Diesel Particulate Filter (DPF)

A diesel particulate filter (DPF) is similar to a diesel oxidation catalyst and is one of the two major technologies being employed to meet the 2007 emissions regulations. A DPF is considered a “flow-through’ device whereby the exhaust is forced through a honeycomb shaped, ceramic filter that is blocked at one end. Because of this design, it is important to monitor the exhaust back pressure and ensure the DPF is cleaned properly so that the filter does not become blocked. Most filters are designed to clean themselves (referred to as passive regeneration) but this requires an elevated engine temperature to burn off the trapped PM. For vehicles that don’t meet the minimum temperature requirements, the filter will trigger what’s referred to as an ‘active regeneration event’. This means that some diesel fuel will be allowed to pass through the engine un-combusted and will be burnt over the catalyst, allowing the PM within the filter to be burned away. One major difference between the DOC and DPF is that the DPF requires the use of ultra low sulfur diesel (ULSD) fuel with sulfur content at or below 15 parts per million. Emission reductions are approximately 50 - 90% for PM, 90% for hydrocarbons and 90% for carbon monoxide.