SCR is On the Way

Avatar photo

There are still two approaches for meeting the 2010 medium- and heavy-duty diesel emissions regulations, but the big picture changed rather a lot midway through last month when Cummins announced that it will use selective catalytic reduction (SCR) technology in its 2010 heavy-duty ISX engines after all.

That reverses the plan we heard last September. Then, the Indiana engine maker said it could meet the 2010 EPA emissions standard with an enhanced version of cooled exhaust gas recirculation (EGR) for its 15-liter engines and the coming 11.9-liter diesel, needing no aftertreatment and thus no SCR. The company also said its medium-duty motors would do the opposite, using SCR in 2010 as they do in Europe now.

So who’s actually using what for 2010?

In fact, there was a split down the middle of the market until the Cummins blockbuster. On the SCR side, as well as Cummins, we have Detroit Diesel and Mack/Volvo, plus the new engines coming from Paccar in 2010, based on Europe’s DAF motor.

On the EGR side we now have only Navistar, its coming heavy-duty MaxxForce engines co-developed with Germany’s MAN. They’ll continue to use a slightly more  ”aggressive” form of EGR with a diesel particulate filter (DPF) for on-highway trucks, saying EPA standards can be achieved by in-cylinder means. They won’t need any NOx aftertreatment.

“We have our strategy and we’re sticking with it," says Navistar spokesman Roy Wiley. “We believe EGR is the right way to go. It can provide customers with the fuel economy they’re asking for.“  Caterpillar had been silent about its 2010 plans until recently, of course, when it announced that it’s getting out of the on-highway engine business altogether at the end of 2009.

Daimler Trucks North America (DTNA) President and CEO Chris Patterson, on the other hand, made his company’s 2010 plans clear back in 2006. Same with Volvo/Mack.

“We will be utilizing Daimler’s BlueTec technology for our Detroit Diesel engines beginning in 2010,” Patterson said earlier this year. “This SCR technology is… the only means of meeting the stringent nitrous-oxides standard for heavy-duty diesel engines in 2010 while actually reducing diesel fuel consumption in comparison with the technology used in 2007 engines.”  “BlueTec” is the Daimler name for the SCR system that’s already being used in thousands of Mercedes trucks in Europe.


Cummins says the fuel economy improvement over EPA-07 engines will be in the five-percent range, and Detroit Diesel has been saying three to five percent, while the EGR system Cummins originally proposed for 2010 would at best maintain the status quo. The advantage of EGR is that trucks don’t need a tank of urea hanging off the frame rails, a tank that has to be re-filled every few thousand miles. They’re also somewhat lighter — about 200 lb — because they don’t carry that tank and the necessary catalytic converter. Cummins also considered EGR a known technology that truck operators were familiar with.

The planned EGR engine doesn’t change much
aside from some programming and SCR aftertreatment.

But that logic must have looked a little weaker every time the price of fuel went up a notch. With that and also the emergence of a new catalyst technology in the last year, Cummins decided a new approach was warranted. It has always said that it could use either technology, so this is not such a big move in engineering terms.

“Our 2010 engine development is progressing on plan, and customers can depend on Cummins to deliver these new products on time,” says Ed Pence, Cummins vice president and general manager of its heavy-duty engine business.

“This is not a new technology for Cummins,“ said Steve Charlton, vice president, heavy-duty engineering, in a telephone press conference after the initial SCR announcement. “We have 200,000 SCR units in service in Europe and we’ve been preparing our mid-range engines for the 2010 launch for the past two years. So we’ll be able to get up the learning curve with our heavy-duty engines very quickly.”

The SCR aftertreatment system will be built in-house, as will all other major emissions components, including turbocharger and electronics. All those emission bits are the same ones planned for use in the EGR engine. Uniquely, in 2010 all Cummins engines from medium-duty to big-bore will use the same ECM and the same software. That’s a first.

“We’re up and running with that now,” says Charlton.

The EGR system in use here will be less aggressive than the one originally planned. The difference is the EGR rate, or the amount of work that the system — and its DPF — has to do.

