After years of emissions hurdles and technology evolutions the current 2010 compliant engines deliver better fuel economy, will likely last longer, and, in some cases, offer longer oil change intervals than past engines. The following is a quick guide to what is being offered today from the major engine manufacturers in the Class 8 market.
Cummins’ ISX15 was introduced in 1998. Design of its block was optimized through new electronic tools to minimize noise and weight. The engine also had an integrated engine brake.
The cylinder liners got an improved hardening process in 2002 because exhaust gas recirculation can cause corrosion of the wear surface. Also, the piston pin was supplied with lube oil under pressure to allow the piston to carry the additional cylinder pressure of EGR. The harder liners actually extended life. Other features include a combination full-flow and bypass oil filter from Cummins Filtration.
torque: 1,450-2,050 lb.-ft.
Bore and stroke: 5.4 in. by 6.7 in.
Displacement: 15 liters
Lube Oil capacity: 14 gallons
In 2007, a new combustion chamber was introduced. It stirs up the air around the fuel sprays to allow increased EGR levels with less air. The result was little or no increase in cylinder pressure while other engines were forced to handle more pressure in their cylinders.
2010 brought a new injection system, the XPI common rail design. The original, simple ISX fuel system was not able to split each injection cycle into separate shots of fuel. The XPI system allows a “pilot” shot of fuel early in compression to produce much quieter and faster ignition, and enables each main shot of fuel to be split up, to reduce nitrogen oxide (NOx) and soot. It provides fuel pressure independent of rpm to a large pipe, or common-rail. Maximum injection pressure even below the torque peak means a better torque curve, improved fuel economy, less soot for the DPF to handle, and faster, quieter cold starts.
Equipping 2010 and 2011 models with Cummins Filtration’s own integrated DPF and SCR system with a copper-zeolite catalyst means less EGR and more favorable engine tuning. This gives 3 to 5 percent better fuel economy, depending on the application.
Cummins also offers the ISX 11.9-liter engine, which has the XPI fuel system and a rear-driven camshaft. It offers maximum ratings of 425 horsepower and 1650 lb.-ft. of torque.
Detroit Diesel, which will be rebranded as Detroit later this spring, and its parent company, Daimler AG, developed the DD13, DD15 and DD16. The DD16 is an owner-operator/heavy-haul version of the platform displacing 15.6 liters.
The 15- and 16-liter versions have a turbo-compounding system, says Admir Kreso, senior engineering manager at Detroit. The turbo-compounding turbine sits behind the regular turbo, but instead of driving a compressor for the intake air, it drives the crankshaft through hydraulics and a geartrain. It recovers energy that would otherwise be lost, so, in addition to saving fuel, it increases power output.
The turbo-compounding system also provides the exhaust backpressure necessary to make the EGR system work without a variable geometry turbo. So the DD16 also uses a simple, non-wastegate turbo, which is claimed to provide quick throttle response.
Says Kreso, “There are many design elements of the Detroit DD16 that enable it to deliver outstanding power, torque response and fuel economy.” The engine includes an integrated Jacobs engine brake, integrated coolant passages (to reduce leak points), a webbed engine block, patterned cylinder liners, the amplified common rail fuel system (ACRS), and Detroit BlueTec emissions technology. Webbing on the block increases its strength and rigidity without adding much weight; and patterned liners do a superior job of retaining oil in their bores to lubricate the pistons and rings. Detroit’s proprietary 1-Box emission package forces exhaust through two identical diesel oxidation catalysts, diesel particulate filters, and selective catalytic reduction catalysts rather than one, which the company claims reduces backpressure and helps conserve fuel.
Torque: 1,750-2,050 lb.-ft.
Bore and stroke: 5.47 in. by 6.73 in.
Lube Oil capacity: 47 quarts
The ACRS system provides injection pressures well over 30,000 psi, yet the external piping needs to carry only about 13,000 psi. This pressure is hydraulically amplified inside each injector as it delivers fuel. It’s a common-rail design, with an external pump that supplies fuel pressure independently of rpm, so full injection pressure is available even below the torque peak. This optimizes the torque curve and reduces emissions. Each injection cycle has rate shaping, delivering fuel more slowly at first to keep emissions low, but speeding up later to give good fuel economy.
The combination of a sophisticated integral full-flow and bypass oil filter and the efficient combustion produced by the ACRS means maximum oil change intervals up to 50,000 miles for on-highway engines.
