Exam Question

The crankcase oil mist detector is a critical safety device fitted to internal combustion engines to prevent catastrophic crankcase explosions. Its primary function is to continuously monitor the atmosphere within the crankcase for the presence of oil mist, which, when combined with air in certain concentrations, can become highly combustible, especially in the presence of a hot spot.
### Sketch and Description of Operation
#### A. Principle of Operation
Oil mist in a crankcase typically forms when lubricating oil comes into contact with an excessively hot surface (a 'hot spot') within the crankcase, causing the oil to vaporize and then condense into fine droplets. Such hot spots can arise from failing bearings, overheating piston skirts, or defective oil-cooled components. The oil mist, when mixed with air, forms a flammable mixture within specific explosive limits (typically 0.5% to 5% by volume). A crankcase oil mist detector operates on the principle of light scattering or light obscuration to detect these fine oil droplets.