Automotive Exhaust Systems Research Articles

Creep Behavior of 409L and 436 Ferritic Stainless Steels Applied for Automotive Exhaust System

In order to investigate the creep behavior and understand its deformation mechanism of automotive exhaust pipe materials, this study conducted creep experiments of 409L and 436 ferritic stainless steels at both 600°C and 750°C under different stress levels. After creep tests, crept specimens were analyzed on the microstructure and fracture surfaces by the use of scanning electron microscopy. From creep data, two important material coefficients, namely, M of Monkman-Grant relationship and K of Coble creep equation are calculated for predicting the material creep life. Results show the creep resistance of 436 stainless steel is better than that of 409L stainless steel, because the 436 stainless steel has more Ni, Cr, and Mo contents. As the creep mechanism, all tests show grain boundary diffusion or Coble creep is the dominate deformation mechanism, except at higher temperature 750 °C and higher stress levels.

ATI 409HP

Abstract ATI 409HP (UNS S40900) ferritic stainless steel was introduced by ATI Allegheny Ludlum to provide improved oxidation and corrosion resistance for automotive exhaust systems in comparison to carbon steel. The alloy was designated "MF-1", indicating its end use: automotive mufflers. The good fabricability of this alloy, combined with its basic corrosion resistance and economy have significantly broadened the utility of ATI 409HP stainless steel. ATI 409HP consists of four grades: UNS S40900, S40910, S40920, and S40930. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as forming, machining, and joining. Filing Code: SS-1135. Producer or source: Allegheny Technologies Inc..

Aging characterization of metals for exhaust systems

The mechanical characteristics of four materials used in automotive exhaust systems have been compared after an aging treatment to evaluate the combined effects of thermo-mechanical fatigue and corrosion. For this purpose, an experimental aging procedure has been developed. This procedure is composed of chemical, thermal and mechanical cycles, which are combined and repeated to simulate the actual operating conditions of automotive exhaust systems. Three austenitic steels (AISI 309, AISI 316Ti, and AISI 321) and a nickel-based alloy (Inconel 625) are tested. The results show that Inconel 625 and AISI 309 are less affected by the aging process than the other materials.

Simulation Research of Vehicle Exhaust System Hanger Location

To reduce the impact of exhaust system hanger layout on the vehicle vibration performance and research the method about the reasonable layout of the hanger, forst established the FE model of an automotive exhaust system and fixed up hanger locations by modal analysis and load distribution by statics analysis. Then according to the displacement and force response to the engine’s torque loaded on powertrain’s mass centroid, adjusted hanger locations. At last, got the reasonable hanger location layout. The exhaust system hanger layout is used on a heavy truck and has the obvious effect.

607 自動車用排気系システム内部で気流により発生する音場の可視化(機械力学・計測制御II)

607 自動車用排気系システム内部で気流により発生する音場の可視化(機械力学・計測制御II)

Design of a Web-Based Information Management Platform for Automotive Intake and Exhaust System

The management and sharing of varied automotive intake and exhaust system data makes it imperative for modern automotive companies. Based on needs of a certain company’s NVH department, much work has been done to analyze the data management method and data features, then a web platform based on B/S model has been built and also the solutions to transformation methods between different data types, data visualization, processing of massive data and data dynamic expansion are presented. Based on the key technologies, a practical web-based information system is designed for the management of intake and exhaust system data, which remarkably facilitates the company’s data management work.

Experimental source characterization techniques for studying the acoustic properties of perforates under high level acoustic excitation

This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristic. The methods developed are intended both for studies of non-linear energy transfer to higher harmonics for samples only accessible from one side such as wall treatment in aircraft engine ducts or automotive exhaust systems and for samples accessible from both sides such as perforates or other top sheets. When harmonic sound waves are incident on the sample nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea is that these sources can be characterized using linear system identification techniques similar to one-port or two-port techniques which are traditionally used for obtaining source data for in-duct sources such as IC-engines or fans. The starting point will be so called polyharmonic distortion modeling which is used for characterization of nonlinear properties of microwave systems. It will be shown how acoustic source data models can be expressed using this theory. Source models of different complexity are developed and experimentally tested. The results of the experimental tests show that these techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

Dual layer automotive ammonia oxidation catalysts: Experiments and computer simulation

