Low-cycle Thermal Fatigue and High-cycle Vibration Fatigue Life Estimation of a Diesel Engine Exhaust Manifold☆

The muffler is the main part of the Automobile Exhaust System, consisting of fibrous and porous materials to absorb noise and vibrations. The exhaust gas mass coming from the engine can produce resonance, which may be the source of fatigue failure in the exhaust pipe due to the presence of continuous resonance. The modes on the muffler should be located away from the engine’s operating frequencies in order to minimise the resonance. The objective of this paper is to determine the frequencies that appear at the modes, which have the more adverse effect during the operation of the automobile. An impact test has been conducted by applying the force using a hard head hammer, and data generated have been used for plotting a graph of the transfer functions using MATLAB. Six points have been selected, namely 1, 2, 3, 4, 7, and 11 on the muffler for the impact test. The collected data from theses six points have been analysed for the addition of damping. Results suggests that increasing the mass increases the damping and lowers the modes of the transfer function. Further research will identify higher strength materials that can withstand the higher gas temperatures as well as the corrosion and erosion by the gas emitted from the engine.

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Optimal automobile muffler vibration and noise analysis

A Systems Approach to Automotive Exhaust System Development

Die Entwicklung moderner Fahrzeuge hat zunehmend hohere Anspruche zu erfullen. Zum einen werden die Entwicklungszeiten immer kurzer, zum anderen die Anforderungen an die Bauteile komplexer. Dieser Trend trifft auch auf die Entwicklung von Abgasanlagen zu. Hier erschwert zusatzlich die groβe Anzahl von Varianten das Ziel, die Entwicklungszeiten zu verkurzen. Fur jede Motor-Fahrzeug-Kombination muss die Abgasanlage neu ausgelegt werden. Am Lehrstuhl fur Verbrennungskraftmaschinen an der RWTH Aachen wurden in Zusammenarbeit mit der FEV Motorentechnik neue Rechenverfahren entwickelt, um Zeit und Kosten in der Abgasanlagenentwicklung zu sparen.

Mechanisch und akustisch optimierte Abgasanlagen - Neue Entwicklungsmethoden mittels CAE

To facilitate overall lay-out optimisation inexpensive dynamics simulation of automobile exhaust systems is desired. Identification of possible non-linearity as well as finding simplified component models is then important. A flexible joint is used between the manifold and the catalyst to allow for the motion of the engine and to reduce the transmission of vibrations to the rest of the exhaust system. This joint is significantly non-linear due to internal friction, which makes some kind of non-linear analysis necessary for the complete exhaust system. To investigate the significance of non-linearity and internal vibrations of other components a theoretical and experimental modal analysis of the part of a typical exhaust system that is downstream the flexible joint is performed. It is shown that non-linearity in this part is negligible. It is also shown that shell vibrations of the catalyst and mufflers as well as ovalling of the pipes are negligible in the frequency interval of interest. The results implies, for further dynamics studies, that the complete system could be idealised into a linear sub-system that is excited via the non-linear flexible joint, that the pipes could be modelled with beam elements and that the other components within the linear sub-system could also be modelled in a simplified way. Such simplified component models are suggested. The agreement between theoretical and experimental results is very good, which indicates the validity of the simplified modelling.

http://www.wseas.us/e-library/conferences/skiathos2002/papers/447-192.pdf

Significance of non-linearity and component-internal vibrations in an exhaust system

The problem of mechanical vibration for an automotive exhaust system is investigated using the modal analysis method. Using a finite–element mathematical model it is possible to calculate the vibration eigenfrequencies and the medal shape. In assembling the mathematical model the major points are the correct evaluation of the excitation sources of the actual temperature and of the effects of the pipe bends. Moreover, through dynamical analysis the real displacement and the related stresses can be determined. Some calculated results are reported in order to illustrate the most specific aspects of the proposed method.

S. Leonti

Papers

Modal analysis in the design of an automotive exhaust pipe