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Staff Accomplishments

Diesel engine pollutants fuel research at PNNL

September 2005
Researchers at the Pacific Northwest National Laboratory are studying how tiny particles emitted by truck engines are caught - or not - by filters in the exhaust system. Capturing these particles without clogging the filters is important for developing fuel-efficient vehicles and relieving the air of pollutants. Currently, no filtration technologies exist that can be universally applied to on-highway heavy-duty diesel engines such as dump trucks, fire engines, and freightliners. PNNL researchers hope to resolve this problem by helping diesel engine manufacturer's meet quickly approaching Environmental Protection Agency regulations. "Understanding the filtration mechanisms will allow the design of filters which are effective, reliable, and have less of a negative impact on fuel efficiency than currently available devices," said PNNL researcher Mark Stewart. The EPA's emission standards mandate a 90% reduction in particulate matter over current levels. Particulate matter from diesel exhaust passes through the nose and throat and becomes lodged into the lungs causing major health problems for society. These fine particles can cause lung damage, premature death, and aggravate respiratory conditions such as asthma and bronchitis. To reduce particulate matter from the air, PNNL researchers use the Lattice-Boltzmann method to study the interaction between the diesel engine's exhaust characteristics and the filtration device. The Lattice-Boltzmann method is a computer-aided modeling method that allows scientists to see how liquids and gases move through complex systems, from soil at a nuclear cleanup site to the filters inside a public transit bus. The Lattice-Boltzmann method is used to predict the complex exhaust flow patterns through the twisting and branching of a filter's microscopic pores. Individual particles are introduced to the incoming exhaust stream, and the model simulates their flight paths and collisions with the filter and with other particles. As individual particles are captured, soot deposits form. The forming soot deposits in turn alter the flow patterns, which are continuously resolved by the Lattice-Boltzmann model. The model also predicts the pressure drop through the filter during loading, which can have a major impact on fuel economy. "Our hope is that the model will provide more information about the size, shape, consistency and location of the soot deposits within and upon the filter material," said Stewart. "This information tends to be difficult to obtain by direct observation because of the size scales involved and how fragile the soot deposits are." Mark Stewart and David Rector have presented their first status report of the multiyear project (available at http://fluidcomp.pnl.gov/research_areas/sae2003-fl-46.pdf). In the coming years, they will validate the model by conducting further experiments. The development of this study is funded by U.S. Department of Energy through the Office of FreedomCar and Vehicle Technology. Contact: Wally Weimer, Process and Measurement Technology Product Line Manager.

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