Diesel particulate filter systems explained

DPF stands for diesel particulate filter. The filters are employed to reduce the number of dangerous particulates that get into the engines of diesel engines. The aim is to make the surrounding air healthier and more secure, particularly in tight spaces. Continue reading to find out more.

Euro 5 standards

Since 2009, when the ‘Euro 5‘ standard was put into the market, exhaust emissions standards for diesel vehicles have required the fitting of the DPF in the exhaust systems. Indeed, a lot of cars that were registered prior to 2009 will have an exhaust filter installed as well.

These measures are well-intentioned because diesel particulate (soot) emissions can cause serious health issues in humans. DPFs cut down on diesel soot emissions by 80percent, but they aren’t suitable for all. Even if your driving style is not predominantly urban or stop-start, adjustments to your driving habits may be necessary to ensure that these systems are operating correctly.

What is the process by which diesel particulate filters function?

DPF Filter (DPF) captures soot particles and prevents them from leaving in the system of exhaust. Like all filters that are used, they need to be cleaned frequently to ensure their performance. For the case of a DPF this is known as “regeneration”. This process involves the soot that has been collected being burned off at high temperatures leaving only the ash.

Regeneration can be active or passive

Passive regeneration

Passive regeneration occurs automatically on motorways when the temperature of the exhaust is high. Since a lot of cars aren’t driving on motorways very frequently, car manufacturers have developed “active” regeneration. In this case, an engine control computer (ECU) is in charge of the process.

Active regeneration

If the filter is filled with soot up to the limit set (about 45percent) it is possible that the ECU will trigger post-combustion fuel injection to raise the temperature of the exhaust and initiate regeneration. If the engine is turned off while regeneration is taking place, the regeneration may not be complete, and the warning light will turn on to indicate that the filter is blocked partially.

It is possible to complete the cycle of regeneration and remove the warning light by driving, and then increasing the temperature in this manner.

Signs of active regeneration

In the course of active regeneration, you could be able to observe the following signs:

  • Cooling fans on
  • Increased idle speed
  • Deactivation of the automatic Stop/Start
  • A small increase in the amount of fuel consumed
  • A strong, bitter smell emanated from the exhaust.
  • Change to the engine note

If the regeneration fails because of a lack of operating cycle, the additional fuel that is injected into the cylinders won’t be burned and will flow to the sump. In the end, the quality of the oil will decrease and the level of oil will increase.

The majority of DPF-equipped engines have an oil quality/viscosity gauge, however, it is essential to ensure that the oil level is not higher than the limit of the dipstick since diesel engines are able to run with their own oil when the level is too high – usually to the point of destruction.

If you do not pay attention to the diesel particulate filter warning light and continue driving slow, stopping and starting, the soot will increase until it reaches 75%. At that point, you should expect to see additional dashboard warning lights turn on. At this point, driving at a high speed will not suffice to clean the filter, and you’ll have to take your car to a repair shop to undergo “forced” regeneration.

Forced regeneration

Forced regeneration is necessary when “active” regeneration criteria have not been fulfilled and soot levels within the DPF have increased to around 70%. If left unattended, the load of soot will continue to increase. At this point, the diagnostic tool should be utilized to trigger regeneration. When you reach 85% soot loading, regeneration can no longer be done on the vehicle. You must remove it from the DPF to be replaced or cleaned.