Diesel Particulate Filters – Everything You Need to Know About DPF

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Does your vehicle have a diesel particulate filter? If you run a diesel vehicle, then the answer is probably yes. However, unless you have spent excessive amounts of time learning about your car, the chances are you know little about this vital part, including what it does, why it is crucial, and how to maintain it.

In this blog, we explain more about diesel particulate filters, including what they are, what they do, and how to look after them. We also take a brief look at the history of diesel particulate filters and the regulations that surround them.

Diesel Particulate Filters - Everything You Need to Know About DPF

What is a Diesel Particulate Filter?

A diesel particulate filter (DPF) is also commonly referred to as a soot trap. It is a filter that captures and stores exhaust soot, consequently reducing emissions from diesel cars. A DPF system has a finite capacity. This means that it must either be replaced when full or the trapped soot must be burned off or emptied periodically, resulting in DPF regeneration.

DPF regeneration cleanly burns off the excess soot that is deposited in the filter. Doing so reduces harmful exhaust emissions and helping to prevent the tell-tale black smoke, mostly seen when accelerating, which was previously an integral part of operating a diesel vehicle.

The DPF filter should not be tampered with, so you must know whether you have a single-use filter or one that can undergo filter regeneration. If you have a single-use filter, it should only be replaced with the appropriate part by a certified and experienced motor mechanic.

Understanding Diesel Exhaust Emissions

A diesel engine produces a range of particles during the combustion process. The particle composition that is produced depends on a variety of elements, including the age and type of engine and its specific emissions specifications. Generally, a four-stroke diesel engine produces less particulate per unit of power than a two-stroke diesel engine. This is because the four-stroke burns the fuel-air mix more completely.

Black carbon (soot) particles are produced as a result of the incomplete combustion of diesel fuel. Included in this matter are nanoparticles that cause air pollution and are known to be harmful to human health. A DPF filter can capture up to 95% of these harmful particles.

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Diesel particulate filters were first considered in the 1970s and have been used in non-road machines since 1980. They were first introduced into automobiles in 1985; however, there was no regulation for medium and heavy-duty diesel engine emissions until 1987. The California Heavy Truck rule saw emissions being capped at 0.60 g/BHP Hour.

Tighter emissions standards have since been introduced across North and South America, Europe and much of Asia. It is the introduction of such standards that has fueled the introduction of filters into most modern vehicles. Many countries and states within the USA are also investing, or have invested, in retrofitting programs to introduce filters to older automobiles and off-road vehicles.

Is it Illegal to Remove a Diesel Particulate Filter?

Section 203 of The Clean Air Act makes it illegal to remove, tamper with, or knowingly allow the deletion of a DPF system. Doing any of the above can land you with a hefty fine. The amount of the fine depends on several different aspects, including the reason why you intended to tamper with or remove the DPF, the weight of your vehicle, the number of miles covered, and your income. Fines from $2500 to $400,000 have been levied against those who have been caught.

How do I Tell if My Diesel Particulate Filter is Blocked?

There are several ways to tell if your DPF is developing a fault or becoming blocked with soot. Firstly, you may feel a loss of power in your engine. You may notice a pungent smell of diesel and an increase in black smoke releasing from your vehicle. Passive and active regeneration may fail, and the automatic stop-start system may stop working. As well as any or all of these, you should also receive a warning on your dashboard. The DPF warning light is most commonly a piped box with dots in the middle. If you are unsure of the warning lights on your dash, refer to your vehicle’s handbook.

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What Causes a Diesel Particulate Filter Blockage?

The most common cause of diesel particulate filter blockage is undertaking short journeys at low speeds. An excess of these types of journeys does not provide the conditions necessary for regeneration to occur. It one of the reasons why diesel vehicles are not recommended for city-bound drivers that only make short drops.

Poor or infrequent servicing is another common cause of DPF blockages. If your car is poorly maintained, your diesel particulate filter is likely to fail sooner than one on a regularly serviced vehicle. If you have your vehicle serviced regularly and carry out maintenance as required, your DPF should last for at least 100,000 miles.

The oil that you use in your vehicle can also affect the performance of your diesel particulate filter. The additives that re contained within some oils can block DPF systems.

Other causes of particulate filter blockage include low-quality fuel, frequently running on low fuel levels, and performance modifications that are made to the vehicle.

How do I Maintain a Diesel Particulate Filter?

If you have a single-use DPF, then it is vital to replace the filter as soon as it is full. Not doing so will cause a rise in emissions that are ejected from your vehicle as well as affecting your vehicle’s performance. For DPF systems that utilize regeneration, maintaining them involves ensuring that they are fully able to regenerate when full. There are two types of diesel particulate filter regeneration: active and passive. As passive regeneration should be the most common, we will look at this first.

  • Passive regeneration

Passive regeneration takes place when your vehicle is running at speed on long motorway journeys. This enables your exhaust temperature to increase to a higher level and cleanly burn off the excess soot in the filter. To achieve this, it is recommended that diesel vehicles are run on highways or other main roads for up to 50 minutes at sustained speeds.

  • Active regeneration

Not all drivers can drive in this manner regularly enough to achieve effective passive regeneration. With this in mind, manufacturers designed an alternative form of regeneration – active regeneration.

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During active regeneration, extra fuel is injected automatically, as part of the vehicle’s ECU, when a filter reaches a predetermined limit (usually about 45%). This raises the temperature of the exhaust, allowing stored soot to be burnt off. However, if the journey is too short, problems can occur, and the regeneration process may not be completed leading to a partially blocked filter.

The warning light on the dash should come on in such instances. The best way to solve this is to drive for at least 10 minutes, sustaining a speed of over 40mph.

If your vehicle is engaged in active regeneration, you should notice the following:

  • Cooling fans running
  • Engine note change
  • Increased idle speed
  • A hot, acrid smell from the exhaust
  • A slight increase in fuel consumption
  • Deactivation of automatic Stop/Start

What Do I Do if Neither Active nor Passive Regeneration Work?

If neither passive nor active regeneration works, the warning light will remain on; it may also turn red or be joined by further warning lights. If you have already taken the step noted above, then it is time to get your vehicle checked out by a qualified mechanic. Failing to take action can cause further damage and lead to a more expensive fix than was first needed.

Some mechanics can clean blocked DPFs, using a process called forced regeneration. The process is not cheap and is not guaranteed to fix the problem completely. However, it is usually successful in removing enough soot for the passive and active systems to kick in and remove the rest effectively.

Originally posted 2023-11-19 09:46:36.

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