International impressed the market with the 2008 introduction of its 11- and 13-liter MaxxForce Big Bore engines, featuring common-rail injection and a compacted graphite iron block. In 2010, the truck and engine maker declared it would use advanced EGR, rather than SCR, to meet the low 0.2 grams/horsepower/hour NOx standard for 2010.
Part of the recipe is International’s ability to burn credits, killing NOx down to about 0.5 grams per horsepower-hour while further development work proceeds. The result, claims International, is an engine that delivers fuel economy that is at least as good as its 2008 version. The combination of a relatively small 12.4-liter block of CG iron, and a vehicle that has no SCR catalyst or DEF tank, also helps ensure maximum payloads.
International says that because CG Iron is incredibly strong, castings don’t have to be as heavy, reducing weight by 500 pounds.
An important part of the design is the common-rail injection system. The fuel pressure is generated by a crankshaft-driven pump in which output can be adjusted for the conditions. It feeds a large pipe called a “common-rail” that is connected to all six injectors. It can generate maximum injection pressures even at 1,000 rpm. The company keeps raising the pressure to improve the system’s performance as it develops the engine.
Another secret is the engine’s “redesigned, double combustion bowl, which combines with the higher fuel injection pressure to break the fuel up into a finer mist spread evenly inside the cylinder,” says Tim Shick, director of marketing and field support in International’s big bore engine business.
MaxxForce Big Bore
Horsepower: 410, 430, 475
Torque:1,450, 1,550, 1,700, plus 1,750 multitorque
Bore and stroke: 4.96 in. by 6.54 in.
Displacement: 12.4 liters
Lube Oil capacity: 42 quarts
These features combined with cracked cap technology in the connecting rod bearings allow the engine to develop peak torque all the way down to 1,000 rpm.
The engine’s air handling system combines twin series turbochargers with an inter-stage cooler that uses low temperature coolant to remove the heat created by the primary turbocharger. This “increases air density to maintain peak power as speeds increase,” the company says. Also, “the smaller, primary turbo responds quickly for immediate takeoff at low engine speeds, and the larger, secondary turbo provides peak power at higher speeds and on steep grades.”
The exhaust entering the intake system is cooled to a low temperature in the final stage of the EGR cooler using low temperature coolant. Twin EGR circuits take advantage of exhaust pulses to help recirculate the exhaust with a minimum of backpressure, too.
2010 revisions include a Spinner centrifugal oil filter that increases change intervals for vehicles getting 6.5 mpg from 25,000 to 40,000 miles.
The Mack MaxiDyne engine of 1965 offered an unusual, flat power curve. Says David McKenna, Mack’s director of powertrain sales and marketing, “This was achieved with a broad expanse of torque at the bottom end. Where torque tapered as rpm rose, horsepower picked up the slack.”
Mack’s modern on-highway MaxiCruise engine, the 13-liter MP8, resembles the Maxidyne, though the curves are slightly different. “Customers always look for that bottom-end grunt that Mack engines offer,” McKenna says. “We had to maintain that.”
Where it distinguishes itself from its predecessors, though, is where its horsepower peaks. McKenna says Mack dubbed the engine a “hump horsepower engine,” meaning it offers more horsepower when running at cruise speed than at higher rpm levels.
“At 1,400 rpm, you could have 505 horsepower, yet at 1,800 rpm, you might be down to 420,” he says. “This encourages drivers to operate closer to what benefits them. It offers them a lot of power in and around the sweet spot.”
Mack’s engine shares architecture with the Volvo D13, an engine that was beefed up in 2007 with a cylinder block and internal components that were different from the earlier design. The changes were aimed at both Mack and Volvo. Its piston stroke was increased to make it larger, which helped to minimize the mechanical stress that came as EGR levels were increased. The taller cylinders lowered the engine’s sweet spot rpm, which meant an improvement in fuel economy and low speed torque. Modifications also included a more powerful unit injector injection system with the capability to deliver extreme pressure, split injection and, now, rate shaping. This delivers the fuel at a varying rate during each power cycle to help control emissions and optimize fuel economy.
Mack has distinguished the engine from Volvo’s by using different external parts that help serviceability in Mack’s different chassis, and the Mack engines perform quite differently. McKenna says this is because of the MaxiCruise’s torque and power curves.
Horsepower: 415, 445, 505
Torque: 1,460 to 1,760 lb.-ft.
Bore and stroke: 5.16 in. by 6.22 in.