Today, platinum based ammonia oxidation catalysts are applied in automotive exhaust systems to avoid ammonia slip from the SCR catalyst. In this paper we present a dual layer catalyst design with an additional SCR layer on top of the Pt/Al2O3 layer. Laboratory experiments show that the additional SCR layer significantly reduces NO formation, improves N2 selectivity but also reduces the overall NH3 conversion.A mechanistically based kinetic model for NH3 oxidation on platinum is presented. The model is parameterised using experiments with a single layer Pt/Al2O3 catalyst and well describes the NH3 conversion and the selectivities for the products N2, N2O and NO. Additionally NO oxidation to NO2 is included in the model.Based on the mechanistic model for the platinum layer and a previously published model for the SCR layer, a 2-D model of the dual layer catalyst is set up. This model takes into account the diffusion and reaction in the two washcoat layers of one monolith channel. The 2-D model reproduces the experimental data well, with the mechanisms for the two layers parameterised in separate experiments and no additional parameters adjusted for the dual layer model.Finally, the model is used to study the effect of some design parameters such as catalyst size, NO oxidation capacity of the Pt-layer and the thickness or diffusion coefficient of the SCR layer.

Implementation of a quality procedure based on Delphi method and the ISO/TS 16949:2009 in the production of stainless steel tubes for automotive exhaust systems

PurposeThe purpose of this paper is to present the application of a procedure for the quality control of stainless steel tubes produced for automotive exhaust systems from a leading company in the steel sector, based on the Delphi method in accordance with the ISO/TS 16949:2009 and the ISO 9000:2008. Using Delphi methodology, it was possible to identify the main problems in the production lines object of the study, the main defects and their causes. Statistical methods were used to monitor process compliance and capacity. The panel of experts involved in Delphi method was able to identify causes of non‐compliance and suggest corrective actions.Design/methodology/approachThe quality procedure implemented involves the application of the Delphi method and the ISO/TS 16949:2009 standard in conjunction with ISO 9000:2008 to the production line of welded tubes for exhaust systems. The statistical methods used to monitor the process were mainly control charts. Capability index, Cp and Cpk, were used to measure the process attitude to produce compliant outputs. Dimensional data were acquired by non‐destructive testing on diameters and X‐R charts were used to graphically represent the process state of control. Destructive tests were performed to monitor the welding quality and P‐chart were used to assess the proportion of nonconforming units.FindingsIn this work, a procedure was developed in order to characterize the production process of TXM tubes realized in the line 31 of the leader company plant. The use of Delphi methodology, in order to incorporate experts opinions in the quality control of stainless steel tubes, was one of the main points of this work. The panel of experts worked together to identify process issues, define their causes and propose corrective actions. The paper provides an overview about the quality approach of one of the world's largest companies in the production of steel and shows also how the statistical tools are used in order to manage process behavior.Originality/valueThe value of this paper is to illustrate an innovative approach to a real life quality problem; it demonstrates how the application of qualitative and quantitative quality instruments in accordance with technical specification can help in increasing and maintaining product compliance and in optimizing the management of resources.

EXHAUST SYSTEM RELIABILITY EVALUATION

Road vibrations cause fatigue failures in the automotive exhaust system. Evaluation of exhaust system reliability is investigated by using bivariate joint distribution model to account for dependence between exhaust components. Cumulative damages are derived to be used as the random variables in the distribution model. In the case study with a light duty truck exhaust system, the model parameters were estimated using maximum likelihood method based on marginal distributions. The dependence parameters between components were determined through bench tests of twelve (12) exhaust systems. Result comparison demonstrated the influence of component dependence on the point estimate and statistic inference of the system reliability.

An empirical approach to predicting heat transfer within single- and twin-skin automotive exhaust systems

This paper describes the further development of an exhaust system model based on the experimental characterization of heat transfer in a series of different pipe sections. Building on previous work published in this journal by the present authors, this study was undertaken to improve the operating range, accuracy, and usability of the original model as well as to introduce the ability to model twin-skin exhaust sections with an air gap. Convective heat transfer relationships for nine stainless steel exhaust bend sections of various wall thicknesses and radii were experimentally characterized over a range of steady state conditions. In each case a correlation between the observed Reynolds number Re and the Nusselt number Nu was developed. Based on measured experimental data, a generic model was built using MATLAB/Simulink; this model is capable of predicting the relationship between the Nusselt number and the Reynolds number for previously unseen pipe geometries falling within the experimental design range. To develop the usefulness of the model further, 15 twin-skin test sections, intended to represent a range of geometries applicable to production automotive gasoline exhaust systems, were also fabricated and characterized. Within the model, both skins of each pipe section were split into five axial elements and five radial elements with the inner and outer skins linked via the modelling of free convection and radiation between them. The predicted Reynolds–Nusselt relationships for each bend section and twin-skin configuration were validated using transient experimental data over a portion of the US06 drive cycle. The final model demonstrated an improved accuracy of exhaust gas temperature predictions, compared with the previous model iterations, with typical errors of less than ±1 per cent and a mean error over the US06 cycle of +0.2 per cent.

