Particulate Filters

particulate filters are based on a ceramic honeycomb structure. The exhaust gases flow through the porous honeycomb walls, and this process traps over 99% of even the tiniest particles between 20 and 300 nanometers.

The type of catalytic coating used for the filter depends on the individual application.

Particulate Filtration

Exhaust gas filtration involves separating out soot particulates (amorphous components of the exhaust gas mixture that have not been burnt) and ash (amorphous, completely burnt exhaust gas components) on a filter surface.

Wall Flow Filters

In the case of wall flow filters, the unfiltered stream of exhaust gases from the diesel engine containing soot and ash particulates is forced through a porous filter wall. This is where the particulates are filtered out. Because of particulate agglomeration and adhesion, the particulates do not necessarily have to be larger than the tiny holes in the filter wall through which the exhaust gases flow in order to be separated.

In operation, the process leads to a build-up of a particulate layer in the wall, known as the filter cake. This makes it possible to separate out very fine particles. When the filter cake is fully established, the filter can trap over 97% of the particulates. The wall pore size and the wall porosity of the particulate filter are kept as large as possible to minimize counter-pressure against the flow of gases.

Regeneration

Most of the soot particulates trapped during this process can be burnt off on the filter. This is known as soot regeneration. It can either take the form of passive regeneration (continuous burn-off while the engine is running) or active regeneration (involving a system that heats the filter when activated).

Active Regeneration:

• Active regeneration with full-flow regeneration burner
• Active electrical regeneration (e-power)

Passive Regeneration:

• Catalytic particulate filter
• CRT system (Continuous Regeneration Trap)

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