In research funded by the National Aeronautics and Space Administration NASA , Yale mechanical engineers Marshall B. Long and Mitchell D. Smooke are probing the mysteries of a methane flame in an environment that simulates the microgravity conditions of space.
Controlling fire in the confines of a space vehicle is a high-priority safety issue for NASA, but the Yale studies conducted aboard a specially equipped airplane in late February also could reveal basic mechanisms of fire leading to more efficient combustion engines, better fuels and less pollution.
“While combustion is one of the oldest and most essential technologies ever mastered by humans, it is extremely complex and remains nearly as mysterious today as it was to our ancestors sitting around hearth fires in caves,” said Long, who dissects flames atom by atom with lasers in his Yale laboratory.
Aboard a modified KC-135 transport dubbed the “vomit comet” because of its roller-coaster ride, Long and graduate student Kevin Walsh recently observed a flame in a 250-pound sealed chamber with both video and digital cameras. During four flights over a period of three days, the pair experienced near-weightlessness for about 20 seconds each time the KC-135 reached the apex of its climb as it traced parabolic arches across the sky. The aircraft repeated the steep climb-dive maneuver a total of 205 times with the Yale engineers aboard.
As expected, flames not distorted by gravity have a subtly different appearance. “Because hot air doesn’t rise in a weightless environment, the shape of the flame changes from that observed on earth. One major advantage of the NASA experiments is that the process of combustion is easier to watch when you don’t have to worry about buoyancy,” said Long, who is sorting through data from the flights to find out how dozens of chemical compounds formed, interacted and decomposed as the flame turned methane into carbon dioxide and water.
The engineers will be comparing the data with their computer predictions. “A great deal of our work is computational, and it’s relatively easy to turn gravity off in the computer model to predict how the flame will react,” Long said, adding that about half a dozen other research teams were aboard the NASA airplane during his flights.
Observations aboard the NASA flight will enable Smooke to refine his computer models with the goal of being able to predict the efficiency of a new design for a combustion engine or a trash incinerator. Reducing the amount of pollutants created when fuels burn would reduce smog and ameliorate greenhouse warming caused by carbon dioxide and other gases trapped in the upper atmosphere.
In Yale’s Center for Laser Diagnostics, Long will continue bouncing laser beams off the chemical compounds produced during combustion and recording patterns of scattered light. When a compound reacts with the laser beam, it fluoresces, giving off a characteristic color signal that reveals its identity. Long specializes in shining broad sheets of laser light through flames to capture their three-dimensional structure and turbulence.
While the Yale engineers are still digesting their NASA experience, Long says they tolerated the dives with little discomfort and look forward to a repeat excursion over Lake Erie near the NASA Lewis Research Center in Cleveland. In fact, he likens the experience to the thrill of hang-gliding.
