Diesel particulate filters

What is a particulate filter?

Particulate filters are one of the main elements that vehicle manufacturers rely on to ensure that vehicles meet the limits set by emissions regulations. Despite advances in engine efficiency, even today it is not uncommon to see vehicles with black clouds coming out of their tailpipes, especially when accelerating sharply. This smoke is a sign of inefficient combustion, which leaves a lot of residue.

Polluting gases such as carbon monoxide or hydrocarbons are dealt with by catalytic converters, but what about solid micro soot particles? They are also a serious health threat, because when suspended in the air they are easily transportable. Because of their size, they easily reach the lungs and are linked to respiratory, cardiovascular and carcinogenic health problems. Particulate filters are used to eliminate them.

What is the purpose of the particulate filter?

Like a catalytic converter, particulate filters are an exhaust emission control device. Their purpose, however, is to trap solid soot particles from the operation of the combustion engine and subsequently disintegrate them.

As mentioned above, it has been fitted to diesel vehicles since 2000 and is currently fitted to virtually all diesel vehicles. On the other hand, although the concept is the same, the technology is still in its infancy in petrol models, as they tend to operate at a higher temperature and do not generate as many particles.

It is common for the exhaust line to have a pre-catalytic converter at the front, or even inside the metal casing itself. As we will see below, its operation requires high temperatures, so it is usually located close to the engine, where the exhaust gas is hotter. Externally, they vary in size and shape, depending on their location on the vehicle.

Similar in appearance to a catalytic converter or a silencer, they are also often thermally shielded. Internally, they consist of a ceramic substrate with alternately arranged non-through channels, held in place by a protective heat shield between the ceramic and the steel casing.

How does a particulate filter work?

The incoming exhaust gases penetrate the porous ceramic walls and exit at the other end in the direction of the exhaust pipe. The soot particles, on the other hand, are retained and gradually accumulate. When a certain level of accumulation is reached, a process called regeneration must take place. Similar to pyrolysis, regeneration is a temperature increase of the exhaust gas to 700-800°C, which disintegrates the stored particles so that they can pass through the ceramic and out of the filter. Such regeneration can be achieved either passively (by simple high speed driving) or actively (with engine management intervention, via post-injections to increase the temperature). Some vehicles (especially PSA group models) have a system that mixes a special additive with the fuel to ensure that the particles disintegrate at a lower temperature.

The main problem with this component is excessive soot build-up, which could block the exhaust line and prevent the vehicle from running.

There are different strategies to monitor the degree of accumulation (by time since the last regeneration, by a differential pressure sensor between the filter inlet and outlet...) in order to ensure that the filter never becomes blocked.

If a certain threshold is exceeded, the dreaded particulate filter warning light on the instrument panel comes on. One way to clean the particulate filter is to drive for about 15 minutes at continuous high speed with a lower gear than usual so that the filter temperature rises, the regeneration cycle is completed, and the filter is ready to continue to perform its function. However, if this warning is ignored and soot build-up increases, it is possible that a certain level may be exceeded which prevents regeneration and the only solution is to replace the particulate filter.

At Kat Europe we have a wide range of particulate filters to cover the needs of over 90% of the European vehicle fleet, with the best price in the market and fast and efficient delivery. If you have any questions about how a particulate filter works or how to find the right one for your vehicle, please do not hesitate to contact us or consult our help centre.