Question - Describe The Events Leading To A Crankcase Explosion On A Main Engine ?
Answer -
The atmosphere inside a crankcase is stable and will not allow combustion or an explosion to occur as there is no ignition or fuel source.
Hence the first event is the production of an explosive mixture. This will occur when the lube oil in the crankcase is heated by a “hot spot” and lube oil coming into contact with this will be evaporated. The evaporated oil then rises within the crankcase, and then condenses in a cooler part of the crankcase. The resultant white mist is within the explosive range, and is thus flammable.
The second event is the ignition of this white mist by either the same or another hot spot within the crankcase. When the oil mist is ignited, a crankcase explosion will occur, which will raise the pressure within the crankcase.