Diesel Exhaust Regeneration & Particulate Filters

How Diesel Exhaust Regeneration Works:

Diesel Exhaust Regeneration Basics:

Diesel particulate filters are designed to trap particulate matter resulting from diesel fuel combustion, using ceramic or wire mesh to remove PM from the exhaust. They are installed as part of the diesel exhaust system, either in front of or behind the catalytic converter. Particulates are trapped as exhaust gases pass through the filter.

Under low-load conditions, particles remain trapped in the filter and gradually build up enough to trigger the differential pressure sensor (the DPS measures and compares the air pressure going in to the air pressure going out) and begin the regeneration process. Dash indicator lights will let the driver know that DPF regeneration is necessary.

Certain makes of DPF's are designed to regenerate based on mileage or amount of fuel used, rather than with a DPS. Many newer trucks will include, in addition to dash lights, a DPF regeneration switch as seen in the video below.

Regeneration is essentially the cleaning out of the DPF. During regeneration, the temperature of the DPF is raised to above 600 degrees C, and provided with extra oxygen. The increased heat burns off the excess particulates, blowing some of the resulting ash out of the exhaust, while retaining some inside the core of the DPF.

DPF's have a specific lifespan of between 75,000-150,000 miles, and will need to be serviced by a mechanic.

• Passive Regeneration:

  Happens automatically while the vehicle is being driven. On medium-to-long trips in which the vehicle is driven relatively hard, and using the normal temperature of exhaust gases to continually oxidize PM, DPF regeneration will take place automatically and without driver interaction.

• Active Regeneration:

  When the truck is driven for shorter stretches, in a more stop-and-start manner, or is idling, the exhaust temperatures may be irregular or may not reach levels high enough to trigger passive regeneration. When soot levels build up to 45-50% without passive regeneration having been performed, the ship's on-board computer will take over and initiate Active Regeneration.

  The Engine Control Unit (ECU) will make adjustments to the engine RPM's and diesel fuel injection, either through fuel injection directly through the exhaust system into the DPF, or changing the EGR valve, injection timing, or intake air flow, resulting in higher temperatures (600 degrees C) in order to burn off soot buildup.

  Active Regeneration, because it often happens at lower cruising speeds, can have an effect on performance and MPG for a short time. Excess smoke from the exhaust is not uncommon during the process. Frequent stops and starts may interrupt and reset the DPF regeneration process.

  Some newer vehicles will be equipped with a DPF regeneration switch, and specific dash lights, that will alert the driver to perform the process while stationary and idling.

• Forced Regeneration:

  In the event that both Passive and Active regeneration have failed to eliminate sufficient PM from the DPF, the truck may operate on reduced power and "limp" along due to excessive clogging, or may not run at all, and a Forced Regeneration will need to be performed by a qualified mechanic.

  Forced regeneration is performed by instructing the engine to regenerate the DPF using a diagnostic scan tool hooked up to the vehicle's on-board computer.

• DPF Cleaning:

  In certain circumstances, DPF regeneration will fail or will not be possible due to long-term or excessive particle buildup, and will be indicated by the DPF lamp coming back on after regeneration.

  In this case, the DPF cleaning would involve a lengthy, complicated, and expensive process that would only be performed by a mechanic or otherwise trained professional. Generally, under normal operation, DPF's will need to be cleaned every 6 months, or replaced.