These images show the particulate matter from an emissions stack of a heavy-duty diesel truck before (a) and after (b) the addition of the SwRI-developed water + EGR system.

A consortium organized by engineers at Southwest Research Institute (SwRI) is developing low-emissions strategies that diesel engine manufacturers can use to improve air quality and meet stringent regulations. The four-year, $5.9 million Clean Diesel III program is composed of 18 participating engine manufacturers, component suppliers, and petroleum companies from eight countries.

"Our goals are ambitious - to reduce emissions by 90% over the next four years," said Program Manager Daniel W. Dickey, a Director in SwRI's Engine and Vehicle Research Division.

The diesel engine is an efficient internal-combustion engine. Its reputation for durability is excellent, but it produces oxides of nitrogen (NOx) and particulate matter (PM) emissions that can be harmful to the environment. A three-way catalyst, such as used on gasoline engines, isn't available to reduce those emissions on diesels.

"NOx emissions have already been reduced by a factor of five," said Dickey. "Despite this, an increase in the number of diesel vehicles on the road has caused emissions to actually rise over the last 10 years."

The consortium members select the areas of investigation and, as such, have opted to pursue five technologies that show promise for reducing diesel engine emissions. One of the most successful has been "water + exhaust gas recirculation (EGR)." In traditional EGR, a portion of the exhaust is routed back to the intake manifold, helping to reduce the combustion flame temperature, which in turn lowers NOx emissions. SwRI recently developed and patented an EGR valve that is being considered by commercial clients to meet 2002 regulations.

NOx emissions are easily reduced with EGR technology; however, PM emissions increase during the process. PM emitted by diesels is a suspected carcinogen. Several researchers are looking at the use of exotic fuels, such as dimethyl ether, to help reduce the occurrence of PM in various EGR schemes. SwRI's approach uses water, a much more readily available liquid. The addition of water to the EGR process serves two functions. It acts as a dilutent to reduce peak flame temperature and thus reduce NOx. The water also tends to boil before the fuel, breaking up the fuel particles and reducing particulates. A unique metering system developed by SwRI and Delphi mixes the water with diesel before injecting it into the engine.

Other technologies being researched by the consortium include a novel direct-injection homogeneous charge compression ignition system, model-based engine controls, variable valve actuation systems, and medium-duty gasoline engines. Additional projects will be addressed following completion of these tasks.

For more information, visit www.swri.org