What’s Your Choice: EGR, or SCR

July 1, 2010

It’s all the buzz in trucking: Air-quality regulations are prompting significant changes in diesel-engine exhaust systems. If and when you buy a 2010 diesel truck, the new hardware it takes to meet the Environmental Protection Agency’s (EPA’s) clean air regulations will cost you thousands of dollars more than earlier trucks did. The primary air pollutant being targeted for 2010 is oxides of nitrogen, or NOx gases. Rules from both EPA and the California Air Resources Board (CARB) require a reduction in oxides of nitrogen from 1.2 grams per horsepower-hour to 0.2 grams, an 83% reduction. No further reduction is required in particulate matter as compared with previous EPA regulations.

In diesel engines, there are two ways to achieve that NOx reduction. (Natural gas engines also can meet EPA 2010.) One way is to increase the amount of exhaust gas circulated back into the engines. Exhaust gas recirculation (EGR) displaces oxygen as it is brought into the cylinders of an engine, thereby reducing the heat of combustion and reducing NOx formation.

Photo: International
International is meeting 2010 NOx emission standards with Exhaust Gas Recirculation technology.

That is the route chosen by Navistar. Officials say combustion, fuel economy, and performance can be optimized through the elements of what Navistar calls Advanced EGR: advanced fuel and air management; proprietary piston-combustion-bowl design; and rigorous electronic calibration.

The second method-chosen by all other domestic diesel engine manufacturers, including Cummins, Detroit Diesel, PACCAR and Volvo/Mack-is called selective catalytic reduction (SCR). With SCR, a fine mist of a urea-water mixture is sprayed into the hot exhaust stream. The urea-water mixture, called diesel exhaust fluid (DEF), breaks down into ammonia during a chemical reaction called hydrolysis. The NOx and ammonia pass into the SCR element, where a catalytic reaction takes place, converting the NOx into harmless nitrogen and water vapor.

Higher Cost
Navistar has announced that Advanced EGR will add $8,000 to the cost of a heavy-duty engine and $6,000 to the price of a medium-duty diesel engine. (We asked Navistar what emissions technology will be featured in the new Caterpillar trucks produced by Caterpillar and Navistar. The official simply said that all Navistar MaxxForce engines in North America will use Advanced EGR for the foreseeable future.)

Navistar says that the major advantage of EGR over SCR is that the EGR, the in-cylinder solution, will not

Photo: Cummins
The Cummins ISX15 engine meets EPA 2010 emissions standards.

require additional apparatus to be installed on the vehicle to store and dispense the liquid urea solution. On a long-haul truck, this SCR hardware reportedly can be as large as a fuel tank and can weigh in the area of 400 pounds when filled with liquid urea.

By contrast, Navistar Advanced EGR engines do not require regular replenishment with liquid urea. “Most communications we have seen note that SCR vehicles must be replenished with liquid urea at least every other fill-up with diesel fuel,” says Tim Shick, director of sales and marketing for the Navistar Engine Group.

Navistar finalized the decision to pursue Advanced EGR for 2010 shortly before 2007 engines were introduced. “Our development work on 2007 EGR engines made it clear that Advanced EGR could meet 2010 requirements with minimal customer involvement,” says Shick. “Advanced EGR achieves the goal of 2010 compliance with engines that provide fuel economy and performance as good or better than 2007 engines.”

Advanced EGR engines, Navistar says, will have lower overall operating costs compared to SCR engines when you consider the cost of diesel fuel, liquid urea, lost revenue due to increased vehicle weight, and the training and maintenance required for SCR systems. However, Navistar concedes, SCR engines likely will use less diesel fuel.

Advanced EGR requires dual turbochargers. The first, smaller turbo spins up immediately to provide boost at low engine speeds. The second, larger turbo provides maximum power at higher engine speeds. Navistar also placed an inter-stage cooler between the turbochargers to help reduce air temperature going into the cylinders, allowing more air to be packed into the large second-stage turbo for maximum power at high engine speeds.

Fuel Economy
Cummins says it has tested an in-cylinder approach (EGR only). But the company says its research indicates a 5 to 10% advantage in fuel economy relative to EGR-only solutions for mid-range and heavy-duty engines. The Cummins ISX15, a heavy-duty 15-liter engine, will deliver a 5% fuel economy improvement over the company’s 2007 ISX engine.

