Designing Exhaust Manifolds Using Integral Engineering Solutions

Exhaust manifold cracks from Thermomechanical Fatigue (TMF) are often seen on highly loaded engines, due to increasing marketplace demands for performance and emissions. A constant search for higher strength materials is needed, due to maximum gas temperatures that in some instances are already above 1000°C. The use of virtual prototypes for creating a development strategy for testing will reduce expense and time as opposed to using physical prototypes. The design and analyses engineers are assisted through advanced simulation technologies, which help locate critical areas during the early phases of development so that local structural weaknesses can be removed. A variety of studies have been published over the last few decades regarding the identification of these critical areas, which include considering kinematic and isotropic hardening, creep in material modeling and consideration of plasticity, creep and oxidation in lifetime modeling. This study focuses on the development of a reliable approach to predict failure of exhaust manifolds and on the removal of structural weaknesses through the optimization of design. The failure modes for TMF cracks, vibration and exhaust manifold gaskets are emphasized. The resulting optimization used both manual and automatic methodologies, which highlight the correlated advantages and disadvantages of the proposed design. Examples of the applications show that automatic shape optimization is a powerful tool in the development of exhaust manifolds, which face ever decreasing development time. Engineering expertise is still needed required to fully utilize this technique, because the results strongly depend on defining the problem. The optimization of cast and fabricated manifolds (single or dual wall design) requires different techniques, due to the production restrictions. The locations where failures occur, on both the exhaust manifolds (cast or fabricated) and exhaust manifold gaskets, are predicted with high degree of accuracy. This study also shows an optimization package, which provides practical solutions to engineering problems through the removal of local structural weaknesses on highly loaded exhaust manifolds.