Diesel Particulate Filter (DPF)

 A diesel particulate filter (DPF) is an emissions-control device that traps soot and other particulate matter from diesel exhaust before it leaves the tailpipe.

The filter is typically a ceramic honeycomb (often silicon carbide or cordierite) with channels that are alternately plugged at each end. This forces exhaust gas to pass through the porous channel walls, which capture the solid particles while letting the gases through. Modern DPFs can remove more than 95% of particulate matter, including the fine particles linked to respiratory and cardiovascular problems.

Because the trapped soot accumulates over time, the filter has to be cleaned through a process called regeneration. In passive regeneration, high exhaust temperatures during normal driving burn the soot off. In active regeneration, the engine control system raises exhaust temperature, usually by injecting extra fuel, to burn off the buildup at around 600°C. Non-combustible ash, which comes mainly from engine oil additives, can’t be burned away and eventually requires the filter to be professionally cleaned or replaced.

DPFs often work alongside SCR systems, with the DPF handling particulates and the SCR handling NOx. Their main drawbacks are added cost, a small fuel economy penalty, and clogging problems if the vehicle is driven mostly on short trips that never get hot enough for regeneration.