fires up electrical devices
Technology Research News
On a plane trip in the not-too-distant
future, the hum you hear coming from your seatmate's laptop computer might
not be its hard drive but rather its power source.
Researchers at the University of California at Berkeley have developed
an internal combustion engine that could replace batteries as the power
source for portable electronic devices.
Though internal combustion engines are a decidedly 19th-century technology,
the Berkeley engine's small size -- about the size of three stacked pennies
-- opens up a new range of potential applications. The researchers are
also building a still smaller micro engine from silicon components that
could power microelectromechanical systems (MEMS).
The researchers' aim is to take advantage of the high energy density of
liquid hydrocarbon fuels like butane, propane and gasoline to produce
electrical and mechanical power for small-scale devices. A particular
volume of a liquid hydrocarbon fuel can produce about thirty times as
much energy as a battery of the same size, according to the researchers.
The mini engine will run for about two hours on one fluid ounce of fuel,
and the micro engine could run for about 67 days on the same amount of
fuel, said Aaron Knobloch, a graduate student at Berkeley.
"The long-term objective of this research is to develop a millimeter-scale
rotary internal combustion engine that produces tens of milliwatts [of
power]," he said.
The mini engine, which is made of steel and aluminum, turns at 3000 revolutions
per minute and produces about half a watt of power. The engine weighs
22 grams, or about 4/5 of an ounce, and its combustion chamber measures
12.5 by 9.5 by 3.6 millimeters, said Knobloch.
Like the engine in your car, the mini engine works by igniting a mixture
of fuel and air to create a series of small explosions. The Berkeley engine
is a Wankel engine, which, instead of using the force of the explosions
to drive pistons, uses it to spin a triangular rotor inside an oval chamber.
Of course, it remains to be seen whether people will be willing to trade
changing batteries for loading flammable liquids into their laptop computers.
"Safety is definitely a concern. However, we envision the engine, with
its fuel, to be equivalent to a Bic lighter," said Knobloch, adding that
people are allowed to carry butane lighters on airliners.
Batteries also have the advantage of not producing air pollution in their
immediate environments. The main pollutant produced by combustion engines
is carbon dioxide, which is a greenhouse gas.
"The mini engine produces as much carbon dioxide as one person at rest,"
or about one 400th the exhaust of an automobile traveling at 60 mph, said
Knobloch. One hundred micro engines would produce the same amount of carbon
dioxide as one mini engine, he added.
The researchers' next step is producing the prototype micro engine out
of silicon and silicon carbide with the photolithography fabrication process
used to make computer chips. The combustion chamber of the prototype will
measure 3.3 by 3 by 1 millimeter, said Knobloch. The micro engine could
be used to generate electricity and to drive small robots and other mechanical
The mini engine could be used in practical applications within a couple
of years, said Knobloch. The researchers expect to build a prototype of
the micro engine within six months and aim to use it to power devices
within four years, he said.
Knobloch's research colleagues were Carlos Fernandez-Pello, David Walther,
Kelvin Fu, Fabian Martinez, Bryan Cooley and Dorian Liepmann of Berkeley,
and Kenji Miyaska of Fukui University. They are scheduled to present their
work at the 35th National Heat Transfer Conference in Anaheim in June.
The research was funded by the Defense Advanced Research Project Agency
Timeline: < 2 years
TRN Categories: Microelectromechanical Systems (MEMS)
Story Type: News
Related Elements: Technical paper, "Micro-Scale Combustion
Research for Applications to MEMS Rotary IC Engines," 35th National Heat
Transfer Conference, June 10-12, 2001, Anaheim, CA
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