DIESEL PARTICULATE FILTERS (DPFs)
Diesel particulate filters (DPFs) have been used in the industry for a while, often in specialized applications like garbage packers that must run indoors for extended periods of time. They were once called as particle traps for this sort of application. The world has evolved. Every on-highway diesel engine that wants to fulfill 2007 emissions standards and beyond must must have a DPF.
A DPF is an exhaust aftertreatment device that is intended to remove diesel particulate matter (PM), often known as soot, that is created during the combustion process of an engine’s cylinders. A muffler body houses the extruded DPF substrate, which is commonly made of cordierite or silicon carbide. Over 95% of the diesel PM is normally captured by DPF substrates, however unless they are cleaned or renew, they may clog.
Regeneration Methods
The two basic methods of regeneration are passive and active. Platinum and palladium, two precious metal catalysts, are coated on passive DPFs. These allow the oxidation or flameless burning of the diesel PM. The catalysts’ job is to lower the temperature at which diesel PM oxidizes to 300°C (as opposed to 650°C in air). These temperatures are within the usual diesel engine’s operational exhaust temperature range. The low threshold temperature for passive regeneration must be met, though, so that filter regeneration is successful. This may be done by monitoring the exhaust temperature.
Instead of using catalysts, active regeneration processes utilise alternatively produced heat to rebuild the DPF substrate. Fuel injection and fuel burners are two examples of active system technologies now used by engine OEMs. Also employed in retrofit or aftermarket applications are electric systems. Diesel fuel is injected into fuel injection systems over a diesel oxidation catalyst, which ignites and produces heat. Temperatures are intended to reach 650°C by controlled fuel injection (dosing). This temperature will cause the DPF to burn off accumulated soot.
Regen Chemistry
The oxidation process produces CO2 and H2O from HC matter, such as diesel PM. While inorganic substances, such as lubricant additives, may release CO2 and H2O, they also leave behind a residue or ash. Over time, ash accumulates in the filter, eventually causing a blockage and raising exhaust backpressure. As a result, engine performance ultimately declines, necessitating periodic aggressive DPF regeneration and cleaning.