How a diesel particulate filter works

Modern particulate filters are able to filter out and to burn in the filter more than 90% of the particulates - also including many superfine particles featured so much in the press these days.

Thousands of channels

With their characteristic honeycombed structure, which consists of innumerable channels arranged in parallel, particulate filters are similar at a first glance to ceramic catalytic converters. However, the channels in the particulate filter are closed off alternately. Among ceramic materials, silicon carbide (SiC) and cordierite have the best performance.

The filtering process

In the filtering process the exhaust gas flows through the porous ceramic walls. The exhaust gas diffuses through the pore walls - the particulates remain trapped there. With increasing loading of the filter with particulates, a particulate layer also forms on the channel walls.

Regeneration of the filter

One of the main tasks of the particulate filter technology is to ensure the effective combustion of the trapped particulates - therefore effective regeneration of the filter.

Since the particulate ignition temperature is more than 550 °C, and this temperature is usually reached only at very high engine power and high engine speeds, additional measures are necessary. Either the exhaust gas temperature is raised periodically or the particulate ignition temperature is reduced. This is achieved by additives in the fuel or, in filters of the new generation, by a catalytically active platinum layer on the porous walls of the filter material.