Diesel engines go green

Researchers at the US Department of Energy’s Pacific Northwest National Laboratory have combined an electrically charged gas with a specialised catalyst to reduce oxides of nitrogen in diesel engines.

Researchers at the US Department of Energy’s Pacific Northwest National Laboratory have successfully reduced harmful oxides of nitrogen in a diesel engine by half by combining an electrically charged gas with a specialised catalyst.

The foundation for the research was laid several years ago when PNNL scientists showed that an electrically charged gas, called plasma, along with a catalyst, could convert nitrogen oxides to nitrogen. They developed a small reactor to house the plasma reaction and discovered that the packing material used in the reactor affected the chemical reaction.

‘Our scientists began looking at various materials and found a specialised catalyst that selectively reduces oxides of nitrogen,’ said Chuck Peden, principal investigator for the project. Those initial laboratory studies showed that the process reduced nitrogen oxide by 70 percent.

‘But our lab results over the past six months now show that greater than 90 percent reduction can be achieved,’ Peden added.

As part of the United States Council for Automotive Research’s (USCAR) Low Emissions Technologies Research and Development Partnership, PNNL scientists are utilising their findings to help develop a vehicle envisioned by the Partnership for a New Generation Vehicle (PNGV).

USCAR formed PNGV with the US government in 1993 to develop technologies for a new class of vehicles that will travel up to 80 miles on a gallon of petrol whilst reducing the emission of greenhouse gasses.

New hybrid, light-duty diesel engines, such as those used in passenger cars and small trucks can already meet target fuel economy requirements and are said to emit fewer greenhouse gasses than petrol engines. However, unlike petrol engines, there is no technology that can sufficiently reduce nitrogen oxides in the lean burn exhaust typical of diesel vehicles.

‘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 sulphur 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.’

Recent prototype reactor tests conducted on a diesel engine at DOE’s Oak Ridge National Laboratory show a 50 percent reduction of Nitrogen oxide.

Researchers are continuing to refine the plasma reactor system, which received a patent in 1999, to achieve even greater reduction of Nitrogen oxide. PNGV targets are a 90 percent reduction in Nitrogen oxide emissions at 80 miles per gallon.