Trucks at Work

The next step in smaller diesels

A lot of interesting stuff gets unveiled at the annual Mid America Trucking Show (MATS), but one of the more interesting things that will make an appearance this year is a new small-size four-cylinder 2.8-liter prototype diesel engine developed by Cummins Inc. as part of a four-year joint program with the U.S. Department of Energy (DOE).

The DOE’s effort, dubbed the Advanced Technology Light Automotive Systems or “ATLAS,” aims develop a commercially viable diesel engine for the half-ton pickup truck market that is capable of meeting future Tier 2 Bin 2 emissions regulations as well as corporate average fuel economy (CAFE) and stringent greenhouse gas (GHG) requirements out to the year 2025.

Cummins plans to show off its 2.8-liter diesel prototype in a 2010 model Nissan Titan pickup – meaning this small-sized diesel is designed to do the same work that the truck’s original gasoline-fired V8 engine performed, which translates into maintaining a torque output of 385 lb.-ft., noted Michael Ruth, director/technical project leader-advanced light-duty for Cummins in a statement.

“When we launched ATLAS, the team understood that they had to think outside the box to achieve our targets,” he explained. “Specifically, we knew that weight reduction, advanced emissions control technologies, advanced thermal management and powertrain integration would be critical to meeting all of the requirements. The challenge was making those significant advancements while ensuring that the engine we produced would be commercially viable.”

The end result after four years of work is this 362-lb. 2.8-liter engine that features an aluminum block, head and oil pan, a magnesium valve cover and an engine-mounted emissions control system. Altogether, Ruth said that Cummins’ ATLAS engine, including its on-engine aftertreatment system, weighs in at approximately 80 lbs. lighter than the all-aluminum gasoline-powered V8 in replaced in the Titan test truck.

He added that Highway Fuel Economy Test (HFET) and FTP-75 Test (city) cycles showed that the 2.8-liter could attain fuel economy of over 35 miles per gallon (mpg) and 25.5 mpg, respectively -- approximately a 53% increase in CAFE fuel economy as compared to the gasoline V8’s fuel economy of 18.9 mpg.

Just as critical, Ruth noted that the new 2.8-liter’s emissions are lower than the Tier 2/Bin 2 GHG levels.

So how did Cummins get such a small diesel to deliver all these goodies? The first part is the all-aluminum block, Ruth explained. Next, though not visible from the outside, the engine is a through-bolt design with a structural cradle above the oil pan and another above the cylinder head, “sandwiching” the block and head and enabling very high cylinder pressure capabilities.

A “dual loop” exhaust gas recirculation (EGR) system with both low- and high-pressure circuits and switchable valve timing improve light load emissions output and allow for increased power density of the engine. Then there’s the overhead camshaft, driven by belt-in-oil technology that is designed to last the life of the engine.

Ruth noted that Cummins’ 2.8-liter ATLAS engine also uses ceramic glow plugs, a high pressure common rail (HPCR) piezo-style fuel system complete with a Bosch high-pressure pump and variable geometry turbocharger.

In partnership with Johnson Matthey, Cummins developed an on-engine exhaust aftertreatment catalyst that features selective catalytic reduction (SCR) wash-coat technology applied directly to the particulate filter.

Finally, an 8-speed ZF 8HP70 transmission keeps the ATLAS 2.8-liter operating at an optimum speed, helping to achieve a more than 50% fuel-economy improvement over the gasoline V8. Ruth added that only the transmission and engine in the 2010 Titan pickup test truck were changed; the rest of the vehicle’s components remained untouched.

Cummins added that the official closing of the four-year ATLAS project occurs June 8-12 in Arlington, Va., at a special ride-and-drive event at the DOE's 2015 Annual Merit Review.

Then we just need to wait and see if and when a version of this new “small sized” diesel makes its way into the U.S. pickup market.

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