Diesel's Partners in Reduction

It's going to take more than just engine-design changes to meet the January 2007 federal deadline for low emissions standards set by the Environmental Protection Agency (EPA) for on-highway diesel engines. A combination of technologies must come into play, including a new ultra-low-sulfur diesel (ULSD) fuel, which will be nationally available in 2006; aftertreatment devices (particulate traps) now being developed for use with the fuel; and newly formulated oil that has a lower ash content.

To put a backdrop to what lies ahead, today's diesel engines emit 500 parts per million (ppm) of sulfur and the low-sulfur diesel fuel now on the market ranges from 15 to 30 ppm. That all has to change by 2006 when most of the on-highway ULSD fuel will be required to have no more than 15 ppm sulfur level at the pump. EPA prescribes similar reductions for off-road or construction equipment beginning in 2011.

The combination of '07 engines, ULSD fuel, particulate traps and low-ash oil, say the experts, will lower fine particle emissions by more than 90 percent and reduce hydrocarbons to near-zero level. The impact of these changes on fleet maintenance and operation is more difficult to quantify.

First of all, the 2007 engines will cost more, although engine manufacturers say it's premature to put a number on the price tag. Cyndi Nigh, Cummins' on-highway communications manager says engine pricing is confidential. "As a guideline, however, we anticipate a similar incremental increase to that of the 2002 product," she says.

At International Truck and Engine, Tim Shick, director of marketing, big-bore engine business, says the industry is "refining" the cost impact as it refines specific engine changes. "As always," he says, "the goal is to offer the best balance of performance, operating cost and initial cost along with emissions reduction."

Tony Greszler, vice president of engineering at Volvo Powertrain, says both Volvo and sister company Mack Trucks will add costs, but he didn't know what the total price of the truck will be.

Manufacturers also said all engines, including pre-2007, could use ULSD. Even engines now in service, claimed one report, "will achieve small but significant environmental advantages with the new fuel." On the other hand, existing diesel fuel should only be used with '07 engines occasionally or for emergencies.

Volvo's Greszler says fuel economy may suffer slightly with the new fuel. "The only issue we've noted in the low-sulfur fuel is a slightly lower power density, meaning less energy per gallon," he says. "You have to burn a bit more of it to get the same [energy] out. We've seen a two- to three-percent difference." Other than that, Greszler says, tests using Volvo and Mack engines show that the engines work well with the fuel.

By contrast, Caterpillar has experienced fuel-efficiency improvements during its field tests, according to Jason Phelps, customer communications. "Our C7 and C9 engines used in concrete mixers, dump trucks and in vehicles that haul construction materials, are actually getting about three-percent improvement in our '07 engines." That improvement, he says, is the result of changes made in turbochargers, in the fuel system, as well as some software changes. Caterpillar's heavy-duty engines, the C13 and C15, are maintaining fuel economy, he says.

Not surprisingly, ULSD fuel will cost more, but nobody is offering an educated guess as to how much. Department of Energy statistics say the price increase will be between five and seven cents a gallon, Nigh says, "but that's DOE statistics, not Cummins. We don't know." International's Shick says individual fuel providers would set fuel prices.

Fleet managers who remember the engine problems that cropped up in the 1990s, (seal leakage and other issues) when changes were made to diesel fuel, should not be worried this time around, according to engine manufacturers. Then, the seal leakage problem was caused by significant changes in the fuel aromatics level. "Processing of ULS fuel will have only a very minor impact on aromatics," International's Shick says. "Engine seal issues are not expected with ULS."

Volvo's Greszler agrees. "We have run a lot of ultra-low diesel in our products," he says. "In fact, Sweden [where Volvo's headquartered] has been almost all low-sulfur diesels for 20 years now. We don't expect to see any real problems, although there will have to be more flushing of the fuel delivery system, including the tank and the trucks. There is a potential for more debris to end up in the fuel filters. Filters may have to be changed more frequently during the transition."

At Cummins, Nigh says, there were injection-system leakage problems when diesel fuel was changed. "The seals were shrinking due to the levels in the sulfur making the elements in the seals contract," she says. "The seals were made of nitrile. What we did as a company was change the seal material from nitrile to vilon. Vilon doesn't have the significant difference in the swell between high- and low-sulfur fuel. We don't anticipate that this is going to be an issue at all."

Federal regulations require ULSD fuel be available nationwide by the fall of 2006. The fuel is already available in certain parts of the country, such as Washington and California, where school buses and municipal vehicles are the primary users. Transit buses also use the fuel in metropolitan areas such as Chicago, Denver, Washington, New York City and some parts of Texas.

Once fleet operators start to use ULSD fuel, it has to be kept separately. "That really means flushing out the tank, the pumps and plumbing that deliver it," says Volvo's Greszler. "All this has to be cleaned out, because it doesn't take much current fuel to contaminate ultra-low sulfur."

Biodiesel is an alternative fuel, but engine makers differ on their counsel pertaining its use. International has not made a final determination, Shick says, and Caterpillar doesn't have an official stance, pending ongoing test to determine long-term benefits, according to Phelps.

Greszler, however, says Volvo has approved its '07 engines for up to B5 biodiesel (five percent pure biodiesel and 95 percent standard petroleum diesel). "Beyond that," he says, "it's very specialized because there are really no good controls on the fuel." Cummins has similar recommendations, Nigh says. "B5 diesel blend is suitable for use in a wide range of applications, she says. "There's no impact on engine performance, durability or maintenance. The only thing we caution fleet managers about is to ensure that the B5 is a consistent high quality standard."

