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The nitrogen oxides (NOx) emission standard has become more stringent in the past decade due to the critical global air pollution. In order to reduce the amount of NOx generated from automobiles, improving the performance of selective catalytic reduction (SCR) systems which can reduce NOx emissions becomes an important topic in the automotive industry. Due to the large gas flow rate in commercial vehicles, the packaging constraints and the sizes of SCR catalysts in the market, the SCR systems installed in the commercial vehicles consist of a number of SCR catalysts, either in parallel or in series, and connected by pipes and chambers. There are three major factors which can improve the performance of a SCR system - creating even gas flow rate, uniform speed through the catalysts, and lower total pressure loss. The first two can help operate the SCR catalyst efficiently and even life cycle, at the same time the lower total pressure loss can improve the performance of the engine system.

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.

In order to meet the mandated EPA2010 emissions for heavy duty commercial vehicle regulations, most applications require very large, complex, yet compact exhaust after-treatment systems. These systems not only contain the necessary substrates and filters to perform the proper emissions conversion, they also typically will consist of mixing pipes and internal reversing chambers all within very tight space proximity. Some of these systems are able to accomplish the complete emissions reduction and conversion within a single, large packaging unit. While there are advantages in fuel efficiency and perhaps overall packaging with these “single box” units, the disadvantage of these types of designs is that it prohibits many internal components from cooling down by the outside environment, which can pose thermal mechanical durability challenges.

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.