Because of greater combustion efficiency, Detroit Diesel’s Siler says trucks equipped with SCR will see significant improvements in fuel economy. “Our 2010 DD15 engine will get between 3 and 5 percent fuel economy than our current engine and we think those numbers will only improve in the long run,” he says. “Most fleets would switch engines over a 2 percent increase in fuel economy. So even after factoring in the new cost of buying diesel exhaust fluid, we believe — that for the first time – that our emissions technology will actually deliver a positive economic impact for end users while delivering clean air to our environment.”

Given all the passion and controversy surrounding DEF, the fluid itself is largely unremarkable. It’s colorless and odorless. It is not classified as a hazardous or toxic material by the EPA. “Some of the claims that were made were about DEF over the past couple of years are patently untrue,” says Ed Saxman, product manager, drivertrains, Volvo Trucks. “DEF is not explosive, it’s not flammable, it’s not an aggressive substance. Put it on your hands and they are no less irritated than if you get diesel fuel on them. You want to go wash your hands, of course, but it’s not any worse than that. It’s mostly water. It has a residue to it when it dries, but that easily washes off.”

Siler says it’s important to remember that DEF usage rates are only 2 to 3 percent of a truck’s fuel consumption. “Daimler tanks will be offered next year with 6, 13 and 23 gallon DEF tanks. (We suspect the 13-gallon option will be the most popular.) For some perspective, a 23 gallon DEF tank gives you a range of 6,000 miles before a refill is necessary. A 13 gallon tank will have a range of 3,900 miles before a refill is needed.”

If a DEF tank does run dry, the driver will have powerful incentives to pull over and fill it back up. In Daimler trucks, a series of color-coded dash lights green, yellow and red – in addition to a DEF gauge – will keep a driver informed of the tank level. When the DEF tank runs dry, or if sensors detect high emissions due to improper fluids in the tank (water, for example), the engine will derate to 35 mph – enough to get to a refill point for the DEF tank. Eventually, the engine will derate to only 5mph in extreme cases. But given DEF’s long legs, Siler thinks it is highly unlikely drivers will be unable to find DEF and keep their tanks full.

As for DEF’s freezing at 12 degrees, that’s simply chemistry. But all SCR manufacturers have placed immersion heaters in their DEF tanks. And as Mack’s McKenna explains, DEF thaws rapidly and is not adversely affected by freezing. “SCR trucks will start and run with frozen DEF in the tanks,” he stresses. “We have done extensive cold-weather testing and found no operational issues related to frozen DEF.”

Gregg Stumbaugh corporate equipment director, with California-based Biachi Brothers is worried about the additional cost of SCR technology, which some analysts predict could be as high as $8,000 per new truck and the additional weight SCR adds to each chassis. “We also don’t know enough about the additional costs for maintenance and repair of SCR systems over the life of the truck,” he notes. “And we don’t know how reliable the SCR system as a unit will be over the life of the truck. The bottom line is that our company does not want to be a “guinea pig” for the SCR system. We are in the process of running a demo International truck with the Maxforce engine with the enhanced EGR system and see the International as a possible option.”

Although Shick believes EGR will work well in all trucking applications, he feels there are specific applications where it will prove to be the preferred emissions solution. “Since the big advantage of EGR is it adds no weight and bulk from additional apparatus and requires no technician/driver involvement, we think its biggest impact would probably come in complex vocational body applications like aerial lift trucks, municipal vehicles/snowplows, digger derricks, and refuse packers that will be challenged by additional weight/bulk of SCR apparatus,” he says.

It’s an argument Detroit Diesel’s Siler isn’t buying. “With the Detroit Diesel BlueTec emissions technology we know that our customers will benefit from not only better fuel economy but also a cleaner running system,” he counters. “Plus, we aren’t ready to concede the question regarding complexity and packaging. With Damiler’s BlueTec 1-Box system we have been able to integrate the aftertreatment and chassis into a surprisingly compact and simple design. In 2010, we expect at least 80 percent of all 2010 compliant trucks to be SCR.Eventually, we believe that share will increase even more as the full benefits of SCR are proven.”

“Remember,” says Saxman, “SCR is not new technology. It’s been used for five to seven years around the world in heavy trucks and other applications for even longer. We’ve built well over 150,000 trucks in our group of companies with SCR and have over 2 million test miles on SCR trucks in the United States alone. The emissions technology we introduced in both 2002 and 2007 was all new, by comparison. We’re going into to 2010 with far more testing and experience behind SCR than we ever had on our previous emissions systems.”v

Diesel Exhaust Fluid

Its basic stats are pretty straightforward: Diesel exhaust fluid (DEF) weighs 9.2 pounds per gallon. It starts to turn to a gel at 25 degrees Fahrenheit and freezes at 12 degrees. And it is true that onboard sensors will derate an SCR-equipped truck if DEF is not being injected into its exhaust stream – whether because of a frozen solution or a dry DEF tank.

There are some warm-climate DEF concerns as well. Despite rumors that DEF breaks down at 86 degrees, Fahrenheit, David Siler at Detroit Diesel says testing has shown it has a shelf life of 44 months when kept at a constant 74 degrees and can last as long as 7 months at 95 degrees.

Still, the lack of a DEF infrastructure in the United States was an initial reason the EPA opposed SCR technology when it was first suggested as path for meeting EPA ’10. According to Cliff Dean with the EPA’s Office of Transportation and Air Quality, the agency is now convinced DEF will be readily available in January and is, in fact, the best way available now to meet emissions regulations when they come in effect.