Detecting crankcase explosion

IACS Rules state that for an unmanned engine room the main engine must be fitted with EITHER an oil mist detector of an approved type OR main bearing temperature monitors.

A manned engine room does not require any crankcase monitoring equipment to be fitted.

Bearing temperature monitors can be fitted not only to the main bearings, but also to the bottom end bearing where the temperature is transmitted to a static pick up device from the revolving transmitter once per revolution. Some schools of thought claim that bearing temperature detection is not reliable enough using only one probe per bearing, and that the temperature should be monitored at several points around the bearing. However, although the majority of crankcase explosions are caused by bearing failure, there are other sources, esp. piston/ liner overheating in trunk piston engines, and monitoring of this should also be considered.

MAN B&W, as well as using oil mist detectors and main bearing temperature monitors, also offer a system on their medium speed 32/40 to 58/64 engines known as splash oil monitoring. The company's service letter states

These facilities ( Bearing temperature monitors and OMD ) cannot prevent damage, but they can considerably restrict its extent and consequences. To do this, they must respond rapidly and early to incipient damage, so as to prevent expensive components being affected to such an extent that complicated repairs or complete replacement become necessary. Experience shows that this last requirement is not always met satisfactorily. To eliminate this uncertainty, we have developed a monitoring system that reacts spontaneously and functions reliably - the "Splash Oil Monitoring System".

The system works by constantly monitoring to within very close limits the temperature of the oil being splashed about in each crankthrow space, and comparing it with the temperatures in the other spaces. It will alarm when either maximum value has been exceeded or when a maximum permissible deviation has been exceeded, generating an engine stop signal if the permissible operating values have been exceeded.

Intensive experiments have shown that the "Splash Oil Monitoring System" responds even to a slight increase in the local lube-oil temperature, due to bearing damage or seizures. This ensures an exceptional level of protection against malfunctions, and proven prevention of severe and expensive damage, by stopping the engine immediately.

Of course an engineer may be alerted to a potentially dangerous situation when on watch that all is not well using his senses of sight hearing and smell.

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