2010 Engine Performance
Manufacturers say EPA-driven changes yield better fuel economy and other benefits.
The 2010 drop in NOx to 0.2 grams has been accomplished by most truck makers with selective catalytic reduction. Even with SCR’s requirement for adding diesel exhaust fluid, SCR has brought basic improvements.
That’s because letting SCR handle much of the NOx means less exhaust gas recirculation. Reducing EGR means the cylinders will need to contain less pressure, inviting modest performance and fuel economy improvements.
Torque curves are improved, too. Schneider National Vice President of Purchasing Steve Duley notes that “the engine manufacturers have taken advantage of having injection pressure available at any time during or after the compression stroke. Drivers report better acceleration and quieter running engines… Drivers like the power and overall performance.”
In Cummins’ case, the reduction in the amount of air plus exhaust needed is compounded by the adoption of the new XPI, high-pressure common rail injection system for 2010. Unlike unit injectors, the common-rail system provides whatever injection pressure is needed even at low rpm.
“With the rocker actuation of injectors in the past,” says Zack Ellison, Cummins’ technical director of customer support, “we had to tune the rocker lever for system performance in a way that gave less than optimum performance at low rpm” because of reduced atomization.
The result, says Ellison, is the ability to produce more torque at a lower rpm, and a more favorable torque curve, which “reduces the need to downshift.” He says peak torque is maintained down to 1,100 rather than 1,200 rpm on many of the ratings. So while Cummins has not introduced higher maximum power or torque ratings, an engine at a given rating will pull better and feel more powerful. They have, however, enhanced the number of SmartTorque ratings – 200 lb.-ft. of additional torque that shows up in the top two gears, giving drivers an incentive not to downshift.
Daimler Trucks made “no fundamental changes from EPA07 to EPA10” in engine power ratings for its Detroit Diesels, says Brad Williamson, engine and component marketing manager. “We have biased all benefits toward gains in fuel economy and durability.”
Mack’s David McKenna, director of powertrain sales and marketing, says EGR flow rates in 2010 engines are down to EPA02-like “light EGR” levels. “The peak power on the Mack MP8 engine has jumped from 485 to 505 hp, and from 1,660 lb.-ft. of torque to 1,760, with lower rejected heat. If you look back, each time the heavy-duty diesel industry has increased EGR flow rates, fuel economy suffered significantly. Mack ClearTech SCR reverses this trend.”
International’s Tim Shick, director of marketing for MaxxForce engines, the only on-highway engines not utilizing SCR technology to meet the 2010 standards, says the Big Bore engine’s maximum rating remains at 475 hp at 1,700 lb.-ft. Its performance curves have not changed.
However, the company has also introduced two multi-torque ratings – 430 hp with 1,550/1,750 lb.-ft and 450 hp with 1,550/1,750 lb.-ft. Although the base ratings remain the same, other changes like higher injection pressure and an improved charge air cooler mean the engine is “if anything, even more responsive than before,” Shick says.
Volvo’s Jim Fancher, powertrain product marketing manager, notes a power boost along with a reduction in the amount of cooled exhaust gas added to the mixture. “This decrease in exhaust gas results in a more efficient combustion event, yielding improved fuel efficiency, and an increase in horsepower/liter density. The decrease in exhaust gas also reduces the amount of ambient heat that must be dispersed.”