Modelling the effects of condensation and evaporation of water on the transient temperatures inside the exhaust system of an internal combustion engine

Abstract

A one-dimensional model of the transient temperatures in the exhaust system of an internal combustion engine, including the effects of condensation and evaporation of water, is used to predict the warm-up characteristics of the exhaust system. The aim of the model is to reproduce theoretically a ‘plateau’ observed in the experimentally measured temperatures in the catalytic converter, and to predict whether this plateau influences the light-off of the catalyst. The results of the numerical simulation are compared with the temperatures measured in a Volkswagen 1.6 l engine exhaust system. The simulation results exhibit the temperature plateau, but with some deviations from the experimental results. It was found that both evaporation and condensation must be included in the simulation for the plateau to be successfully modelled. It is concluded that in the real system these processes occur simultaneously as a series of microtimescale events as the system strives towards an equilibrium moisture condition. This moisture behaviour is responsible for the step up to the plateau temperature, but it was found that the final temperatures achieved by the system are not significantly influenced by the moisture behaviour. The presence of the moisture in the exhaust gas therefore decides the temperature profile during the early stages of warm-up (up to approximately 100 s after ignition) but is not expected to delay the light-off of the catalytic converter.

Keywords

internal combustion engine exhaust transient temperatures catalytic converter water vapour

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