Truck Engines Incorporate Advanced Engineering to Meet Phase 1 Greenhouse-Gas Standards
This story appears in the March 13 print edition of Equipment & Maintenance Update, a supplement to Transport Topics.
The diesel engines built this year are more efficient as the second step of greenhouse-gas Phase 1 standards takes effect. These power plants also offer improved reliability, advanced engineering, reduced maintenance and performance improvements that fleet managers and truck drivers will notice, industry experts said.
According to the Federal Register, diesels used in heavy-duty tractors will have to consume, in a particular duty cycle, 15 fewer grams per horsepower-hour of diesel fuel, a savings of 3.08%. The new engines incorporate many components that reduce friction. In addition, they feature longer oil-change intervals, in most cases made practical via the use of the new American Petroleum Institute PC-11 engine oils.
All of these engines are on the road today, having been extensively tested not only by the manufacturers but also in significant numbers in daily service in large and medium-size fleets during much of 2016, according to the engine makers.
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Tim Proctor, technical leader for heavy-duty products at Cummins Inc., described changes in the new version of its 15-liter platform, the X15. The X15s are in two families — the Efficiency Series, which provides 400 to 500 horsepower and up to 1,850 pound-feet of torque, and the Performance Series, which provides 485 to 605 hp with up to 2,050 pound-feet of torque. The Cummins-Eaton SmartAdvantage powertrain will use the Efficiency Series.
The engine maker prioritized reliability over fuel economy, said Clint Garrett, X15 product manager at Cummins Inc. “One day of downtime can wipe out a 2% reduction in annual fuel consumption,” he said.
Both engines offer improved fuel economy via changes, such as improved passages in the cylinder head.
But the Efficiency version includes the “Atkinson Cycle.” This involves subtly altering the opening and closing of the intake and exhaust valves. Ultimately, this means the 15-liter power plant behaves like a smaller engine in terms of breathing, while taking advantage of its larger cylinders to provide more expansion of the hot gases, converting more cylinder pressure into horsepower.
Proctor and Garrett noted the improved piston, which carries heat away from the combustion bowl more effectively, allowing a reduced volume of piston cooling oil, thus enabling downsizing of the oil pump. The smaller pump saves fuel, and, because the oil spends less time exposed to intense heat, oil changes under linehaul operating conditions have been extended.
At Navistar International Inc., the company will be replacing the N-13 engine with the A-26, said Darren Gosbee, Navistar’s vice president of engineering. The A-26 is a 12.4 liter engine.
A three-year project had redesigned all the engine components while retaining the bore and stroke, which was determined to be “optimum for performance,” Gosbee said.
The A-26 will be branded “International,” Gosbee said. It’s the new 13-liter engine is compliant with the 2017 Phase 1 GHG standards. “The biggest challenge was optimizing the breathing and fuel systems,” Gosbee said.
A new Bosch common-rail injection system will supply fuel, while a new single, variable geometry turbo will supply air through valves placed at a more ideal angle in the cylinder head. Gosbee said easy breathing, termed “gas exchange” by engineers, is critical in reducing carbon dioxide. Removing the second turbocharger and inter-stage cooler greatly simplifies service and repair, making the side of the engine “much cleaner,” Gosbee said.
Navistar’s software allowed accelerated development of its proprietary digital engine controls. Many functions that used to be performed with hardware have been replaced by software, which further increases reliability and optimizes fuel consumption, Gosbee said. New specifying tools will tailor the cruise rpm to the fleet’s operating speed so as to avoid “shift busyness,” he said.
The N-13 will be available in parallel with the A-26 in linehaul and regional haul vehicles, while availability of the A-26 won’t come until the end of the year in vocational and severe-service applications, Gosbee said.
As for Volvo and Mack, the biggest change in their 2017 engines is the Wave piston, said Volvo’s John Moore, powertrain product marketing manager. With a traditional combustion bowl, as the six spray jets of fuel contact the wall of the bowl, they spread out and contact each other, he said, noting they “compete for each other’s oxygen.” These rich zones of unburned fuel leave the combustion chamber as soot, Moore said. The Wave piston includes protrusions that turn the spray jets around and divert them back into the center of the combustion chamber, using all the available oxygen, he said.
Soot is reduced by 90%, but this improvement also enabled the companies to increase their engines’ compression ratio from 16:1 to 17:1, yielding higher efficiency.
