Particle filter

The diesel particulate filter is an increasingly spoken word not only when visiting a mechanic, but above all when buying a used car. What is it really and should one be afraid of problems connected with it?

WHAT IS A PARTICULATE FILTER?

The particulate filter is part of the exhaust system, and more specifically the filter responsible for the purification of exhaust from soot particles and ash. The particle filter in most cases is called DFP (Diesel particulate filter) or FAP (Filtre a particules). The reason for introducing particulate filters was to tighten emission standards, and more precisely to introduce Euro IV, which significantly reduced particulate emissions compared to previous standards. Particulates concern soot generated in the process of incomplete fuel combustion. It includes, among others, hydrocarbon and carbon as well as sulphates, sulfur oxides and metals. Its location is also not accidental – it is just behind the catalytic reactor (catalyst). Unfortunately, its presence in the system enforces the introduction of additional modifications of the system – the pressure sensor, the exhaust temperature sensor before and after the filter and the wideband lambda probe. Information from individual sensors is passed to the controller, which on their basis calculates the level of filter clogging and is responsible for carrying out the regeneration (firing) process.

HOW IS BUILT?

The particulate filter is made of a ceramic body in a metal housing. The particle filter housing is in most cases made of stainless steel, because the use of this material ensures a longer service life. The interior of the particulate filter are channels that are arranged side by side in parallel. A very important fact is that each channel has a closed one end – some of the clogged channels have an inlet and the other outlet. Their arrangement is not accidental – the whole creates a grid. Channels that have clogged outlets are called inlet ducts – they get fumes. The reverse situation occurs in the case of outlet ducts where the inlets are clogged. The use of this solution contributes to the forced flow of exhaust gases through the porous walls of individual channels. The ducts are made of silicon carbide, which is coated with aluminum oxide and cerium oxide, additionally platinum particles are deposited on them. The porosity of the channel walls allows the exhaust to flow, during which particulates of soot are retained and collected. The side effect of the diesel particulate filter is its clogging, which leads to a reduction in engine power and a message informing about a problem with the filter, and in some cases a clogged particulate filter leads to the engine going into emergency mode. Then what? In most cases, the filter can burn itself, which will result in returning to the normal engine mode. If self-tests do not help, we have to go to the service / mechanic who will perform the regeneration of the filter. Unfortunately, this treatment is not always helpful and in this case we will be forced to replace it. The purchase of a new particle filter is associated with a considerable expense.

The particle filter should not be afraid of regular servicing of the vehicle. Unfortunately, if the drive unit is in a bad technical condition, we will probably have a problem with the particulate filter in a short period of time.