An Integral Engineering Solution for Design of Exhaust Manifolds 2009-01-1229

Thermomechanical fatigue (TMF) cracks on exhaust manifolds are often observed for highly loaded engines due to increasing performance and emission demands from the market. Continuously, higher strength materials are searched for, where maximum gas temperatures in some cases are already in excess of 1000 °C. In order to save cost and time, development strategy is built on performing tests on a virtual prototype instead of a physical prototype. The use of advanced simulation technologies enables the design and analyses engineers to identify critical locations in an early phase of development and to meet measures in order to remove local structural weaknesses. During the last decades, several methods are published for the identification phase; considering kinematic and isotropic hardening, creep in material modeling and considering plasticity, creep and oxidation in lifetime modeling.

In this paper, in addition to a reliable approach for failure prediction we focus on the removal of structural weaknesses by design optimization of exhaust manifolds. Failure modes of TMF cracks, vibration and exhaust manifold gasket are underlined. Both manual and automatic design optimization methodologies are presented, emphasizing the correlated advantages and disadvantages. Application examples show that automatic shape optimization is a powerful and effective way for the development of exhaust manifolds facing the need of ever decreasing development times. However, engineering expertise is required to make use of this technique, while the results strongly depend on the problem definition. Differentiated techniques for optimization of cast and fabricated manifolds (single or dual wall design) are required due to the production restrictions. It is shown that, failure locations both on exhaust manifold (cast or fabricated) and exhaust manifold gasket are predicted with high accuracy. In addition, an optimization package is highlighted, which delivers practical solutions to engineering problems in terms of removing local structural weaknesses on highly loaded exhaust manifolds.