Jet Engine On A Chip

By Roland Piquepaille

Today, our handheld devices are powered by batteries, which are heavy and inconvenient. Fuel cells are just arriving on the market as a replacement. But there is a new contender: micro gas turbine engines under development at the MIT. Engineers there shrunk jet engines to the size of a coat button. And their blades which span an area smaller than a dime can spin a million times per minute and produce enough electricity to power your PDA or your cell phone. While there are still a few hurdles to overcome, these micro turbine engines should be operational in two or three years, with commercial products available four years from now. These micro jet engines also have the potential to free soldiers or travelers to carry heavy batteries. The engineers even think their engines on a chip could be used in poor countries to bring electricity there. Read more...

Here is the flashy introduction of the Technology Review article.

Alan Epstein is quick to tell you he's a "jet engine guy" - just in case you haven't guessed as much from the turbine engine parts strewn around his office or the museum on his lab's ground floor, which includes a rare example of a 1944 German engine that helped kick off the jet age. For the director of MIT's Gas Turbine Laboratory, who stands a slightly stooped five foot six, the fascination has to do with raw power. "The engines on a Boeing 747 shove air through at Mach 1 with 120,000 pounds of force," says Epstein. "The engines on three 747s put out as much power as a nuclear power plant."

Gas turbines powered much of 20th-century technology, from commercial and military aircraft to the large gas-fired plants that helped supply U.S. electricity. But these days it isn't the hulking machines in the lab's museum that capture Epstein's enthusiasm. Instead it's a jet engine shrunk to about the size of a coat button that sits on the corner of his desk. It's a Lilliputian version of the multiton jet engines that changed air travel, and, he believes, it could be key to powering 21st-century technology.

On this photograph, Epstein holds a nonfunctional prototype of a gas turbine engine. (Credit: Kathleen Dooher, for Technology Review).

What can bring us these micro engines?

In the foreseeable future, Epstein expects, his tiny turbines will serve as a battery replacement, first for soldiers and then for consumers. But he has an even more ambitious vision: that small clusters of the engines could serve as home generating plants, freeing consumers from the power grid, with its occasional black- and brownouts. The technology could be especially useful in poor countries and remote areas that lack extensive and reliable grids for distributing electricity.

Before it happens, some problems need to be solved.

Earlier this year, Epstein and his coworkers finished making engines in which each of the individual parts functions: the combustion chamber burns fuel, and the turbine blades spin. The resulting device is sealed all around, with holes on the top and bottom for air intake, fuel intake and exhaust. One shortcoming: it doesn't run continuously. The obstacle, says Epstein, is imperfections that imbalance the blades and cause them to wobble. "We think we know what to do to correct it," he says. "The problem is that it takes three months to get new parts when you make an adjustment, so we're just waiting for the new parts." Epstein predicts the chip will be functioning within months -- a little ahead of schedule. Spearing estimates a version capable of putting out enough power to run devices would take two to three years more, with another year or two beyond that to produce a marketable version.

By that time, some competitive products, such as fuel cells, will be on the market, but Epstein is optimistic.

"Our competition is fuel cells, absolutely," says Epstein. But he insists that turbine chips can make up any lost ground. "Up to now a few million dollars has been invested in microturbines, compared to the billions invested in fuel cells," he points out. Epstein's faith is fueled by the inherent advantages he sees in turbines. Even micro fuel cells are larger, and they're much more finicky about fuel than a turbine engine. But in the end, it all comes down to power. Most micro fuel cells struggle to put out a watt or two, while Epstein's prototypes could provide 15 to 20 watts, more than enough to keep a power-hungry handheld device going. Laptop computers can require 50 watts, but a few turbines working together could easily pump that much power out. Likewise, Epstein envisions that a cluster of tiny engines, each capable of producing up to a hundred watts, could supply a home with an efficient and reliable source of electricity.

Will this technology be successful? And will batteries and rechargers become things from the past? We'll know around 2008.

Source: David H. Freedman, for Technology Review, November 2004