ULSD fuel will permit the use of aftertreatment devices, or particulate traps. Ted Angelo, director of product development for Donaldson, says government standards of a 90-percent reduction in particulate matter (PM) from today's levels is "a very difficult target."

"The most efficient way to remove PM is through the use of a particulate filter, or PTF," he says. "The problem is, like any other filter, PTFs will eventually clog unless they have a start-up treatment, or control, that goes with it."

Angelo identifies two basic forms of control. One is a passive filter that relies on a catalytic coating and sufficient temperature in the exhaust gas to remove the soot as it accumulates during vehicle operation. The second is an active system, used when the engine isn't producing enough heat or the exhaust chemistry is such that eventually the filters clog up. Active control monitors the system and initiates the heating process that burns the soot from the filter, he says.

Everybody most likely will use one of two active particulate-matter aftertreatments in 2007, Angelo says. Fuel burners combust right before the filter, and the heat burns the soot from the filter. The second active aftertreatment is fuel injectors, a technique preferred by Donaldson.

"This is a similar process, in that we inject diesel vapor into the exhaust gas," Angelo says. "The vapor passes over a diesel oxidation catalyst and that catalyst converts to heat and that heat burns the soot in the filter. We've evaluated both types and decided that fuel injection, with its compatibility with future generations for 'nox' aftertreatment control, is the best system for us."

Durability of such a system, says Angelo, is spelled out by the EPA. "The EPA has a caveat that they call 'useful life,' which says the system should function for 435,000 miles and/or 10 years," he says. "That's essentially the warranty period everybody has to meet."

In Donaldson's system, a stand-alone control unit monitors the operation and decides when it's time to regenerate, or burn, the soot from the filters. "It automatically does that without any operator intervention," Angelo says. "When it's complete, it resets itself, monitors, and waits for the next cycle. On some applications, that cycle could be daily. On others it might not be that frequent, depending on application and how cold or hot the vehicle operates," he remarked.

The off-road application of these on-road devices in 2011 will be "much more challenging," Angelo says. "Your typical over-the-highway tractor has either one or two cylindrical-shaped mufflers in the back of the truck, and that's the standard size and shape." But that doesn't hold true with off-highway equipment. "In trying to package one of these systems to marry different systems will make things interesting," he says.

Servicing aftertreatment devices boils down to simply maintaining the filters. "EPA has rules for this as well, Angelo says. "With on highway, the first ash cleaning can occur at less than 150,000 miles." Fleetguard, a sister company of Cummins, also manufactures aftertreatment equipment. Nigh says Cummins's 2007 engines will add exhaust aftertreatment to the 2002 versions. "Our aftertreatment will maintain the reliability and durability of performance that customers expect today," she says. "They'll have the same in 2007 [because now] we have [developed] the stable architecture."

As for off-road equipment, Cummins can move to Tier III with an in-cylinder solution and the only change is the addition of the exhaust aftertreatment, Nigh says.

"Right now we are testing the addition of the Cummins particulate filter, and that filter will be a maintenance item," she said. "Although the filter is designed to last the life of the engine, eventually it will have to be cleaned."

The cleaning service interval will vary, depending on application. "The ECM (electronic control module) will monitor as ash builds up in the filter. An in-cab display and diagnostic software will alert the driver when maintenance is needed," she says. Users can either have basic ash removed by a cleaning machine at a Cummins service location, or they can exchange the old particulate filter for a new one that is installed. Cummins does not recommend manual cleaning.

Federal standards also include the gases from the crankcase. Cummins uses crankcase ventilation, a simple, serviceable filter that separates the oil from the crankcase and then returns the oil to the oil pan. The filters, made by Fleetguard, will have to be replaced. Called EnviroGuard, it pulls oil out of the air, sticks it together and eventually that drip drops down and oil is returned to the oil pan, Nigh says.

Both the particulate filter and the EnviroGuard filter will have to be replaced every year, she says.

The key maintenance item for 2007, Volvo's Greszler says, is the particulate filter, which will require cleaning at a minimum of 150,000 miles. In a vocation operation, it would be 4,000 hours.

"The ash collected from the crankcase oil doesn't burn, and it collects in the filter," Greszler says. "At some point, that filter has to be cleaned out by essentially blowing air backwards through the filter. You have to pull the filter element out to do that, and that requires equipment to collect the ash. This is an additional maintenance item.

"We don't foresee any other real changes. Oil-change intervals should be comparable. Other than this, there should be no additional maintenance requirements."

Another piece of the puzzle in reaching federally mandated emissions standards is newly formulated oil. The new low-ash oil prevents particulate filter plugging and will be "backward compatible," Nigh says, meaning it can be used with older engines as well.

Another watchful area for fleet managers is the cooling system. "We haven't changed our cooling system requirements for present day engines or '07 engines," says Volvo's Greszler. "We are concerned that there is more heat load in the cooling system, so operators need to keep their cooling systems in good maintenance, which is what we recommend today. Properly maintaining the cooling system for '07 engines is probably a little more important, but there are no new requirements."

International's Shick agrees. "Good cooling-system maintenance according to OEM recommendations will continue to be a key component of a comprehensive maintenance program. Cooling-system capacities are increasing with increasing heat load. However, the coolant itself and maintenance requirements are not expected to change."

As far as engine and aftertreatment equipment manufacturers are concerned, the technological transition necessary to meet January 2007 on-highway emissions standards should be a smooth one — for them and for fleet professionals.

"We're way ahead of where we were in 2002, says Caterpillar's Phelps. "That's important for people to understand. It's not going to be like 2002. This is much less of a change, I think, that people are anticipating."