Simulations that burn
by David Pescovitz
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Fabrizio Bisetti is a native of Italy where he earned a second Master's of Science in Engineering from Politecnico di Milano after graduating from the University of Texas.
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Combustion is the chemical reaction that keeps our cars driving, planes flying, homes heated, and electricity flowing. How can the process be improved to make our automobiles more efficient and reduce the pollution that spews out of industrial facilities? Design better combustion chambers, says Fabrizio Bisetti, a PhD candidate in UC Berkeley's Department of Mechanical Engineering. To aid in that endeavor, Bisetti and his colleagues are simulating the complexity of combustion in a computer.
"We develop physical and computational models for turbulent combustion," says Bisetti, a graduate student in the research group of UC Berkeley professor Jyh-Yuan Chen and winner of the 2006 Chevron-Berkeley Fellowship in Mechanical Engineering. "The idea is to create models that capture the physics in an accurate manner to provide tools for designers in industry."
At its simplest, combustion is a chemical reaction where a fuel such as oil, coal, wood, or natural gas 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, the interaction between the oxidizing gas and the fuel is marked by a lot of commotion. The molecules behave erratically both in their speed and direction of movement. Turbulent combustion is mostly used 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 esoteric mathematics and statistics to create numerical models that represent the reaction. The math is then used to construct computer simulations of turbulent combustion.The researchers use their own custom software to build the simulations because commercial software, Bisetti says, isn't up to the job. 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 (LLNL) and Sandia National Laboratories.
"That data is an experimental benchmark for us to test our models," Bisetti says.
Recently, the researchers examined a highly-detailed turbulent combustion simulation developed by Sandia that took a month to run on a supercomputer. Using the Sandia data, Bisetti and his colleagues built their own coarse model that employed statistical techniques and approximations. Instead of modeling every bit of detail, the simulation represents just "the big picture." It also took just a few hours to compute.
"With a turnaround time of a day instead of a month, someone could consider using this for combustor design," he says.
Bisetti believes that someday designers 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 and carbon dioxide 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.
"Most of the energy in the world comes from burning stuff," Bisetti says. "So even just a little boost in efficiency or reduction in pollution could have enormous impact."
Fabrizio Bisetti's home page
UC Berkeley's Combustion Modeling Laboratory
"Fabrizio Bisetti wins 2006 Chevron-Berkeley Fellowship in Mechanical Engineering"
Professor Jyh-Yuan Chen's home page
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Updated 8/21/06.
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