Some design optimization studies of automotive exhaust systems are carried out using numerical simulation. The numerical simulation involves computational fluid dynamics (CFD) for fluid flow and temperature distribution and finite element analysis (FEA) for subsequent structural analysis. The emphasis is given to optimization related to exhaust system design parameters such as shape and profile of manifold, catalyst inlet tube, inlet cone, exit cone, and exit tube under a given exhaust gas conditions. Several examples of optimization involving study of design parameters on the index of flow uniformity and backpressure are illustrated. Some studies in the past have shown that angular inflow in to catalyst substrate would give high flow uniformity index and flow out let profiles may not significantly affect the uniformity flow index near the inlet of catalyst. The present study shows that this is not always the case and some examples are illustrated to highlight these aspects.
The second part of this study involves finite element calculation of stresses and strains. Due to high temperatures involved in the exhaust system both material and geometric non-linearity are considered in structural analysis. Specifically, the study involves the calculation of material response behavior under several thermal cycles, each cycle involving a heating and a cooling stages, and finally comparative study of suitability of cast steel and fabricated steel for exhaust manifolds are discussed.