Aftertreatment devices are well known and widely used in various internal combustion engine applications for the aftertreatment of engine exhaust gases. Such devices as diesel oxidation catalysts and diesel particulate filters have been useful for handling and/or removing diesel exhaust materials, including carbon monoxide, nitric oxide, unburned hydrocarbons, and soot in the exhaust stream of an engine.
Although particulate filters are sometimes not catalyzed, many oxidation catalysts commonly employ a catalyzed material applied to interior surfaces within fluid passageways of a cellular structure. Undesired exhaust material(s) react with the catalyst material, thus diminishing the undesired exhaust material(s).
However, inlet face plugging (coking) of diesel oxidation catalysts and diesel particulate filters continues to be an issue for vehicles with transient or less aggressive duty cycles, during cold ambient operating conditions, and during extended idling conditions. Other conditions that may lead to inlet face plugging can include frequent start and stop operation and engine operation during relatively low exhaust temperature ranges, such as 220° C. to 400° C. Face-plugging or fouling has been known as residue, such as exhaust materials and/or soot particles that accumulate on the outer surface of the cellular and channel structure at the inlet face of an aftertreatment device, and effectively reduces the open frontal area of the aftertreatment device.
Face-plugging is problematic, because it can result in a sharp rise in backpressure in aftertreatment or exhaust systems, which in turn may affect engine operation and decrease system efficiency. For example, face plugging of the aftertreatment device prevents effective conversion of injected hydrocarbon across the aftertreatment device, resulting in ineffective particulate filter regenerations due to low temperatures. Face plugging can also result in fuel penalty as fuel is being dosed for extended amounts with no benefit to filter regeneration. Face plugging can eventually lead to filter failures due to uncontrolled thermal events during transient driving conditions. Thus, preventing the formation of the soot/coke deposits on the inlet face of the aftertreatment device under all operating conditions is desirable.
Current closed loop control strategies to clean the aftertreatment device have tracked the amount of time spent dosing fuel in the exhaust using a straight time based count down timer to predict face plugging on the device. On reaching a threshold, the engine operating mode is switched to a high NOx, low particulate matter condition to oxidize any carbon deposits and clean out the aftertreatment device. However, such a method can take approximately 3 to 4 hours to clean the aftertreatment device and may not be completely effective. The reason being plugging of the flow channels usually begins from the front or inlet face at the end of the aftertreatment device. The level of NO2, which is known as a primary oxidizing agent, is found in low quantities in engine out diesel exhaust and is not effective in oxidizing soot on the inlet face.
There is a need to provide an improved engine exhaust system that can prevent and/or eliminate face-plugging or fouling at the inlet face of such aftertreatment devices.