Thermo-Mechanical Analysis of an Automotive Diesel Engine Exhaust Manifold

Abstract

The following paper presents a detailed description of a thermo-mechanical analysis method of an exhaust manifold for a four-stroke automotive Diesel engine, where the focus is on the physically correct description of the transient heat transfer on the hot gas side. For this purpose a simple, but very effective method has been developed to calculate the quasi steady statae heat transfer conditions and gas temperatures along the inner manifold gas path. The method is based on a coupled 1-dimensional exhaust gas flow and a 3-dimensional FE thermal analysis. The influence of the operational characteristic of a four-stroke engine on the local heat transfer is considered by appropriate correction factors. The impact of the transient consideration on the stress-strain state of the component and therefore on the life is verified and explained via a dedicated example. The analysis results show very clearly the impact of the transient consideration on the stress distribution. The peak stresses do not occur at full load conditions, but at a transient state. Taking this transient peak stress with the corresponding strain range over the cycle at cyclic stabilized material conditions and the peak temperature, the life of the component can be analysed with the help of appropriaate fatigue data.