COLUMBUS, Ind. In one fell swoop, engine builder Cummins Inc. has thrown cold water all over the heated battle over 2010 diesel engine technology.

Last month, Cummins reversed its decision to use only exhaust-gas recirculation to meet 2010 heavy-duty diesel engine emission standards, saying it would instead use urea-based selective catalytic reduction, or SCR, in order to improve its engines fuel consumption rate.

"Our SCR system will deliver up to a 5 percent increase in fuel efficiency over todays solution, and that was the most compelling reason to make this change," said Jeffrey Jones, Cummins vice president for sales and market communications.

Company executives noted that fuel prices have increased 70 percent since Cummins originally rejected selective catalytic reduction for its big, heavy-duty engines.

Cummins decision is of great significance to the motorcoach industry because starting in 2010 it possibly could be the only engine supplier to four of the companies that build motorcoaches for the North American over-the-road bus industry.

Caterpillar revealed in June it will not manufacture any 2010-compliant power plants for the U.S. bus and truck market (See July 1 and June 15 issues of Bus & Motorcoach News), and Detroit Diesel will only supply engines to Setra, starting in 2010.

Cummins' big switch,

A year ago, Cummins executives were saying selective catalytic reduction was impractical for over-the-road trucks and buses because drivers would have to constantly replenish their supply of urea, an essential ingredient in the systems process of converting nitrogen oxides to harmless nitrogen and water.

They also had said that meeting tighter federal standards for emissions of NOx and soot using enhanced exhaust gas recirculation, commonly known as EGR, would offer commercial vehicle buyers engines with known, familiar technology.

However, "after a significant amount of thrashing it out and thinking, in light of new inventions and the drift in fuel pricing going up 70 percent, we decided to take a deeper look at fuel economy, and that formed the backbone of our decision," said Jim Kelly, president of Cummins engine division.

"The development of copper-zeolite for a catalyst that has very good properties for NOx conversion has allowed us to optimize engine and after-treatment performance, for better fuel mileage and to meet EPA standards," said Steve Charlton, Cummins vice president of heavy-duty engineering.

Charlton said copper-zeolite became available for commercial use less than a year ago and "proved far superior to the iron-zeolite catalyst available when Cummins ran its original SCR tests three years ago."

Fight avoided

The looming choice between 2010 engines that use exhaust gas recirculation or selective catalytic reduction was poised to become the most hotly contested argument in over-the-road bus equipment in a generation. (See June 15 Bus & Motorcoach News.)

High-ranking executives on both sides of the engine debate had taken passionate, public stands to back their technology choices.

Cummins decision to adopt SCR leaves Navistar Inc., which has begun making its own heavy-duty engines for International trucks, as the only engine manufacturer planning to use EGR to meet 2010 emission standards.

Navistar spokesman Roy Wiley expressed confidence in the companys decision to avoid SCR. "We said all along we believe were going with the solution that best fits commercial (vehicle) customers, which is EGR," Wiley told one trucking publication. "EGR doesnt have the extra weight of urea systems, and our customers wont have to go looking for it."

Navistar has declined to comment on questions whether it has been contacted by U.S. over-the-road bus manufacturers about using its new large-bore, heavy-duty MaxxForce engine line in their coaches.

Decision welcomed

Trucking industry analysts and executives generally welcomed Cummins decision, saying it was good for the industry because now all major engine OEMs are using the same after-treatment system. Additionally, the Cummins switch further strengthens the viewpoint that SCR is good for fuel efficiency.

Spokesmen for Detroit Diesel have been quoted as saying that companys switch to SCR should improve fuel economy on the companys DD15 heavy-duty flagship engine by about 3 percent.

Starting in 2010, Detroit Diesel engines only will be available to the motorcoach industry in Setra coaches.

Similarly, spokesmen for Volvo, parent company of Prevost Car, have been quoted as saying their companies engines should post fuel economy improvements of 2 to 3 percent by using SCR.

Cummins executives deny the company was experiencing problems meeting 2010 mandates with EGR. Cummins still intends to use EGR engines but will be able to "dial it back a little" for greater efficiency because much of the NOx will be removed by the after-treatment system instead of the original plan of inside the engine only.

Using SCR to remove NOx allows engines to run hotter, which means using less recirculated exhaust gases to cool combustion and allowing the engine to burn more efficiently.

Cummins already has experience with SCR technology. The company is running 200,000 SCR powertrains in Europe and has been preparing for U.S. midrange SCR for two or three years.

Particulate matter standards for diesel engines dropped to 0.01 gram per unit of output in 2007 and will stay at that level in 2010. However, NOx standards are still moving, having dropped to 2.5 grams from 4 grams in 2002 and proceeding to 0.2 gram in 2010. In 2007 the nature of the standard shifted, temporarily, to a sliding average of about 1.2 g/bhp-hr.