Transient heat transfer modelling in automotive exhaust systems

Abstract

Transient heat transfer computations in automotive exhaust systems are increasingly employed in the design and optimization phases. The complex geometry of the exhaust line and the special flow conditions complicate the problem of accurately estimating several important heat transfer parameters. This paper initially summarizes the current status of knowledge regarding heat transfer phenomena in automotive exhaust systems. A comprehensive transient computer model covering all exhaust piping configurations (single wall, double wall with air gap or insulation) is presented. A novel solution procedure is proposed, resulting in significant savings in processing time. Two-dimensional heat transfer in connecting flanges is also accounted for. The model is validated with the help of full-scale measurements on vehicles. Examples are presented, illustrating the application of the model in the comparative assessment of different exhaust configurations. In conjunction with existing models, which simulate the operation of three-way catalytic converters and of other exhaust gas after-treatment devices, the model can be integrated in a CAE (computer aided engineering) package for the support of exhaust system design optimization.