The present paper describes the results of a joint development program focussing on a system approach to meet the EURO IV emission standards for an upper class passenger car equipped with a newly developed high displacement gasoline engine.
Based on the well known catalyst systems of recent V6- and V8-engines for the EURO III emission standards with a combination of close coupled catalysts and underfloor catalysts, the specific boundary conditions of an engine with an even larger engine displacement had to be considered. These boundary conditions consist of the space requirements in the engine compartment, the power/torque requirements and the cost requirements for the complete aftertreatment system.
Theoretical studies and computer modeling showed essential improvements in catalyst performance by introducing thin wall substrates with low thermal inertia as well as high cell densities with increased geometric surface area.
Various substrates with different cell densities and wall thicknesses were investigated regarding emission performance, back pressure (power loss) and mechanical durability.
The washcoat for ultra thin wall substrates was optimized to obtain the best catalyst activity with acceptable back pressure.
The final catalyst system consists of four close coupled catalysts with 600 cpsi and 3.5 mil wall thickness and two underfloor converters with 400 cpsi and 4.3 mil wall thickness. The stringent EURO IV hurdle could be met even after 100,000 km vehicle aging under German high speed conditions. The catalyst system showed not only good emission performance in the MVEG-B test cycle but also in the high speed driving range of the vehicle.
With the combination of thin wall technolgy (600 cpsi/3.5 mil) and an optimized washcoat the power and torque requirements were also fulfilled.