BEHAVIOR OF 3-WAY CATALYST IN A HYBRID DRIVE SYSTEM

The dynamic behavior of a Pt-Rh/CeO2-Al2O3 three-way catalyst (TWC) un der pulsed flow operation conditions (intermittent mode), such as occu r in a newly developed hybrid drive system, has been studied experimen tally in a laboratory apparatus with simulated exhaust gas. The parall el hybrid system is based on the combination of an Otto-cycle engine w ith an electric motor and a flywheel providing a short-term energy sto rage. This configu ration permits intermittent charging of the flywhee l by the combustion engine which runs only during about 10% of the dri ving time. Each exhaust gas pulse (duration typically ca. 3 s) is prec eded by an air pulse, which results from the filling of the engine cyl inders with air at start up and shut off. Experimental studies indicat ed that the air pulses have a negative impact on the performance of th e catalytic converter, reducing the inherent benefits resulting from t he intermittent operation mode of the combustion engine. Forced asymme tric lambda-cycling during exhaust pulses was found to be most benefic ial for improving catalyst performance. A simple reduced kinetic model derived from a Langmuir-Hinshelwood model for CO oxidation, which was extended by introducing CO and O-2 equivalents to mimic the complex e xhaust gas, was used to describe the dynamic behavior of the TWC, The model proved to be useful for finding the optimal lambda-cycling condi tions. Experiments with a real Otto-cycle engine exhaust proved that t he reduced kinetic model is suitable for use in a closed loop lambda-c ontrol.