Home Car Maintenance What is a DPF filter?

What is a DPF filter?



A diesel particulate filter, often known as a DPF, is an exhaust aftertreatment tool that collects small particles like soot and ash. The substrate for a DPF is typically made of ceramic and is shaped into a honeycomb structure. 

Diesel particulate filters, which cut emissions from diesel vehicles, collect and store exhaust soot, which needs to be periodically burnt off to regenerate the filter. Excess soot that has been accumulated in the filter is burned off during the regeneration process, which reduces dangerous exhaust emissions and the black smoke that diesel vehicles frequently release when accelerating. 

A diesel particulate filter in the exhaust system in a car on a lift in a car workshop. 

Get to know more about the DPF filter 

Some filters are single-use devices that are meant to be thrown away and replaced after becoming full of ash buildup. Some are built to burn off the collected particulate either actively, using a fuel burner to heat the filter to soot combustion temperatures, or passively, using a catalyst. 

This is done by programming the engine to run when the filter is full in a way that raises exhaust temperature, or by using another fuel injector in the exhaust stream to inject fuel to react with a catalyst element and burn off accumulated soot in the DPF filter. Filter regeneration is the term for this.

As part of routine maintenance, cleaning is also necessary, but it must be done carefully to protect the filter. Cleaning may also be required if fuel injectors or turbochargers fail and contaminate the filter with engine oil or raw diesel. 

Vehicles that are exclusively driven at low speeds in urban traffic may occasionally need to make excursions at higher speeds in order to clear up the DPF because the regeneration process happens at speeds that are greater than those that can typically be reached on city streets.

The DPF may not regenerate effectively if the driver ignores the warning signal and waits too long to operate the car above 60 km/h (40 mph), and continuing operation past that threshold may completely ruin the DPF, necessitating replacement.

How does a DPF work? 

Although there are many different kinds of DPFs (including cordierite, metal fiber, and silicon carbide DPFs), cellular ceramic honeycomb filters are the most widely utilized variety. Ceramic materials offer exceptional thermal stability and resistance, including cordierite, silicon carbide, and aluminum titanate. 

The exhaust gas containing soot particles is forced through the filter wall of the ceramic honeycomb DPF, which is made up of channels with blocked ends. Despite the filter’s ability to let gas through, it still has deadly soot clogging its pores. 

A DPF, however, has a limited capacity. For the filter to operate properly, the soot that has been caught must be eliminated. DPF regeneration is the name of this procedure. Excess soot in the filter is burnt off during this process. 

What signs indicate a DPF is blocked?

Short distances traveled at moderate speeds are frequently the source of clogged diesel particle filters. The requirements for the filter to self-clean are not met by vehicles traveling short distances at low speeds. Poor servicing might cause DPFs to malfunction as well. Depending on the application, a diesel particulate filter’s life expectancy varies. 

If DPFs are not properly maintained, they may fail earlier. Also, using the incorrect oil, making performance modifications, using poor fuel, or even constantly driving with low fuel levels might result in filter blockage.

An orange light will typically display on your dashboard when the filter clogs or a system issue occurs. The type of light depends on the manufacturer. If this shows your filter is probably blocked and may need to be regenerated. 

There are two different sorts of cleanings necessary, just as there are two main particles being filtered. As the ash is removed by removing the filter and cleaning it in a machine with compressed air, regeneration removes the soot by converting the carbon to carbon dioxide.

Maintaining DPFs

The best way to maintain a DPF is to ensure that it has enough capacity to regenerate when it fills with soot and the warning light comes on. Regeneration comes in two types: passive and active.

  • Passive regeneration – When the car is moving quickly along a long stretch of motorway, passive regeneration takes place, allowing the exhaust temperature to rise and efficiently burn off the excess soot in the filter. To help clear the filter, it is advisable that drivers give their diesel car a good 30 to 50-minute run at steady speed on a freeway or A-road. The fact that passive regeneration is a fully automated process is one of its greatest advantages. Even drivers are not aware of it.  However, passive DPF regeneration is not possible until the engine achieves the necessary temperature, which typically happens on longer trips and at higher speeds.
  • Active regeneration – When a filter hits a preset limit (often around 45%), the vehicle’s ECU immediately injects additional fuel to increase exhaust temperature and burn off any retained soot. This process is known as active regeneration. However, if the trip is too short, issues could arise since the regeneration process might not finish. The warning light will continue to indicate that the filter is still partially obstructed if this is the case. In which case, driving for roughly 10 minutes at speeds more than 40 mph should be sufficient to finish a regeneration cycle and turn off the warning light.

What to do when both passive and active regeneration don’t work

The vehicle may require an operator-activated parked regeneration when operating conditions prevent DPF cleaning by active or passive regeneration. The car needs to be at a complete stop for this to happen. By turning on the dash controls, the driver or mechanic warms up the engine and starts the parked regeneration. 

Depending on the ambient temperature, the engine or DPF system type, and other factors, this could take anywhere from 20 minutes to an hour. The driver or technician must make sure the exhaust outlets are pointed away from buildings, plants, trees, combustible objects, and anything else that could be damaged or hurt by exposure to intense heat before starting a parked regeneration. A parked regeneration feature is not present in all DPF systems.

How much will a new DPF cost?

The cost of diesel particulate filters is high. A brand-new one from the automaker can cost between £1,000 and £3,500, possibly knocking out any cost savings from using a diesel vehicle. As cars get older, the cost of the replacement DPF may exceed the value of the vehicle, and older, higher-mileage vehicles are more likely to need a new DPF. 

Understanding how these filters function and carrying out routine maintenance are crucial because replacing a diesel particulate filter is far more expensive and difficult to do. Be cautious if a parts supplier offers a DPF at a lower price; the filter needs to be the right kind for your car. 

Wrapping it up 

In order to lessen the quantity of dangerous soot and particles produced during combustion, diesel vehicles have a device called a diesel particulate filter installed in their exhaust systems. The DPF is an essential feature of an automobile’s exhaust system since it aids in meeting current emissions laws. Additionally, it’s critical to maintain the filter on a regular basis because a clogged filter might affect how well the car performs. 

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