Jellyfish Flames on the ISS
 
Sept. 10, 2014:  Fire is inanimate, yet anyone staring into a flame could
be excused for thinking otherwise: Fire dances and swirls.  It reproduces,
consumes matter, and produces waste. It adapts to its environment. It needs
oxygen to survive.
 
In short, fire is uncannily lifelike.
 
Nowhere is this more true than onboard a spaceship.
 
http://www.youtube.com/watch?v=bE13FREpFVo&feature=youtu.be
 
A new ScienceCast video looks at the lifelike behaviour and underlying
physics of jellyfish flames on the ISS. Play it
Unlike flames on Earth, which have a tear-drop shape caused by buoyant air
rising in a gravitational field, flames in space curl themselves into tiny
balls. Untethered by gravity, they flit around as if they have minds of
their own. More than one astronaut conducting experiments for researchers
on Earth below has been struck by the way flameballs roam their test
chambers in a lifelike search for oxygen and fuel.
 
Biologists confirm that fire is not alive.  Nevertheless, on August 21st,
astronaut Reid Wiseman on the ISS witnessed some of the best mimicry yet.
 
"It was a jellyfish of fire," he tweeted to Earth along with a
video. Wiseman was running an experiment called FLEX-2, short for Flame
Extinguishment Experiment 2.  The goal of the research is to learn how
fires burn in microgravity and, moreover, how to put them out.  It's a
basic safety issue: If fire ever breaks out onboard a spacecraft,
astronauts need to be able to control it.  Understanding the physics of
flameballs is crucial to zero-G firefighting.
 
"Combustion in microgravity is both strange and wonderful," says
Forman Williams, the PI of FLEX-2 from UC San Diego. "The 'jellyfish'
phenomenon Wiseman witnessed is a great example."
 
He points out some of the key elements of the video:
 
"Near the beginning we see two needles dispensing a droplet mixture of
heptane and iso-octane between two igniters.  The fuel is ignited . then
the lights go out so we can see what happens next."
 
http://tinyurl.com/mowyyqw
 
Click to visit the FLEX-2 home page.
 
"The flame forms a blue spherical shell 15 to 20 mm in diameter around
the fuel. Inside that spherical flame we see some bright yellow hot spots. 
Those are made of soot."
 
Heptane produces a lot of soot as it burns, he explains. Consisting mainly
of carbon with a sprinkling of hydrogen, soot burns hot, around 2000
degrees K, and glows brightly as a result.
 
"Several globules of burning soot can be seen inside the sphere,"
he continues. "At one point, a blob of soot punctures the flame-sphere
and exits. The soot that exits fades away as it burns out."
 
There is also an S-shaped object inside the sphere.  "That is another
soot structure," he says.
 
The 'jellyfish phase' is closely linked to the production of soot.
Combustion products from the spherical flame drift back down onto the fuel
droplet. Because sooty material deposited on the droplet is not perfectly
homogeneous, "we can get a disruptive burning event," says
Forman. In other words, soot on the surface of the fuel droplet catches
fire, resulting in a lopsided explosion.
 
Remarkably, none of this is new to Forman, who has been researching
combustion physics since the beginning of the Space Age.  "We first
saw these disruptive burning events in labs and microgravity drop towers
more than 40 years ago," he says.  "The space station is great
because the orbiting lab allows us to study them in great detail."
 
"Tom Avedisian at Cornell is leading this particular study,"
Forman says. "We're learning about droplet burning rates, the soot
production process, and how soot agglomerates inside the flame."
 
At the end of Wiseman's video, the soot ignites in a final explosion. 
That's how the fire put itself out.
 
"It was a warp-drive finish," says Wiseman.
 
For more amazing tweets from the ISS, follow Wiseman {at}astro_reid.
 
Credits:
Author: Dr. Tony Phillips |  Production editor: Dr. Tony Phillips | Credit:
Science{at}NASA
 
More information:
 
Flame Extinguishment Experiment -- FLEX home page
 
More information about FLEX -- from the Glenn Research Center
 
 
Regards,
 
Roger

--- D'Bridge 3.99