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UConn Study Finds No Emissions Benefit From Hybrid Buses.

The University of Connecticut (UConn) recently announced that newly completed research conducted at the university indicates that particle emissions from two hybrid diesel-electric buses purchased by CTTransit and emissions from two comparable CTTransit diesel buses were statistically identical.

Additionally, UConn noted that while the company that manufactures the hybrid buses -- Allison Transmission, a division of General Motors -- claims that the fuel economy of the hybrids is 50 percent better than that of diesel buses, CTTransit data reveals that fuel economy for the hybrids was only 10 to 15 percent better.

UConn said the researchers measured the mass of the particulate emissions and the number of particles being emitted per second.

"The ultra fine particle data were surprising because we expected significant reductions for the hybrid technology," said UConn associate professor of civil and environmental engineering and lead study researcher Britt Holmen. "That proved not to be the case."

UConn noted that CTTransit, which oversees bus service in Connecticut and is operated by the state Department of Transportation (DOT), purchased two "parallel design" hybrid electric buses from Allison Transmission in June 2003.

UConn's School of Engineering was contracted by the Connecticut Department of Transportation and the Joint Highway Research Advisory Council to test the particle emissions of the hybrids as well as two diesel buses manufactured around the same time that have the same emissions standards, and to compare the results.

The UConn researchers tested all four buses on actual roadways, as opposed to using a "chassis dynamometer," employing regular diesel fuel and the new ultra-low sulfur diesel fuel that will be implemented in buses next year.

"We found that the only testing variable that reduced particulate emissions was use of a diesel particulate filter, and these reductions of more than 90 percent were similar for both the hybrid and conventional diesel bus types," said Holmen. "Without the particulate filter, the particulate emissions from the hybrid buses were not statistically different from the particulate emissions of the diesel buses, regardless of fuel sulfur content. "

Contact: Britt Holmen, UConn School of Engineering, phone 860-486-3941.

(EIN STAFF: 9/15)
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Publication:Mobile Emissions Today
Date:Sep 27, 2005
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