The DPF may be manufactured from different materials (Cordierite or Silicon Carbide for example) and in its most common form consists of a substrate of narrow channels in which each channel is blocked at one end. Adjacent channels have this blockage at alternate ends. With this construction exhaust gas may enter at one end, but must pass through the wall of a channel before exiting and is thus termed a wall flow device.
Field and laboratory experience has demonstrated that the DPF is easily capable of retaining more than 80% of total DPM emissions. This excellent efficiency is maintained for the range of particle sizes commonly found in diesel exhaust. As the DPMaccumulates the exhaust backpressure caused by the combination of the DPF and its contained DPM increases. To date the challenge for the DPF has been reliability. For reliable passive operation the DPF is very sensitive to the characteristics of the engine operation. With the currently available technology this demands a careful study of each new application. The requirements are to accurately identity possible applications and to accurately select an appropriate DPF. In order to fulfil these requirements an understanding of the DPF operation is necessary. The actual filtration mechanism may be adequately described by the concepts of direct interception and Brownian diffusion and this results in the accumulation of DPM within the filter.