The ultra-lowdown

New ultra-low sulfur diesel is coming to a pump near you. It’ll cost slightly more, with slightly lower fuel economy, but it’ll run cleaner. Here’s what you need to know.

By this fall, most of the diesel fuel available in truck stops will be ultra-low-sulfur diesel, or ULSD, with sulfur content of less than 15 parts per million. Currently available low-sulfur diesel contains up to 500 ppm sulfur, 33 times more than the new federal standard.

federal standard. For refineries, a crucial deadline already has passed. As of June 1, at least 80 percent of the diesel each refiner produces must be ULSD. All fuel sold as ULSD must meet the 15 ppm spec’ by Oct. 15th.

“Most retail service stations and truck stops that have only one diesel tank will sell ULSD exclusively,” says Shell spokeswoman Karyn Leonardi-Cattolica. “Larger service stations and truck stops with more than one diesel tank, and the ability to completely segregate these products to avoid contamination, will be more likely to have ULSD and LSD available. All retail outlets selling ULSD and/or LSD are required to label their diesel fuel dispensers to indicate which fuel is being sold from that dispenser.”

The super-refined fuel is designed not only to curb emissions but to prevent sulfur damage to the diesel particulate filters used on 2007 trucks. The DPF’s biggest downside is the need to clean it of ash every 150,000 to 300,000 miles, depending on application. The ash is a consequence of the oil additives that protect the engine from sulfuric acid.

Because ULSD is much less corrosive in that respect, it accommodates a new engine oil, CJ-4, which generates less ash. This will help engine makers maximize the interval between DPF cleanings. More importantly, the lower fuel sulfur levels are likely to be good for your engine. ULSD will cost a few cents more per gallon, though the volatile nature of diesel prices makes it almost impossible to pinpoint its actual retail impact.

Drivers of pre-2007 trucks shouldn’t be overly concerned about the effects of the new fuel, Leonardi-Cattolica says. The transition to 500 ppm sulfur back in 1993 “changed the fuel chemistry to a much greater degree than the upcoming introduction of ULSD,” she says. “ULSD will neither smell nor appear any different from any other diesel fuel.”

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There are subtle differences, however. Here’s a rundown of the changes and how they could affect your truck and your business.

FUEL ECONOMY. Unfortunately, ULSD will contain 1 percent to 2 percent less energy. The refining process that removes the sulfur also removes high-energy “aromatics” and may make the fuel slightly less dense, Leonardi-Cattolica says. This means a corresponding 1 percent to 2 percent increase in fuel consumption.

Any small decrease in fuel economy can easily be handled with sensible conservation efforts, says Cummins spokeswoman Cyndi Nigh. Less time idling, more time in top gear, choosing the proper gearing spec and using electronic controls can more than make up for a 1 percent drop in economy.

International Truck and Engine is seeing “nearly equivalent” fuel economy on ULSD and still is improving calibrations, says Mark Stasell, vice president of engine engineering and product development.

He adds that fuel economy in 2007 engines will depend even more on the duty cycle, thanks to active regeneration, when fuel is pumped into the exhaust system at low speeds to keep the DPF working. In other words, while city driving always has used more fuel than highway driving, an urban detour in a 2007 truck will use even more.

“We’ve developed our engines and chassis for 2007 in close collaboration with component suppliers with the goal of delivering fuel economy neutrality, which means offsetting the 1 percent loss of energy from using ULSD fuel through the design of our engines and trucks,” Stasell says.

Mack Engines’ product manager for marketing, David McKenna, says it’s too soon to say what the fuel economy change will be, but he’s optimistic. “We are looking for some significant improvement in fuel consumption, as much as 2 to 4 percent when comparing the new MP7 with the present ASET engines. The percentage might rise to as much as 6 percent when compared to the ASET AI engines.” Mack’s ASET AI engines were designed for on-off road vehicles and used internal exhaust gas recirculation, a simpler form of EGR that requires less maintenance, but uses a bit more fuel.

LUBRICITY. Traditional diesel fuel is a very effective lubricant, which is vital because the lower portions of the injector that meter and pressurize the fuel are not lubricated by the engine oil. Without sufficient lubrication from the fuel, they fail.

When sulfur is removed from diesel fuel, lubricants come out as well. But refiners “will be producing a better, more highly refined product, and adding a non-sulfur-based lubricity agent,” McKenna says. “Refiners and marketers do have to test the fuel for lubricity, and they know what they have to do to the fuel to make it pass the test.”

International materials note that the ULSD must meet the same standards for lubricity as traditional diesel. Cydni Nigh of Cummins and Tim Tindall, EPA ’07 director at Detroit Diesel, agree that lubricity additives should take care of any problems before the fuel reaches the pump, even without the fuel additives and premium diesel grades that will be marketed as lubricity enhancers.

