A Diesel Particulate Filter, sometimes called a DPF, is device designed to remove Diesel Particulate Matter or soot from the exhaust gas of a Diesel engine, most of which are rated at 85% efficiency, but often attaining efficiencies of over 90%. A Diesel-powered vehicle with a filter installed will emit no visible smoke from its exhaust pipe.
In addition to collecting the particulate, a method must be designed to get rid of it. 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, or through engine modifications (the engine is set to run a certain specific way when the filter load reachs a pre-determined level, either to heat the exhaust gasses, or to produce high amounts of No2, which will oxidize the particualte at relatively low temperatures). This procedure is known as 'filter regeneration.' Fuel sulfur interferes many 'Regeneration' strategies, and all jurisdictions that are interested in reduction of particulate emissions, are also passing regulations governing fuel sulfur levels.