Building jet engines out of superconducting materials may offer a way to lower aircraft emissions in the long run. Researchers have determined that superconducting turbines would be lightweight and powerful enough to run on electricity from clean-burning hydrogen fuel cells or generators that consume relatively small amounts of fossil fuel.
Although such technology would be costly to develop, "it will become a viable option, I'm pretty confident," says electromechanical engineer Philippe Masson of Florida A&M University and Florida State University, both in Tallahassee.
Aircraft account for a growing proportion of global greenhouse emissions, including about 3 percent of the U.S. total as of 2003. Jet engines ignite a mixture of air and jet fuel, which spins a turbine that creates thrust. More efficient gas turbines might burn 10 to 15 percent less fuel, Masson says, but not enough to make them greenhouse gas–free.
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NASA and the Department of Defense funded Masson and colleagues to design an electric jet engine, which would use opposing magnets to spin a turbine. Engines based on conventional magnets would have to be several times heavier than current gas turbines, as well as less fuel efficient, to achieve the same power, Masson says.
A superconducting magnet, however, would be much more efficient and powerful for its size. When chilled to 77 kelvins (–321 degrees Fahrenheit) or colder, so-called high-temperature superconductors such as the ceramic YBCO (yttrium barium copper oxide) begin to carry electricity without resistance, which produces a strong magnetic field without wasting energy.
Liquid hydrogen (20 K, or –424 degrees F) could chill the superconductor as well as power a hydrogen fuel cell to send electricity through it, he and co-workers report in the journal Superconductor Science and Technology. Masson says that based on their designs, a YBCO turbine would generate as much power as a single-engine Cessna aircraft for roughly half of the mass. A commercial aircraft might require a fossil-fueled electrical generator to magnetize the superconductor, he says.
Creating a superconducting jet engine would require improvements in fuel cells and other electronics, and the price tag alone—$1 million to $2 million for a prototype—may keep superconducting turbines grounded for some time, Masson says. "The market is so small nobody wants to invest."
