Tiny turbine

MIT researchers are putting a tiny gas-turbine engine inside a silicon chip about the size of a 10 pence piece which could run 10 times longer than a battery of the same weight.

The microengine is made of six silicon wafers, piled up and bonded together. Each wafer is a single crystal with its atoms perfectly aligned, so it is extremely strong. To achieve the necessary components, the wafers are individually prepared using an advanced etching process to eat away selected material. When the wafers are piled up, the surfaces and the spaces in between produce the needed features and functions.

Making microengines one at a time would be prohibitively expensive, so the researchers use computer-chip techniques to make 60 to 100 components on a large wafer at a time.

The MIT team has now used this process to make all the components needed for their engine, and each part works. Inside a tiny combustion chamber, fuel and air quickly mix and burn at the melting point of steel. Turbine blades, made of low-defect, high-strength microfabricated materials, spin at 20,000 revolutions per second, which is 100 times faster than those in jet engines. A mini-generator produces 10 watts of power. A compressor raises the pressure of air in preparation for combustion. The researchers believe cooling will be manageable by sending the compression air around the outside of the combustor.

The next goal is to get the components all working together. Ultimately, hot gases from the combustion chamber need to turn the turbine blades, which must then power the generator. The researchers aim to have a complete engine working by the end of this year.