Passive regeneration – a process of soot reduction via natural conversion. Occurs when ideal driving conditions apply (60mph for 15 minutes – e.g. motorway driving). The DPF becomes hot enough to burn off some of the trapped particulates naturally between 350 and 500°c. The carbon soot particles are converted into carbon dioxide by a reaction with nitrogen oxide using the coating of the DPF which works as a catalyst.
Active regeneration – occurs when the optimum exhaust gas temperatures can no longer be maintained, meaning passive regeneration can no longer take place. Therefore, active regeneration is an ECU-led process that increased the exhaust gas temperature to 500-800°c. When the carbon soot deposits in the filter reach a certain level, the engine management system initiates the regeneration process which lasts around 10 minutes. DPFs can hold several hundred miles worth of soot before this process is initiated. The ECU may also trigger vehicles into limp mode to help protect other components when it senses that the DPF is becoming blocked.
Forced regeneration – involves very high temperatures and is carried out by garages with diagnostics equipment.
Warning! The very high temperatures applied during active and forced regeneration can lead to an accumulation of ash, otherwise known as ‘aging’. The build-up of ash is treated by physical intervention such as chemical cleaning, ultrasonic cleaning or replacement of the DPF.