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Clean Machines

Changes to the next generation of diesel engines are fairly easy to spot. You can trace the path that exhaust gases will follow on their way to new Diesel Particulate Filters (DPFs). A careful eye wil...

Changes to the next generation of diesel engines are fairly easy to spot. You can trace the path that exhaust gases will follow on their way to new Diesel Particulate Filters (DPFs). A careful eye will identify the additional insulation and larger radiators that have been introduced to compensate for higher underhood heats, which are a byproduct of the combustion process that controls smog-producing NOx.

Look at Caterpillar’s 2007-compliant engine design, and you’ll even catch the glimpse of a spark plug that fits neatly into the tip of a chamber – a furnace of sorts – that will ignite small amounts of fuel when higher exhaust heats are needed to burn off excess soot in the DPF. Other manufacturers point to their systems that generate the heat by spraying fuel onto the precious metals inside a Diesel Oxidation Catalyst.

“We’re on the threshold of a lot of new technology,” Caterpillar’s Bob Wessels agreed during the recent meeting of the Technology and Maintenance Council.

In the coming months, Mack and International will both unveil new engine families. International’s new “big-bore” 11- and 13-litre designs will be unveiled this fall. Mack will launch its new 13-litre design with a single overhead cam in the fourth quarter of the year. And every other manufacturer has unveiled design changes to meet the tightening emission standards.

In general, manufacturers say there’s no need to worry about the pending changes. This technology wasn’t rushed to market as quickly as the equipment that was needed to meet 2002 regulations. Challenges during that round of standards ranged from lost fuel economy to a host of heat-related component failures.

“The net effect to all this is performance is unchanged, service interval is unchanged, and fuel economy will be very comparable to what we have today,” added Bill Stahl, Cummins’ director of OEM service.

Chuck Blake, Detroit Diesel’s manager of technical sales support, notes that the fuel economy of his company’s test engines is already within 1% of 2004 designs.

“That’s today. We still haven’t really frozen the iron in the engine,” he adds. Software can be tweaked up to the last possible minute.

Still, some of the latest equipment changes will present their share of challenges.


While previous rounds of emission standards have focused more on reducing NOx, the most prominent change in 2007 will require filters to capture tiny flakes known as particulate matter, which would otherwise float out of exhaust pipes. And like any other filter on an engine, the DPF will need to be maintained.

A DPF that’s plugged with soot from the exhaust system could create higher back pressures, which would lower performance and fuel economy as effectively as a potato in the exhaust pipe.

In most cases, traditional exhaust heats that reach about 1,200OF should burn away the related soot in a process known as “passive” regeneration, says Bob Keene of Caterpillar. International has 250 school buses in San Diego, Calif., that have relied exclusively on this approach, thanks in part to warm weather and a filter that sits close to a warm engine because of the layout of a bus.

But there are times when such temperatures can’t be reached. The cold air of a Canadian winter could suppress the required temperatures, as could engines running under a light load.

“Airport refulers that are idling most of the time in a cold climate will need to regenerate more often,” says Tim Shick of International Truck and Engine. If too much soot accumulates in the filter, the engines will then rely on an “active” regeneration process that feeds additional heat into the exhaust system.

“The driver will not even know that this is going on,” Stahl says of most regeneration efforts, which will vary depending on specific truck applications.

Although, there may be times that the higher exhaust temperatures won’t be welcome, such as in the midst of a refinery yard, under overhanging tree branches, or in the presence of customers who won’t appreciate the noise associated with higher idle speeds that feed air into the combustion process.

As a first line of defence, engine manufacturers are looking to limit the speeds at which these regenerations can occur. Mack, for example, wants trucks to be traveling about 25 km/hr, while Caterpillar wants them to be moving at twice that speed. The idea is that a moving truck won’t be parked next to something that could catch fire.

Truck manufacturers may also offer the option of switches that would allow drivers to postpone the regeneration cycle, or decide when to manually start the process.

“There are several schools of thought,” explains Ed Saxman of Volvo Trucks North America, referring to the option that may be requested by some fleets.

In these cases, drivers will need to watch for new warning lights. One symbol that appears to be the combination of a thermometer and a puff of smoke will indicate the higher exhaust temperatures associated with a regeneration process. The image of a similar puff of smoke next to the symbol for a filter (it looks something like a domino) will indicate that an active regeneration is required.

Procrastinators should beware. If a driver continues to pause the regeneration cycle, the engine will eventually de-rate and shut down. “This will not happen on the next event or event after that,” Dave McKenna of Mack Trucks, says. But the warnings can’t be ignored.

Under US Environmental Protection Agency standards, the related DPFs will need to last a minimum of 240,000 km before they need to be cleared of ash that will accumulate in the filter. Still, manufacturers are indicating that their cleaning intervals will actually range between 320,000 and 640,000 km.

