The Difference Between DPF Regeneration And Cleaning

You may not believe it, but DPF technology is not at all a new technology. The first time DPF was used was in 1980. There wasn’t a market for it until the environmental ball started rolling in 1987 in California. DPF itself wasn’t mandated until 2008. The rest is history, but for some reason, misunderstandings survive about this relatively simple and old technology. At the end of the day, the DPF is a filter. It is like any other filter in that it needs to be a part of your maintenance schedule. It differs in that the filter can last hundreds of thousand kilometres, and to get there needs regular attention. That regular attention is the reason for this article.

The difference between a regeneration and a cleaning differs in a few very important ways. I will explain what each one does, and how they affect the filter. I’ll also give useful tips on how to get the most out of both, which will help you reduce the need for both. Reducing the need for them not only saves you money but keeps you running, making money. We’ll start with the regeneration because it affects more people and will happen much more often.

DPF Regeneration

The way that a regeneration works is actually really straightforward. Unfortunately, when the DPF was mandated and manufacturers rushed them to market, two things happened. Some mistakes were made by the OEM’s, and a lot of people pretended to know what they were talking about. A lot of misinformation was spread. To make matters worse, SCR would come not long after, adding to the confusion.

All that anyone really needs to know about a DPF, in a practical, day-to-day sense, is that like any other filter, the DPF will absorb what should not be getting through. In this case, it is the diesel particulate. Diesel particulate makes up the D and the P in DPF. All that diesel particulate is, is the black soot that comes out of a diesel engine. Black soot is nothing more than unburned diesel fuel. Unburned diesel fuel is one of the worse things we do for the environment and that is why it is regulated by the EPA.

The purpose of the DOC is to ignite fuel, which is injected into the exhaust system after the exhaust headers, and before the DOC, to heat up the DPF to the temperature it needs to effectively burn out the soot.

Passive Regeneration

The reason that a regeneration is needed is that the filter has been working and therefore filling. Instead of needing to replace or at least remove, clean and reinstall, the driver can perform a regeneration. Often enough conditions allow for what’s called a passive regeneration.

A passive regeneration happens, typically, during long trips at consistent speeds. The aftertreatment system is very close to hot enough to clean itself or at least close enough that it doesn’t need any assistance. The soot or diesel particulate is literally burned out of the filter. Remember, diesel particulate is unburned fuel, and so having been trapped, it can be burned off and made safer for the environment.

Active Regeneration

An active regeneration is what needs to happen if conditions never allow for a passive regeneration. The goal and the effect of an active regeneration and a passive one is exactly the same, to clean out the filter and renew its capacity as much as possible. This happens much more often to a city truck than a long-haul truck. The reason that it needs to be done stationary is that cooling down and warming up over and over is bad for the filter and ineffective for a regeneration. It can lead to burning it out and otherwise damaging it.

It isn’t at all uncommon for a regeneration of either type to happen every 30-50 hours. The longer you can go without a regeneration, the better. Too long, however, can lead to the filter being overfilled and that will not only scrap the filter but will lead to a serious back pressure in the exhaust system, which means an inefficient truck (more fuel burned). Too often, such as every 5-10 hours, will also lead to damage of the DPF and is a sure sign of other problems as well.

Cleaning

With all this talk of active and passive regeneration, it may seem unclear why the filter ever needs to be taken off the truck to be cleaned and possibly replaced. One reason is that the filter or “brick”, which is what manufacturers call the material block inside the filter, needs to be inspected for damage. The other reason is that the best regenerations won’t clean it out completely and the filter will eventually need to be thoroughly cleaned or replaced.

The filter should, as per most manufacturers, be cleaned every 150,000kms or more. Cummins, for example, usually recommends every 320,000kms, depending on engine, service type, etc. The best bet is to either check with the owner guide or get in touch with any relevant dealer to find out exactly when you should do this.

Amongst the worst is the pressure washer method. The problem is that the water pressure causes damage to the brick and the coating inside the filter gets worn down or washed away. The best methods tend to revolve around heating the brick and blowing out with air from both sides at the same time. You should always verify the flow restriction before and after to make sure that the filter is not only well cleaned but also within spec for reinstallation.

Conclusion

The DPF and the basic aftertreatment system isn’t all that complicated. Unfortunately, many people have misunderstood how it works. This hasn’t slowed down many people from sharing what they thought they knew. There really is no reason why the average mechanic, who is regularly trusted with oil changes and other small jobs, cannot be trusted with removing, inspecting, cleaning and reinstalling a DPF filter the same way he found it.

Drive safe,

Kevin Gauthier