Diesel Particulate Filters(DPF)

           

Why is a Diesel Particulate Filter (DPF) on my truck? What is a Diesel Particulate Filter (DPF)?

DPFs, or Diesel Particulate Filters, are required to reduce exhaust emissions on virtually all diesel engines. Whether you have an over-the-road truck or industrial equipment, you likely have a DPF attached to the exhaust system. Diesel engines emit pollutants and to reduce the amount of these pollutants diesel engines have been fitted with a filter in the exhaust pipe to capture soot particles.

The materials in a DPF traps the particulates (black smoke / soot) flowing out the exhaust pipe. The filter element has reached the end of its life when holes or cracks appear that allow unfiltered exhaust to flow downstream. During its lifetime, the DPF are typically removed and cleaned 2-3 times. The range of DPF service intervals is between 80,000 miles to 250,000 miles depending on operating conditions. Typical long haul heavy duty diesel truck travels more than 80,000 miles per year so depending on the severity of the duty cycle, off-truck cleaning of the DPF could take place between once a year and once every three years.

Diesel Particulate Filters capture soot until they fill up and create too much backpressure.
At that point Diesel Particulate Filters use one of two approaches to regenerate (clean) themselves.

Diesel Particulate Filter Cleaning and Regeneration / Re-Gen are not the same thing.

Active or Passive.

  • Passive (DPF) systems rely on metal-coated substrates to heat the normal exhaust flow to temperatures that trigger regeneration.
    Although more sensitive to duty cycle and temperature, once installed, these DPF systems are considered to be more user friendly, as they do not require fuel additives, have no moving components, and only need to be serviced for annual cleaning.

  • Active (DPF) Regeneration Systems:
    Active regeneration is accomplished by changing parameters to increase the exhaust temperatures in the DPF.
    To accomplish this the computer changes parameters such as:

    • Late or post-injection of fuel into the combustion chamber.

    • Changes to the turbo boost Pressure.

    • Changes to the EGR valve, intake air throttling,

    • Retarding the injection timing.

    • All the above methods can raise the exhaust temperature, but they also have negative impacts on the vehicle’s fuel economy, power, and engine wear. Post-injection (late-cycle injection) in particular causes increased engine wear by diluting the engine oil film with fuel.

The DPF technology currently available utilizes what’s called a wall-flow filter that’s positioned in the exhaust system.
As the exhaust gases pass through this filter, emissions of particulate matter are trapped in the filter and reduced by more than 90 percent.
This trapped diesel particulate matter (DPM) settles inside the filter walls until temperatures reach levels that allow for DPM combustion.

The process of combusting these trapped particulates inside the filter without an intolerable buildup of engine backpressure is called filter regeneration. If you think of this as a self-cleaning you're only half right.

Filter regeneration reduces back pressure, but to really clean the DPF involves taking the filter out of the exhaust system and putting it in a special cleaning chamber.

Starting in 2007, the US Environmental Protection Agency (EPA) made DPFs mandatory for highway diesels to achieve the low soot emissions limits.

 

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