Try setting fire to biofuel on a commercial flight, and you'd probably get taken in by Homeland Security. But try the same thing on a jet simulating the weightlessness of space and it's called science.
"I'm very shocked actually, that they let us do this," said Sam Avery, a UC San Diego mechanical and aerospace engineering major who just got back from NASA's Johnson Space Center in Houston. "Every time I've talked to anyone, they've said, 'You're actually blowing something up on a plane. What are you doing?'"
Avery led a team of UCSD undergrads who wanted to see how biofuels burn when gravity is taken out of the equation. Their experiment builds on the research of UCSD professor Forman Williams.
They got to pull off their firebug study thanks to NASA's Microgravity University program, which chooses seven undergrad teams each year to conduct research on a microgravity flight.
Avery and two other students boarded a jet that soars and dives through a series of steep arcs, kind of like a microgravity roller coaster. Initially, the weightlessness feels exactly like the peak of an amusement park ride, said Avery.
"The moment you're gone from that peak, it's very different," he said. "Wherever you pushed off from, you will keep going in that direction no matter what you do. You can spin yourself, but you'll just keep floating until you hit something."
When the jet reached the lowest point in its descent, passengers would go through a period of double gravity.
"You're just pressed down and you can feel your face droop," Avery said. "I did a sit-up, and it was really hard."
Just like roller coasters, these flights can give some passengers a mean bout of motion sickness ("Vomit Comet" is the jet's unofficial nickname). Daneesha Kenyon, one of the three UCSD flyers, succumbed to nausea. "Our friend was back there," Avery recalled, "just vomiting into a bag."
But illness could not prevent the intrepid UCSD team from successfully carrying out its biofuel burn.
Once they started floating, they ignited a droplet of butanol inside a specially designed box and filmed the results.
They had to build a triple-contained chamber in order to convince NASA that their experiment was safe. It works by using a syringe to drop a small amount of fuel at the intersection of two thin fibers. Then, a robotic arm drops to spark the fuel. All this had to happen in less than 20 seconds, the duration of each weightless period aboard the jet.
"This was completely programmed and built by undergraduate students," said team member Nico Montoya, showing off the machine back on solid ground.
Avery said experiencing microgravity was awesome, but he's also glad he and his teammates got to do serious work up there.
"Being able to see the effects of microgravity on the flame we were combusting," he said, "that was definitely a success."
Just like they predicted, the flame changed shape without gravity to weigh it down, looking more like a sphere than a teardrop. It also expanded much more than it would in normal conditions.
The team's findings could help improve fuel efficiency here on Earth, as well as fire extinguisher designs and other applications in weightless environments such as the International Space Station.