And Cummins touts several other advantages of SCR technology:

Performance– Cummins heavy-duty and mid-range engines will deliver the same power and torque as previous products without increasing displacement. “Our experience with in-cylinder technology confirms a deterioration of 50 to 100 horsepower in performance for the same displacement,” says Cummins. Throttle response will be improved relative to previous excellent products and will be much more responsive than a 2010 EGR approach.

Driveability– The engine has a larger “sweet spot” for easier driveability, producing optimum fuel economy and performance.

Reliability– The new Cummins SCR system is much less complex than the in-cylinder approach, which requires significant changes to the EGR system, air-handling system and vehicle cooling system. “In addition, our experience with the in-cylinder approach showed (less durability) due to internal engine condensation issues,” says Cummins.

SCR technology is not new to Cummins. In 2006, the company launched its Mid-Range engines certified to Euro 4 standard, using SCR for commercial vehicle applications in Europe. Cummins says it has built and shipped over 50,000 SCR engines to date that meet European standards. Additionally, Cummins Emission Solutions has built and shipped over 250,000 SCR systems.

Cummins initially explored an in-cylinder approach for heavy-duty engines and had always planned to use an SCR technology for mid-range engines. Then in August of 2008, Cummins announced that it would use SCR technology for both heavy-duty and mid-range engines to meet 2010 emissions regulations. Cummins and other engine manufacturers will continue to use cooled EGR technology in 2010.

Finding Urea Fluid
Diesel exhaust fluid, the urea solution required for an SCR system, is readily available at numerous retail locations including all Cummins distributor locations in the US and Canada. Cummins says operators will need to top off their DEF tank to ensure that the SCR system is working properly. DEF is a nontoxic, nonhazardous fluid that is available in a variety of packaging sizes from 1 gallon up to a 330-gallon intermediate bulk container. There are also solid plans in place for an “at-the-pump” offering of DEF; numerous locations in the US and Canada have this option available.

The sizing of DEF tanks may vary by vehicle manufacturer, but the typical consumption rate of DEF is 2% as compared to the rate of diesel fuel consumed. Cummins says that aside from the relatively infrequent fill-ups of the DEF tank, a gauge on the vehicle dash will illuminate or indicate a low DEF level. “That will serve as a friendly reminder for drivers to top off the DEF tank,” says Cummins.

Natural Gas Engine
Kenworth Truck Co. has introduced the Cummins Westport ISL G natural gas engine as available in its T800 short hood and W900S models. The natural gas models are focused on vocational, municipal, pickup and delivery applications.

The ISL G engine operates on either compressed natural gas (CNG) or liquefied natural gas (LNG), both of which are cost-effective, low carbon and low emissions fuels. Rated at 320 horsepower and 1,000 foot-pounds of torque, the ISL G is 2010 compliant with a maintenance-free, three-way catalyst and does not require the use of SCR or a diesel particulate filter. CNG and LNG tanks can be configured to suit customer applications and range requirements, Kenworth says.

In June 2009, Kenworth introduced its new T470 model for snowplow, construction dump, mixer, winch, refuse and other applications. The truck is powered by a 9-liter Cummins ISL engine with 345 horsepower and 1,150 foot-pounds of torque. Other features include a range of manual and automatic transmissions; and 12,000-pound to 22,000-pound rated front axles; 21,000-pound to 26,000-pound-rated single rear axles and 40,000-pound to 46,000-pound-rated tandem rear axles.

New From Volvo
Volvo Trucks North America has introduced two new heavy-duty truck engines, both manufactured in Hagerstown, MD. The company replaced its 12-liter engine with the D-13, a 13-liter engine that ranges from 375 horsepower and 1,450 foot-pounds of torque up to 500 horsepower and 1,750 foot-pounds of torque. What’s more, says Frank Bio, trucks product manager, the company now makes the D-11, an 11-liter heavy-duty engine that’s a bit lighter for appropriate applications, such as concrete mixers. The D-11 ranges from 325 horsepower to 405 horsepower and from 1,250 foot-pounds of torque up to 1,450 foot-pounds.

From the factory, Volvo now makes dual Power-Take-Off options for construction trucks-front and rear mounted.

“And we’re extremely excited about the new Volvo I-shift transmission,” says Bio. I-shift is an automated manual transmission. That is, it shifts electronically without a clutch. “In 2010 we’re introducing a new version of the I-Shift called P-Plus,” says Bio. “It provides for faster shifting-performance designed for construction. It will skip-shift-go into the gear it needs.” The Volvo I-Shift is only available on trucks with Volvo engines.

