Experimental Approach to Optimize Catalyst Flow Uniformity 2000-01-0865
A uniform flow distribution at converter inlet is one of the fundamental requirements to meet high catalytic efficiency. Commonly used tools for optimization of the inlet flow distribution are flow measurements as well as CFD analysis. This paper puts emphasis on the experimental procedures and results. The interaction of flow measurements and CFD is outlined.
The exhaust gas flow is transient, compressible and hot, making in-situ flow measurements very complex. On the other hand, to utilize the advantages of flow testing at steady-state and cold conditions the significance of these results has to be verified first. CFD analysis under different boundary conditions prove that - in a first approach - the flow situation can be regarded as a sequence of successive, steady-state situations. Using the Reynolds analogy a formula for the steady-state, cold test mass flow is derived, taking into account the cylinder displacement and the rated speed.
At cold test conditions the flow field downstream of the converter is visualized by Particle Image Velocimetry (PIV) in terms of planar velocity fields. The flow structure is shown to be significantly one-dimensional. Therefore a single hot wire probe is sufficient to scan the axial component directly at converter outlet. Results of PIV and Hot Wire Anemometry (HWA) are compared.
The planar mass flow distribution downstream catalyst is essential to analyze and optimize the exhaust system upstream of the converter. Nevertheless, to quantify the success of a geometric modification a more condensed result is favorable. In this paper the velocity density function is presented as a helpful method to characterize the flow uniformity. Furthermore it is shown that this distribution curve contains both characteristic numbers, which are commonly used to quantify catalyst flow distribution. This method is applied to a typical HWA result.