The active regeneration of diesel particle filters requires the use of an external energy source to raise the gas temperature to the point where regeneration of the filter can occur. This technique is suitable for situations where the exhaust gas temperature rarely if ever exceeds the threshold for passive regeneration or where the duty cycle (and therefore the exhaust gas temperature) is difficult to predict with any degree of certainty.
Diesel particulate matter generally requires temperatures of at least 550 Centigrade (1020 Fahrenheit) before it will burn naturally and in the simplest examples of active regeneration the approach is to use either an electric heating element or a fuel burner to periodically raise the temperature to this level (for convenience, the fuel burner will normally be supplied with diesel from the same tank which supplies the engine). In many cases however, a combination of passive and active approaches is adopted. This lowers the temperature threshold which must be attained, but still relies on heat from an external source to raise the exhaust gas temperature to this point.
Apart from the choice of heat source, other decisions which have to be made when opting for active regeneration are whether it will be carried out with the filter in-situ, and if so whether the engine will be stopped, idling or running normally.
The most frequently adopted methods of active regeneration are summarised in the table below:
