Investigation into Ash Loading and Its Relationship to DPF Regeneration Method 2009-01-2882

A diesel particulate filter (DPF) controls and maintains a constant pressure drop across the filter by repeating the regeneration process for PM (Particulate Matter). However, the regeneration results in ash accumulation on the DPF. Although this ash accumulation is very slow, it eventually causes increased pressure drop which affects the product life of the DPF.

Metal elements in the lubricant additives in the engine oil are the source of the ash. Since ash is an oxidized substance, the amount of ash produced depends on such factors as the amount of oil consumed in the engine and the kinds of lubricant additives contained in engine oil. According to the reference literature [1-3], ash accumulates on a DPF differently depending on use of either a passive regeneration system or an active regeneration system. With the passive regeneration system, ash accumulates uniformly on the filter wall while ash accumulates near the outlet of the filter with the active regeneration system. Even though the amount of ash collected on the filter is same regardless of the regeneration method, the difference in the way ash accumulates on the filter between the two regeneration systems affects the characteristics of pressure drop across the filter. Therefore, the regeneration method is another parameter that affects filter performance, and the selection of a regeneration strategy is important to extend the useful life of the DPF.

According to observations of ash accumulating on a DPF through both bench and engine tests of the regeneration process and accumulated ash removed from the DPFs of fleets, the authors found that ash is different in its particle size depending on temperature of PM combustion during regeneration. The particle size was smaller at lower combustion temperatures and larger at higher combustion temperatures as in the cases of the passive and active regeneration systems, respectively. As a result of these observations, a hypothesis was developed to explain the effect that the regeneration system had on how ash would accumulate on a DPF.

The authors investigated the effect that ash accumulating on a DPF had on pressure drop across the filter and PM filtering performance. DPFs were sampled from a high-mileage fleet and evaluated for both pressure drop and PM filtering performance. Subsequently, the DPFs were cut to observe how ash had accumulated on the filter. Various patterns of ash collection on a DPF were artificially created using fly ash, and their effects on both pressure drop and PM filtering performance were evaluated. The results of these investigations revealed how ash collected on the filter would affect the pressure drop and PM filtering performance.

According to the results of various tests and evaluations, the authors describe the mechanism of ash loading on the DPF and propose a DPF regeneration system that produces an ideal accumulation pattern of ash on the filter to keep PM filtering performance at the optimal level for useful life.