For the purpose of establishing the monitoring technique for wear condition of liner/rings in large marine engine of 2-stroke cycle, the method using vibration signals of cylinder liner was examined, and for the first step preliminary test was carried out in shop trial of engine. Measurements made it clear that vibration signals include several kinds of vibrations induced by closing of exhaust valve, flow of exhaust gas, combustion, opening/closing of F. O. needle valve, contact of piston rings with non-continuous parts of cylinder liner besides friction between liner and rings. In addition, the time-frequency analysis revealed that rubbing vibration appeared distinctively at the crank angles which maximize piston speed.
To examine the changes of rubbing vibrations of liner/rings, measurements were made in the period of running-in of the engine and after 20 hour's running. As a results, in the spectrum of rubbing vibration measured at cylinder liner, the significant decrease in vibration responses of high frequencies was observed with the change of rubbing condition, which occured simultaneously with a lapse of time. To the contrary, if the abnormal wear such as scuffing happens in ship's service, then vibration responses of high frequencies are expected to increase. For example, in the case of stick of piston rings, the abnormality is possibly diagnosed by the increase of vibration responses at the crank angles which maximize piston speed.
In addition, according to the results of damage investigation, the wear of a cylinder liner is prominent usually on the upper side as shown in Fig. 12. Hence, for the diagnosis of the wear condition in the vicinity of this position, it may be required to develop the specific method for signal processing which enables the analysis of rubbing vibration in combustion process.
The results of preliminay test indicated a prospect of vibration monitoring for detecting abnormal wear. In this test, however, actual wear of liner/rings has not been measured. For further examination on the effectiveness of vibration monitoring, it is necessary to investigate the relationship between vibrations and actual wear conditions by the monitoring of full-scale ships.
Fig. 12 Wear of cylinder liner
5. References
[I] S. Mitsutake, S. Ono, K. Maekawa, K. Inaba, "Evaluation Method of Lubrication by Oil Sampling from Liner Wall for Marine Diesel Engine," Journal of the M. E. S. J., Vol. 25, No. l (1990), p. 24
[2] R. Kimura, W. Terashima, N. Nakai, T. Yamada, S. Takeda, "Diagnostic Method for 2-Stroke Cycle Diesel Engine by Measurement of Vibration on Cylinder-Jacket- Observation of Change in Normal Vibration Pattern -," Journal of the M. E. S. J., Vol. 33, No. 10 (1998), p.738
[3] T. Yumiba, T. Kawano, Y. Inui, H. Kondoh, "Detecting Measurement of Needle Valve Lift Behaviour in Diesel Fuel Injector," Journal of M. E. S. J., Vol. 34, No. 3 (1999), p. 204
[4] M. Nagai, S. Hirano, T. Kawasaki, H. Akane, S. Ogino, "Research in Early Detection of Cylinder Liner Scuffing of Piston Engine," the Proceeding of the I. S. M. E. Tokyo' 78 (1978), p. 325
