A catalytic pre-filter coated with precious metal is installed upstream of the particulate filter or, alternatively, the particulate filter itself has a precious metal catalytic coating. The pre-filter or the particulate filter coating encourage oxidation, thereby converting nitrogen oxide (NO) in the exhaust gas into nitrogen dioxide (NO2). In turn, this nitrogen dioxide (NO2) is significantly more reactive than oxygen in regard to the soot and so enables regeneration of the particulate filter at lower temperatures.
This technology is used for applications powered by low-sulphur fuels (< 50 ppm) but is avoided in combination with sulphurous fuels. This is because the oxidisability of the coating causes the SO4 emissions to continue their oxidation process into SO3 and SO4 when exposed to the residual oxygen. These can then precipitate into sulphurous or sulphuric acid if the temperature falls below the dew point.
If the natural temperatures of the exhaust gas are not sufficient for this form of regeneration, a HeliosFFB or E-Power thermal management system can be placed upstream of the DOC/DPF.
