With Cummins’ new engines, “Customers will see up to a 5 percent improvement on some ratings,” says spokesman Lou Wenzler. Cummins’ plan to increase the displacement of its ISX engines from 15 liters to 16 liters for the higher power ratings in 2010 has been scrapped since it will no longer be necessary for the engine to swallow more exhaust than in 2007.
Paccar’s new heavy-duty engines will make their debut as 2010-compliant. “Our tests and experience with SCR in Europe indicate the improvement in fuel economy can be as high as 5 percent,” says Allan Treasure, Paccar marketing manager. Paccar expects DEF consumption will be about 2 percent of diesel fuel in normal conditions. Cummins also puts DEF usage at 2 percent.
Cummins uses the example of a truck running 120,000 miles per year and getting 6 mpg, which means 20,000 gallons of diesel fuel. That truck would use 400 gallons of DEF (at a 2 percent consumption rate), requiring 20 fill-ups of a 20-gallon DEF tank, which means a refill every two to three weeks. DEF is forecast to cost the same as or less than diesel fuel.
Mack’s McKenna says that EPA wants the DEF tank to hold enough fluid to last through two diesel refueling cycles. A 100-gallon diesel capacity and a DEF dosing rate of 3 percent would dictate a six-gallon DEF tank. A truck that achieves 6 mpg will get 200 miles per gallon of DEF.
Operational costs and inconvenience is one reason Navistar, maker of International Trucks, is staying away from SCR and using only enhanced EGR, says Tim Shick, director of engine marketing. “One estimate is that DEF will cost half of what diesel fuel costs,” he says. “But, we asked ourselves, how variable is the cost?”
Also, Navistar believes the volume of DEF consumed is typically very close to the amount of fuel saved by an SCR system, meaning little or no net reduction in overall fuel cost.
SCR also has the handicap of “250 to 500 pounds added weight,” Shick says. Detroit Diesel estimates 250 to 400 extra pounds, says spokeswoman Hallie Fisher.
Shick also says EGR alone is simpler and “transparent to the customer. There were initial problems with EGR valves, but now they are reliable.”
Because “maintenance and related problems would go up without high-pressure common rail,” Shick says, the 2010 MaxxForce engines will use a high-pressure common-rail injection system developed even beyond what’s on the engine today to optimize performance and minimize engine stress. This system will also allow the engine to cruise efficiently at very low rpms.
Navistar’s strategy will be to introduce an engine that doesn’t quite meet the EPA standard but will be legal because it uses emission credits the company accumulated from exceeding standards with prior engines. Meanwhile, engineers will continue to calibrate functions inside the cylinder to achieve a fully compliant engine.
In 2010, Cummins will introduce its new XPI common-rail fuel system, which, at low rpms, operates at a much higher pressure than the present system and allows multiple injections. It enables the engine to burn cleanly while ingesting less air. Wenzler says, “This allows for flexibility in tuning for fuel economy and low emissions, while also minimizing engine stresses.”
Detroit Diesel’s DD15 has what it calls an amplified common rail fuel system. It has all the same advantages as other common-rail systems, but the piping that carries the fuel around the engine handles much less pressure. A double-ended amplifier piston located near the injector increases the fuel pressure to the desired value hydraulically.