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February 9, 2007 Vol. 77,
no. 5S
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| BURNING MAN: ME graduate student Fabrizio Bisetti won an award for his work on turbulent combustion.
RACHEL SHAFER PHOTO
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Simulations to improve air quality
ME researcher studies turbulent combustion to reduce industrial waste
Combustion is the chemical reaction that keeps our
cars driving, planes flying, homes heated and electricity flowing.
How can the process be improved to reduce the pollution that spews
out of industrial facilities? Design better combustion chambers, says
ME Ph.D. student Fabrizio Bisetti. To aid in that endeavor, Bisetti
and his colleagues in ME professor Jyh-Yuan Chen’s research group
are simulating the complexity of combustion on a computer.
“The idea is to create models that capture the physics in an accurate
manner to provide tools for designers in industry,” says Bisetti,
winner of the 2006 Chevron-Berkeley Fellowship in Mechanical Engineering.
At its simplest, combustion is a chemical reaction in which a fuel
is burned to release energy. The fuel, heated to its ignition point,
reacts with an oxidizing gas, like oxygen, and produces heat and light.
Turbulent combustion, the focus of Bisetti’s work, is a bit more
involved. In this case, interaction between the oxidizing gas and the
fuel is marked by a lot of commotion. The fluid behaves erratically
in both its speed and direction of movement. Turbulent combustion is
used mostly for industrial applications because the turbulence helps
mix the fuel and oxidizer for an increased burn rate.
“Understanding turbulence has been a problem for the last 100 years,” Bisetti
says. “Some progress has been made, but not to the point that
people can really use predictive tools. Combustion adds another level
of complexity to the problem.”
Bisetti and his colleagues use stochastic processes and statistics
to create numerical models that represent the reaction. The math is
then used to construct computer simulations of turbulent combustion
using custom software. Finally, the simulations are run on supercomputers
at the San Diego Supercomputer Center and other research facilities.
As the simulations run, their accuracy is checked against real-world
data provided by combustion research facilities at Lawrence Livermore
National Laboratory and Sandia National Laboratories.
“That data is an experimental benchmark for us to test our models,” Bisetti
says.
Bisetti believes that designers someday might virtually prototype new
combustors and run them in simulation before they’re actually
built. Today, for example, the emissions from huge gas turbines must
often undergo afterburn treatment to minimize the nitrous oxides (NOx)
expelled into the air. New designs for combustors that eliminate the
need for post-processing while also burning the fuel more efficiently
would be welcomed by both industry and environmental advocates.
In addition, the researchers are working on other ways to reduce fuel
consumption and the release of pollutants, such as developing something
called Homogenous Charge Compression Ignition (HCCI) engine technology,
which holds the promise to reduce NOx and soot emissions and increase
efficiency.
“The overwhelming majority of the energy in the world comes from burning
fossil fuels,” Bisetti says. “So even just a little boost
in efficiency or reduction in pollution could have enormous impact.”
— Written by David Pescovitz
For more information, go to www.me.berkeley.edu/%7Efbisetti.
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