what is a dpf

A Diesel Particulate Filter (DPF) is an exhaust aftertreatment device that traps particulate matter such as soot and ash from the exhaust gas of a diesel engine. The DPF captures and stores exhaust soot in order to reduce emissions from diesel cars. The DPF typically uses a substrate made of a ceramic material that is formed into a honeycomb structure. Unlike a catalytic converter which is a flow-through device, a DPF retains bigger exhaust gas particles by forcing the gas to flow through the filter; however, the DPF does not retain small particles. DPF filters go through a regeneration process which removes the soot and lowers the filter pressure. There are three types of regeneration: passive, active, and forced. Passive regeneration occurs when the car is running at speed on long motorway journeys which allows the exhaust temperature to increase to a higher level and cleanly burn off the excess soot in the filter. Active regeneration occurs when the engine management system senses that the DPF is becoming blocked and injects extra fuel into the engine to increase the exhaust temperature and burn off the soot. Forced regeneration is when a mechanic uses a diagnostic tool to force the regeneration process. If the driver ignores the warning light and waits too long to operate the vehicle above 60 km/h (40 mph), the DPF may not regenerate properly, and continued operation past that point may spoil the DPF completely so it must be replaced. In 2018, the UK made changes to its MOT test requirements, including tougher scrutiny of diesel cars. One requirement was to have a properly fitted and working DPF. Driving without a DPF could incur a £1000 fine.