Regeneration

Passive
During the passive regeneration, the accumulated diesel particulate matter (DPM) oxidises at the prevailing temperature of the exhaust gas (usually above approximatel 550 degrees Celsius.) As this high temperature is rarely reached in a diesel exhaust system, techniques were developed to achieve oxidation at lower temperatures.
The first option increases the nitrogen dioxide (NO2) content of the exhaust. NO2 oxidises diesel particulate matter around 300 degrees Celsius. When nitrogen oxide (NO), a by-product of the diesel fuel combustion, comes into contact with a catalytic coating, the quantity of NO2 required for the burn-off of soot is produced . The catalyst coating can be applied directly to the filter, or onto a separate converter installed upstream of the device.
The second option adds a fuel borne catalyst (FBC) to the diesel fuel. The FBC burns with the fuel in the diesel engine, and is then carried into the diesel particulate filter together with the particulate matter (PM). Here, it catalyses the reaction of soot with oxygen in the exhaust gas. The FBC reduces the temperature from over 550 to approximately 350 degrees Celsius, depending on the engine emissions.

Active
At the active regeneration, the temperature of the exhaust gas or, preferably the filter itself, is raised to the point where the diesel particulate matter (DPM) or soot starts to oxidize. The Alantum Alloy Foam based DPF works exceptionally well with active regeneration.
Various active regeneration technologies are possible:

• The exhaust temperature can be raised during engine operation by means of diesel fuel post-injection during combustion, or through injection of fuel into the exhaust system by an extra diesel injector or evaporator after the engine. The fuel evaporates in the hot exhaust gas and is than catalytically converted into heat on a diesel oxidation catalyst (DOC) located before the DPF. Because of the relatively inexpensive hardware those systems are used in OEM applications.

• Full burner systems, similar to a central heating boiler, can be employed. In a full burner system, a flame is burning in the exhaust system upstream of the DPF, capable of heating the exhaust gas to the required temperature of approximately 550°C. Safety concerns, the complex system setup, limitations in thermal power output and high price limit the number of applications so far. Active regeneration of the DPF-systems in applications where regular returns to base or regular engine idle times are guaranteed can be regenerated with stand still burner systems requiring a lower total power or electrically heating systems.  If the electrical heating option is taken, the normal procedure is to connect the filter to a power supply at the end of a day, or at the end of a shift. Unfortunately, it’s human nature to forget things and that can sometimes pose a problem for this system of regeneration. However, there are applications where it works very well, For instance, a diesel generator’s own power can be used to switch the heater on automatically if required.

• Systems based on combinations of the above methods are known as well. The combination of diesel fuel injection into the exhaust with a downstream DOC is sometimes combined with an electrical pre-heating of the DOC using the electric on-board power. A quicker and safer regeneration start can be achieved, but conscientious control of the electrical heater is crucial for the electrical power management.
  Various other active regeneration systems using plasma to initiate the soot burn off are in use as well.