The Effects of Catalytic Converter Location and Palladium Loading on Tailpipe Emissions 2012-01-1247

Meeting regulated tailpipe emission standards requires a full system approach by automotive engineers encompassing: engine design, combustion system metrics, exhaust heat management, aftertreatment design and exhaust system packaging. Engine and combustion system design targets define desired engine out exhaust constituents, exhaust gas temperatures and oil consumption rates. Protecting required catalytic converter volume in the engine bay for stricter tailpipe emission standards is becoming more difficult. Future fuel economy mandates are leading to vehicle downsizing which is affecting all aspects of vehicle component packaging.

In this study, we set out to determine the potential palladium (Pd) cost penalty as a result of increased light-off time required as a catalyst is positioned further away from the engine. Two aged converter systems with different Pd loadings were considered, and EPA FTP-75 emission tested at six different catalyst positions. Testing began with the front face of the close-coupled catalyst 469 mm from the cylinder head, which is 228 mm from exhaust manifold pierce point (P-point, Figure 2), and increased in five additional increments of 75 mm. Exhaust gas temperatures were measured at every 25 mm. The negative impact on NMHC emissions as the catalyst sets moved further from the exhaust manifold were investigated. Likewise the effect of increasing Pd loading in offsetting the delayed light-off times associated with increased catalyst distance from the engine was studied. As a result, an attempt was made to develop a cost model of increasing the catalyst distance from the exhaust manifold in order to achieve equal NMHC EPA FTP-75 emission performance.