A monolithic ceramic filter captures the carbon particles (soot) emitted by a diesel engine extremely efficiently. However, after a certain time the filter requires cleaning to prolong its operational life. The most widely accepted cleaning method incinerates the captured soot. This cleaning process is called filter regeneration.
Filter regeneration requires a defined amount of thermal energy. In some cases the energy contained in the exhaust gas may be sufficient to initiate and maintain filter regeneration. This is often the case with loaded engines (high exhaust gas temperature) operating uninterruptedly for a sufficient length of time. Under such circumstances a catalysed, so called self-regenerating, filter may be installed. Self-regenerating filters are normally installed on engines that run on fuels containing very low level of sulphur .
When an engine runs on fuels containing 0.1% sulphur or if the exhaust gas temperature fluctuates, energy must be added in order to guarantee the regeneration process.
A reliable way to supply the required energy is to incorporate a burner into the exhaust gas system. Self-regenerating system are referred to as being passive, while an energy assisted system is an active system. The EmiGreen Delta is a passive system (self-regenerating). The EmiGreen Alfa-Alfa is an active system, it uses a burner to add the required energy.