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?
CLEARING UP THE CONFUSION
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.