The job of the particulate filter is to retain the ash particles that are generated in the diesel engine during the combustion process, thus preventing the ash particles being emitted to the atmosphere.
To prevent the filter from becoming saturated these particles are periodically eliminated by means of a process called regeneration, which consists of combusting the ash particles into other less harmful particles by raising the temperature through catalytic processes.
There are two types of diesel particulate filters:
- Particulate filter with catalytic additive
- Particulate filter with catalytic recovery
The first requires a cerine (eolys) based additive fluid which facilitates the regeneration process and the second type of particulate filter does not require an additive because it burns the particles in a dry state.
Particulate filter with catalytic recovery
This type of filter uses a ceramic monolith with a platinum coating that acts as a catalyst.
The current trend is to fit these types of filters because they are easier to produce and do not require maintenance because they do not have the additive system.
For the ECU to be able to calculate the degree of filter saturation it needs to be able assess the soot content of the filter. The particulate filter has two pressure ports, one before the filter and one after the filter. If there is a significant pressure difference between the two pressure ports then the system will start the regeneration process to remove the ash particles.
Filter regeneration can be carried out in three different ways: