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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.

This paper describes the simulation and experimental work recently carried out during a typical exhaust manifold system development utilizing fabricated stainless steel manifolds. The exhaust manifold bridges the gap between the engine block and the catalytic converter. Bolted tightly to the engine with a gasket in between the manifold and the engine block, the engine's exhaust dispenses spent fuel and air into the manifold at an extremely high temperature. The automotive exhaust manifolds are designed and developed for providing a smooth flow with low/least back pressure and must be able to withstand extreme heating under very high temperatures and cooling under low temperatures. This paper describes all the analytical steps, procedure and tools such as CFD and FEA used in the development of a manifold system. The CFD tool utilizing conjugate heat transfer is used to calculate temperature distribution on the manifold. The manifold system durability is calculated using FEA.

Stricter emission standards are forcing automakers to attach catalytic converters directly to the exhaust manifold. Mounting catalytic converter at or near the exhaust manifold helps to reduce the increase in emissions that occurs during the first few minutes after a cold engine is started. The spike occurs because cold engines require a richer air-fuel mixture to run smoothly. The emission standards can be met only by new designs of exhaust system with the catalyst being as close as possible to the engine, and with the thin walled exhaust manifolds. With concept-to-customer timing continuously shrinking in the automotive industry, the need to quickly validate the engineering designs is becoming ever more critical. It is no longer acceptable to design a component, produce soft tooling, build and test a prototype, analyze what failed, and then redesign.