JUST ADD SUPERCONDUCTIVITY: Researchers propose that conventional jet engines such as this one could be fitted with superconducting turbines that would produce low greenhouse emissions. Image: &copy; ISTOCKPHOTO/CHRISTOPH ERMEL
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.
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."