SCR Technology Cleans Up Truck Emissions

In fact, Cummins reports significant fuel savings during testing. "For our midrange engines, our testing indicates a 5% to 9% advantage relative to an in-cylinder solution," says Nycz. "Cummins heavy-duty products will deliver up to a 5% fuel economy improvement over our 2007 products, and our testing indicates that this improvement is even greater when compared to in-cylinder solutions."

There are other performance benefits, as well. "Cummins heavy-duty and midrange products will deliver the same power and torque as today's products without increasing displacement," says Nycz. "Throttle response will be improved relative to today's products. The engine has a larger 'sweet spot' for easier driveability, producing optimum fuel economy and performance."

Cummins also claims SCR is less complex than if the company had chosen to use an in-cylinder approach, which would require significant changes to the EGR system, air-handling system and vehicle cooling system.

Siler backs up these claims, noting, "The biggest benefits of SCR are that it is clearly more fuel efficient, is proven and reliable and meets or exceeds any known emissions standards in place for 2010 or beyond. The trade-offs are the addition of an SCR catalytic converter and the need for consumption of a secondary fluid.

"But it is Daimler's experience, as well as nearly the entire rest of the world's," he continues, "that the convenience and reliability of SCR, combined with its proven economic and emission-reducing advantages, build an almost insurmountable advantage over any other technology being considered to meet 2010 emission regulations."

The operating costs of SCR systems are also expected to be significantly lower than other alternatives being considered. "This has proven to be the experience of customers of all sizes or vocations around the world," Siler asserts.

Recent industry forums have placed the cost of a gal. of DEF at around $2.70, and Mack estimates only 2 or 3 gal. will be needed per every 100 gal. of diesel consumed.

However, the cost of the additional fluid will be more than offset by the savings in fuel economy. McKenna adds, "Mack Trucks is confident we will achieve a minimum 2% to 3% gain over our current engines - which are already achieving +3% in highway and +10% in Mack vocational applications vs. U.S. '04 - and at least the same over heavy-duty engines using non-SCR solutions for 2010, even if the latter operate above the .2 g NOx standard." (Note: .5 is the allowable maximum under the 2010 regs.)

Operating costs will actually decrease compared to the previous-generation trucks. For example, Saxman reports, "The total cost of fuel plus DEF for Volvo's EPA 2010 D13 engine will be 5% less than the acclaimed 2004 Volvo D12 engine under similar conditions."

But what happens if the system runs out of DEF? Let's look at a Mack truck as an example. "Each 2010 SCR chassis will be furnished with a clearly marked and ISO symbolled DEF tank gauge, which is in addition to the fuel gauge," says McKenna. "When the DEF level drops to a preset level, a small indicator lamp will illuminate the dash, indicating approximately 25% of DEF capacity remaining. At approximately 2.5% to 5%, there will be an audible tone now sounding, as well. When the DEF tank is completely empty, the engine will go into a power de-rate so as not to create high levels of NOx."

What about maintenance?
According to Saxman, "The SCR components will require minor maintenance, the same as any other components on a truck.

Siler adds, "The only scheduled maintenance that is new on SCR 2010 vehicles will be a low-priced, medium-efficiency DEF filter that can be replaced every 300,000 miles or so. The remaining maintenance items on 2010 vehicles will be the same or even less frequent than EPA 2007 vehicles."

Likewise, life expectancy is not expected to be much of an issue. "The SCR system is robust to say the least, with all double-wall stainless steel construction, stainless steel inlet and outlet piping with stainless hardware," says McKenna. "We are expecting something in excess of 22,000 engine hours or approximately 10 years [life expectancy]. There will be some variables that will positively or negatively affect this time, such as application, location and duty cycle.