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Flying the Efficient Skies

Fuel cells could cut jets’ energy consumption, emissions.

Passenger jets on the tarmac are noisy and smelly, kicking out 20 percent of all airport emissions. That’s because jets burn fuel in auxiliary power units to generate the electricity that keeps air conditioners and other equipment humming. To take just one example, the auxiliary power unit in a Boeing 777 produces as much smog-causing nitrogen oxide as 155 Chevrolet Impalas.

But a new class of fuel cells, which use solid-oxide technology rather than the proton-exchange-membrane technology favored for cars and small electronics, may eventually do the same job more cleanly-plus allow greater efficiencies in-flight. Solid-oxide cells can use jet fuel as an energy source, and while they’re still at the laboratory prototype stage, recent advances have led Chicago-based Boeing and NASA to consider them serious contenders for planes. If all goes well, Boeing will begin developing a tail-mounted fuel cell prototype next year that could be commercialized in about 10 years. “It’s going to provide about a two-times improvement in efficiency, and will totally eliminate ground-based emissions coming out of the auxiliary power unit,” says Anita Liang, a chemical engineer at NASA’s Glenn Research Center in Cleveland, which is helping to develop the devices.

The aircraft application for solid-oxide fuel cells is especially compelling because less fuel lightens the plane, meaning less power is needed to take off and fly. The cells would eventually generate power in-flight, too, replacing the pneumatic systems that suck energy from a jet’s engines to power components like cabin-pressurization and anti-icing systems. What’s more, aircraft can make use of the fuel cells’ chief by-products: water and heat. “There is a potential for getting some synergies out of this,” says Dave Daggett, technology leader for energy and emissions at Boeing’s facility in Seattle. But despite recent advances, to make it into aircraft, completed fuel cell generators will need to become lighter, cheaper, and more powerful-by about 450 kilowatts, enough to power about 20 houses. But Liang says she expects research being done by NASA-building on work by the U.S. Department of Energy and companies like Delphi, General Electric, and Siemens Westinghouse Power-will deliver the improvements in several years. Volume production and modular designs should make the fuel cells affordable. Much further out, they could power electric jet engines. But for now, it’s enough to make airports quieter and cleaner.

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