FILTERS AND SEALS. Fuel filters and seals are much cheaper than injector parts, but experts urge users to keep an eye on them during the transition, especially in pre-1993 vehicles.

“Fuel chemistry changes can also affect the way fuel interacts with storage and vehicle fuel tanks,” Leonardi-Cattolica says. “Depending on the chemistry of ULSD, some deposits may be removed from the tank, resulting in the need to change fuel filters ahead of their regularly scheduled maintenance.”

The transition also might cause some older seals to leak, especially in pre-1993 high-mileage trucks with the original seals still in place, she says. The problem stems from chemistry’s change when the sulfur is removed, causing seals to behave differently. Avoid trouble by making sure older seals have been upgraded as recommended by the manufacturer. Engine makers are confident of the filters and seals on more recent models.

COLD WEATHER. The engine makers mostly see cold weather as a non-issue, and testing will back them up because U.S. standards require blending that makes the fuel suitable for the average temperature in each area of the country throughout the winter.

“Jelling will be a problem handled by an additive program,” McKenna says. “Do not blend in kerosene. The sulfur content of regular kerosene is extremely high, and will have a negative impact on PDF operation.”

If No. 1 fuel labeled ULSD becomes available in your area, it should be safe for blending.

CONTAMINATION ISSUES. ULSD that meets the sulfur standard when it leaves the refinery may pick up leftover sulfur residue from older fuel in the pipeline. “It may be hard to predict contamination of the supply,” says Bob Costello, American Trucking Associations chief economist. “Preserving the integrity of the fuel at the end of a long trip through a pipeline is difficult, and there may be problems. But the pipeline companies have been working on this.”

What happens to the DPF if the sulfur level creeps above 15 ppm? “The Cummins aftertreatment system keeps itself clean in a passive mode the majority of the time,” Nigh says. “As the sulfur level increases, the ability to passively keep the after-treatment clean deteriorates.” That means active regeneration is more likely to kick in.

Otherwise, don’t worry, Nigh says. “An inadvertent tank of 500 ppm fuel will not damage the engine and aftertreatment system. The system will clean itself out when ULSD is reintroduced.” The use of high-sulfur fuel would not void the Cummins warranty, she says.

The same is true for International engines, says Mark Stasell. “We have designed our trucks’ systems to handle some fuel variability, and slightly higher sulfur content will not be an issue for International customers. Our conservative approach to the design of the aftertreatment system and robustness due to the selection of materials make this possible.”

Emissions are the chief concern, says Scott Zechiel, Detroit Diesel’s manager of fuels and lubes for 2007. “The after-treatment devices require that only fuel with less than 15 ppm sulfur be used,” Zechiel says. “Filters that are not operating properly can be inspected to determine if, in fact, the filter was exposed to high levels of sulfur.”

Accidentally buying the wrong fuel will be unlikely, McKenna says. “The fuel tanks on ’07 trucks and dispensers will be identified with a large green label. Under the warranty, we cannot be held responsible for any damage that might occur to the emission system due to misfueling. We would treat it as any other misfueling issue.”

EXTENDED OIL INTERVALS. The cleaner fuel carries the potential of extended oil changes.

If you’re getting “reasonably good fuel economy with existing equipment, it’s quite possible that using CJ-4 and ULSD could extend drain intervals,” Stasell says. “Get the oil analyzed, and let the data help with the decision.”

One possible mistake would be switching to CJ-4 oil while still using LSD 500 ppm fuel in an older engine; the buildup of sulfuric acid could cause serious oil deterioration. Check with your oil supplier and engine maker.

Using LSD 500 in a 2007 vehicle with a crankcase full of CJ-4 could create a similar problem plus DPF trouble, to say nothing of warranty issues.

Accidentally using CI-4 in a new engine also could stress the engine because CJ-4 offers superior protection. Besides possible warranty issues, it would shorten DPF cleaning intervals.

The best recommendation for engine life and emissions control is to only use ULSD and CJ-4.

“If you have two barrels of oil in your shop, somebody will put the wrong oil in,” McKenna says. “As soon as you start using ULSD, switch to CJ-4 oil in both new and older engines.”

Jason Phelps, customer communications manager at Caterpillar, says, “The fuel and oil spec’s are designed to enable the engines to meet the 2007 emission levels. It’s a whole system, not just one or two parts.”

June 1, 2006: At least 80 percent of diesel production must be ULSD.
Oct. 15, 2006: Retails must meet 15 ppm sulfur standard.
Jan. 1, 2007: Trucks produced from this date on must use ULSD. Older trucks can use ULSD or low-sulfur diesel.
Dec. 1, 2010: ULSD becomes only fuel available for highway use.