Exhaust gas from diesel engines contains solids known as diesel particulate matter, which are hazardous to health.
This particulate matter is largely comprised of carbon, but also contains hydrocarbons and a certain amount of metallic particles as a result of engine wear and the burning of lubricating oil. The role of a diesel particulate filter is to separate these from the exhaust gas stream before they enter the environment.
However, the amount of particulate matter produced by even a modern diesel engine is quite significant, so the challenge is to prevent the filter from becoming blocked.
Fortunately diesel particulate matter can be made to burn given the right conditions, and this is known in the trade as ‘regeneration’. Getting diesel particulate matter to start burning requires a certain amount of heat, and this can either come from the exhaust gas itself, or from an external heat source. If the heat of the exhaust gas is relied on, this is referred to as ‘passive regeneration’, whilst if an external heat source is used, it is called ‘active regeneration’. In some cases, both types of regeneration may be used, with active regeneration serving as the backstop in case the required conditions for passive regeneration do not occur before the exhaust back pressure has become excessive.
Regeneration is a complicated subject, but unless it is properly considered the result will be blocked diesel particulate filters, which can stop or damage the engine.