Volvo and Mack, which are part of Volvo Group, also replaced their previous unit injectors with a common-rail injection system. Common-rail allows the companies to create as many as 10 injection events per combustion cycle versus four with the old system, Moore said.
Scott Barraclough, Mack technology product manager, added that due to the flexibility of the injection system and the effectiveness of the Wave piston, combustion has been improved throughout the torque range. Sound quality has been improved, leading to a quieter driver environment, he added.
Volvo also will market the D13TC mid-year, Moore said. This is a 13-liter engine equipped with turbo compounding, which provides a second turbine located behind the turbocharger in the exhaust system. The system is tuned so peak torque is carried down to 950 rpm versus 1,050 with the standard turbo. This allows use of a 2.41:1 rear axle ratio and a cruise rpm of 1,069 at 65 mph versus 1,142 with the standard XE package.
A Mack version, available with the Super Econodyne drivetrain, will be called the “MP8 with turbo compounding,” added Barraclough, who said that peak torque will be available down to 900 rpm.
At Detroit, a unit of Daimler Trucks North America, Ed Byk, product manager for medium- and heavy-duty engines, said the company’s GHG 2017 engines have been in production since January 2016. The engines employ both the enhanced ACRS, or amplified common-rail injection system, and the asymmetric turbocharger.
The DD15 got the second-generation ACRS in 2014 and the DD13 and DD16 have it on all 2017 GHG-compliant engines. It provides injection pressures up to 38,000 psi and “improves performance and lowers emissions throughout the torque range,” Byk said.
The DD13 and DD15 have a new piston that has a new oil control ring with reduced tension and contact pressure, which reduces friction.
The asymmetric turbocharger is a custom design that Byk said is simpler, without the wastegate used on earlier designs, more efficient and better matched to the exhaust gas recirculation, or EGR, system.
A redesigned EGR valve is located in the center of the exhaust manifold and manages EGR flow better, enabling elimination of the turbo’s wastegate. Better matching of exhaust flow to operating conditions aides fuel economy, too, which is 1% better on the DD15 and 2.5% better on the DD13 for 2017, Byk said.
The Detroit diesels also all offer a downspeeding rating, and peak torque is provided down to 950 rpm.
As for a fleet perspective, Randy Swart, chief operating officer at A. Duie Pyle, said his fleet purchased a mix of more than 200 Volvos and Freightliners in 2016 with 13-liter engines. The Freightliners have Detroit diesels that are 2017 GHG compliant. Average fuel economy for the entire fleet improved from 6.25 mpg during the first quarter to 6.5 mpg during the fourth quarter. A few minor electronic glitches have occurred, but there has been no trouble with the engines, he said.
At Paccar, Jason Johnson, director of aftermarket, said the Paccar MX-13 and MX-11 will deliver peak torque down to 900 rpm instead of at 1,000 for the majority of ratings. Also the MX-13’s maximum output has been increased to 510 hp and 1,850 pound-feet of torque, while the MX-11’s maximum ratings are now 430 hp and 1,650 pound-feet.
“Moving peak torque to begin at 900 rpm was done to further improve the driver experience,” he said, noting Paccar is maintaining current gearing recommendations for 2017.
Another fleet, Walpole Inc., has 275 power units operating in several different segments, said Ryan Walpole, director of corporate purchasing and maintenance at the Florida-based fleet. The company is predominantly Paccar MX-powered, at 215 units. The fleet converted to the MX-11 when spec’ing newer units.
“We haul both sugar and flour over-the-road,” Walpole said. He said he spoke with several drivers “and found there is a learning curve. They needed to learn to downshift at a different point because of the new torque curves.”
But, they said both fuel economy and performance are excellent, Walpole said.
The company gets an average of 6.3 mpg with its 2012 engines and its 2017 engines get 6.9 to 7 mpg, he said.
Paccar’s Johnson, meanwhile, wouldn’t detail internal hardware changes but only said that Paccar “did make several changes to improve air management, combustion, and to reduce friction losses.”
Other changes were described in a release: “The 2017 Paccar engines include a new, single cylinder air compressor, variable displacement oil pump, and variable speed coolant pump providing customers with fuel economy gains over the previous design.”
None of the OEMs would comment on the pricing of their engines for this story.