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Crankcase oil mist detector of a marine diesel engine

Crankcase oil mist detector of a marine diesel engine 
Consequence of oil mist in the crankcase

The diesel engine is a type of internal combustion engine which ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber. In common with all internal combustion engines the diesel engine operates with a fixed sequence of events, which may be achieved either in four strokes or two, a stroke being the travel of the piston between its extreme points. Each stroke is accomplished in half a revolution of the crankshaft.

The presence of an oil mist in the crankcase is the result of oil vaporisation caused by a hot spot. Explosive conditions can result if a build up of oil mist is allowed. The oil mist detector uses photoelectric cells to measure small increases in oil mist density. A motor driven fan continuously draws samples of crankcase oil mist through a measuring tube. An increased meter reading and alarm will result if any crankcase sample contains excessive mist when compared to either clean air or the other crankcase compartments. 

The rotary valve which draws the sample then stops to indicate the suspect crankcase. The comparator model tests one crankcase mist sample against all the others and once a cycle against clean air. The level model tests each crankcase in turn against a reference tube sealed with clean air. The comparator model is used for crosshead type engines and the level model for trunk piston engines.


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