DPFs have been shown to significantly reduce PM emissions from diesel engines. However, regeneration process still presents challenges in engine-DPF operation. Knowledge of how PM is trapped and, in turn, affects the regeneration mechanisms need to be established. By gaining a fundamental understanding of the effects of the key variables on the mechanisms by which PMs are deposited and regenerated, the design and operation of the DPF can be optimized to maximize the system efficiency while minimizing environmental impacts.
In the full-scale DPF research study, the experiments were performed to identify key parameters that most influence DPF performance. DPFs with various components and surface treatments were filled with selected engine modes. The pressure drop across the filter, filtration efficiency, and downstream emissions were measured during filtration and regeneration. Changes in filtration mechanisms as seen from the pressure drop and filtration efficiency evolution among examined engine modes correlate well to the unit collector theory via diffusion, interception, and impaction mechanisms. These mechanisms depend on the particle diameter and the filtration velocity for a given filter. Results show that the filtration velocity and PM characteristics highly influenced wall loading and catalytic (LT) oxidation performance.
In the wafer research study, the new sampling system where similar experiments on full-scale DPFs can be scaled to a smaller filtration geometry (a wafer), of the same material, was developed. The system allowed precise control of the filtration velocity in the DPF while sampling PM whose composition and size distribution were well characterized. Deposition processes of PM in the wall and on the filter surface were evaluated according to changes in the filtration performance. Results indicate that the filtration velocity significantly impacted the wall loading capacity. The increase of SOF absorption level was proportional to the increase of filtration velocity which could lead to better PM/catalyst contact and higher LT oxidation effectiveness. PM characteristics were seen to influence not only the wall loading but also the soot cake layer characteristics.