Optimisation Development of Advanced Exhaust Gas After-treatment Systems for Automotive Applications

Future emission legislation can be met through substantial improvement in the effectiveness of the exhaust gas after-treatment system, the engine and the engine management system. For the catalytic converter, differentiation is necessary between the cold start behavior and the effectiveness at operating temperature. To be catalytically effective, a converter must be heated by the exhaust gas up to its light-off temperature. The major influential parameter for the light-off still is the supply of heat from the exhaust gas. Modification of the cold start calibration of engine control such as spark retard or increased idle speed can increase the temperature level of the exhaust gas. One further possibility is represented by a reduction of the critical mass ahead of the catalyst (exhaust manifold and pipe). Nevertheless the best measure to obtain optimal cold start effectiveness still seems to be locating the converter close to the engine. Depending on the individual application, limited installation space may only be available. Therefore the design target is a low volume, high effective catalyst with optimized thermodynamic properties to obtain maximum advantage of the thermal energy coming from the exhaust gases. The present paper deals with the cold start of a generic test cycle that can be subdivided in different phases, each characterized by different design parameters of the converter that are to be specifically tailored in order to achieve the maximum possible overall efficiency for the whole test.