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Although the technology of combustion engines is reasonably well developed, the degree of efficiency is considerably low. Considerable amount of the energy of around 35 % is lost as exhaust waste heat, and up to 30 % is dissipated in the cooling circuits. Due to this, thermal recuperation has a great potential for raising the efficiency of combustion engines. In order to meet the ever-increasing consumer demand for higher fuel economy, and to conform to more stringent governmental regulations, auto manufacturers have increasingly looked at thermoelectric materials as a potential method to recover some of that waste heat and improve the overall efficiency of their vehicle fleets. Seeking new possibilities to make vehicles greener and more efficient, the industry wants to use the waste heat which passes through the exhaust system almost completely unused in the past.

Computational Fluid Dynamics (CFD) is becoming a very popular tool for numerical predictions of flow distribution, pressure loss, heat transfer, internal and external combustion and has been widely used in automotive, aerospace, marine and even medical industries. In automotive industry, CFD tool is used and customized in five major areas: vehicle aerodynamic effect; thermal management (cooling and climate control); cylinder combustion; engine lubrication and exhaust system performance. Current paper will focus on CFD applications in one of vehicle subsystems - exhaust system. Increasingly stringent emission requirements are enforced by Environment Protect Agency (EPA) to reduce harmful chemical components such as CO, NO, NO2. Exhaust systems are becoming more complicated and usually consist of one or multiple catalytic converters with one or multiple substrates inside.

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.

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.