The smallest engine of its kind anywhere in
the world, created in a University of California, Berkeley,
laboratory, could someday replace batteries as an efficient
power source for mobile devices like laptop computers.
Not much bigger than a stack of pennies, the "mini engine"
is 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 endeavor to create an even smaller engine
chemically etched from silicon.
"We are at the frontier of research into how to generate
power using the smallest of components," said Carlos Fernandez-Pello,
a mechanical engineering professor at UC Berkeley who developed
the engine with the help of Kenji Miyaska of Fukui University
in Japan, UC Berkeley post-doctoral researcher David Walther
and graduate students Kelvin Fu, Aaron Knobloch and Fabian
At present, the engine, built by Berkeley's Mechanical
Engineering Machine Shop, can produce up to 2.5 watts of
electricity, enough to power a bicycle headlamp. But Fernandez-Pello
and his team are ramping the engine up to produce 30 watts,
enough to power a weak light bulb, but plenty to power electronic
Like the engine in your car, the mini engine produces motion
from controlled combustion, which takes place when a fuel
such as gasoline is combined with oxygen and a spark in
a chamber. The released energy drives the movement of a
rotor that can be attached to a gear system to make automobile
wheels turn or drive other machinery.
The mini engine is designed to run on liquid hydrocarbon
fuels such as butane or propane, chemical cousins of gasoline.
One shot glass of fuel (a fluid ounce) will keep the motor
running for two hours. Once it is optimized, the tiny engine
will be able to run 10 times longer than a conventional
lithium ion battery, meaning that refueling will be required
10 times less often than changing a battery. The motor and
fuel together weigh only a fraction of the weight of a standard
battery such as the one powering your digital camera.
Unlike most automobile engines where combustion occurs
in a piston/cylinder assembly, the rotary engine has a flat,
peanut-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. Called a rotary engine
or Wankel engine after its inventor, this engine design
has not been as widely used as the piston-style engine found
in most automobiles today, although the rotary did appear
in the Mazda RX-7 and is reappearing in the concept cars
Also like a car engine, the mini engine produces exhaust
that contains carbon dioxide and water, about the same amount
as is exhaled by one and one half persons at rest. While
this is hardly enough to generate substantial pollution,
the researchers are now developing a miniature catalytic
The Berkeley team hopes that some day the mini engine can
be used to power electronic devices, like computers or robots.
The U.S. military is 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 ideal for miniaturizing because
of its simplicity, and the components are relatively easy
to make using silicon etching technology.
The size of a pinhead, such a miniaturized engine will
be made from parts etched out of silicon in a process similar
to that used to make computer microprocessors. In this process,
light is used to burn away areas of silicon until only the
desired shape remains. The researchers envision a Micro
Engine capable of producing power for cell phones and other
small electronic devices. This truly tiny engine will have
similar proportions as are used in the steel mini engine,
but would use about one-thousandth of an ounce of fuel for
two hours of operating time.