The Effect of Lubricant Derived Ash on the Catalytic Activity of Diesel Particulate Filters

A diesel particulate filter (DPF) is an aftertreatment device used to remove hazardous particulate matter (PM) from diesel engine exhaust. Modem emission restrictions have limited the acceptable amount of PM output by diesel engines to the extent that a filtration strategy, such as the use of a DPF, is necessary. Diesel PM is comprised primarily by black carbon soot. Once trapped in the filter, the soot can be oxidized into CO 2 and pass out of the exhaust system during what is referred to as regeneration. Metallic lubricant additive derived compounds, which make up a small fraction of PM, cannot be oxidized and remain inside the DPF until regular maintenance calls for the removal and cleaning of the filter. The buildup of ash increases the pressure drop across the filter, resulting in a direct fuel penalty to the engine. The oxidation of soot can be carried out actively at high temperatures or passively at low temperatures with the aid of a catalyst. Active regeneration requires more energy than passive regeneration because the stream of exhaust gas must be heated to a higher temperature. However, catalysts are expensive, and therefore there is a significant additional capital cost associated wit