Modeling the Effect of Flow Pulsations in Close-Coupled Catalytic Converter Light-Off 2004-01-1835

In close-coupled catalytic converter applications, the exhaust gas mass flow may present fluctuations with a timescale in the order of milliseconds, as a result of periodic valve operation. Such flow pulsations are likely to affect catalytic converter performance, due to mass transfer limitations. A fully transient channel model is developed, to study pollutant conversion under pulsating flow conditions. This model is applied to evaluate the effect of pulsations in catalyst conversion. Firstly, the effect of flow pulsations during the warmed-up operation is studied. Then, we focus on the effect of pulsations during the light-off phase, during which significant temperature and therefore activity gradients are observed in the monolith. The new model is also used to assess the accuracy of the traditional “quasi-steady state” approach, when applied to simulate converters under pulsating flow.