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.
