The use of the Diesel engine is increasing, while at the same time emission limits are becoming more stringent. To reduce emissions, novel catalyst converter designs have been proposed, including the placement of a small converter before the turbocharger. The role of this catalyst is to provide some reduction of the pollutant level prior to the main catalyst. This catalyst is typified by high flow rates. In this paper the performance of small catalytic converters operated at high flowrate is examined using computer simulation. The oxidation of CO is used as a model reaction. It is shown that for a typical oxidation catalyst, conversions of the order of 30% can be achieved at typical temperatures and a GHSV of 5 million h )1 .

This paper presents the results of a series of simulations of the light-off of carbon monoxide in excess oxygen in a single channel monolith reactor. The catalytic washcoat geometry is tested for its effect on the light-off position and shape. The simulations used a combination of two and three-dimensional modelling with non-linear oxidation kinetics. Different temperature ramp rates were employed. It is seen that the shape of the washcoat has an influence on the shape of the light-off curve, especially for high values of gas hourly space velocity and larger temperature ramp rates. The washcoat geometry that gives the fastest rise to complete conversion is the one that is the most non-uniform in shape; that is, the one that has thin sections. Nomenclature: a i : Species dependent constant in the Fuller diffusion equation; C i : Molar concentration of species i, mol/m 3 ; C p : Heat capacity, J/(kg K); d p : Pore diameter, m; D eff : effective diffusion coefficient in washcoat, m 2 /s; D i : Bulk diffusion coefficient, m 2 /s; DH R : Enthalpy change of reaction, J/mol; k f : Thermal conductivity of fluid, W/(m K); k eff : Effective thermal conductivity of the solid, W/(m K); k CO : Reaction rate constant, s )1 ; K CO : Adsorption equilibrium constant, m 3 /mol; M i : Molecular mass of species i; P: Total pressure, Pa; ()R i ): Reaction rate based on washcoat volume, mol/(m 3 s)

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