Passive regeneration is the term given to techniques for burning the trapped DPM without the requirement for additional energy inputs. This approach involves lowering the temperature at which the DPM will burn from its ‘natural’ level of about 550C to one which will be present in the exhaust gas for a significant proportion of the time (i.e. at least 25% of the duty cycle). Depending on which route is taken, passive regeneration is possible at temperatures as low as 260 Centigrade (500 Fahrenheit). Note that in many cases the necessary exhaust gas temperature will not be available with the required level of predictability and therefore passive regeneration will not be a viable option. The most common methods of passive regeneration are summarised in the following table:
