- What is the purpose of a particulate filter and how does it work?
- How does the FAP regeneration process occur?
- How to understand if the FAP is clogged?
- What to do if the particulate filter is clogged?
The problem of thepollution The air quality in our cities has become a central topic in Italian public opinion, especially since the Po Valley has sadly become one of the most polluted areas in Europe. In recent years, regional and national news programs have often featured reports of anti-pollution measures, including road closures for certain vehicle categories. These measures are designed to reduce the concentration of particulate matter (PM10 and PM2.5), among the main causes of the deterioration of air quality in large urban centers.
To further reduce emissions of these harmful substances from cars, which are among the main culprits of urban smog, since 2008, coinciding with the introduction of the new Euro V pollution class, it has become mandatory for diesel-engined cars to be equipped with a particulate filter, without which they cannot circulate.
What is the purpose and how does the particulate filter work?
The particulate filter, also known by the technical term exhaust gas aftertreatment system, is a universal component of diesel engines essential for filtering and trapping particulates produced during fuel combustion and thus preventing their dispersion into the environment. This filter was first used in 2000 on the Peugeot 607 and soon found progressive and constant use by other European car manufacturers as well, although it may present some differences.
The flat, elongated structure of the filter, which is common across all types, is similar to that of a catalytic converter but with a sealed end. The filter's interior is composed of a long series of small channels that allow filtered exhaust gases to escape, retaining the particulate matter, which is then stored within them. In terms of operation, there are two main types: the FAP (Filtré a Paricules) and the more common DPF (Diesel Particulate Filter). These differ in their regeneration process, which involves the combustion of fine particles to clean the filter and restore its efficiency.
How does the FAP regeneration process occur?
Periodically, the filter reaches a saturation threshold of the particulate matter inside it, compromising its filtering capacity. Depending on the type of car, saturation can occur more or less quickly, generally every 500 km traveled or 10 hours of continuous use. As soon as the accumulation of fine particulate matter reaches an excessive amount, the engine control unit automatically triggers the regeneration process.
Whether it's a FAP or DPF filter, during regeneration the filter must reach a temperature of approximately 650°C: at this temperature, all the particulate matter is combusted and converted into carbon dioxide. To reach this temperature, the engine control unit completely or partially seals the EGR (Exhaust Gas Recirculation) valve, a special engine component that lowers the temperature of the cylinders and exhaust.
DPF filters also use a special additive called cerine, which contains cerium dioxide (CeO2), which lowers the combustion temperature of particulate matter from 650°C to 450°C. The additive is contained in a special tank connected directly to the fuel tank, with which it is mixed. To initiate the regeneration process, the control unit operates after fuel injections, warming the exhaust system and cleaning the filters of fine particulate matter.
DPF filters do not use any type of additive and reach temperatures of up to 650°C. Here too, the temperature increase occurs through a series of post-injections with subsequent post-combustion. To facilitate the regeneration process, the filter walls are coated with noble metals, which act as catalysts, including rhodium, palladium, and platinum. Once combustion temperature is reached, the particulates sublimate, completely cleaning the filter.
How to understand if the FAP is clogged?
In some cases, regenerative processes fail and to understand if the particulate filter has reached the saturation limit threshold, it is necessary to pay attention to some signs:
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- The first and most obvious is the yellow FAP warning light on the dashboard, which indicates that the control unit may have detected a malfunction in the regeneration process. This is certainly the first warning sign that should not be ignored. However, be aware that on older diesel cars, the warning light does not necessarily indicate a malfunction but is sometimes a warning that the regeneration process has begun. For this reason, it is advisable to keep the car at 3,000 rpm to increase the temperature and facilitate the regeneration process. If, despite this, the warning light remains on and other warning signs appear, which we will discuss later, it is absolutely necessary to perform a check to verify the integrity of the filter and avoid further damage.
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- A second common sign of a malfunction is the engine warning light coming on, accompanied by a significant loss of power. This is usually caused by the automatic intervention of the engine's electronic self-protection system, which serves to prevent serious damage to the cylinders, pistons, and other mechanical components. This is a critical event because it means that air circulation within the engine is not occurring properly, and exhaust gases are unable to filter out and remain trapped.
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- A final visible sign is the release of thick black smoke from the exhaust pipe, a direct consequence of a lack of filtering of exhaust gases, which indicates a malfunction of the particulate filter.
What to do if the particulate filter is clogged?
Since it is an extremely delicate and essential component for the vehicle's circulation, checking the correct functioning of the particulate filter and, if necessary, adding the additive are procedures that cannot be performed alone but necessarily require the intervention of a specialized technician. It is therefore essential to immediately go to an equipped workshop.
The specialist will first attempt to clean the filter through a forced regeneration. To do this, after adding a specific additive, they will run the car's engine for about ten minutes at around 3,000 rpm. This procedure usually restores the filter's functionality. In the unfortunate event that this procedure is not sufficient, a specialized company will be required to assess the filter's condition and thoroughly clean all components, or replace it entirely if it is beyond repair.
It's important to emphasize that removing the particulate filter to avoid clogging is not only prohibited by law and punishable by heavy administrative fines, far exceeding the cost of maintaining or replacing the component, but it also causes serious air pollution, resulting in harm to the health of the entire community.