Investigations Regarding Deposit Formation on Diesel Oxidation Catalysts

Catalyst fouling by deposit formation on components in the exhaust aftertreatment system is critical since RDE limits must be obtained at any time. Besides, uncontrolled oxidation of carbonaceous deposits might damage the affected exhaust aftertreatment component. To comply with current and future emission standards, diesel engines are usually operated with high EGR rates leading to increased soot and hydrocarbon emissions, which increases the likeliness of the formation of carbonaceous deposits on EAT components. With this background, a research project investigating the influencing parameters and mechanisms of deposit formation on DOCs was carried out. In a follow-up project, the results will be used in order to compare different deposit removal strategies. Within the scope of the presented project, a reference driving cycle was developed in order to create deposits within a short time. The driving cycle was modified during further endurance runs and analyzed for changes in the deposit’s properties. Furthermore, the engine was operated using different fuels and under various operating modes. The stability of the deposits was highly affected by the engine operation mode and the engine load within the driving cycle. On the other hand, the thermal stability of the deposits did not change over time within a single endurance run within the periods covered by the investigations. A sequence of typical stages of deposit formation was observed and was found to be mainly initiated at the catalyst inlet. This result was supported by 1D simulations and destructive testing of drill cores. With increased run time, a discharge or migration of existing deposits in single channels of the DOC occurred, while the growth of existing deposits occurred in other channels. During the later stages, compact deposits were built along the whole channel. These deposits consist mainly of soot particles that were separated from the exhaust gas.