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Single seam stuffed converters are often used to house ceramic substrates due to the simplicity and low tooling cost of the canning process. However, stuffing thinwall substrates requires careful GBD (gap bulk density) control because of their low isostatic strengths. Statistical simulation results indicate that the stuffing process can be performed within the required GBD range of 0.8 to 1.2 g/cm3 using vermiculite mats with the current tolerance specifications. A nominal value of 0.925 g/cm3 is recommended to minimize substrate breakage. Experimental results show that prototypes can be built with a GBD accuracy of 0.05 g/cm3. This paper describes the requirements needed to design and validate single seam stuffed converters.

Typically, the maximum converter skin temperature occurs when the catalytic converter is in the cool down process after the engine is shut-off. This phenomenon is called temperature soaking. This paper proposes a numerical method to simulate this process. The converter skin temperatures vs. time are predicted for the converter cool down process. The soaking phenomenon is observed and the maximum temperature is determined. Temperatures are also predicted for the exhaust gas, substrate, mounting mat and shell of the converter assembly. The numerical results are validated with measurements, and an acceptable correlation is achieved. This study focuses on converters with ceramic substrates; however, this methodology can also be used for converters with metallic substrates.

Generation of discretization with prescribed element sizes are adapted to the geometry. From the rules of thumb, for a complicated geometry it is important to select the reasonable element order, shapes and size for accurate results. In order to that, this paper describes the influence of elemental algorithm of the catalytic converter mounting brackets. Brackets are main source of mounting of various systems mainly intake and exhaust in the engine. In hot end exhaust system, a bracket design plays a vital role because it has to withstand heavy structural vibrations without isolation combined with thermal loads. Bracket design and stiffness determines the whole catalytic converter system's rigidity. So, here discretization of converter brackets by linear and parabolic elements is studied with different elements types and compared.

Simulation's drive towards reality boundary conditions is the toughest challenge. Experience has shown that often the most significant source of error in thermal and dynamic analyses is associated within specified boundary conditions. Typically, validating the system by considering both thermal and dynamic loads with predefined assumptions is time consuming and inconclusive when confronted with reality boundary conditions. Thus, the solution comes in unique way of combining thermal and dynamic loads with specified boundary conditions and will convey computational results closer to the real scenario. As a consequence, strain concentrated regions due to thermal expansion are aggregated more, when coupled with dynamic loading. The stress generated by the coupled analyses will prove to be critical in concerning the durability issue of the hot end system. These conditions are evaluated by a finite element model through linear and non-linear approaches and results summarized.

A compact, knitted, crimped wiremesh mixer disposed in the exhaust system of an internal combustion engine, between the reductant injection and the urea SCR unit, increases the uniformity of the reductant in the exhaust stream by the time the stream reaches the SCR catalysis unit. Wiremesh mixer enhances thermolysis of urea into ammonia and iso-cyanic acid (HNCO). Computational Fluid Dynamics (CFD) modeling shows improved uniformity index from 0.94 to 0.99 within 35 mm travel length due to longitudinal and radial flow of the exhaust gas through the body of the wiremesh mixer. The higher thermolysis and rapid warm-up nature of the wiremesh provides enhanced ammonia production from urea thermolysis. Wiremesh physical attributes such as material composition, geometry and structure, wire diameter, mesh crimp pitch, crimp depth, crimp angle and the contour are optimized for minimum back pressure and maximum mixing efficiency.

While advanced automotive system assemblies contribute greater value to automobile safety, reliability, emission/noise performance and comfort, they are also generating higher temperatures that can reduce the functionality and reliability of the system over time. Thermal management and proper insulation are extremely important and highly demanding for the functioning of BSVI and RDE vehicles. Frugal engineering is mandatory to develop heat shield in the exhaust system with minimum heat loss. Heat shield design parameters such as insulation material type, insulation material composition, insulation thickness, insulation density, air gap thickness and outer layer material are studied for their influences on skin temperature using mathematical calculation, CFD simulation and measurement. Simulation results are comparable to that of the test results within 10% deviation.

