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Clean and lean

Wednesday, July 1, 2015 - 07:00
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The light truck sector is one of the most competitive sales segments in the U.S. auto industry.  Sporting lofty price tags and higher profit margins, pickup trucks are the bread and butter for many manufacturers and their dealers. It’s easy to make money selling pickups...when people are buying them. In that respect, light trucks generally sell like hotcakes when gas is cheap and credit is easy to come by. This is the confluence of events that we are witnessing now, with interest rates and crude oil prices both at multi-year lows.

The VM Motori 3.0 liter EcoDiesel has been available in the 2013+ Jeep Grand Cherokee as well as the 2014+ Ram 1500. Photo: FCA US LLC

The 3.0 liter EcoDiesel is a turbocharged DOHC V-6.  Its high-pressure common rail injection system can develop pressures up to 29,000 psi (2000 bar). Photo: FCA US LLC

The Ram 1500 EcoDiesel uses urea SCR to meet 50-state emission standards.  The diesel exhaust fluid (DEF) filler is located behind the fuel door on the driver’s side of the truck. Photo: FCA US LLC

Yes, conditions are perfect for increased light truck sales, but the consumer is still faced with a dilemma. What happens if I buy a new truck and fuel prices go back up? Certainly, the fun factor tapers off when you are making hefty payments on your rig and now it’s costing you the remainder of your disposable income to keep the tank filled.

Times have changed mightily. Federal regulations regarding fuel economy have brought the light truck into a new age, one where its gas-guzzling ways are being reformed. This has also led to intense competition between the auto manufacturers to claim the fuel efficiency crown and its associated bragging rights. No stones are being left unturned in this clash of competing technologies: gas versus diesel, aluminum versus steel, etc.

The current fuel economy champion in the light truck sector is the Ram 1500 EcoDiesel.  Powered by a 3.0 liter V-6 diesel built in Italy by VM Motori, this truck is putting up impressive fuel economy numbers as well as meeting tough emissions regulations that put it on par with many passenger cars. It is the only diesel-powered light truck currently in the U.S. market, going where other manufacturers have feared tread. Numerous technologies have been utilized to achieve the goals of clean emissions and high fuel economy, and the purpose of this article is to present an overview of how Ram truck engineers made it happen.

Clean emissions
The North American (NAFTA) version of the VM Motori 3.0 liter EcoDiesel was first used in the 2013 Jeep Grand Cherokee. It was MY2014 when it appeared in the Ram 1500 pickup, where it immediately left an impression on the truck-buying public. It is a turbocharged 60-degree V6 with 24 valves and double overhead cams (DOHC). While it produces a modest 240 horsepower, the peak torque output is 420 lb-ft @ 2000 RPM, giving the EcoDiesel V-8 torque with 4-cylinder fuel economy.

Building a clean diesel is one thing, but having it meet light-duty vehicle emissions regulations is another level of difficulty. Heavy-duty pickups with diesel engines have strict emissions regulations, but these are not as tough as those that apply to half-ton pickups and other vehicles under 8500 lbs. Gross Vehicle Weight Rating (GVWR).

The holy grail of diesel emissions is known as Tier 2 Bin 5 (T2B5). T2B5 is the minimum EPA emissions rating required for a passenger vehicle to be sold in all 50 states. A car or light truck with a lesser rating does not qualify for sale in California or any of the 14 states that have adopted California emissions regulations (also known as “Green States” or “CARB States”). This rating is critical to vehicle sales, because the Green States are major car-buying markets and represent a high percentage of new car registrations in the U.S. If you can’t sell in those states, you may as well not bother at all.

Diesel engines struggle with two regulated emission gases: particulate matter (PM) and oxides of nitrogen (NOx). While engine tuning has a direct impact on the production of these gases, whatever is done in the combustion chamber to minimize one will typically result in an increase in the other. For instance, PM levels tend to decrease when combustion temperatures rise, but the hotter flame causes an associated increase in NOx. The reverse is also true; cooling the flame will reduce NOx output, but PM then rises. This is the classic two-edged sword, with one caveat: a hotter flame increases engine power output and overall efficiency.

With these dynamics in mind, VM Motori designed the 3.0 liter EcoDiesel to use a hotter combustion flame and then deal with the increased NOx after the fact. This requires the use of urea Selective Catalytic Reduction (SCR) as an exhaust aftertreatment system to reduce NOx to acceptable levels, but brings with it the following advantages:

1.     Increased engine power output and fuel economy

2.     PM production is lowered, relieving the load on diesel particulate filters and limiting associated regeneration issues.

3.     NO2, a component of NOx, is a powerful oxidizer and helps regenerate diesel particulate filters.

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