Automotive Exhaust Systems Research Articles

Application of shell vibration theory to automotive muffler design and development

The muffler shell of an automotive exhaust system can cause numerous NVH (Noise, Vibration and Harshness) issues such as radiated noise, buzzing, rattling and implosion. In general, the problems are detected and solved after the mufflers are built and assembled in a vehicle, which are expensive and time consuming to correct at that stage. It would be beneficial to develop an analytical technique to predict the vibration behavior of a muffler shell during the early stages of exhaust system design. In this paper, shell vibration theories are investigated by comparing the solutions with the results from modal tests and finite element analysis. Utilizing these theories, an analytical model to predict the natural frequencies and mode shapes of muffler shells with circular cross section, elliptical cross section and cross section with two constant radii has been developed. A novel approach for accurately predicting the natural frequencies of muffler sections with two constant radii is also presented in this paper. Case studies are presented to demonstrate that the theoretical analysis can be applied effectively to predict and solve NVH issues of muffler shells

페라이트계 스테인리스강의 고온염 부식특성에 관한 연구

It is very important to choose optimal material having good corrosion resistance and capabilities for the part materials such as the automotive exhaust system under a hot salt corrosion atmosphere. Generally, two types of corrosion come into the automotive exhaust system. One is ‘Condensate Corrosion’, which is occurred by exhaust gas condensate formed at the inner surface of exhaust system heated up during driving, which results in the acid condensate pitting. The other is ‘High Temperature Salt Corrosion’ occurring from the interaction between the chloride ion coming from salt at the seaside district or snow salt and the outer surface of exhaust system. By the corrosion attack, the main muffler is firstly damaged and the life cycle of an automobile is significantly decreased. It has been investigated that the hot salt corrosion properties of a STS 409L and 436L ferritic stainless steels which are well-known for the materials of the automotive exhaust system. In addition, the corrosion properties of hot dip aluminum coated STS 409L have been compared with uncoated steels. Aluminum coated STS 409L showed a superior corrosion resistance than uncoated STS 409L, and futhermore showed a better corrosion resistance than a STS 436L, which is an expensive ferritic stainless steel having a excellent corrosion resistance caused from more chromium content of an alloying element.

Intergranular corrosion of Ti-stabilized 11 wt% Cr ferritic stainless steel for automotive exhaust systems

Intergranular corrosion (IGC) of type 409L ferritic stainless steel (FSS) was investigated. A free-exposure corrosion and a double loop electrochemical potentiokinetic reactivation (DL-EPR) tests were conducted to examine IGC of the FSS. IGC occurred in the specimens aged at the temperature range of 400–600 °C that has the sensitization nose located around 600 °C. The critical I r/ I a value was determined to be about 0.03 above which IGC occurred. Based on the analysis of the intergranular precipitates by an energy dispersive spectroscopy (EDS) and a transmission electron microscopy (TEM), IGC was induced by the Cr depletion zone formation due to Cr segregation around intergranular TiC.

페라이트계 스테인리스 강 MAG 용접의 기계적 물성에 관한 연구

Ferritic stainless steels have a good heat resistance and economic advantage. They are used for applications such as automotive exhaust systems where resistance to general corrosion is superior to carbon steels. However, there are not enough research for ferritic stainless steels on weldability mainly used as automotive exhaust manifolds. In this study, mechanical and microstructure properties of as-welded STS 429L and STS 444 ferrite stainless steels were confirmed by tensile, bending, hardness test, optical microscopy and scanning electron microscopy. Tensile strength of the STS 444 is higher than the STS 429L when it is a raw material. In contrast to this fact, STS 429L indicated higher tensile strength after butt welded. In addition, the hardness have a increasing tendency as getting down on the bead.