With the ever increasing need for diesel exhaust particulate filters to meet the stringent emission regulations, it is imperative that a system approach be adopted in the design and optimization of these filters. A performance study is conducted to study the effect of filter parameters like aspect ratio. An extension of this study includes the effect of inlet and outlet cones on the contraction and expansion of flow at inlet and exit of the filter channels. The study covers both cordierite and silicon carbide (SiC) diesel exhaust particulate filters. The experimental data is used to validate the pressure drop models developed previously in the literature. Also the effect of the system parameters on the acoustic performance parameter transmission loss of the particulate filters, Light-, Medium- and Heavy duty truck exhaust mufflers and integrated particulate filter/muffler is investigated.

Due to the large size, high bulk density and high thermal expansion coefficient of the diesel particulate filter substrate; the conventional mounting system cannot provide the necessary radial mounting pressure. Mathematical and experimental results give the vibration and the back pressure force needed to mount the diesel particulate filter in the exhaust system. L-seal mounting support used in diesel particulate filter provides cushion to accommodate the linear tolerance of the substrate and the cone and also the necessary axial and radial mounting forces. L-seal axial and radial mounting forces are altered by type of material, surface characteristics, heat treatment and wire geometry. The proportional increase in compression force per unit weight during cycling shows dimensional consistency of the L-seal. The compression characteristics of A286 tremendously increase (>20%) during heat treatment as precipitation and hardening occurs.

Advanced substrate design, efficient washcoat/catalyst formulation and robust packaging are critical elements to assure performance and durability of catalytic converters and diesel particulate filters. Radial seals, axial seals and L-seals made of knitted wiremesh are used with conventional mounting systems to provide compressible and durable support cushions for catalyst and filter substrates. Axial and radial mounting forces of the seals are optimized by material type, seal density, wiremesh strand, wiremesh surface profile (flat or round), wiremesh surface characteristics, wiremesh temper, thermal impacts, and wiremesh geometry. Compression characteristics of stainless steel alloy A286 tremendously increase (>20%) during heat treatment as precipitation and hardening occurs. Compression force tends to stabilize during cycling, retaining a residual force. Radial seals provide radial mounting pressure and mat erosion protection.

A combined Computer Aided Engineering (CAE) simulation and physical fatigue testing of a passenger car exhaust system resonator with wire mesh seal between the inlet and outlet pipe is performed to evaluate the durability and improvise the design. The outlet pipe end cap of the exhaust system resonator deformed and cracked at the fillet region repeatedly upon the application of the maximum load from a pre developed accelerated specification test. However, the system meets the end usage on-road durability target of 5 years / 1,00,000 km. There is a gap between the accelerated bench test and the end usage durability target. The current study correlates CAE simulation and biaxial fatigue testing and improvise possible alternate resonator design. Conventionally, components passing the accelerated test always meets the end usage durability target whereas components meeting the end usage durability target need not necessarily pass the accelerated test.

Tube bends are critical in an exhaust system. The acceptability of tube bends is based on the induced level of shape imperfections considered. An analysis is presented for the performance tuning of the genetic algorithm including the importance of raw material selection, ovality and elongation property. This study is an attempt to analyze the ovality effect of STAC 60/60 material. CAE tools are essential to exploit the design of experiments and find out the optimum values of the design parameters in comparison with full factorial designs. Especially the effects of materials, dimensions and geometry shape of the ultimate strength were discussed by both CAE and experiments. The ultimate strength of steel tube was evaluated at least 20-30% as a local strain independent of the materials. The dependency of ultimate bending angle on original centre angle of the tube bend was clarified.

Conventional catalytic converter developments driven by trial and error attempts by experts who successfully employ heuristics (a set of empirical rules gained through time and experience) will not be able to meet the current demanding needs. The cost and time involved in testing every catalytic converter mandates new approaches aimed at improving efficiency and reducing development lead time. Computational tools such as HeatCad, P-Cat, CatHeat, WAVE, Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA) and Monte-Carlo simulation are sequentially applied to design, optimize and manufacture catalytic converter. Heatcad analysis provides the way to identify thermal management issues and to optimize runner lengths and material thickness of the manifold, and downpipes. P-Cat is used to estimate back pressure due to substrates, washcoat, end cones, and inlet/outlet pipes. CatHeat analysis is used to predict the temperature profile across the converter.

