A diesel particulate filter removes particulate matter from diesel exhaust by physical filtration. The common type is a ceramic (cordierite or silicon carbide) honeycomb substrate. The structure like an emissions catalyst substrate with the channels blocked at alternate ends. The exhaust gasses must therefore flow through the walls between the channels and the particulate matter is deposited on the walls.
Other filter types are available, using sintered metal plates, foamed metal structures, fibre mats and other materials as the filtration medium.
The filtration efficiencies of diesel particulate filters is more than 99% in solid matter. Since diesel particulate matter has a non-solid portion, the total efficiency for DPM is lower than 90%. The advantages are lower back pressure and a lower risk of blocking.
1. Carborundum wall flow filter: