Development and Demonstration of LNT+SCR System for Passenger Car Diesel Applications 2014-01-1537

The regulations for mobile applications will become stricter in Euro 6 and further emission levels and require the use of active aftertreatment methods for NO_X and particulate matter. SCR and LNT have been both used commercially for mobile NO_X removal. An alternative system is based on the combination of these two technologies. Developments of catalysts and whole systems as well as final vehicle demonstrations are discussed in this study.

The small and full-size catalyst development experiments resulted in PtRh/LNT with optimized noble metal loadings and Cu-SCR catalyst having a high durability and ammonia adsorption capacity. For this study, an aftertreatment system consisting of LNT plus exhaust bypass, passive SCR and engine independent reductant supply by on-board exhaust fuel reforming was developed and investigated. The concept definition considers NO_X conversion, CO₂ drawback and system complexity. The passive SCR significantly contributes to the total NO_X conversion over a broad temperature range. In contrary to conventional LNT applications, the LNT NO_X slip does not directly reduce the system NO_X conversion but can be converted over the passive SCR. Thereby, the NO_X adsorption duration might be prolonged, resulting in lower LNT regeneration frequency and less fuel consumption, resp. CO₂ emissions. Additionally, the engine independent LNT enrichment is beneficial regarding fuel consumption in comparison to conventional engine internal enrichment.

The system has been tested in a vehicle in combination with a highly efficient Diesel engine. Results regarding CO₂ and NO_X as well as their dependency on temperatures are shown here.