Diesel engines are widely used throughout the Department of Defense (DoD) for powering tactical and non-tactical vehicles and vessels, off-road equipment, engine-generator sets, aircraft ground-support equipment and for a variety of other applications. Human health concerns have greatly increased regarding the penetration of the small particulate matter (PM) [particularly those less than 2.5 microns in diameter - PM2.5] from diesel engine emissions into the deeper regions of the lungs. However, unresolved technical and economic problems have prevented widespread application of soot filters to reduce these emissions. Two approaches for resolving the most important of these problems, regeneration of the soot filter on-line during engine operation, by using self-regenerating soot filters were investigated during this demonstration.

Technology Description

The first approach was a passive, platinum-catalyzed soot filter (CSF) developed by Nelson Industries of Stoughton, Wisconsin (a Cummins, Inc. subsidiary) and Engelhard Corporation of Eagan, Minnesota. The CSF contains a porous cordierite ceramic substrate impregnated with a platinum catalyst. Particulate matter is captured within the ceramic where it is completely oxidized to carbon dioxide by the thermal energy of the exhaust gas flow, at temperatures as low as 360°C. The other approach was an active, electrically regenerating soot filter, developed by Rypos of Medway, Massachusetts. The Rypos filter consists of a non-catalyzed, sintered metallic fiber, the resistive properties of which allow an electric current to be applied to regenerate this filter without relying on high exhaust temperatures.

Demonstration Results

Field tests were completed on eight engines installed in on-road buses and trucks at Camp Pendleton and Fort Irwin, California, from June 2001 to March 2002, all using their normal duty cycle. Individual vehicle mileages ranged from 1,000 to 25,000 miles. PM emission reductions of greater than 90 percent, which met the 2007 Environmental Protection Agency heavy-duty, on-road engine standard of 0.01 gram per brake horsepower-hour, were obtained consistently. The CSFs also demonstrated a minimum 72 percent reduction in hydrocarbon emissions and a minimum 49 percent carbon monoxide emissions reduction, which were below target levels. The capital cost of a passive CSF for a Cummins 5.9-liter engine is $7,000, which is approximately 90 percent of the cost of the engine. Annual operating and maintenance costs were estimated to be approximately $300. The performance of the active Rypos filter tested on two tactical diesel generators at Edwards Air Force Base, California was inferior. There was only a 62 percent reduction in PM emissions, which did not meet target performance criteria.

Implementation Issues

The use of self-regenerating CSFs would enable the DoD to operate its diesel engines in a cleaner and less noisy manner, thereby reducing adverse health effects. The reduced particulate emissions also would allow the DoD to ease its air pollution regulatory burden, saving both time and funds from the use of normal diesel fuels. Other technologies under development require very low sulfur fuels. However, for the passive filters, most of the test vehicles experienced continuously increasing back pressures and while limits were not exceeded, this would suggest that these filters are probably only applicable to less than 25 percent of the total diesel engines operated by either DoD or commercial interests. (Project Completed - 2003)