Diesel Particulate Filter (DPF) Regen is a relatively recent issue facing truck and fleet owners.
Starting with 2007 model years, diesel trucks are “blessed” with a diesel particulate filter (DPF). DPFs grab soot from your exhaust before it blows out into the environment. It’s a wall-flow filter usually made of cordierite, silicon carbide, or a ceramic monolith.
As the exhaust gases pass through the filter, it captures somewhere between 85%-100% of diesel particulate matter (DPM). So much of the DPM is removed that you could place a white handkerchief over the exhaust pipe and it would stay white.
DPF maintenance is relatively straightforward. Over time, soot builds up in the filter walls and must be cleared out. A warning light usually shows up indicating it is time to literally burn out the accumulated soot. This process of burning is called regeneration. In addition to regeneration, periodic DPF cleaning is required too.
Diesel Particulate Filter (DPF) Regen
DPF regen happens when the trapped particulates heat up enough to combust and turn to ash. The built-up soot is thereby removed as gaseous carbon dioxide. Regeneration may happen one of three ways: passive, active, or forced.
Passive regeneration happens automatically. Once the exhaust temperature reaches a certain point, for example while driving at high speeds, the built up matter in the DPF turns to ash. No active changes in engine operation are involved. Diesel trucks on a heavy duty cycle, for example climbing a lot of hills, should have no problem passively regenerating their DPF. Under these conditions, soot burns off as fast as it is generated.
Active regeneration happens when changes in engine operation are required to get the ECM to burn out, or some catalyst is introduced, or both. This is common among trucks with a lighter duty cycle, because soot accumulates while idling or going slowly through traffic.
One method involves the ECM tweaking engine parameters to increase the exhaust temperature. Then it switches on an extra fuel injector that shoots fuel into the exhaust stream. This fuel reacts with a catalyst and burns the built up soot out of the DPF. Newer engines allow parked regeneration.
When active regen requirements aren’t met, or when soot levels rise to a certain point, a forced regeneration may be required. A diagnostic tool is required to force regeneration. Continuing to operate the vehicle at this stage can ruin the DPF and cause other damage.
But even a forced regen will not work if soot levels have grown so high they have overwhelmed the DPF. At about 85% soot capacity and above, the DPF will need to be either removed and cleaned, or replaced. A new filter can cost $5,000 or more.
The DPF must be cleaned every 150,000 to 300,000 miles to remove accumulated ash. This ash buildup is not necessarily related to regens, but is most often due to sulfated ash in the engine oil. The filter must also be cleaned if a fuel injector or turbo problem causes contamination with engine oil or non-combusted diesel. This contamination causes unacceptable back pressure.
Cleaning methods include air blasting, the use of de-ionized water, and a vacuum-like system. Cleaning must be done very carefully so as not to damage the filter. The particulate matter removed must be carefully handled so technicians are not exposed to its extremely fine contaminants.
Timewise, cleaning a DPF should be quick enough to be accommodated during an oil change.
What’s coming out of the exhaust
While expensive for truck owners, the removal of diesel particulate matter before it blows into our breathing air certainly has its benefits. Following is a table showing the different elements that make up the matter DPF filters capture:
|Pollutant||How it's made||Impact on air quality||Impact on humans||Impact on vegetation|
|Particulate Matter (PM)||Incomplete combustion||Causes smog||Causes cancer||Harmful|
|Nitrogen Oxides (NOx)||Combine nitrogen molecules with oxygen in extreme heat||Causes smog and acid rain||Destroys passages in lungs||Harmful|
|Hydrocarbons (HC)||Incomplete combustion||Causes smog||Harms cardiovascular and nervous systems. Reduces delivery of oxygen throughout body.||Harmful|
|Carbon Monoxide (CO)||Incomplete combustion||Causes smog||Causes cancer||Harmful|
|Carbon Dioxide (CO2)||Combustion||Humans breathe it out||Nontoxic||Trees breathe it like humans breathe oxygen|
DPF and Preventive Maintenance
The diesel particulate filter is one more thing that must be tracked and maintained on a heavy duty truck. Making sure the truck is on a regular preventive maintenance program will help ensure the long life of the DPF. Regularly replacing air filters and fuel filters, and using the correct type of oil for the engine will help prevent unnecessary wear, and even catastrophe, with the DPF.
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