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IN PRINT — Clear the Air: Know how to care for your DPF

Posted: December 23, 2016 by Jim Park

It’s not quite the “blue screen of death” that appear on troubled Windows computers, but an engine fault indicator still means a bad day is about to get worse – especially if it means a parked regen. Few drivers or fleets can afford more than an hour to solve a problem that should have been addressed earlier.

Aftertreatment systems are one of the most expensive maintenance items on today’s trucks. Parts are costly, the associated downtime can be crippling, and many people are still confused about how to care for the systems, even though the equipment has been in the field for eight years.

“When they were first deployed, they were supposed to be a hands-off, self-maintaining component that would look after itself behind the scenes with some simple cleaning procedure required sometime in the future,” says Scott Perry, Ryder Fleet Management Solution’s vice president – supply -management. “We’ve learned since then that’s not always the case.”

Ryder has customers that are just now ordering their first aftertreatment-equipped trucks. Fleets with extended trade cycles and those that put off buying such equipment are just now learning about the systems.

The greatest challenge in establishing a Predictive Maintenance routine for aftertreatment systems is that no two trucks are the same. Even when there are no underlying mechanical problems, the Diesel Particulate Filter’s condition depends highly on duty cycles.

“Additional soot is created during erratic duty cycles and/or stop-and-go traffic,” notes Kurt Swihart, Kenworth’s marketing director. “Highway trucks running heavier loads in a constant power output are less likely to experience the need for supplemental regens.” 

Maintenance consultant Darry Stuart believes many challenges are caused by upstream failures.

“Very few people accept the fact that they have to change and do more preventive aftertreatment system maintenance,” he says. “The delicacy of the aftertreatment system can be disrupted by many things. Any upstream failures, many of which you may not even be aware of, can have disastrous consequences. For example, something as simple as a leaking exhaust manifold gasket cannot be tolerated today. They can cause heat loss that affects the passive regen performance.”

Upstream failures can include leaky injectors, exhaust pipes, manifold gaskets, or Exhaust Gas Recirculation coolers. So too can they include coolant leaks, problems with the so-called seventh injector (doser valve), turbo failures, or problems with sensors and wiring.

A new maintenance view

With thousands of vehicles in different age groups, in different applications, and different brands, Perry now has a pretty good idea of when certain trucks need attention.

“We look at the history of the vehicle and its applications and we apply a service recommendation based on mileage, fuel consumed, and hours in service,” he explains. “The data we’re getting from the newer vehicles is improving and they are able to give us a better indication of the soot load, etc. There’s more insight and visibility there now. But the older vehicles still require planning and scheduling of a cleaning cycle as opposed to the system telling you when a cleaning is due.”

Stuart says fleets are just now beginning to accept that they have to change their ways when it comes to maintaining aftertreatment systems. “Fleets have spent years streamlining their PM [Preventive Maintenance] processes to be as efficient as possible, but being proactive on aftertreatment systems may mean the 2.5-hour PM is a thing of the past,” he explains.

Among other things, Diesel Particulate Filters are subject to a lot of vibration and possible impact damage, so canisters should be inspected regularly for damage, cracks and breaks. Stuart also suggests inspecting and cleaning the sensors and exposed contacts to ensure they have good electrical connections and are not gummed up by the contaminants that could cause false fault codes.

He has also been pushing his fleets to perform forced regens during Preventive Maintenance service intervals.

“It may add an extra hour of labor, but considering the possible cost of not taking that extra step, it’s a bargain,” he says.

Things like oil consumption cannot go unchecked, either. Fleets typically let older engines continue to use oil until they were traded out because it wasn’t worth the cost of the repair. Now, a Diesel Particulate Filter contaminated with oil can lead to expensive repairs and unscheduled downtime.

“If [oil or coolant] levels are dropping with no external signs of leakage, you have to know it’s going somewhere,” notes John Moore, product marketing manager – powertrain at Volvo Trucks North America. “Check fuel filters for blackening that may result from -crankcase oil mixing with fuel from a leaking injector. Check the fuel tanks for blackening of fuel, which indicates a mixing with crankcase oil.”

In previous generations of engines, meanwhile, oil and coolant leaks were obvious because of the smoky exhaust. That’s all trapped in the Diesel Particulate Filter now, so monitoring oil and coolant use (and using the correct oil formula) is critical.

Even minor exhaust leaks cannot go unchecked.

