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Technical Paper

Criticality of Tube Bending Through CAE Understanding

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.
Technical Paper

Effective Methodology for Backpressure Prediction of Hot Exhaust Gas in Cold Flow Bench Test

The numerical methodology is developed to estimate the backpressure value acquired from the cold flow bench into the hot flow conditions by equalizing various gas flow properties such as gas density and gas constant. The exhaust muffler geometry is adopted for virtual analysis. Computational Fluid Dynamics (CFD) modeling of the exhaust muffler in hot and cold flow conditions shows 60% of difference in back pressure values. The same muffler sample is tested in hot and cold flow test bench for back pressure on same measurement location used in CFD tool, the test result difference between these two conditions is obtained as 61%. By using derived 1D calculation, the cold flow back pressure results are extrapolated to generate hot flow back pressure values for the exhaust muffler system. These extrapolated values are then validated with the back pressure analysis results performed in both CFD and flow test bench using cold and hot flow conditions.
Technical Paper

Computational Simulation to Validate Resonator through Bending Moment

Bending moment is one of the strongest pursuits in resonator's structural validation. Eigen problems play a key role in the stability and forced vibration analysis of structures. This paper explains the methodology to determine the weak points in the resonator assembly considering the additional effects of the installation forces and temperature impacts. Using strain energy plots, weakest part of the product is identified in the initial stage. The solution comes in unique way of utilizing the worst case scenarios possible. As a consequence, the stress generated by these analyses will prove to be critical in concerning the durability issue of the system. These conditions are evaluated by a finite element model through linear approaches and results are summarized.
Technical Paper

Influence of Linear and Parabolic Elements in Structural Rigidity of Converter Mounting Brackets

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.
Technical Paper

Computational Simulation to Ascertain Hot Vibration Test Assembly for Converter Validation

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.
Technical Paper

Partial Controlled Canning for Thin Wall and Ultra Thin Wall Substrates - A New Approach

The trend lately has shifted towards usage of thin wall and ultra-thin wall substrates. This change has come to existence due to the increased acting surface area available in these substrates. However these types of substrates have reduced isostatic strength comparatively, reducing its canning durability. This phenomenon has induced a new canning methodology which shall not disturb the substrate integrity during canning and also perform effectively to the requirements. This can be achieved by controlled canning which includes a huge investment and so a new methodology has been devised using the available resources and a partial controlled canning process is established and verified for canning performance and found to be effective. The paper shall include the procedural explanation and a set of results obtained by the new methodology to support its effectiveness.
Technical Paper

Influence of Coupled Analysis for a Hot End Exhaust System Validation

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.
Technical Paper

Improved NOx Reduction Using Wiremesh Thermolysis Mixer in Urea SCR System

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.
Technical Paper

Durable Catalytic Converter Mounting with Protective and Support Seals

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.
Technical Paper

Wiremesh Mounting System for Low Temperature Diesel Catalytic Converters

Knitted wiremesh along with radial gas tight seals provide reliable mounting system for low temperature underbody converters. The compression characteristics of the wiremesh is modified by wire material, wire diameter, wire geometry, mesh crimp heights; wire density, wiremesh courses per inch, needle count, number of strands, wiremesh temper, wiremesh surface profile and surface characteristics. The radial mounting pressure provided by the wiremesh is matched with the mounting pressure requirement. Wiremesh systems can be tailored to any required radial mounting pressure from conventional to ultra thin-wall substrates. The wiremesh mounting system is proven durable, without any failure on more than 25 million underbody converters in light duty vehicles. Cp and Cpk show the capability of the manufacturing process. Thus the wiremesh mounting support is a viable alternate for low temperature gasoline and diesel applications.
Technical Paper

Edge Seal Mounting Support for Diesel Particulate Filter

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.
Technical Paper

Catalytic Converter Design for Manufacturing Using Monte-Carlo Simulation

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.
Technical Paper

Numerical Simulation and Experimental Validation of the Catalytic Converter Cool Down Process

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.
Technical Paper

Single Seam Stuffed Converter Design for Thinwall Substrates

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.
Technical Paper

CFD Investigation of Thermal Fluid Flow and Conversion Characteristics of the Catalytic Converter

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.