Displacement: 13 liters
Lube Oil capacity: 33 quarts
A 2010 change to the engine was its migration from straight EGR to selective catalytic reduction. McKenna says Mack dialed back the EGR rate “substantially,” and increased the engine-out NOx to help keep the diesel particulate filter cleaner.
Mack also offers the MP7, an 11-liter engine with up to 405 hp and 1,560 lb.-ft. of torque, and the MP10, a 16-liter engine with up to 605 hp and 2,060 lb.-ft. of torque.
Paccar’s MX engine has one unusual design feature that enhances low rpm pulling power. It’s called “fractured cap technology” and involves the controlled breaking of a solid connecting rod or main bearing saddle and cap when they are made. The perfectly matched, rough surfaces that result hold rod and main bearing caps in more perfect alignment, allowing the bearings to handle more torque and vibration. This makes it possible to tune the engine to produce a “wide horsepower range and longer torque and power curves for more efficient operation,” says the company.
The engine uses compacted graphite iron (CGI) in both the block and cylinder head. “Using CGI in the block and head reduces weight and provides for a very high strength, reliable and quiet engine,” says Preston Feight, chief engineer for Kenworth Truck Co. The company says this also allows a B10 service life for the engine of 1,000,000 miles, which means 90 percent of engines produced are expected to last that long.
An unusual feature of the design is the single, in-block camshaft, which is driven from the flywheel end of the engine to minimize noise and vibration. The camshaft operates unit pumps to supply the injectors, four valves per cylinder, and the integral engine brake, which is rated at 465 hp. The in-block location allows a low total engine height for easier fit under hoods designed for ideal aerodynamics.
Those unit injector pumps are linked to the injectors through short pipes capable of handling extreme pressure. Electronically controlled valves on both the pumps and the injectors they feed coordinate fuel delivery.
Torque: 1,450-1,650 (1,550/1,750 multitorque) lb.-ft.
Bore and stroke: 5.2 in. by 6.5 in.
Displacement: 12.9 liters
Lube Oil capacity: 42 quarts
The MX also features an encapsulated wiring harness mounted directly to the block, said to “protect wiring from the elements and remove stress from connectors,” the company says.
“The oil filter module, which consists of a cartridge-style filter in combination with a centrifugal element, offers a maintenance interval of 40,000 miles. The module is located for easy access during service. When the cover is loosened, oil in the filter module drains back into the oil pan, which reduces the cleanup normally associated with an oil change,” Feight says.
Ed Saxman, Volvo Trucks North America’s director of powertrain marketing, says the Volvo D16 engine is “a standalone engine.”
“We have three engines that all have the same DNA, all using parts designed with the same basic concept. Yet the engines are clearly different, with dimensions like the spacing of the cylinders changing with the size.”
The 16-liter machine has a maximum rating of 550 horsepower with 1,850 lb.-ft. of torque. The design was optimized for the 2007 engine introduction, with the block and major parts receiving a redesign to strengthen them, and the engine getting a new EGR valve, a much larger EGR cooler and a new variable geometry turbocharger.
The engine uses camshaft operated unit injectors. The camshaft is driven at the rear, another change that came in 2007. This allows the flywheel to greatly smooth out operation and reduce noise produced by the gears that drive it, in spite of helping to produce extreme injection pressures. Saxman says the injectors were replaced recently with a new design that has special internal valves that allow rate shaping. This means the rate at which fuel goes in starts out slowly to make the engine quieter and help control peak combustion temperatures, and then accelerates to reduce particulate and fuel consumption. This means less work for the DPF and SCR systems
Torque: 1,850 lb.-ft.
Bore and stroke: 5.76 in. by 6.64 in.
Capacity: 16.1 liters
Lube oil capacity: 55 quarts
All Volvo engines have an engine brake with an extra bump from the cam that activates the brake. This charges the cylinder with pressurized air before compression, enhancing brake performance.
Saxman says D16 owners can get plenty of power, yet use it with a 3.08 rear axle and an overdrive I-Shift transmission to lower cruise rpm below what is normally seen to optimize fuel economy.
Volvo also has the D13, sized for good fuel economy and ideally adapted for highway operation with normal loads. Although the D13 is smaller than the 15-liter engines many truckers run, the block and internal parts are designed to deliver a service life comparable with larger engines. The D13 offers up to 500 horsepower and 1,750 lb.-ft. of torque.
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