Diesel Particulate Filters

A diesel particulate filter, sometimes called a DPF, is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. Wall-flow diesel particulate filters usually remove 85% or more of the soot, and can at times (heavily loaded condition) attain soot removal efficiencies of close to 100%. A diesel-powered vehicle equipped with functioning filter will emit no visible smoke from its exhaust pipe.

Some filters are single-use (disposable), while others are designed to burn off the accumulated particulate, either through the use of a catalyst (passive), or through an active technology, such as a fuel burner which heats the filter to soot combustion temperatures, through engine modifications (the engine is set to run a certain specific way when the filter load reaches a pre-determined level, either to heat the exhaust gases, or to produce high amounts of NO2, which will oxidize the particulates at relatively low temperatures), or through other methods.

While no jurisdiction has made filters mandatory, the increasingly stringent emissions regulations that engine manufactures must meet mean that eventually all on-road diesel engines will be fitted with them. The American 2007 heavy truck engine emissions regulations cannot be met without filters. In the European Union, filters are expected to be necessary to meet Euro.VI heavy truck engine emissions regulations currently under discussion and planned for the 2012-2013 time frame. PSA Peugeot Citro�n was the first company to make them standard fit on passenger cars in 2000, in anticipation of the future Euro V regulations.

http://en.wikipedia.org/wiki/Diesel_particulate_filter