Selective catalytic reduction (SCR) technology is allowing European heavy-duty diesels to reduce emissions levels to near U.S. 2007 levels, while also increasing fuel economy by up to 7% compared to trucks using exhaust gas recirculation (EGR) and diesel particulate filters (DPFs) according to the chief truck powertrain engineer for DaimlerChrysler AG.

Nearly identical to U.S. EPA 2007 standards, Euro 5 levels do not take effect until 2009, but tax incentives combined with fuel economy improvements have caused fleets to pre-buy 20,000 trucks powered by the cleaner SCR-equipped engines, says Bernard Heil, DaimlerChrysler's vp of Truck Product Engineering Powertrain. While the emissions reduction systems add approximately $4,000 to the cost of a new truck, the ROI from the tax and fuel savings is just one year for over-the-road operations, he points out.

In the U.S., the company is using the EGR/DPF combination for its MB4000 heavy-duty diesels installed in 2007 Freightliner, Sterling and Western Star trucks.

For comparison purposes, the company has been running a U.S. 2007 spec engine alongside SCR versions in its Mercedes-Benz Axor tractor. “From a torque perspective, there's not a big difference, but the fuel economy is completely different,” Heil told Fleet Owner. “We've seen a 7% difference.”

SCR injects liquid urea into the exhaust stream from an auxiliary fuel tank to achieve the lower emissions levels without a DPF. The U.S. EPA objected to the use of SCR technology for 2007 because allowing the urea tank to run dry or diluting the urea with water does greatly increase tailpipe emissions. Europe has addressed that concern by requiring new tailpipe emissions sensors that identify trucks running without urea.

Heil believes the new sensors will “help answer EPA's concerns” so the company can use SCR to help achieve even tighter U.S. emissions standards coming in 2010.

The 2010 levels, which will probably be matched by Euro 6 requirements in 2012, “will certainly require a combination of both” SCR and DPF technology, Heil says.

“The good news is that [with 2007 U.S. requirements] we are now gaining a lot of experience with DPF systems.,” says Heil.