| abstract |
Proceeding downstream from the engine, a first catalyst converts at least the HC- and CO components. One further catalyst at least, converts the HC-, CO- and NOx components. Whilst the engine is running, both these catalysts in series, receive the entire flow, i.e. there is no bypassing at any time. During the cold start phase, to reduce HC- and CO emissions, the first catalyst is worked leaner than stoichiometric. In a further step, the exhaust gas composition is controlled by adjusting the mixture lambda value to stoichiometric. Catalytic conversion becomes largely inactivated in the first catalyst (1,1'), and continues in the second (2,2'). The catalyst substrates, and the action of catalysts, including platinum and the rare earths cerium and lanthanum oxide, are also discussed. Details of a device to carry out substantially the process above, are also claimed. |