DPF

A DPF is a Diesel Particulate Filter. It allows gases to flow through it while trapping solid particulate matter. The DPF does this by having several channels in parallel with the ends plugged in a checker board pattern. A DPF is usually followed by a lean NOx catalyst in a proprietary catalytic converter for diesel engines. By trapping the particulate matter, soot, the DPF allows the lean NOx catalyst to work without being cloggeg by the soot. Hence the effectiveness of the lean NOx catalyst isn't reduced due to soot covering the active sites of the catalytic converter. The DPF eventually becomes clogged with soot. Consequently a soot burn off is required. The DPF is heated to a temperature that fully combusts the soot. This heating enables the DPF to be used continuously, however; it requires a fuel penalty as extra fuel is combusted to heat the DPF. A sensor that measures back pressure determines when the DPF needs to be heated.

Also see dpf entry - these pages should likely be merged.