lundi 5 juin 2017

Fanning the Flame a Little Faster in Space

NASA - Saffire Mission patch.

June 5, 2017

NASA will start another large fire in space on June 4, when ground controllers ignite the third in a three-part series of spacecraft fire experiments (Saffire-III). Set inside a cargo spacecraft that is filled with trash and disposal items from the International Space Station and is orbiting Earth, the flame will spread across a 3.28-foot-long (1 meter) sample of cotton-fiberglass fabric.

Saffire-I, conducted in June 2016, burned an identical cotton-fiberglass sample inside an identical flow duct with fans controlling a low flow rate. Saffire-III will be ignited under the same conditions, except this time, the fans will run faster to produce a higher flow rate on the flame. Saffire-II burned nine different, smaller samples.

Image above: The Saffire compartment holds the fabric sample, fans, a power and avionics panel, and cameras. Image Credit: NASA.

Gary A. Ruff leads Saffire at NASA’s Glenn Research Center in Cleveland. He explains that increasing the flow rates for Saffire-III will improve the accuracy of computational models that NASA uses to predict flame spread in microgravity. “For Saffire-I, we measured flame spread rates for burns both in the same direction as the air flow and in the opposite direction of the air flow,” Ruff said. “We need to get additional data at another air flow speed using the same material to compare with the predictions of the computational model.”

Before Saffire, the largest fire experiments in space were conducted with much smaller (3.9 inches or 10 cm) samples, and showed that flames in space burn at a lower temperature, lower rate, and with less oxygen than in normal gravity. Even with this existing data, researchers encountered new surprises with Saffire.

“The biggest surprise is how slowly the flame are spreading across the samples,” said Ruff. Based on smaller samples in controlled burns on the space station, we expected flames on these larger samples to be up to three times faster than we’ve observed.”

Image above: A clean-room team stands behind Saffire before it is loaded into the Orbital ATK Cygnus cargo module, shown in the background. Image Credit: NASA.

A slow-moving flame might seem more favorable than a fast flame, but it also means that smoke production could be slower, resulting in a time delay for a smoke detector to detect a fire. Slow-moving fires also produce larger amounts of carbon monoxide, the leading contributor to suffocation in house fires.

Understanding fire detection and the build-up of toxic gases is an important part of fire protection. Saffire IV-VI, in development now, are being designed to continue to address large scale flammability, but also to investigate fire detection and post-fire monitoring and cleanup.

Saffire is managed at Glenn, and is funded by NASA’s Advanced Exploration Systems Division as part of its ongoing work to develop habitation systems for astronauts on future missions beyond Earth orbit.

Related links:


NASA’s Advanced Exploration Systems:

Images (mentioned), Text, Credits: NASA/Erin Mahoney.


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