Experimental study on the effectiveness of monitoring techniques for main bearings of marine diesel engines

摘要

Failures of main bearings of marine diesel engines are one of the major causes of the loss of propulsion power, which in some cases could lead to serious crankcase explosion. To date periodic overhaul inspections are conducted as the class requirements to ensure the integrity of the main bearings of marine diesel engines. While the periodic overhaul inspections may have prevented some bearing failures, it is, however, costly and time-consuming and could even pose a slight risk of causing a major engine failure such as breakage of connecting rod bolts due to possible faulty reassembly. Therefore the need for more sophisticated preventive measures is increasing. As one possible answer to the demand, reliable bearing condition monitoring techniques are long expected. The symptom based bearing condition monitoring systems are expected to be much more efficient and effective by avoiding unnecessary overhauls and preventing any major bearing failures at an early stage, if the monitoring system is reliable. The usefulness of any bearing monitoring systems is very much dependent on whether the adopted technique has the capability to detect any indications of impending problems as early as possible to give sufficient time for the system to be activated for preventive actions such as slowdown or shutdown. In most cases, the direct cause for main bearing failure is the metal-to metal contact as a result of deteriorating lubrication regardless of specific root causes such as overloading, edge loading or no flow of lubrication oil and etc. An experiment aiming to evaluate the effectiveness of various techniques for a bearing condition monitoring system is conducted using a small journal bearing modelling main bearings of marine diesel engines. Temperature sensing, vibration sensing, measurement of the electrical resistance between the shaft and the bearing as well as monitoring of shaft center trace are investigated. The test is continued until the bearing white metal becomes melting. This paper presents the details of the experiment, the results and recommendation on which techniques should be preferentially used in the future bearing condition monitoring systems and on how to set the limits for activating the preventive actions such as alarms, automatic slow down or shutdown.