Update 2: Cummins, Feds Developing Four-Cylinder Diesel for Nissan Titan

Photos by Cummins, Nissan as published by the U.S. Department of Energy

Cummins is developing a high-efficiency inline-four-cylinder diesel engine with money from the U.S. Department of Energy and in partnership with Nissan for demonstration in the Titan light-duty pickup truck. The project was announced at the DOE’s 2011 Merit Review in Washington, D.C..

Most half-ton truck makers are betting on small-displacement direct-injection gasoline engines to meet future fuel economy regulations, but Cummins expects its small displacement oil burner to get 40 percent better fuel economy over current light-duty V-8 truck engines. The Cummins average fuel economy target for this new diesel engine is 28 mpg while meeting tough U.S. Tier 2 Bin 2 emissions limits, according to the presentation.

Getting 28 mpg combined mileage could mean more than 30 mpg highway, by our estimate, which could help Nissan meet strong new EPA regulations that will raise fleet fuel efficiency standards for light trucks and SUVs to 30 mpg by 2016. The standard for passenger cars is set at 39 mpg by 2016.

Prototype Cummins four-cylinder inline diesel in a current Nissan Titan's engine bay.

Though the project started in September, Nissan and Cummins have already built a prototype version of the four-cylinder diesel and installed it in a current-generation Titan mule for drive testing. Pictures of the engine show four high-pressure fuel rails feeding the engine’s cylinders.

Four cylinders might not seem like enough to power a full-size pickup but that architecture would be ideal to meet fuel economy goals while delivering almost as much torque as some small displacement gasoline V-8s.

The engine has a 2.8-liter displacement (170 cubic inches). Initial power figures on the engine dyno have the mule test engine producing 350 pounds-feet of torque at around 1,800 rpm. A chart in the presentation shows targeted power levels to be approximately 220 horsepower and 380 pounds-feet.

The engine is a derivative of the four-cylinder ISF architecture that Cummins builds overseas, with 2.8-liter and 3.8-liter displacements, according to a Cummins spokesman. The overseas 3.8-liter is rated at 168 horsepower and 443 pounds-feet of torque.

Side profile CAD rendering of the prototype I-4. Note the EGR cooler (purple) and turbo just below it. The front of the engine is to the right.

Innovations highlighted by Cummins in their presentation include the use of high-strength steel pistons instead of conventional aluminum pistons. Steel pistons can handle high power loads with a shorter stroke, which also helps reduce the overall height of the engine for improved underhood packaging. Cummins is also studying the use of variable valve technology, according to the presentation.

To meet U.S. clean-diesel standards, the 2.8 would use diesel exhaust fluid to scrub nitrogen oxide emissions, like Ford and GM use today in their heavy-duty diesel pickups. It would also feature a so-called passive NOx storage system that would capture and hold NOx during cold starts, releasing the gas when temperatures rise to levels of max efficiency for DEF. The passive system would save fuel used today to jumpstart NOx scrubbing when the system is cold.

The total size of the Cummins light-duty clean diesel project is a $30 million effort, with the DOE contributing $15 million. The program is scheduled to run through September 2014, the year in which we expect the to debut.

Nissan for several years studying the potential for a light-duty diesel in the Titan.

The current Nissan Titan is only available with a 5.6-liter V-8 gas engine that's rated at 13/18 mpg city/highway and 15 mpg combined fuel economy.

Stay tuned for more information as it develops.

[Sources: Cummins, U.S. Department of Energy]

Update 2: May-19, 2011 10:15 pm Pacific

We originally reported that "LA-4" was the codename for the engine. That's incorrect. LA-4 refers to the EPA's Urban Dynamometer Driving Schedule, also known as "the city test." It represents city driving conditions and is used for light-duty vehicle testing.

Cummins says it plans to demonstrate the diesel in a truck chassis using the EPA's Federal Test Procedures (FTP) for emissions certification at Tier 2 Bin 5 levels – used by today's clean diesels – by December 2013 and at Tier 2 Bin 2 levels by September 2014.

LA-4 refers to EPA dyno test procedure for city driving conditions, FTP = EPA Federal Test Procedure, A/T = Aftertreatment (emissions cleaning technologies for soot, NOx, etc.)

We also heard back via e-mail from Nissan spokesman John Schilling after we called the company asking for comment.

"This isn't something we are going to discuss right now," Schilling said. "We don't discuss future product plans including Titan."

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Update 1: May-19, 2011 12:05 pm Pacific

In the first version of this post, we said the Cummins I-4 diesel would meet Tier 2 Bin 5 emissions standards. Cummins says it expects to meet Tier 2 Bin 2 emissions standards with the 2.8-liter engine.

Tier 2 Bin 2 is a stricter standard than the current Tier 2 Bin 5 rules required to qualify as a "clean diesel." Tier 2 Bin 2 standards are the same for internal combustion engines regardless of fuel type (gasoline or diesel). It's equivalent to California's super-ultra-low-emission-vehicle (SULEV) standard.

We've also confirmed with a Cummins spokesman that the 2.8-liter diesel is a derivative of the 2.8 that Cummins builds overseas.