The use of multi-variate models for the prediction of heat transfer in vehicle exhaust systems

Abstract

This paper describes the development of an exhaust system model based on the characterization of heat transfer in a series of 11 test sections designed to represent a range of configurations seen in production exhaust systems. These sections include variations in the wall thickness, diameter, bend angle, and radius. This work is part of a larger activity aimed at the accurate modelling of heat transfer and subsequent catalyst light-off in production exhaust systems consisting of similar geometries.

For each section a range of steady state tests was performed on a dynamic test cell using a port injected gasoline engine. In each case a correlation between the observed Reynolds number Re and the Nusselt number Nu was developed. A model of the system was implemented in MATLAB—Simulink in which each pipe element was split into 25 subelements by dividing the pipe into five, both axially and radially. After each individual section had been characterized, a generic model was built that was capable of determining the relationship between the Nusselt number and the Reynolds number for previously unseen pipe geometries. Complex exhaust systems can be constructed from smaller elements of defined geometry. The modelling approach was validated using experimental data gathered from vehicle testing on a chassis dynamometer.

The steady state relationship between Re and Nu allows heat transfer in the test section to be predicted over transient test cycles and demonstrates good agreement with relationships in the literature.

Keywords

multi-variate models prediction of heat transfer vehicle exhaust systems

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