University of Virginia School of Engineering & Applied Science

U.Va. Department of Mechanical & Aerospace Engineering

SPRING 2014

News

School of Engineering and Applied Science

taming high-temperature
surfaces in propulsion systems
Scramjets may be experimental, but they’re not science fiction. In May
2013, an unmanned aircraft developed for the U.S. Air Force — the
X-51A WaveRider — flew at more than five times the speed of sound
in a test off California. Just 111 years after the Wright brothers’ first
flight at Kitty Hawk, we’ve now entered the era of hypersonic speeds.
The Wrights’ first flight was 12 seconds long. WaveRider’s lasted
a little more than three minutes. If sustained hypersonic flight is to
become a reality, researchers must find ways to tame the tremendous
heat — exceeding the melting point of most metals — that hypersonic
flow generates.
That’s the challenge taken up by Professor Harsha Chelliah and
his interdisciplinary team of researchers. A traditional liquid coolant
system capable of controlling temperatures of this magnitude would
be prohibitively heavy. With a $2.2 million grant from the U.S. Air
Force Office of Scientific Research, the team is seeking to produce a
viable cooling system that uses a scramjet’s own fuel as a coolant.
“This approach has many well-known advantages in addition to
eliminating the excess weight of a traditional system,” Chelliah says.
The high temperatures crack the fuel, a process that absorbs much
more energy than heating water. In addition, cracking smaller fuel

molecules leads to rapid combustion, a key requirement for hypersonic
combustion. But cracking, or pyrolysis, has a significant downside. It
produces coke, which soon clogs the scramjet’s cooling channels.
Chelliah has teamed with Department of Chemical Engineering
Professors Bob Davis and Matt Neurock to explore and to synthesize
a robust catalytic coating to maximize pyrolysis while minimizing
coke formation. It would do this by refocusing energy on breaking
the carbon-carbon bonds in the fuel, rather than the carbon-hydrogen
bonds. He has also partnered with Department of Materials Science
and Engineering Professor Hayden Wadley, a specialist in directed
vapor deposition techniques, to develop methods to apply this
catalytic coating to the cooling channels. Colleagues from North
Carolina State University and the University of Maryland also are
participating.
“I think we have assembled a world-class team with the right
combination of expertise to attack this challenging problem,” Chelliah
says. “We are very hopeful about the outcome. The coatings developed
can have other applications — for example, to prevent coking in fuel
lines of gas-turbine engines.”

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