A New Type of Muffler Based on Microperforated Tubes

Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple: It is to create a surface with a built in damping, which effectively absorbs sound waves. To achieve this, the specific acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium (∼400 Pa s/m in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source for noise control in ducts. In this paper, the possibility to build dissipative silencers, e.g., for use in automotive exhaust or ventilation systems, is investigated.

Influence of Intermetallic Precipitates and Heat Treatment on the Mechanical Properties of High-Temperature Corrosion Resistant Ferritic Steels

High-temperature corrosion resistant ferritic steels are commonly used in heat exchangers for auxiliary power units (APU), automotive exhaust systems and structural parts of solid oxide fuel cells (SOFC) due to their excellent thermal fatigue resistance. As the process temperatures in these applications are primarily limited by the materials high temperature strength, the main focus of this work is on the improvement of this property by adjustments in the material design. Generally, two mechanisms were used to increase the high temperature strength, solid solution strengthening and precipitation hardening. Due to their large atomic radii and high solubility in α-Fe, W and Mo were used for solid solution strengthening. Furthermore, the content of niobium, which is well known to form Laves phase precipitates, was raised. This led to a higher content of Laves phase precipitates compared to the reference material. The analyses concentrated on the effect of the Laves phase. Strength at elevated temperature was investigated in compression tests at 900̊C with respect to the annealing time which was varied between 1h and 1440 h.

Overview on the application of ISO/TS 16949:2009, in a worldwide leader company in the production of stainless steel tubes for automotive exhaust systems

This paper presents an overview on the quality approach of a company that is at the leading edge in the sector of stainless steel-based products and represents an example of best practice in pursuing a continual improvement and the customer satisfaction. In this study, the attention has been focused on the application of the technical specification ISO 16949:2009 in accordance with the ISO 9000:2008, for the quality control of stainless steel tubes produced for automotive applications in one of the company plant devoted to the realisation of welded tubes for mufflers and exhaust pipes. The case study examined demonstrates how the effective adoption of the standards can help in reaching the highest level of performances in the production process, giving high-quality products and consolidating the company position on the market.

Transverse plane wave analysis of short elliptical chamber mufflers: An analytical approach

Short elliptical chamber mufflers are used often in the modern day automotive exhaust systems. The acoustic analysis of such short chamber mufflers is facilitated by considering a transverse plane wave propagation model along the major axis up to the low frequency limit. The one dimensional differential equation governing the transverse plane wave propagation in such short chambers is solved using the segmentation approaches which are inherently numerical schemes, wherein the transfer matrix relating the upstream state variables to the downstream variables is obtained. Analytical solution of the transverse plane wave model used to analyze such short chambers has not been reported in the literature so far. This present work is thus an attempt to fill up this lacuna, whereby Frobenius solution of the differential equation governing the transverse plane wave propagation is obtained. By taking a sufficient number of terms of the infinite series, an approximate analytical solution so obtained shows good convergence up to about 1300 Hz and also covers most of the range of muffler dimensions used in practice. The transmission loss (TL) performance of the muffler configurations computed by this analytical approach agrees excellently with that computed by the Matrizant approach used earlier by the authors, thereby offering a faster and more elegant alternate method to analyze short elliptical muffler configurations.

The study of 430Ti and 430LNb ferritic welding wires for application in the cold part of automotive exhaust systems

Ferritic stainless steels have been extensively used in automotive exhaust systems. Ferritic stainless steel wires have been recently introduced in the fabrication of these components to reduce costs (hot and cold parts) and improve the quality of hot part components, mainly thermo-mechanical fatigue resistance, and their use has been growing since. This study compares mechanical and metallurgical characteristics of fusion zones obtained with 430Ti and 430LNb welding wires. The influence of Ar 2%O2 and Ar 2%N2 3%CO2 shielding gases was also studied. Metallographic analysis was performed by optical and electronic microscopy, revealing the main characteristics of the fusion zone obtained with these welding wires and shielding gases. Welded joint ductility was measured using the Erichsen test. The results indicated that ferritic stainless steel wires could be used to produce welds with adequate ductility. However, this depends critically on the choice of the welding wire and the shielding gas to maximize mechanical and metallurgical properties and to avoid any future problems.

