Investigations on Chemical Ageing of Diesel Oxidation Catalysts and Coated Diesel Particulate Filters

For medium- and heavy-duty diesel engines, the development of new catalyst technologies and particulate filters is necessary to fulfill increasingly stringent emission regulations. An important aspect is the durability of the after-treatment system and therefore its efficiency over lifetime. Lubrication oil additives contain components such as phosphorous or zinc to ensure engine durability. Diesel oxidation catalyst (DOC) and coated diesel particulate filter (cDPF) catalytic coatings are negatively influenced by contamination on the surface with these components (chemical ageing). The components have a negative impact on the exhaust after-treatment systems performance. Additionally the cDPF is filled with oil ash.

Engine tests are conducted to analyze the effect of lubrication oil additives on after-treatment system performance. In one study, lubrication oil with increased sulfur ash content is used. In another study, the same liquid oil is additionally sprayed directly into the after-treatment system. The performance of both after-treatment systems is measured at regular intervals during testing. The results show that the NO₂ make on DOC and cDPF deteriorates severely due to chemical and thermal ageing. However with increased operation time, the effects stabilize. In addition to the test bench investigations, the accumulation of poisoning elements on the washcoat surface is analyzed using XRF analysis. Ash accumulation in the cDPF is studied and ash composition is analyzed. Selected results of this study are compared to results of measurements on durability run aged after-treatment systems from EPA-07 development.