Exam Question

Crankcase oil mist detectors are critical safety devices onboard large internal combustion engines, particularly main propulsion and auxiliary engines. Their primary function, mandated by international regulations such as SOLAS Chapter II-1, Regulation 37, is to detect the formation of oil mist within the crankcase. Oil mist formation is a strong indicator of localized overheating (hot spots) caused by issues like bearing failure, piston seizure, or inadequate lubrication. Early detection of this mist is paramount to prevent a build-up of flammable vapor, which could lead to a highly destructive crankcase explosion.
### Sketch and Description of Operation
**Operational Principle (Photo-electric Absorption Type)**
The most common type of oil mist detector operates on the principle of photo-electric light absorption. When oil mist is present, it absorbs and scatters light, thereby reducing the intensity of a light beam passing through it. The detector continuously samples the atmosphere from individual crankcase compartments, comparing its optical density against a clear air reference.