“Cummins recommends placing the aftertreatment as close as possible to the engine and using double-wall exhaust piping or insulation wrap to retain heat,” says Mario Sanchez-Lara, Cummins director of on-highway communications. “An aftertreatment architecture that has less surface area exposed to elements will retain heat and reach temperature -ranges needed for passive or active regeneration more easily.”

At some point the Diesel Particulate Filter will have to be cleaned, and proper cleaning procedures will help extend service intervals and prolong the life of this expensive ash can. But the cleaning intervals are unique to every vehicle – and depend on duty cycles; the amount of fuel burned over time; mechanical factors such as fuel, oil and coolant -contamination; and even fuel quality.

High-temperature exhaust usually turns that soot into unburnable ash over time. Engines operating at low exhaust temperatures will see more -frequent active regenerations to make this happen, and they may require forced regens. Bear in mind, though, a regen will not remove ash. Once it’s in there it’s there to stay, and it reduces the filter’s -effectiveness over time.

Cleaning a Diesel Particulate Filter usually involves removing it from the truck and using high-pressure air to -loosen material within the filter’s tiny channels. A high degree of remaining material may require the DPF to be baked, or exposed to very high -temperatures for up to eight hours, to further reduce the material so it can be blown free.

“Depending on what’s in there, some material may remain,” says Drew Taylor, director of global sales for FSX, which makes DPF cleaning equipment. “You might succeed in removing 90% of the material, but you could well have a permanent restriction because some material that cannot be removed by this process remains entrained in the filter.”

Material left behind in the first cleaning event will shorten the next cleaning interval, which might throw your maintenance schedule into disarray.

Daimler Trucks North America, however, does not endorse the so-called “bake and blow” cleaning method for all engines, and instead finds a full reman cleaning to be more effective. That includes compressed air and heat as well as a liquid wash.

Dale Allemang, Daimler Trucks North America’s director of field service, says the air cleaning will clean the center portion of the filter, but it’s likely to leave material around the circumference. “Our system is set up to give you an ash cleaning code after you have burned a certain amount of fuel [based on the application],” he says. “If you reset the ash accumulator, it assumes that you have installed a reman filter, and so it resets the cleaning interval to the prescribed number. But in our experience, the -bake-and-blow cleaning is usually good for [around less than half] of that.”

And here’s a final word to the wise for used truck buyers. The vehicle’s first owner probably spec’d and maintained the vehicle to run to the trade-out point and no further. Chances are they tried to avoid a second cleaning or replacement interval, and may have even ignored problems in the final weeks or months of service. When buying used, you can almost count on having to put money into the aftertreatment system. It might be better to get it addressed up front, roll that cost into the price of the vehicle, and build it into the payments.  

  

5 strategies to reduce DPF downtime

 

1. Match the engine size to its intended application

Don’t spec’ a big-block engine to run stop-and-go all day with short runs on the highway. Choose a smaller engine with a higher power-to-displacement ratio that will generate more exhaust heat and allow more passive regeneration and increase -intervals between parked regenerations.  –  John Moore, Volvo Trucks North America

2. Observe the regen cycle frequency

Increasingly frequent active regens or parked regen requests could indicate the filter is becoming severely plugged. Onboard diagnostic systems are more sophisticated today and can alert you to the need for service, but older trucks can still be hit or miss. There is no harm in pulling the Diesel Particulate Filter for cleaning earlier in its life rather than later, and scheduled maintenance is always less expensive than -emergency service.  –  Scott Perry, Ryder System

3. Consider performing a parked regen at the beginning or end of a work shift

Vehicles in light-duty, high-idle, or stop-and-go service can avoid disruptions to the workday by performing a scheduled regen rather than having to park for up to an hour during the shift.  –  Dale Allemang, Daimler Trucks North America

4. Perform regular and documented fluid level checks

An internal oil or coolant leak will no longer change the color of the exhaust because of the Diesel Particulate Filter. Such contamination increases the risk of plugging the Diesel Oxidation Catalyst, which will increase backpressure. After ineffective active or even passive regenerations, the system monitors will trigger fault codes and activate dash lamps to recommend inspection.  –  Mario Sanchez-Lara, Cummins

5. Watch fault codes

The days of performing Preventive Maintenance without a computer are over. Respond to fault codes immediately and be proactive. A parked regen is a last resort, not a first warning.  –  Darry Stuart, DWS Fleet Management Services

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