronaut turns the flow down again, the flame is not able to reestablish a stagnation flame. There seems to be a critical length, if the flame is blown past downstream, it is unable to recover.

This acrylic rod burns from ignition until what’s called quenching extinction. In this case, the flame isn’t blown out, but is unable to persist because there’s not enough oxygen. After ignition, the flame grows and produces a lot of soot; it also sends out jets of flame caused by the rod releasing pockets of gas that are created as the solid fuel is heated and aerosolized. The astronaut controlling the experiment decreases the airflow incrementally; the flame shrinks in length and becomes less sooty shortly after each flow change. As the airflow drops, the flame turns all blue, and it dimples as the regressing molten tip of the rod distorts with every bubble rupture and associated vapor jet. Just before it quenches, the flame becomes a small blue cap at the end of the rod.

This post is published in The Long View

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