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Gas Turbine Engine Fits on a Chip
Tracy Staedter, Discovery News
Oct. 10, 2006 — A tiny gas-turbine engine that fits on a quarter could replace batteries currently used to power laptops, cell phones, radios, and perhaps even home generators.
The micro-engine, being developed by a team led by Alan Epstein, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology in Cambridge, could provide five times as much power as a laptop battery for the same cost.
"My laptop battery now runs my computer for about three hours before recharging. A micro-engine power system — engine plus fuel — with the same weight as the battery should run the laptop for 15 to 20 hours before refueling," said Epstein.
The engine works on the same principle as a jet engine: a compressor sucks in air from the outside and compresses the air. Fuel injectors add fuel to the compressed air and the mixture gets ignited. (Epstein’s engine will run on a variety of fuel, including kerosene, propane, ethanol, methanol or hydrogen.)
The hot gas produced expands rapidly to turn a turbine, which turns a coil inside a magnet to create electricity.
A jet engine has thousands of parts assembled into the few components that comprise the compressor, combustions chamber and turbine.
Epstein’s micro-engine only has two parts: a movable rotor and a stationary structure that together function as the compressor and combustor.
And this jet engine would fit into a matchbox. The compression chamber is about the size of a pencil eraser, the fuel injectors are pen-point holes and the turbine is about the size of a dime.
Such teeny components require a much different manufacturing process than large-scale jet engine parts.
Epstein and his team, like other researchers in this field, turned to the field of micro-electromechanical systems, or MEMS, which is used to fabricate miniature devices ranging from computer chips to biological sensors to chemical processors.
They etch out the parts from wafers of silicon. The etching requires incredible accuracy with little or no room for error.
"They are bringing the field of MEMs to levels that a few years ago it would have seemed impossible," said Carlos Fernandez-Pello, a professor of mechanical engineering at the University of California, Berkeley.
Pello’s team is working on a similar micro system that works like a car engine.
A bigger challenge for Epstein may be getting the individual components to work as a single engine, said Pello.
At that tiny scale, the heat produced can spread across the whole device, causing parts to expand and not work well.
But if they can find a way to insulate the combustor from the other components, a final working product would be about the size of a Bic lighter—with the engine up top and the fuel below.
"The size of that Bic lighter is the size of two AA batteries. But the time it would give you power, it’s potentially 100 times more…maybe 50 or 60 hours," said Pello.
Such a micro-engine would be as safe as a pocket lighter, too.
And if you’re concerned about emissions, just remember that most electrical power plants burn coal or natural gas to produce the electricity available in power outlets.
Epstein says that his micro-engine will produce 1/100th the emissions that a rechargeable laptop battery produces indirectly during the recharging stage.
So far, the micro-engineered components have been micromachined, tested individually and assembled into the quarter-sized test engines.
Now the team has to add fuel and demonstrate a working engine — something Epstein thinks can be accomplished within the next 12 months.
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10-10-2006 07:14 PM
