June 2, 2003
UCSC engineer receives major grant to improve
engine efficiency using nanotechnology
By Shawna Williams
UCSC researchers are leading a collaborative effort to develop new technology
that could increase the efficiency of internal combustion engines by
converting waste heat into electric current.
|Ali Shakouri, an associate professor
of electrical engineering at UCSC, heads the multi-institutional
team of researchers working on the project.
Photo: UCSC Photo Services
The project will use nanoscale engineering of materials to develop
efficient technology for direct conversion of thermal energy to electric
energy. It is funded by a five-year grant from the Office of Naval Research
that provides up to $1.2 million per year spread among seven institutions.
"The Navy is interested in electric ships, but this technology
will also be useful for electric cars and any other vehicle that needs
electricity," said Ali Shakouri, an associate professor of electrical
engineering at UCSC and principal investigator on the grant project.
Car engines are notoriously inefficient: Only about one-third of the
energy they generate goes to propelling the car. The rest dissipates
as heat, and keeping the engine cool presents an engineering problem
of its own. Devising a way to turn some of that heat into useful energy
would enable a car to travel further on less fuel.
"The current systems for converting heat to electricity are turbine-based,
heavy, noisy, and not very efficient," Shakouri said. "What
we are working on has no moving parts."
Shakouri heads the multi-institutional team of researchers working
on the project. The researchers will explore the capacity of thinly
layered materials to channel the random jostling of heat energy into
the orderly flow of electricity. They hope to reach 20 percent efficiency
for this conversion.
Scientists have understood the principles behind the conversion, known
as the Seebeck effect and thermionic emission, for some time. When one
side of a material is hotter than the other, electrons on the hot side
move faster. In the process, some will find their way to the cold side,
and this flow creates electricity. But previous attempts to harness
this principle to generate power have required huge temperature differences
and attained only about 6 percent efficiency.
Shakouri's team hopes to change this using the revolutionary new techniques
of nanotechnology, which enables scientists to manipulate the properties
of a material or device by precisely positioning its atoms.
"The ability to do nanoscale engineering of the materials has
been a major advance," Shakouri said.
Three key properties will enable a material to efficiently convert
heat energy to electricity, Shakouri said. First, it must allow "hot"
electrons to move easily into the cold area, a characteristic known
as electrical conductivity. Since electrons will flow only as long as
the material maintains a temperature difference, the material must also
be a thermal insulator. And finally, "hot" electrons must
flow more easily than "cold" ones. Putting tiny vacuum gaps
between the hot and cold sides of the device are one way this might
be achieved, since hot electrons, but not heat itself, could jump across
Shakouri and some other members of the team have worked on a similar
problem before, but with a different goal: refrigeration. They are currently
improving a nanoscale cooling device that can be applied as a thin layer
on a computer chip. The electric current flowing through the chip creates
a temperature difference between the layers of the device, and suctions
heat away from the chip.
The car engine device would essentially reverse this process, surrounding
the engine and using the temperature difference between the engine and
its surroundings to generate electric current.
"In this project, both solid-state materials and small vacuum
gaps will be investigated to improve the preferential flow of hot electrons,"
The research team is divided into five smaller groups, each assigned
a particular task, such as theoretical modeling, making or testing materials,
or demonstrating the overall system. Though work on the project will
go on at institutions from Santa Barbara to Cambridge, Massachusetts,
its center will be Shakouri's lab, which will perform device design
and system analysis and will determine which paths the research should
The institutions involved are UCSC, Harvard University, Massachusetts
Institute of Technology, North Carolina State University, Purdue University,
UC Berkeley, and UC Santa Barbara.
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