승용차 배기계 벨로우즈의 구조해석에 관한 연구

자동차 배기계는 제한된 설치 공간으로 인하여 내구성과 연계된 형상을 최적화하여야 한다. 본 연구에서는 자동차 배기계를 구성하고 있는 Flexible Tube(Bellows)의 형상에 따른 응력 변화를 해석하였다. 아울러 Bellows의 변위량이 크게 발생하는 것을 고려하여 기하학적 비선형 해석을 실시하였으며 Bellows의 변형량은 끝단에서 6mm의 변위가 발생하도록 하였으며 얻어진 결과는 다음과 같다. (1) Bellows의 두께가 증가하거나 Bellows Tube의 반경이 증가하면 Von-Mises 응력은 비례적으로 증가한다. (2) Bellows의 주름의 반경이 증가함에 따라 주 응력이 감소하다가 증가함으로 Bellows 설계 시 최소 응력 산출을 위한 주름 반경의 선정이 요구된다. As the space for installation of automotive exhaust system is limited, the space should be optimized with relation to the endurance and shape of the system. Geometric nonlinear analysis was used and deflection of bellows was assumed 6mm. Obtained results are as follows; (1) The Von-Mises stress of bellows is increased with increase of thickness or radius of bellows linearly. (2) As the principal stress varies according to the radius of convolution, it is necessary to decide the optimal radius of convolution.

Three-dimensional/one-dimensional numerical correlation study of a three-pass perforated tube

Automotive exhaust systems give a major contribution to the sound quality of a vehicle and must be properly designed in order to produce acceptable acoustic performances. Obviously, noise attenuation is strictly related to the internal gas-dynamic field that, on the other hand, needs to be optimised also in terms of pressure losses. In this work, the noise attenuation characteristics of a typical perforated muffler for automotive applications are investigated. Acoustic performances are quantified by the Transmission Loss (TL) parameter, which only depends on the geometrical characteristics of the device. Different numerical analyses are employed. At first, a one-dimensional (1D) simulation code (GT Power™) is used to predict the TL profile in a low frequency range. 1D simulation, in fact, may be only applied under the hypothesis of a planar wave propagation. A more complex 3D FEM/BEM approach is also realised using the VNOISE™ code, [17], specifically designed for acoustic applications. Obviously, such analysis allows to obtain more accurate results at high frequency, depending on the mesh size. Different flow velocities and gas temperatures are investigated in both 1D and 3D models. The predicted TL profiles are compared and discussed in order to assess the potentiality and limitations of the employed numerical approaches.

Recrystallization of Coarse-Grained Nb-Containing AISI-430 Ferritic Stainless Steel

Ferritic stainless steels (FSSs) have excellent corrosion resistance and good mechanical properties. Applications include heaters, houseware, and automotive exhaust systems. Alloying, even in small amounts, affects the recrystallization behavior of FSSs by selective dragging or pinning effects. In the present study, we present the main results regarding the recrystallization of a coarse-grained Nb-containing AISI 430 ferritic stainless steel. The material was processed by hot rolling and further annealed at 1250oC for 2 h to promote secondary recrystallization. Following, the material was cold rolled to a 80% reduction in thickness and annealed at 400-1000oC for 15 min. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to characterize the microstructure. Recrystallization of this steel begins at 700oC. Important orientation effects were observed in both as-rolled and annealed conditions. Recrystallization kinetics was strongly dependent on the initial orientation of the coarse grains. Results show that grain boundaries, transition bands and coarse Nb(C,N) particles are preferential sites for nucleation at moderate annealing temperatures.

720 特性曲線法による自動車排気脈動シミュレーションの基礎的検討(エンジン回りの振動・騒音,OS-5 サイレント工学,総合テーマ「伝統を,未来へ!」)

Our final target of this study is developing a simulation package for predicting the pressure pulsation inside pipe-system and its sound pressure near the end of automotive exhaust system. This paper reports on the modeling of each components of real automotive exhaust system under the air pulsation by air-blower is working in laboratory. Three kinds of fundamental element model in the characteristic method are considered to construct the models of each component. The comparison of pressure measured and calculated is carried out to improve the models both static and dynamic conditions.