The challenge for engine makers since stringent emission rules were first launched in 2002 has been to limit both particulate matter (PM) and nitrous oxides at the same time while maintaining decent fuel economy and driveability. Limiting one of the two necessarily compromises the other. If the engineers design effective NOx control, then they’ll suffer on the PM front, and vice versa.

“With SCR we’re able to operate the engine at higher NOx levels because some of the NOx is taken care of in the exhaust system,” Charlton explains. “This allows us, combined with our XPI fuel system, to reduce the amount of particulate leaving the engine cylinders. And so we get much more favorable conditions in the DPF.

"So we expect to maintain passive regenerations in 2010, which means we can keep the DPF clean without having to burn fuel to regenerate. We see this as a very positive outcome.”

Charlton also notes, by the way, that every 2010 engine from every manufacturer will still be using EGR even if they’ve opted for SCR.

The two work in tandem, though it’s become routine for many observers to think engines use either one or the other. 

Asked last fall why Cummins would use EGR in big-bore engines and SCR in little ones, Charlton just said it would, as always, provide “the right solution” for the application.

With trucks coming home every night, the potentially spotty availability of urea wouldn’t be an issue. The decision to go with SCR for heavy-duty motors in 2010 implies that it’s now reasonably confident about the development of a urea distribution system.


Urea is common chemical, but it will have to be routinely available because a 20-gal tank probably won’t last much more than 5,000 to 6,000 miles, meaning you’ll have to fill it between normal service intervals. We don’t yet have a distribution system in place, and SCR critics are quick to pounce on this, but DTNA’s senior VP Mike Delaney isn’t worried.

“With the massive effort currently underway to establish the DEF distribution infrastructure in North America, we’re not concerned in the least about availability,” he says.

In many cases, adds Detroit Diesel marketing director Dave Siler, urea will first be sold in 1,000-gal ‘mini bulk’ dispensers, with proper pumps being added as demand dictates.

A combined diesel-urea tank on an MAN tractor with
1,300 liters of fuel in one side, 85 of urea in the other.

As for the claimed poor cold-weather performance of urea, Detroit Diesel’s EPA 2010 program leader Rakesh Aneja says it’s not an issue. Yes, it does gel at about 12 degrees F or minus-11 C, but it warms up and flows in little time. In fact, Aneja says, you can start a cold engine and run it right away with no ill effects. Heaters will be used in many cases.

One of the Environmental Protection Agency’s early worries about SCR concerned what happens if the urea tank runs dry, but this seems to have been resolved. In practice, Detroit engines will offer the driver a warning when the urea tank is down to a quarter full, equal to another 1,500 or so miles. If it runs to empty the engine will be derated, and if shut down in that state, it won’t restart.


A recent week spent in Europe by yours truly included a few hours with a large fleet — about 1,000 power units — that has some 700 MAN and Mercedes-Benz tractors on the road meeting Euro 5 emissions standards via SCR.

So how has LKW Augustin fared with SCR? A big gain in fuel economy is the answer to that one. Oskar Berger, majority owner and the boss, said the Euro 5 trucks are getting in the range of 34 liters per 100 kilometers, with some drivers hitting 30, down from a fleet average of 37-38 L/100km with older non-SCR engines. To translate, Augustin trucks have gone from an average of about six mpg to seven or even eight. That’s huge at a time when fuel costs more than $8.00 a gallon. 

The trucks are normally filled with both fuel and urea (called AdBlue over there) at the same time — the tanks hold 1,300 liters of diesel and 85 liters of urea. That’s 286 Canuck gallons vs 19, or 348 and 22.5 U.S. gallons respectively.

Berger said there have been no real issues with SCR. Drivers don’t carry jugs of the stuff in case their urea tanks run dry because it’s not hard to find. Engines are derated by 150 hp in the unlikely event that they run out.

With any luck, the introduction of SCR on these North American shores will be as uneventful.

Avatar photo

Rolf Lockwood is editor emeritus of Today's Trucking and a regular contributor to

Have your say

This is a moderated forum. Comments will no longer be published unless they are accompanied by a first and last name and a verifiable email address. (Today's Trucking will not publish or share the email address.) Profane language and content deemed to be libelous, racist, or threatening in nature will not be published under any circumstances.