Investigation into Ash from Field Returned DPF Units: Composition, Distribution, Cleaning Ability and DPF Performance Recovery 2016-01-0928

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. Ash samples retrieved from cleaning were analyzed using ICP-OES to determine ash composition and source of origin; they were correlated to DPF operating history.

It was found that lube oil consumption rate and the engine-oil SAPS (Sulfated Ash, Phosphorous, Sulfur) levels were the primary drivers for ash accumulation rates. Ash tends to collect at the channel end plugs in applications that require frequent active regeneration and tends to accumulate as a thin layer on the DPF wall with applications that are more dependent on passive regenerations. On DPFs that had higher regeneration frequency due to more severe cycles, the ash had a tendency to form bridges on the substrates and permanently sinter with the washcoat interface thereby leading to reduced area available for catalytic activity. The cleaning techniques evaluated were quite effective; however they have to be selected based on the ash loading characteristics in the DPF. Improvements in back-pressure, HC light-off and soot storage capacities were quantified for various cleaning techniques.