RICHLAND, Wash. — By combining an electrically charged gas with a specialized catalyst, researchers at the Department of Energy's Pacific Northwest National Laboratory have successfully reduced harmful oxides of nitrogen in a diesel engine by half. Laboratory results show even greater reductions are possible. These reductions are critical to meeting emissions requirements and fuel economy goals in diesel vehicles. A patent is pending on a class of zeolite catalyst materials that appear to be the key to nitrogen oxide, or NOx, reduction in this novel approach to the control of harmful vehicle exhaust emissions.
While current tests show promising results, the foundation for this research began several years ago when PNNL scientists showed that an electrically charged gas, called plasma, along with a catalyst, could convert nitrogen oxides to nitrogen—a component of clean air. They developed a small reactor to house the plasma reaction and quickly discovered that the packing material used in the reactor affected the chemical reaction.
"Our scientists began looking at various materials and found a specialized catalyst that selectively reduces oxides of nitrogen," said Chuck Peden, principal investigator for the project. Those initial laboratory studies showed that the process reduced NOx by 70 percent.
"But our lab results over the past six months now show that greater than 90 percent reduction can be achieved," Peden said.
Laboratory tests also have shown the potential for significant soot reduction. The soot portion of exhaust consists of tiny particles of carbon and organics that are potentially harmful to human health.
As part of the United States Council for Automotive Research's (USCAR) Low Emissions Technologies Research and Development Partnership, PNNL scientists are helping to develop a vehicle envisioned by the Partnership for a New Generation Vehicle. Ford, General Motors and DaimlerChrysler—under the umbrella of USCAR—work together on shared technological and environmental concerns. USCAR formed PNGV with the federal government in 1993 to develop technologies for a new class of vehicles that will travel up to 80 miles on a gallon of gas while meeting reduced emissions levels for nitrogen oxides, carbon dioxide and hydrocarbons.
New hybrid, light-duty diesel engines, such as those used in passenger cars and small trucks, already can meet target fuel economy requirements and actually emit less of the "greenhouse gas" carbon dioxide than gasoline engines. However, unlike gasoline engines, there is no technology that can sufficiently reduce nitrogen oxides in the lean burn exhaust typical of diesel vehicles. Nitrogen oxides cause air pollution.
"Combining the plasma reactor concept with a catalyst was considered to be a left field approach but is now moving to the top of the PNGV list," said Steve Barlow, a PNNL chemical physicist. "Six years ago, this field of non-thermal plasma-activated catalysis didn't exist, but it appears to have many advantages over competing technologies. For example, our catalysts aren't poisoned by sulfur in the exhaust, which is a challenge for other catalytic technologies.
"Since the beginning, we have worked to improve both the electrical discharge designs and the catalyst performance; the resulting hybrid system is vastly more efficient than what we started out with," Barlow said. It is also much more rugged and reliable. One surprising result has been the relative ease with which we have been able to move from the laboratory bench to actual engine testing. This gives us confidence in the soundness of our approach."
Recent prototype reactor tests conducted on a diesel engine at DOE's Oak Ridge National Laboratory show a 50 percent reduction of NOx. Researchers are continuing to refine the plasma reactor system, which received a patent in 1999, to achieve even greater reduction of NOx. PNGV targets are a 90 percent reduction in NOx emissions at 80 miles per gallon.
"We continue to make progress toward achieving the goals with this technology," said Peden. "There is more work to be done to reduce the amount of electrical power required to operate the reactor and to increase the overall NOx reduction from 50 to 90 percent on a real engine."
"This technology, if successful, will reduce NOx and particulate emissions and enable the use of high fuel economy diesel vehicles that will help relieve our dependence on foreign oil," said Kathi Epping, program manager for Combustion and Emission Control Program in the DOE Office of Energy Efficiency and Renewable Energy's Office of Transportation Technologies, which is funding this research.
One proposed timeline for integrating the emission reducing reactors comes from PNGV, which hopes to have a prototype vehicle by 2004. The laboratory also is working with Delphi Automotive, a potential supplier of a plasma-catalyst system. Under a separate Cooperative Research and Development Agreement, PNNL is teaming with Caterpillar Inc. to find solutions to reducing emissions on heavy-duty diesel engines.
Formed in 1992, USCAR leverages Ford's, General Motors' and DaimlerChrysler's research efforts in noncompetitive areas. For more information on USCAR, the LEP or PNGV, see www.uscar.org.
Business inquiries on this or other PNNL technologies should be directed to 1-888-375-PNNL or e-mail: firstname.lastname@example.org.
Pacific Northwest National Laboratory is a DOE research facility and delivers breakthrough science and technology in the areas of environment, energy, health, fundamental science and national security. Battelle, based in Columbus, Ohio, has operated the laboratory for DOE since 1965.
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