CRANKCASE EXPLOSION PDF DOWNLOAD!
Crankcase explosions and secondary explosions causes and effects in slow speed two stroke crosshead diesel engines and four stroke trunk piston marine. Crankcase explosions are also the result of high operating temperatures of the engine. The main cause of crankcase explosions are the development of hot spots at various places in the crankcase. Due to the reciprocating motion of the piston the lubricating oil in the crankcase is splashed in the air. If a large amount of oil mist has developed before ignition, the burning can cause a tremendous rise of pressure in the Crankcase (explosion).
|Author:||Brook Pfannerstill III|
|Published:||11 October 2014|
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Having learnt about one class of fire danger on a ship namely scavenge fireswe will now talk about another possibility of fire rather explosion of the engine and this could occur within the crankcase of the marine diesel engine. Crankcase explosions are also the result of high operating temperatures of the engine.
The main cause of crankcase explosions crankcase explosion the development of hot spots at various places in the crankcase. Due to the reciprocating motion of the piston the lubricating oil in the crankcase is splashed in the air.
Now it is necessary that the flash point of the lubricating oil is maintained at around degree Celsius. If this is not done then there are crankcase explosion chances for the lubricating oil to catch fire.
Hot spots are created in the crankcase as a result of high temperature due to the reciprocating movement of the piston, increase in bearing temperatures, sparks entering the crankcase explosion due to leaky piston rings or piston blow past, fires in the adjacent scavenge trunks.
Now, when these hot spots come in contact with the oil in the crankcase, the oil gets vaporised. When these vaporised particles travel to the cooler part of the crankcase they get condensed into a white mist which has oil particles properly dispensed in it.
The process that takes place is some what similar to atomization. This white mist when again travels to the hot spot area, can easily catch fire, which might also lead to an explosion.
The fire or the explosion create immense pressure inside the crankcase and if this pressure crosses the permissible limit, crankcase explosion takes place. Following the venting of the explosion through the relief valves, there is a drop in crankcase pressure to below atmospheric pressure.
This crankcase explosion cause air to enter the crankcase resulting in another flammable mixture to be developed resulting in a crankcase explosion explosion to occur.
The secondary explosion is more violent and can result in crankcase doors being crankcase explosion off the engine, and fires starting in the crankcase explosion room.
If the relief valves do not reseal after lifting, or if they do not lift at all in the primary explosion due to lack of maintenance etcthen door s may be blown off in the primary explosion, giving a ready path for the ingress of air, which will make a secondary explosion more likely.
Air can also be sucked in via the crankcase vent, although rules state that this must be as small as practicable and new installations must have a non return valve fitted.
Crankcase Explosions in Marine Diesel Engines
If a primary explosion occurs, the pressure wave may send a large amount of oil mist out into the engine room. Although the flame arrestors on the relief crankcase explosion should prevent ignition of this oil mist by the flame front, the mist will be sucked up towards the turbocharger where it may be ignited by an unlagged hot exhaust manifold.
Once the engine is cooled, stop main Crankcase explosion pump, the crankcase should be opened and ventilated.
Inspect all bearings and running surfaces for any hot spots. Inspect the bottom of crankcase for any for any signs of bearing metal. Investigate the cause for the hot spot and engines to be started only after the fault is rectified.
Such a device will detect the presence of oil mist at a concentration well below the level at which explosions may occur, giving a warning in time to take necessary action. The detector consists of two parallel tubes of equal size, each having a photoelectric cell at one end, which generates an electric current directly proportional to the intensity of light.
Two identical beams of light from a common lamp are reflected by mirrors to crankcase explosion along the tubes onto the cells which are then in electric balance.
One tube is sealed to contain clean air and is termed the reference tube. The other, the measuring tube, has connections through which samples of the crankcase vapour are drawn by an crankcase explosion extractor fan.