Extending The Life Of Your DPF System
In the ongoing quest to protect the environment in the early 2000s, the EPA set its sights on heavy trucks, calling for a reduction in diesel particulate emissions. The Diesel Particulate Filter - the DPF System – was born. This is an important – and expensive – piece of equipment. You want it to last as long as possible, so it’s worth it to know what you should and should be doing to maximize the working life of your DPF system.
How DPF Works
Mounted in the exhaust system, the DPF's job is to clean up particulate matter or soot created from incomplete combustion of the fuel. DPFs are commonly made from ceramic or other materials. The diesel exhaust gasses pass through the filter’s honeycomb structure, with as much as 90 percent of the solid particulate matter (soot) getting trapped in the filtering medium. This cleans up the exhaust to the point where a clean linen handkerchief placed over the exhaust remains completely clean and doesn't even smell of diesel exhaust.
DPF Regeneration Modes
It’s useful to know the different Regeneration modes - Passive, Active and Manual.
As the vehicle is driven, the engine gets hot, and so does the exhaust system. This heat causes the DPF catalyst to burn the trapped soot away into non-polluting gasses in a process called “Passive Regeneration”. This passive regeneration is an ongoing process - it occurs automatically when the exhaust gasses are hot enough; as such, it is not noticeable to the driver.
But there will be times where this passive regeneration isn’t enough to take care of things. If the vehicle operates only on short runs, or is idled for long periods of time, the exhaust never gets hot enough to trigger the catalytic reaction of passive regeneration. If the system goes too long without a passive re-gen, soot will accumulate and raise the exhaust backpressure, triggering the “Active Regeneration” process. Here, the engine will artificially increase the exhaust temperature to burn off the particulates while the driver is driving.
There’s a third process called Manual Regeneration, when a vehicle is never driven long enough for the engine to initiate active regeneration. Now, it must be initiated manually by the operator. The vehicle is parked in a secure area, and the engine increases its rpm and artificially adds heat until the soot is burned away.
Things that shorten DPF life
The DPF system does a wonderful job at what it’s designed to do, and is one of the most significant advances in making diesel engines cleaner for the environment. Yet, they can be expensive to repair. And there are certain things that can shorten its life and increase your repair bills - sintering and damage to the monolith.
A primary contributor to DPF problems comes from non-carbon ash accumulation in the filter, mainly from sulfur content of the fuel as well as lube oil components. Ash itself is composed mostly of non-carbon fuel components - the carbon itself should be burned off and leave in the form of carbon dioxide.
This metallic ash accumulation is never burned off (read: it can’t be burned off, because it’s non-carbon), but rather accumulates in the DPF over time until you end up with a clogged filter.
Why is this a problem? Because in the high heat of the regeneration process, the metal ash particles can be fused together into larger solid masses in a process called sintering. Now, the DPF must be removed from the vehicle and physically cleaned of this sintered ash. This can only be done at a service facility.
Damage To The Monolith
The key element in the DPF is one piece of ceramic – called the ceramic monolith - that must retain its integrity in order to cause the diesel exhaust to pass only through the fine-filtering walls of the ceramic material. If the monolith is cracked, either through poor handling by the technician, through vibration, or because the driver has driven over something like a railroad line, it will allow diesel particulates to the downstream side of the filter.
Damage to the filter’s monolith is an expensive repair, so you want to be careful not to be careless with it. Some people think, for example, that in order to clear a filter of ash accumulation (as in what we talked about above), you just need to bang it on the floor. The last thing you want is a technician removing the filter from the exhaust system and banging it on the shop floor to clear out accumulated ash - that’s a recipe for a new monolith and a major hit to your wallet..
Oil or Fuel Contamination
Another cause of early DPF repair can be through an engine problem (like a turbo failure) that allows lube oil into the filter matrix. Or it could be a leaky injector that loads the DPF with raw fuel. Both of these problems will block the through-the-wall flow of exhaust and produce a sudden rise in backpressure. Either problem can spell trouble for your DPF.
Things you can do to make your DPF last longer & prevent problems
Regular DPF cleaning goes a long way
Having your filter removed and cleaned regularly increases its lifetime. This step should be an important part of your regular maintenance schedule.
Be sure to use the correct fuel
Too much soot leads to premature clogging and longer/more frequent change cycles for the DPF. One way to counteract this issue is to focus on removing any controllable sources of soot or particulate matter. Use a quality fuel additive that reduces soot and unburned carbon output. Another particular controllable source is the amount of sulfur in fuel. Continuous use of diesel fuels containing more than the recommended 15 ppm of sulfur will cause a poisoning effect of the catalyst in the exhaust system, which shortens the life of the expensive filter.
Use the right kind of oil
Way back when, to meet 2007 emissions requirements, engine oil manufacturers developed a new oil standard: CJ-4. The standard for pre-2007 oils is CI-4 Plus, which was designed to meet regulations for engines made before 2004. What makes CJ-4 more compatible to newer engines? The difference is lower levels of phosphorus, ash, and sulfur. Using older CI-4 oil in a newer engine could prematurely plug up the diesel particulate filter (DPF), increasing maintenance issues and causing you to have to replace or service the DPF much earlier than anticipated.
Pay attention to both oil levels and oil change intervals
Oil change intervals can have a huge impact on the longevity of the DPF system. If the manufacturer says to change oil at 6,000 miles, you should change it at 6,000 miles. Those numbers aren’t just pulled out of the air. Engines are tested extensively to arrive at those intervals.
You also do not want to overfill the crankcase with oil, as this excess can clog the filter.
Do re-gen the right way
Regeneration processes can be interrupted, and that’s bad for the system. If you override the regen, you risk compaction in the DPF.
Overriding a manual regeneration can happen if you touch the brakes or accelerator pedal or put the vehicle in gear during the regen. This causes a suspension of the regeneration process.
Do this too often and you risk serious consequences with your DPF.