It's Time to Talk Regeneration

Recent changes to diesel emissions standards mandated by the Environmental Protection Agency (EPA) may be causing apprehension for operators of medium-duty vocational trucks. The concern surrounds interrupted duty cycles, fear of the unknown and perhaps some confusion of what will happen with 2007 engines. Exactly what can be expected from now on with active diesel particulate filter (DPF) regeneration?


When Chuck Goode, national acount executive of Cummins, Inc., reads information about how DPF regeneration is going to affect real-life operations, he says most of it has been hype. Goode deals with vocational and refuse trucks in the medium-duty truck class.

"It becomes apparent that there is still a lot of confusion and there is a lot of understanding that needs to take place. Not only has the complexity level gone up a bit, the differences between the chassis and engines going to be probably a little broader than what the assumption is on the functionality," he says.

One in several thousand duty cycles may have instances where interruptions occur, but Goode says "it's very, very rare."

Medium-duty vehicles do not always reach speeds high enough for exhaust temperatures to burn particulate matter in the diesel particulate filter (DPF). These trucks idle for long periods of time with relatively low exhaust temperatures, unlike long-haul trucks that are always on the move. Although heavy-duty trucks can easily achieve passive generation with constant engine temperatures, most medium-duty trucks are specifically configured for active DPF regeneration.

"I think the medium-duty trucks are far more relying more on active regeneration," says Eivind Stenerson of Donaldson Filtration Solutions based in Minneapolis, MN. Stenerson says he wouldn't be surprised if most engine aftertreatment combinations are tuned specifically for passive regeneration on long-haul trucks. In those cases, he thinks there is far less active regeneration than for medium- duty.


According to Goode, however, the Cummins Particulate Filter will allow truck manufacturers to decide how the regeneration process should take place based on how the truck operates or what the truck does.

He says that passive regeneration is something that is going to happen fundamentally on a continuous basis. In the level of complexity within the system, it is completely invisible and an on-going process.

"Active regeneration is when the regeneration process is assisted by adding the diesel fuel, the hydrocarbon dosing, to raise temperatures within the catalyst to allow that regeneration to occur," explains Goode. Basically, active regeneration gives the medium-duty vocational truck a little extra temperature boost that's high enough to burn off the soot and ash particulate matter in the DPF.

Soot and ash are residuals burned from fuel and can be self-cleaned. Goode says the cleaning is a chemical process, using the analogy of a self-cleaning oven. Since ash is the residual from unburned oil and cannot be regenerated, the DPF will require a periodic cleaning as the ash builds up. Typically, DPFs will be cleaned during routine service events such as an oil change.


The Cummins Particulate Filter is modular in design, and can be taken apart. The filter is removed from the aftertreatment can, and is installed into a cleaning filter. During this short service requirement, the filter is cleaned by blasting the ash out of the filter with a burst of air. From there, Goode says it is secured into a cleaning machine. In most cases, it takes approximately ninety minutes to remove, clean and reinstall the filter.

Goode says that another function is also a manual process. When the truck is stopped and parked a regeneration service event is initiated. This takes place when passive regeneration did not clean out the filter completely and remaining particulate must be removed.

There is also a lot of flexibility within the Cummins Particulate Filter, which can be programmed to fit specifications determined by the OEM or the customer. For instance, Goode says that pre-determined values can be programmed to prevent active regeneration from occurring if a truck is going below a certain speed limit.

"This will eliminate the fear that the high exhaust temperatures are going to occur when a truck is parked at a location that may not be conducive for high exhaust temperatures," Goode says.

"In order to alleviate that occurrence and that fear, there is a programmable value to say 'I don't want regeneration to occur if the truck is going below 10, 15, 20 miles per hour.'"

If active regeneration is occurring and the truck goes below the pre-programmed speed limit amount per hour, the regeneration process will stop in mid-cycle.

"Through the sensors on a particular filter, we can say we got 50 percent of it or 60 percent of it clean, but we will reinitiate the cleaning, or active regeneration process the next time we are above that programmed speed value," Goode says.

This means that the system will pick up where it left off, or will, as Goode indicates, be "bookmarked".

For a medium-duty vocational truck, Goode says that maintenance is scheduled in a fairly wide range of intervals, typically between 6,500 and 10,000 hours.


Most DPFs will be in a similar location to where the current exhaust system is located.

According to a spokesperson from Donaldson, the placement of their aftertreatment DPFs are very similar to where the current exhaust systems are located, either under the vehicle between the frame rails, just outside of the frame rail or just behind the cab in a vertical orientation. In general there shouldn't be a need to relocate any items with their system. However, the DPFs are larger than a typical muffler, so there may be items that no longer fit, such as battery or tool boxes.

In addition, Donaldson systems will be made from stainless steel materials with a high degree of longevity, and should not have life-expectancy differences between the heavy- or medium-duty classes from an overall unit perspective.

When viewed in terms of time or number of years in the field, the only difference customers may see is with longevity.

Because medium duty trucks don't put on as many miles as the Class-8 over the highway trucks, it is not comparable in terms of miles.

On medium-duty General Motors vehicles, the DPF is designed to meet or exceed any applicable EPA requirements and is covered under the terms of the warranty, according to Ed Pearce, manager of service support.

