High hopes for micro-engine

The smallest engine of its kind anywhere in the world, created at the University of California, Berkeley, could someday replace batteries as an efficient power source for mobile electronic devices.

The ‘mini engine’ is believed to be the first engine of its size to deliver power on a continuous basis. Fashioned from steel, the engine is also a prototype for a UC Berkeley endeavour to create an even smaller engine chemically etched from silicon.

The engine can produce up to 2.5 watts of electricity but Fernandez-Pello, a mechanical engineering professor at UC Berkeley, and his team are ramping the engine up to produce 30 watts, which would provide enough power for electronic devices.

The mini engine is designed to run on liquid hydrocarbon fuels and one fluid ounce of fuel will reportedly keep the motor running for two hours.

The UC Berkeley team are confident that once it is optimised, the tiny engine will be able to run 10 times longer than a conventional lithium ion battery, meaning that refuelling will be required 10 times less often than changing a battery.

Unlike most automobile engines where combustion occurs in a piston/cylinder assembly, the rotary engine has a flat, oval-shaped chamber and triangular rotor.

As the rotor rotates within the chamber, the edges of the rotor act to partition areas of the chamber into smaller volumes where combustion can occur. Combustion acts to further rotate the rotor around the chamber, transferring force to the shaft that is attached to the rotor.

Also like a car engine, the mini engine produces exhaust that contains carbon dioxide and water. While this is not enough to generate substantial pollution, the researchers are now developing a miniature catalytic converter.

The Berkeley team hopes that some day the mini engine can be used to power electronic devices like computers or robots.

The US military is said to be interested in the device as a way to assist soldiers in the field. For example, the engine could power an apparatus attached at the knees to provide an extra boost to soldiers wearing heavy combat equipment. Another military application is a power source for field sensors to track helicopters.

To Fernandez-Pello and his colleagues, the mini engine is an important first step towards designing a much smaller engine made using microelectromechanical (MEMs) technology. The mini engine design is said to be ideal for miniaturising because of its simplicity, and the components are relatively easy to make using silicon etching technology.