15Cr 페라이트계 스테인리스강의 겹침용접부 고온인장 특성에 관한 연구

Ferritic stainless steels of the 400 series have been available for automotive exhaust system, heat exchanger, radiater etc. in various industrial because heat resistance, corrosion resistance and strength are excellent. Especially, automotive exhaust system is required good heat resistance because typical temperature of exhaust system exposed during operation of engine is reach up to . However, research for effect of high temperature in ferritic stainless steels is not enough. In this study, high temperature tensile properties of lap weld of ferritic stainless steels(STS 429) were investigated. In accordance with heat input, lap welds had been produced and were evaluated at high temperature() to compare high temperature tensile properties. In addition, room temperature tensile tests were carried out for non-aging and aging specimens. As a result of R.T tensile test, non-aging specimens were fractured in base metal except for low heat input specimen and aging specimens were fractured in weld metal. Also high temperature tensile test were carried out by aging specimen. After high temperature tensile test, fracture of aged specimen was occurred in base metal except for low heat input specimen. Fracture surface of low heat input specimen in weld metal was confirmed as brittle fracture with observation using scanning electron microscope(SEM). Significant decrease in ultimate tensile strength (between 82 and 85%) was observed for aged ferritic stainless steels(STS 429) when tested at high temperature.

Function-based cost estimating

Communication between cost estimators with commercial (CE-C) and engineering (CE-E) backgrounds is essential for good internal practice. This paper presents a function-based cost estimating (FUCE) framework to link the commercial and engineering communities through a structured approach at the conceptual design stage. The objective of FUCE is to translate the un-quantified terminology and the requests associated with the product specifications used by CE-C into a medium that CE-E can process using their resources, and creates estimates that are based on a standardized approach. The FUCE approach starts with functional decomposition, and then identifies product parameters that are related to a top level function and finally associate product costs to the function using past knowledge and data. FUCE is developed using a detailed case study on an automotive exhaust system. The methodology is then validated on two case studies from the automotive and aerospace industries.

Corrosion of hot end automotive exhaust components

PurposeTo evaluate the corrosion resistance of four different stainless steels often employed in hot end exhaust components.Design/methodology/approachThis paper evaluated the outcomes of the hot salt test and the cyclic oxidation test on four different stainless steels, used as hot end exhaust components. The specimens were analyzed by means of SEM for surface changes and the weight loss was considered.FindingsThe general corrosion rate and pitting resistance under all the test conditions for hot end exhaust components indicated that 434 was by far the most corrosion resistant alloy, followed by 1.4509 and 321, and lastly 304 was the least corrosion resistant. In general, the ferritic stainless steels, especially 434, outperformed the austenitic ones under all the test conditions.Practical implicationsThe comparison of the corrosion resistance and rate, between the frequently used ferritic and austenitic stainless steels used in the exhaust system, gave a clear indication that the ferritic steels will provide prolonged service and this could be beneficial information to the manufacturers.Originality/valueA new approach to summarise the materials' behaviour and their relative performance in the tests performed was developed. This proposed summary of a number of corrosion indicators could serve as a relative guide to alloy selection for use in hot end automotive exhaust systems for both manufacturers and users.

A thermo-mechanical fatigue damage model for variable temperature and loading amplitude conditions

A fatigue life prediction method for thermo-mechanical fatigue damage under variable temperature and loading amplitudes was proposed. In this approach, a rainflow cycle counting technique was used to extract cycle counts from the mechanical loading history. For each loading cycle, an equivalent damage temperature was determined. Once the equivalent temperature was used, the loop would be guaranteed closed. This approach was based on the assumption that total fatigue damage is defined as the summation of mechanical fatigue damage and oxidation damage. The mechanical fatigue damage was calculated based on the Smith–Watson–Topper (SWT) model at room temperature, while the oxidation damage was calculated based on the Sehitoglu model determined from the stress/strain data at the equivalent temperature. Finally, Miner’s linear damage rule was used for damage accumulation. A case study with automotive exhaust systems was conducted to verify the effectiveness of the proposed method. The effect of creep damage was excluded in this study.

High temperature bending fatigue behavior of stainless steels for automotive exhaust

Abstract Continually increasing working temperatures and a growing need for greater efficiency and reliability of automotive exhaust system require immediate investigation into the high temperature fatigue properties of heat resisting stainless steels. In this study, evaluation method of high temperature bending fatigue life has been established and S–N curves for ferritic stainless steels, such as 409L, 436L and 429EM STS, produced by POSCO have been evaluated at the temperatures of 600 and 800 °C, which are typical temperatures of exhaust system exposed during operation of a vehicle. Endurance limit of 429EM was found to be higher than the other two stainless steels and significantly reduced with increasing temperature, from 150 MPa at 600 °C to 65 MPa at 800 °C. Thickness effect on the fatigue life has also been investigated by varying the thickness of specimen and was found insensitive within the thickness range from 1 to 2 mm.