He says that the addition of the DPF is really not different from any other kind of change made to their vehicles. The company is not suggesting the DPF be moved or relocated due to shielding and routing issues, although some of the upfitter equipment may need to be moved. But in Pearce's opinion, this will not have an impact because any changes are included in the upfitter guide.


There are also new dash lamps for trucks with the Cummins Particulate Filter. The lamps will illuminate, indicating a 'high exhaust system temperature' to tell the driver high exhaust temperatures may exist due to aftertreatment regeneration. Goode says this is when the exhaust temperature is higher than normal. Cummins has made this a variable feature.

"If the truck is en route, then the need to know that the exhaust temperature is high is irrelevant," says Goode. He explains that Cummins allows the truck manufacturer to decide if the lamp should illuminate while the driver is traveling on the highway, or when active regeneration will occur.

Goode says that while the exhaust temperature may be high because of the regeneration taking place while driving, the truck manufacturer might want to keep it 'invisible', or choose not to illuminate, to avoid alarming the driver unnecessarily.

He also explains that if a driver is parked or driving below a certain speed limit, it may be relevant for the operator to know that the active regeneration process is underway and the exhaust temperature is going to be higher than normal during this interval. But he says that decision is up to the end-user.

"Why would you want some level of indication to come on (that isn't normally on) to let you know things are running normally?" Goode says.


When the lamp illuminates under standard conditions, the DPF must be regenerated within two to six hours of operation; if the lamp is flashing, it also must be regenerated, at which time engine power may be automatically reduced. Documentation from Cummins suggests changing to a more challenging duty cycle, such as highway driving, for at least 20 minutes, or performing a 'parked' regeneration.

With this, there may be concern about interruption in duty schedules, but Goode says there is "such a minor, minor incident of it ever happening on a fleet-type operation at all."

"In all of our field tests, there's only been one application that ever needed any of that, for parked regeneration to ever happen," Goode says.

In one testing phase, there was an incident in which a package delivery van required parked regeneration. Goode says drivers were required to shut the engine down at every stop, so it took the exhaust system a long time for the temperature to rise in that kind of day-to-day or start, stop and turn off work flow.

But Goode says regeneration was required in only one test phase. "That was only in one of those particular instances.

"Other trucks with the same type of duty cycle didn't have the need for the parked regeneration requirement," he says.

"It's very, very rare that parked regeneration is going to be needed. If and when it's needed, it's not a mission-disabling requirement at that time," Goode continues.

"When it's needed, you get the DPF lamp illuminated and our card says the DPF needs to regenerate within 2-6 hours of regeneration. And that's real conservative. Fundamentally, that can last you through a shift," he says, and adds that it will never lead to the truck having to be taken out of service immediately.

If it happens, Goode says that there will be ample warning for it to occur during a normal service interval, whether after a shift or the next time it can be scheduled in.

Goode says that he doesn't want to minimize the impact of the changes that have come along as part of the new EPA mandates and for introducing DPFs to the industry.

"It's another one of those events that has been played pretty big. We had been in the mode of engineering. We're through that mode and now we're in the mode of education," Goode says. "I think our company has been very responsible to make this change as invisible to our customers as possible."

With General Motors vehicles, under most circumstances the passive and active regeneration will occur as needed with their systems. Pearce says that it will essentially be transparent to the operator, should the operator never meet the condition for passive or active regeneration to occur.

"So if the vehicle sits for a long period of time at idle, and the light comes on, the intent is that the vehicle needs to be operated under conditions that will permit that regeneration, which is 30 miles per hour for 10 minutes", Pearce says.

"We think the passive regeneration is going to be a minimal need for the trucks. But the medium duty has the ability to regenerate at idle using the switch on the dash. If the amber DPF light is on, you need to make sure the vehicle is parked on a non-flammable surface, set the e-brake and turn the regeneration switch on. That will put the vehicle in a regeneration mode," Pearce continues.

He says that most of the time when the light comes on and when the vehicle is driven under normal operating conditions the next time, it's going to go through the active regeneration process.

Goode says that Cummins allows customers to use CI-4 or CJ-4 oil.

"If you use old oil, that will shorten to the 6,500 range for cleaning intervals and lower the need for cleaning the filter out because the ash buildup is electronically monitored," he says and notes the lamp will illuminate to indicate service is required.
"It's not going to be an issue of anything bad if the lamp goes on," Goode says, it is a simple reminder to schedule a cleaning at the next routine preventative maintenance service interval.


But what will drivers think? Pearce says that a comfort level will develop even though the initial reaction of the driver will vary as familiarity increases with new mandates and a new regeneration process.

"Everyone is in the same boat with DPF regeneration. In other words, it's become standard," he says.

In the field, Pearce was surprised at how 'ready' the industry was for DPF and ultra low sulfur diesel (ULSD); some customers had already made the switch in 2006.

At a customer site visit, he was prepared to ask tough questions about ULSD and active DPF regeneration. As he drove up to a fleet truck being fueled, he saw that the side of the fuel truck read 'ULSD'. He was very surprised at what customers already knew about active DPF regeneration. "They were up to speed, they knew about it, and were prepared for it," Pearce says.