Wall-flow Filters
Wall flow filters are the most widely used technology for reducing diesel particulate
emissions, and derive their name from the fact that all the exhaust gas is required
to pass through the porous walls of the filter. As it does so, particles larger
than the pore size are left behind, and filtration efficiencies of more than 99%
by mass are possible. Wall flow filters are made from a variety of materials, with
the most common being cordierite, silicon carbide and sintered metal. As the filtration
efficiency is so high, any filter will rapidly become blocked unless the accumulated
diesel particulate matter is removed by oxidation at regular intervals. This process
is known as ‘regeneration’ and is so important that diesel particulate filter systems
are usually categorised according to the regeneration principle that they follow.