21601 吸音材を有する自動車用排気系の三次元音響解析(振動解析とその応用I,OS.2 振動解析とその応用)

This paper deals with analysis for acoustic properties of automotive exhaust system having sound absorbing materials. Elements of the sound absorber having complex density are modeled 3D finite element. It was applied to the automotive exhaust system to verify the accuracy of acoustic analysis. The results show good agreement with results from acoustic experiments. Further, using asymptotic method to the equations of motion, explicit expressions of modal loss factor are derived. And the contribution for modal loss factor can be calculated. Applying the proposed method to the automotive muffler, it enables a more efficient layout of the sound absorbing materials.

溶滴移行現象に及ぼす自動車排気系部品用ステンレス鋼溶接ワイヤの組成の影響

19 mass% Cr ferritic stainless steel welding wire has been used for automotive exhaust systems. In proportion as the change of usage condition and variation of base material, the technical need for welding wire has intensified. With regard to solid welding wire, which achieves fine-grained weld metal in MIG welding for ferritic stainless steel, effect of chemical compositions of welding wires on droplet transfer phenomenon has been investigated. Followings were found and confirmed from image analysis and experimental works. (1) It is effective in suppressing the amount of spatter by gas emission from droplet that ΔN [mass%N-{0.519×(mass%Al)+0.292×(mass%Ti)+0.151×(mass%Nb)}] value of welding wire is controlled under 0.01mass%. (2) It is effective in suppressing the amount of spatter by irregular short-circuiting that total amount of Al and Ti content of welding wire is controlled under about 0.1 mass%. (3) Developed welding wire which chemical compositions are controlled appropriately is less spatter and fine-graind.

PM stainless steel's resistance to scaling

In North America, conversion of automotive exhaust systems from carbon steel to stainless steel has been progressing steadily since the mid-1990s. In an all stainless steel exhaust system, PM stainless steel exhaust flanges and HEGO (hot exhaust gas oxygen sensor) bosses are frequently selected over wrought (stamped and formed) stainless steel components. This is because PM stainless steel provides significant advantages in performance, cost and design flexibility, over their wrought counterparts. The improved performance is primarily due to the fact that PM stainless steel is more resistant to spalling of oxide scales in application-specific cyclic oxidation tests, compared with wrought stainless steel…

A novel accelerated corrosion test for exhaust systems by means of power ultrasound

Cycling corrosion tests have been performed to simulate corrosion conditions in the cold end of an automotive exhaust system. A middle range 1.4512 (AISI 409) stainless steel is submitted to a conventional dip dry test (DDT) parallel to a similar test but including an additional external stress thanks to an ultrasonic transducer. This new ultrasonic test (so called UST) is expected to reduce the diagnostic time of the corrosion test by the combined action of the chemical corrosion process and of mechanical degradations. Both corrosion tests are performed in two different media in order to simulate internal corrosion due to exhaust gas condensate and external cosmetic corrosion, greatly enhanced by road salt during winter. It respectively concerns a synthetic gas condensate, the composition of which is derived from what is obtained from motor gasoline combustion, and NaCl solution. In both electrolytes the stainless steel suffers from pitting corrosion. Samples are examined by optical micrography and surface profilometry. The degradation state is quantified according to three parameters: maximum pit depth, average pit diameter and porosity rate. The efficiency of each test is then related to the time of immersion. As expected, use of ultrasound allows pits growth to be achieved from the beginning of the exposure time, so that the maximum pit depth recorded after 180 h of immersion is twice than with the classical dip dry test. It seems that it does not modify the pit initiation mechanism but only increases growth kinetics.

