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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.

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.

In order to have a robust exhaust system design a comprehensive durability analysis is required. This durability analysis should include thermal loads, engine vibration loading, and proving ground road loads. The dynamic performance evaluation in exhaust system development is a valuable tool to identify the best design alternative. The finite element analysis (FEA) applications in the design of automotive exhaust system have become an indispensable tool. Both the cost and cycle of the product development benefit from its usages. This paper presents a robust design procedure for the dynamic performance of exhaust system in a passenger vehicle. For dynamic analyses it is essential that the complete exhaust assembly is modeled, including manifold, a representation of the engine, and a flex decouple model. This is because dynamic excitation is predominantly comprised of unbalanced forces within the engine, which is transmitted to the exhaust system through the flex decoupling element.

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.

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.

In this paper, a combined analytical CAE procedure and durability experiments are used to calculate the durability of complete exhaust system. Detailed analytical calculations are carried out and the results are explained for the typical exhaust system components considering the durability loads such as engine vibration loading, proving ground road loads, thermal loads, loads created due to geometric dimensioning and tolerances (GD & T), and bolt loads. The durability issues associated with the exhaust system components such as hot-end brackets, converter cone-pipe region, exhaust pipe system, muffler-pipe system, muffler hanger designs, and residual stresses in an exhaust system assembly such as ball joint flange-flange interface, and hot-end converters are explained in detail. Both experimental results and analytical calculations are carried out.

F-oval substrates have been widely used in automotive applications for Close Coupled Converters (CCC) of SI engines and pre-Diesel Oxidation Catalysts (DOC) of CI engines under tight packaging constraints where there is no space for other substrates with the same volume such as H-oval, a Y-oval or round substrates. Although flow uniformity in the front of a substrate is extremely important, it is very challenging to obtain excellent flow uniformity with an F-oval substrate. Current study is focused on how to optimize inlet cone design to achieve optimal flow uniformity by using 3-D Computational Fluid Dynamics (CFD) tools. First, exhaust mass flow rate and inlet cone length are investigated to understand their effects on flow uniformity and pressure loss. Then, based on a relatively short straight cone, angle cones are built.

The urea Selective Catalytic Reduction (SCR) exhaust system has been proved to be the reliable aftertreatment device with the capability of reducing tail pipe NOx emission by 75% to 90%, HC by 50% and Particulate Matter (PM) by 30%. Constrained by increasingly stringent packaging envelope, flow mixing in front of substrate is becoming one of the major concerns to achieve ideal performance of higher NOx conversion and lower ammonia (NH3) slip. Three dimensional CFD simulations are performed in current study to investigate flow mixing phenomenon in a SCR system. First, for a traditional tube injector with single or multiple nozzles, the effects of mass flow rates of injected NH3 and exhaust gas on flow mixing and pressure loss are investigated. Then, a concept of ring shape injector with multiple nozzles are initiated and built for 3-D CFD simulations. The comparisons of flow mixing index and injection pressure are made between two type injectors.

The Urea Selective Catalytic Reduction (SCR) technology is one of the major mature exhaust aftertreatment technologies which are demonstrated to be able to lower tail pipe NOx emission by 90%. The system consists of a urea injection at upstream pipe and a downstream SCR converter. A well mixed flow (exhaust gas and NH3) in front of SCR substrate, which is usually constrained by tight design packaging, is very critical to ensure the desired performance. Current paper addresses the geometrical effects on flow mixing by using three dimensional Computational Fluid Dynamics (CFD) tool. The mixing enhancement is achieved by adding flow mixer. The shapes and locations of flow mixers, as well as the number of blades inside mixer are investigated to show the effect on fluid mixing in downstream along the flow direction. Results show great improvement of flow mixing by adding a delta wing mixer.

A uniform flow inside a Diesel Particular Filter (DPF) is very critical to ensure the desired performance and durability of the filter system. In current paper, a systematically study was performed to investigate the geometrical effects on flow uniformity in the front of diesel particular filter by using Computational Fluid Dynamics (CFD) tool. The studies were focused on the effects of spiral rib inside inlet tube; inlet and outlet cones, length and angle of inlet cone. In all the numerical simulations, mesh sizes were carefully controlled to yield accurate and consistent results. No improvement on flow uniformity index was observed by adding a signal spiral rib in the inlet tube in front of diffuser (inlet cone), and even worse in the case with a single deeper rib. On the contrary, pressure loss increases rapidly.

The exhaust system is one of the major P/T systems for sound quality tuning. The many varieties in exhaust pipe routing and the flexibility in muffler design make it possible to design an exhaust system to deliver tailpipe sound for specific sound quality requirements. It is essential that the tailpipe sound be balanced with other P/T sound to yield the overall sound targets. The primary contribution of an exhaust system is the firing and sub-firing orders. The typical tailpipe sound target contains banded targets for “good” orders as well as “do-not-exceed” targets for the rest. Every order target needs to be met in order to yield the right tailpipe sound. In most cases, the pipe routing and the muffler volumes of mufflers are dictated by package constraints, however, the internal design of muffler with a given volume can create quite different tailpipe sounds.