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This paper gives an overview of the development work for a diesel after-treatment system, used in heavy duty trucks to fulfill the new US emissions limits. The paper starts with the description of design evaluation and optimization studies on heavy duty diesel exhaust after-treatment system using numerical simulation. The studies involve initial conceptual design evaluation of the entire after-treatment system for fluid flow, temperature distribution, and subsequent structural loads. Computer modeling, as complementary approach to prototyping and experimental investigations, helps to make basic design decisions and therefore to shorten the overall development process. The numerical simulation involves computational fluid dynamics (CFD) analysis for fluid flow and temperature distribution and finite element analysis (FEA) for subsequent structural analysis. The first part of the paper involves computational fluid dynamic optimization study related to diesel exhaust system.

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.

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.