Passive regeneration involves the slow environment-protecting conversion of the particulates deposited in the filter into carbon dioxide. This regeneration process comes into effect when the filters temperature reaches 250°C+ and occurs continuously when the vehicle is being driven at higher engine loads and speeds. No special engine management intervention is initiated during passive regeneration, allowing the engine to operate as normal.
Only a portion of the particulates are converted to carbon dioxide during passive regeneration and due to chemical reaction this process is only effective with the temperature range of 250°+to 500°C+. Above this temperature range the conversion efficiency of the particulates into carbon dioxide subsides as the temperature of the filter increases.
Unfortunately not all vehicles get the required long journey necessary to complete a passive regeneration of the DPF System so manufacturers have has to adapt the technology and design-in an “active” regeneration process controlled by the Engine Control Unit (ECU).