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Accumulation of lubricant and fuel derived ash in the diesel particulate filter (DPF) during vehicle operation results in a significant increase of pressure drop across the after-treatment system leading to loss of fuel economy and reduced soot storage capacity over time. Under certain operating conditions, the accumulated ash and/or soot cake layer can collapse resulting in ash deposits upstream from the typical ash plug section, henceforth termed mid-channel ash deposits. In addition, ash particles can bond (either physically or chemically) with neighboring particles resulting in formation of bridges across the channels that effectively block access to the remainder of the channel for the incoming exhaust gas stream. This phenomenon creates serious long-term durability issues for the DPF, which often must be replaced. Mid-channel deposits and ash bridges are extremely difficult to remove from the channels as they often sinter to the substrate.

Diesel engine exhaust aftertreatment components, especially the diesel particulate filter (DPF), are subject to various modes of degradation over their lifetimes. One particular adverse effect on the DPF is the significant rise in pressure drop due to the accumulation of engine lubricant-derived ash which coats the inlet channel walls effectively decreasing the permeability of the filter. The decreased permeability due to ash in the DPF can result in increased filter pressure drop and decreased fuel economy. A unique two-step approach, consisting of experimental measurements and direct numerical simulations using ultra-high resolution 3D imaging data, has been utilized in this study to better understand the effects of ash accumulation on engine aftertreatment component functionality.

Current and future diesel engine oil categories have specifications that impose limits on SAPS (Sulfated Ash, Phosphorous and Sulfur) levels that help to minimize accumulation of ash in the DPF originating from oil consumption in the engine. Metallic species in the oil formulation, mostly from detergents and anti-wear additives, have a significant impact on ash behavior when subjected to high temperatures during active regeneration of the filter. Certain compounds in the oil, especially derivatives of ZDDP (Zinc Dialkyl Dithiophosphate), interact with filter substrate and sinter at temperatures that the DPF is exposed to during active regeneration. This phenomenon of sintering or ‘ash wetting’ leads to ash-bridges in the DPF that result in reduction of soot storage capacity, higher back-pressure and possibly reduced active surface area for catalytic conversion of engine-out emissions.

Ash accumulation in the DPF over life results in reduced soot storage capacity, lower catalytic activity and may even alter substrate properties and lead to higher back-pressure; hence ash-cleaning of the DPF is required periodically to extend the life of the DPF and restore its catalytic performance. Several ash cleaning technologies are available which utilize pneumatic, hydraulic and wet-chemical cleaning techniques or their combinations. A batch of DPFs with various ash accumulation levels were recovered from customer field units. X-ray CT imaging was performed to understand the ash distribution in the DPF channels. Field returned DPFs were tested on Engine Dynamometer to determine the impact on overall system performance loss from fresh state. The DPFs were then cleaned using various cleaning techniques; X-ray imaging and dynamometer testing was repeated to evaluate the performance recovery.