MFI zeolite as a support for automotive catalysts with reduced Pt sintering

The noble metals used as catalysts in automotive exhaust systems are subject to sintering at extreme temperatures, leading to deterioration of catalytic activity. Zeolite with the MFI (ZSM5) structure is examined as a support for Pt particulate catalysts. The MFI structure is composed of agglomerates of single-crystal zeolite with interstitial mesoporosity. Pt fixed within these mesopores is shown through high-temperature aging tests in air to be highly resistant to sintering due to the mechanical constraints on particle size imparted by the mesoporous structure. The deterioration of catalytic activity after aging is significantly lower than that for comparable γ-alumina supported catalyst.

Thermomechanical fatigue of stainless steels for automotive exhaust systems

Thermomechanical fatigue of stainless steels for automotive exhaust systems

Thermomechanical fatigue of stainless steels for automotive exhaust systems

Stainless steel grades are now widely used for automotive exhaust systems, in order to increase their durability. Indeed, the exhaust systems are subjected to ever more severe conditions and they include high technology components such as manifolds, catalytic converters and particle filters. This evolution is a direct consequence of the worldwide effort to decrease automotive pollutant emissions in accordance with the new environmental regulations. This paper deals with the thermomechanical fatigue (TMF) of stainless steels at high temperature, specially behaviour and damage models, and with the recent progress in the development TMF fatigue design tools using FEA related to the design of stainless steel exhaust manifolds. A numerical method is proposed for the design and the lifetime prediction of stainless steel exhaust manifold under a thermal fatigue load. It includes the modeling of manifolds submitted to the thermal cycle reproduced from motor bench tests. The identification of the constitutive law, in particular the elasto-viscoplastic model, for a wide range of temperatures, provides the most realistic stress-strain response of the structure. Finally, a dedicated damage criterion is proposed on the basis of the maximal temperature and plastic strain amplitude reached during a thermal cycle (modified-Taira model). Identification of a more general damage model on the basis of TMF tests is also discussed.

J&L TYPE 409NI

Abstract J and L Type 409NI is a ferritic stainless steel with 11% Cr. It exhibits an excellent combination of good formability, economy, and resistance to oxidation and corrosion. It is typically used in automotive exhaust systems or where more forming is required. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming and joining. Filing Code: SS-902. Producer or source: J & L Specialty Steel Inc.

Precipitation sequence in niobium-alloyed ferritic stainless steel

Niobium is an important alloying element in the design of heat-resistant ferritic stainless steels for automotive exhaust systems. When in solid solution, it improves both the high temperature strength and the resistance to thermal fatigue. However, it also forms several kinds of precipitates during service. These reactions have been modelled, taking into account the multicomponent nature of the diffusion process and allowing for capillarity effects. It has been possible to estimate not only the volume fractions but also the particle sizes for Fe2Nb (Laves phase) and Fe3Nb3C (M6C) carbide in a 19Cr–0.8Nb steel, with good agreement against experimental data.

Simulation of road salt corrosion in austenitic alloys for automotive exhaust systems

Simulation of road salt corrosion in austenitic alloys for automotive exhaust systems

Acoustics of automotive catalytic converter assemblies

In an automotive exhaust system, the purpose of the catalytic converter is to reduce pollutant emissions. However, catalytic converters also affect the engine and exhaust system breathing characteristics; they increase backpressure, affect exhaust system acoustic characteristics, and contribute to exhaust manifold tuning. Thus, radiated sound models should include catalytic converters since they can affect both the source characteristics and the exhaust system acoustic behavior. A typical catalytic converter assembly employs a ceramic substrate to carry the catalytically active noble metals. The substrate has numerous parallel tubes and is mounted in a housing with swelling mat or wire mesh around its periphery. Seals at the ends of the substrate can be used to help force flow through the substrate and/or protect the mat material. Typically, catalytic converter studies only consider sound propagation in the small capillary tubes of the substrate. Investigations of the acoustic characteristics of entire catalytic converter assemblies (housing, substrate, seals, and mat) do not appear to be available. This work experimentally investigates the acoustic behavior of catalytic converter assemblies and the contributions of the separate components to sound attenuation. Experimental findings are interpreted with respect to available techniques for modeling sound propagation in ceramic substrates.