Mathematical modelling of precious metals catalytic converters for diesel NOx reduction

Abstract

Precious metal catalysts for NO_x reduction in lean diesel engine exhaust conditions are characterized by a narrow temperature range of efficient operation and require high availability of reducing species in significant concentration. Consequently, there exists a large optimization potential in the design and control of lean-NO_x catalytic conversion systems. A mathematical model of the transport and chemical phenomena in platinum-based lean-NO_x catalysts was formulated, based on the experience with analogous models for gasoline three-way catalysts. A simplified four-reaction scheme is employed, considering the oxidation of CO, H₂ and hydrocarbons (HCs), as well as the reaction between NO_x and HCs. Results are compared with previously published laboratory and engine data in order to assess the capacity of this approach in representing real-world behaviour of Pt-based lean-NO_x catalysts. Initial results illustrate the power and flexibility of the model, which is able to predict the NO_x conversion characteristics in model gas tests as well as in full-scale engine tests with reasonable accuracy.