Active Diesel Particulate Filters (DPF)

In order to reach the new PM standards on all applications, “active” diesel particulate filters are needed. Filtration of exhaust gas to remove soot particles is accomplished using porous ceramic media generally made of cordierite or silicon carbide. A typical filter consists of an array of small channels that the exhaust gas flows through. Adjacent channels are plugged at opposite ends, forcing the exhaust gas to flow through the porous wall, capturing the soot particles on the surfaceand inside pores of the media. Soot accumulates in the filter, and when sufficient heat is present a “regeneration” event occurs, oxidizing the soot and cleaning the filter.

The challenge of particulate filter design is to enable reliable and consistent regeneration, so that soot is removed in all types of duty cycles. For example,
while a line-haul truck that is fully loaded will consistently run hot enough for regeneration to take place, the same truck in stop-and-go traffic or running from Duluth to International Falls in the middle of winter may not. EPA requirements state that every engine has to achieve the required reduction in every operating condition, which is why active controls are needed. The use of this “active” method involves monitoring the particulate filter backpressure and regeneration events and managing the temperature entering the filter. There are several methods to control or raise the exhaust temperature to “actively” manage the DPF. The most promising methods for an active integrated system for 2007 are management of the engine combustion process in combination with an additional oxidation catalyst. This will allow regeneration to take place under low-ambient/low-load conditions when exhaust temperatures are low, and during normal operation as well.