In addition, Volvo offers a full lineup of Eaton and Allison transmissions in VHD models, which are the company’s vocational trucks.

Bio says the EPA is controlling the positions of the exhaust train all the way from the engine to the outlet of the SCR unit. “Those are all certified,” he says. “We’re using the same engine for 2010 as we did for 2007-2009, and the diesel particulate filter is the same. The only thing we’re adding is the SCR units and the tank and the injector for injecting fluid between the diesel particulate filter and the SCR unit.”

The Side-Dump Alternative
If your application permits it, a side-dump trailer can haul and dump more material in a day than an end-dump, says Ralph Rogers, president of Side Dump Industries in South Sioux City, NE.

“Our cycle times are faster,” says Rogers. “And our side-dump trailer is much safer, because it doesn’t upset nearly as easily as an end-dump. And our trailers don’t leak. All end-dumps have tailgates that leak everything from liquid to sand and other materials.”

Tandem-axle trailers from Side Dump Industries feature hydraulic rams that tilt the dump body onto its side. These side-dumps can tilt and dump material to either side of the trailer, and they dump clean.

Raymond Nethercott of Nethercott Inc. says he has used his Side Dump Industries trailer to haul top soil, sand, and rock. A tandem-axle side-dump trailer can average about 25 tons of rock per load. “I like the way it dumps clean and how stable it is,” says Nethercott. “I’m on my second year and still have no stress cracks. It’s been a dependable trailer and has done a good job for me.”

When it’s fully tilted, the side dump’s tub side makes a 50-degree angle with horizontal. “We’re as high as 22% better than other side dumps,” says Rogers. “That 50-degree angle makes it dump very clean. We also dump further away from the wheels than our competition. And we can dump over Jersey barrier [K-rail].”

Mack Debuts Two Hybrid Trucks
Last October, Mack Trucks displayed a diesel-electric hybrid tractor, built for transport use by the US Air Force. The truck was on display at the Hybrid Truck Users Forum national conference in Atlanta. The Mack Granite model represents the latest generation of heavy-duty hybrid technology and meets the near-zero EPA 2010 emissions standards.

The Granite model diesel-electric hybrid power train features an integrated starter, alternator, and electric motor. The system captures energy from braking in the form of electricity, stores it in a 630-V, lithium-ion battery pack, and uses it to power the electric motor, which assists the Mack MP 7 diesel engine with propulsion of the truck.

Depending on the truck’s application, Mack’s hybrid technology demonstrates as much as a 30% fuel economy improvement. Mack says better fuel economy translates into lower emissions of greenhouse gases, a smaller carbon footprint, and less dependence on imported oil.

Earlier in the year, Mack displayed a hybrid refuse truck in Washington DC.

“Our hybrid technology will be commercially viable, yet it will take time to establish a robust hybrid market for heavy vehicles that will enable us to invest in large-scale production,” said Dennis Slagle, Mack president and chief executive officer. “Government incentives will accelerate the adoption of Class 8 hybrids and bring forward positive environmental changes.”

Until such economies of scale are established, most heavy-duty hybrids will be sold at a very high premium compared with non-hybrids, Slagle noted. Once a market is established and production volumes reach the point where the price difference becomes less, the savings from fuel and maintenance with Mack’s hybrid system should be enough to recoup a payback within a few years, the company says.

Here Come On-Road Caterpillar Trucks
Caterpillar Inc. and Navistar International Corp. have signed a definitive agreement to produce Caterpillar heavy-duty vocational trucks for sale in North America.

Under the strategic alliance Caterpillar and Navistar will develop and manufacture a new line of heavy-duty Caterpillar vocational trucks for North America only. The new Caterpillar trucks will be codeveloped by Caterpillar and Navistar and manufactured in Navistar’s facility in Garland, TX. The trucks will be sold and serviced through the Caterpillar North American Dealer network.

Caterpillar is leaving the domestic truck engine business. But Caterpillar did recently do a deal that allows Navistar to base an upcoming MaxxForce engine on technology from Cat’s C15 engine.

The Caterpillar trucks will feature key Caterpillar proprietary components and technology and will target customers who operate in a wide variety of vocational applications, such as earthmoving, quarry, waste, mining, general and heavy construction, logging, and road construction.

The new Caterpillar on-highway vocational trucks will go into full production in mid-2011. The trucks will be sold and serviced exclusively by Caterpillar dealers in North America.