Diesel-fuelled internal combustion engines have traditionally had a big problem with soot particles, and a particulate filter aims to solve this problem. A particulate filter is a device that goes in the exhaust system. They will be mandatory on all new Diesel engines sold in the EU in 2007, when the EU5 emissions regulations kick in.
The interesting bit of this whole malarkey is the Particulate filter - it is so simple, yet rather nifty technology at the same time.
By using a particulate filter on a Diesel, it generally brings the amount of particulates to a point where they can barely be measured (0,004 g/km, according to Peugeot) - equivalent to petrol fuelled cars.
The filters are flow-through filters, usually made of cordierite or silicon carbide. To prevent clogging, new filters are automatically cleaned every few thousand miles, whenever the on-board computer (ECU) notices that the back-pressure in the exhaust system is increasing.
The cleaning works like this: the ECU lets more fuel into the engine, which then burns rich. The burning Diesel goes through the exhaust system, which in turn burns off the particles clogging up the filter, resulting in a clean filter, ready for the next few thousand miles.
Clever, no?