Automotive exhaust system components are exposed to many types of vibrations, from simple sinusoidal to maximum random excitations. Computer-Aided engineering (CAE) plays an inevitable role in design and validation of hot vibration shaker assembly. Key Life Test (KLT), an accelerated hot vibration durability test, is established to demonstrate the robustness of a catalytic converter. The conditions are chosen such a way that the parts which passes key life test will always pass in the field, whereas the parts which fail in the key life test need not necessarily fail in the field. The hot end system and the test assembly should survive in these aggressive targeted conditions. The test fixture should be much more robust than the components that it should not fail even if the components fail. This paper reveals the computational methodology adopted to address the design, development and validation of the test assembly.

The exhaust system design and development need to be more flexible and easily adaptable for the requirement of dynamic changes to meet the upcoming emission and noise regulations. Durability of exhaust system components are evaluated through conventional bending moment testing using specified standard load conditions. Road load re-production test is an improvement of the conventional approach to predict component weld durability. It involves the systematic and sequential process of acquiring road load data such as sensor instrumentation, strain measurement at the test track, data processing and input to Bi-Ax testing. S/N Curve testing is introduced recently as an alternate method to minimize the use of road load reproduction testing. It involves prediction of rough force using transient response analysis followed by Bi-Ax testing for the derived high and low load forces to meet the target number of cycles to failure.

Computer aided engineering is used to design, develop, optimize and manufacture catalytic converter. Heatcad, a transient heat transfer analysis is used to simulate the temperature response in the exhaust system to locate the catalytic converter to achieve maximum performance. Heatcad analysis provides the easy way to identify thermal management issues and to design and optimize the runner lengths and material thicknesses of the manifold, and downpipes. P-Cat is used to estimate back pressure due to substrates, end cones, and inlet/outlet pipes. Catheat, a one dimentional heat transfer tool is used to identify the converter insulation to maintain the required external skin temperature. Computational Fluid Dynamics (CFD) analysis, a powerful means of simulating complex fluid flow situations in the exhaust system, is used to optimize the converter inlet and outlet cones and the downpipes to obtain uniform exhaust gas flow to achieve maximum converter performance and reduce mat erosion.

A stochastic simulation based on the Monte-Carlo method was developed to study the effect of substrate, mounting mat and converter shell dimensional tolerances on the converter manufacturing process. Results for a stuffed converter with nominal gap bulk density (GBD) 1.00 g/cm3 show an asymmetric probability density function ranging from 0.90 to 1.13 g/cm3. Destructive and non-destructive GBD measurements on oval and round production converters show close correlation with the Monte-Carlo model. Several manufacturing options offering tighter GBD control based on component sorting and matching are described. Improvements ranging from 28% and 64% in GBD control are possible.

Fluid flow, temperature prediction, thermal response and light-off behavior of the catalytic converter were investigated using Computational Fluid Dynamics (CFD), combined with a conjugate heat transfer and a chemical reaction model. There are two objectives in this study: one to predict the maximum operation temperature for appropriate materials selection; and the other, to develop a numerical model which can be adjusted to reflect changes in the catalyst/washcoat formulation to accurately predict effects on the flow, temperature and light-off behavior. Temperature distributions were calculated for exhaust gas, catalyzed substrate, mounting mat and converter skin. Converter shell skin temperature was obtained for different mat materials. By changing reactant mass concentrations and noble metal loading, the converter light-off behavior, thermal response and temperature distributions were changed.

An advanced three-way converter system with significant improvements in light-off performance, conversion efficiency, thermal stability and physical durability at high operating temperature is described. The converter system is comprised of a light-weight ceramic substrate with high surface area triangular cell structure, a new catalyst formulation with enhanced thermal stability and good substrate compatibility, and a durable packaging design which together lead to consistent improvements in high temperature performance and durability. Experimental data including FTP performance, canning trials, and high temperature vibration and thermal shock tests for both the advanced and standard three-way converter systems are presented.