In each type of particulate filter, the soot eliminated from the exhaust gas must be removed either continuously or intermittently. In the case of fixed systems, this material is usually removed without dismantling the filter elements for manual cleaning. The soot deposits consists predominantly of carbon and will oxidise when exposed to oxygen, which means they will be “burned” without leaving any residue. Ideally, this will produce CO2 and H2O. The common term for this process in soot filters is “regeneration”.
Soot reacts spontaneously with oxygen at a temperature of over 550° C. This process is also called oxygen-based regeneration. In general, these temperature are rarely reached in most applications, if at all. This is why we use a variety of technologies to ensure that your soot filter system works smoothly. There are active and passive methods of regeneration. We draw on a variety of strategies for both methods, depending on the application.
Active regeneration involves raising the actual exhaust gas temperature by introducing additional thermal energy. In contrast, passive methods are based on lowering the required temperatures to a range within which the available temperature is adequate for regeneration.
If the engine load is regularly high and there are no longer periods of low load, the passive processes are often the most optimal and economical solution.
Additive Regeneration(FBC):
An additive is added automatically to the fuel by the soot particle filter control or manually. The additive lowers the soot ignition temperature (light off temperature term rather applies to CATs) from approx. 550° C to approx. 390° C and also accelerates the soot burn-up considerably.
ContinuousRegeneration (CRT or DOC/DPF):
Either a catalytic pre-filter coated with precious metal is arranged in front of the RPF or the RPF has a catalytic coating containing precious metal. The pre-filter or the coating of the RPF support the oxidation of nitrogen monoxide (NO) from the exhaust gas to nitrogen dioxide (NO2). The nitrogen dioxide (NO2) generated in this way is significantly more reactive than oxygen with regard to soot and is used to regenerate the RPF at lower temperatures.
Soot erosion coating (BMC):
The soot burn-off coating is a non-precious metal coating, which is also called BMC (Base Metal Coating). The coating is applied to the RPF and lowers the soot ignition temperature to approx. 420° C. Our BMC coating is sulfur-resistant in certain areas and can therefore be operated in applications with fuels containing sulfur.
If the engine load is very low over a long period of time or permanently, an active regeneration process is essential.
Catalytic burner: Fischer HCpower
A catalytic pre-filter with a special coating is arranged in front of the RPF. Diesel fuel (hydrocarbons), which reacts exothermically on the surface, is dosed in a controlled manner. The RPF is thus burned free at temperatures of > 600° C.
Electric heating register: Fischer Epower or SMF-AR®
Electric heating coils are arranged in the exhaust system in front of the RPF or in a ring around the filter element and thus actively support the regeneration of the RPF. Without a load, the exhaust gas temperatures in certain applications, such as generators or diesel-electric drives, often do not reach the required regeneration temperature. The duration of the low-load condition is often not known or foreseeable, which is why the heating register located in front of the particle filter starts in a preset exhaust gas temperature range. The heating register achieves a double effect of increasing the temperature: on the one hand, the individual heating elements bring heat into the exhaust gas and, on the other hand, the generator and the diesel engine are subjected to greater loads, which also increases the exhaust gas temperature "passively" within the engine. When a certain target exhaust gas temperature is reached and after a preset time "X", the heating register is switched off again.
