Diesel Particulate Filter

A diesel particulate filter, or DPF, is a device designed to remove diesel particulate matter, or soot, from the exhaust of a diesel engine by forcing the gas through a filter material that traps the larger particles rather than merely catalyzing them the way a catalytic converter does. Wall flow filters typically remove 85 percent or more of soot and can approach full efficiency under favorable conditions. The accumulated soot is periodically burned off in a process called regeneration, either passively using engine heat and catalysts or actively through methods such as extra fuel injection to raise exhaust temperatures. The most common filter material is cordierite, a ceramic offering good filtration at lower cost but a relatively low melting point of about 1200 degrees Celsius; silicon carbide filters withstand higher temperatures, near 2700 degrees Celsius, but cost more. Because ash from lubricating oil cannot pass through the filter walls, DPFs need periodic high speed driving to regenerate effectively and prevent a rise in exhaust back pressure.