Tillmann Braun

Selective Ammonia Exhaust Gas Sensor for Automotive Applications

In order to meet future NOx emission standards for commercial vehicles, so called urea selective catalytic reduction (SCR) systems will be introduced. In the SCR converter ammonia serves as a reducing agent for selective NOx reduction. An ammonia exhaust gas sensor is required to optimize the injected amount of urea and to assure that no ammonia emissions occur. This paper reports on the development of a selective thick film ammonia sensor that can meet the requirements for applications in automotive exhaust gas. Main topic is the development of the functional gas sensitive film. Zeolites were successfully investigated as selective functional materials for this kind of sensors. It is shown, that the type of the zeolite, its module, the working temperature and the working frequency determine sensitivity and selectivity of the sensor. From the most promising zeolite material—zeolite H-ZSM5 with a module of 140, sensors were manufactured and tested in engine test benches. It could be shown, that this kind of sensors is a useful tool to control an ammonia-SCR system and to detect ammonia slip.

Numerical Simulation of Ammonia SCR-Catalytic Converters: Model Development and Application

A two-dimensional numerical model describing the ammonia based SCR-process on vanadia-titania catalysts is presented. The model is able to simulate coated and extruded monoliths. For the determination of the intrinsic kinetics of the various NH 3 -NO x reactions, unsteady microreactor experiments were used. In order to account for the influence of transport effects the kinetics were coupled with a fully transient two-phase 1D+1D monolith channel model. The model has been validated extensively with laboratory data and engine test bench measurements. After validation the model has been applied to calculate catalyst NO x conversion maps, which were used to define catalyst sizes. Additional simulations were conducted studying the influence of cell density and NH 3 -dosage ratio.

Mercedes-Benz diesel technology OM654 near-engine-mounted SCR system for WLTP and RDE

With the launch of the new 4-cylinder engine OM654 Mercedes-Benz continues to build on the advantages of the diesel combustion process and is opening up new potential in the area of emissions reduction and variant reduction.