Once the filter needs to be serviced, many smaller fleets may opt to simply exchange the muffler-sized unit for about US $300 to $500. But some fleets may opt for the related cleaning equipment that’s expected to cost between US $8,000 and $15,000. Some use bursts of air, while Detroit Diesel’s cleaning system includes fluids. Just remember that a simple blast with an air hose won’t be an option because it won’t have a gauge to determine when the filter is clean.

Cleaning methods that last between one and two hours will also vary depending on the manufacturer. For example, the Caterpillar designs will be cleaned while they’re still attached to the truck, while the Volvo filters will need to be removed.

If a turbo seal fails and the filter is coated with oil, however, the filters will need to be sent back to manufacturers, which will be able to bake the contaminants from the related media.

This isn’t the only new filter that requires care, either. New crankcase filters seem destined to be replaced during every third oil change, although that process will take just five to 10 minutes, Stahl says.


Protecting the new equipment will require the use of Ultra-Low Sulfur Diesel (ULSD) and a new generation of oils known as CJ4.

“You want to run them in combination with one another,” says McKenna of Mack Trucks.

High-sulfur fuels that are currently on the market will prematurely plug the particulate filters with soot, while the ash in today’s oil – which prevents sulfur from turning into sulfuric acid – will plug the filter with ash.

“The ash naturally accumulates because of material in the lubricating oil,” explains Jim Clerc of Fleetguard Emission Solutions, noting that it can’t be oxidized (burned away) in a regeneration process.

The ash is generated by detergents that are made from oxides of calcium, sulfur and zinc, adds Etienne van Niekerk of International Truck and Engine. As an aside, zinc oxide is the same stuff that surfers will smear on their noses to avoid sunburns.

In most cases, the new supply of fuel and oils should be readily available. The biggest challenge may involve fleets that need to flush today’s fuel from their storage tanks.

ver the next few months and by the end of this year, you need to work with our fuel jobbers to manage this transition, so you don’t have a big tank of 500 ppm fuel out back someplace that doesn’t get used,” Stahl says. That will also involve draining the tanks down to 10% of their volume on at least three occasions.

Ironically, a clean-burning alternative to diesel fuel may fade away because of the latest emission standards. When asked whether work on CNG or LNG engines would continue, a panel of engine manufacturers was largely silent.

The work will continue, McKenna said after an awkward pause, referring to Mack designs. “Whether it’s a commercially viable product coming forward now that all engines are incredibly clean, we don’t know if there’s a commercial avenue for CNG and LNG engines.”


Undeniably, limits on particulate matter will represent the most radical change to US Environmental Protection Agency standards, but 2007 will also represent further restrictions on allowable levels of NOx.

Most engine manufacturers will meet these tighter standards by accelerating the rate of Exhaust Gas Recirculation (EGR), which controls combustion temperatures by re-injecting cooled exhaust into engine cylinders. (Levels of NOx are controlled by lowering combustion temperatures.) Caterpillar will also re-inject exhaust into the combustion chamber, but will draw the gases from a point further downstream, to protect the engine from what it considers to be damaging soot.

Regardless of the approach, manufacturers say that they will need to compensate for added heat in the engine department.

“Heat rejection is going up significantly in some cases, with some engines more on the water side; with some engines more on the air side,” agrees Al Pearson, director of vehicle testing at Freightliner. “Total heat rejection is up on the order of 25 to 30%.”

Perhaps the biggest challenges will involve the amount of time that engines spend at higher temperatures, rather than the highest-possible heats, he adds. That will require changes to equipment including such things as bigger radiators, added insulation, heat-resistant alternators, and larger condensers for air conditioners.

Kenworth, for example, has increased the size of the radiator on the T2000 by 33%, and incorporated silicone radiator hoses as a standard feature. It has also increased the amount of insulation on the firewall to keep the heat out of the truck cab.

Mack, meanwhile, has added a number of heat shields to protect reservoirs of washer fluid (while it evaporates at 227oF, temperatures had climbed as high as 270oF), and insulation for power steering lines that were cracking when temperatures exceeded their 250oF limit, says Jerry Warmkessel, marketing product manager, highway trucks. Seals around peeper windows even needed to be changed because older versions were deforming from the heat.

They aren’t the only heat-related challenges.

“There are some packaging challenges because the particulate filters are bigger than the muffler they replace, and they also run hotter,” Shick adds. In some cases, that may require additional heat shields. And those who build bodies for “exotic” medium-duty designs will also be limited in how much they move the exhaust system. “It has to maintain the same distance to get that same heat loading [for passive regenerations],” he says.

Whatever way you look at it, the changes are bound to be a hot topic of discussion for months to come.

John G. Smith is a technical correspondent who provides coverage of equipment-related issues. As former editor of Truck News and Truck West, he shows a passion and deep understanding of industry issues.

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