What is crankcase explosion
An explosion occurs in the crankcase. For an explosion to occur there must be in the crankcase a mixture of oil mist and air in the ratio that is within the range of flammability.
In addition there must be a source of high temperature energy sufficient to initiate combustion. Explosion occurred. This source is called hot spot.
Cause of crankcase explosion
The normal content of crankcase is air. In this air there are oil globules (droplets) formed by the mechanical atomization of the oil as it s sprayed from the edge of the bearing and other places and as it is thrown about and churned by the quickly moving parts.
If a hot spot occurs the oil particles in the neighborhood will evaporate. This evaporation may cause the formation of a quantity of white condense oil mist in the cooler regions. The continual generation of heat at hot spot vaporization may proceed a space until the ratio of vapour to air lies within the range of flammability.
If hot spot can provide the necessary heat for ignition of vapour, a primary explosion may occur.
What is hot spot, and why occur ?
It is an overheated part, sufficient to initiate combustion.
A hot spot occur due to –
Failure of lube oil to bearing, sprockets and similar parts.
Hot gas blowing past the pistons may provide spark sufficient to cause an explosion in the trunk type pistons engine. (Hot spot temp: 280-400 °C Above the L.O flash point)
How will you know whether hot spot or not ?
1. By hand feel to crankcase door
2. Abnormal noise in crankcase. Irregular running engine
3. Bearing L.O temperature increase
4. Alarm will operate when it reach at oil mist concentration 2.5 – 5% LEL
5. Smelling & appearance of the dense oil mist when open breather pipe, drain cock.
How to prevent the crankcase explosion ?
To minimize the formation of explosive mixture.
To prevent the formation of hot spot in the crankcase.
a. The bearing should be in correct running clearance.
b. Lubricating oil should be adequately supplied to bearing , chain with sprocket wheels and other running parts
c. The piston with rings and cylinders should be in safe working limits.
d. Good fitting and efficient locking of working parts.
Action after detecting hot spot
01. Inform C/E & Bridge
02. Reduce the engine speed to reduce the heat generation
03. Increase lubrication to the running surfaces
04. Keep clear off crankcase relief door to prevent personnel injury, keep fire extinguisher ready 7 open skylight.
05. Inform bridge, stop engine, open indicator cocks, engage turning gear and turn engine with lub oil circulation continuing to prevent engine seizure.
06. After about 30 minutes or more when the engine is sufficiently cooled down , stop lub oil pumps and open crankcase door.
07. Try to locate the hot spot by hand feeling over and by observation
08. If the hot spot is located, prevent reoccurrence by making permanent repair
09. Make through inspection of crankcase.
10. Pay particular attention to hot bearings, piston, bottom end bolts, guides and piston rod around stuffing box.
11. Start lube oil pumps and check for proper flow of oil from every lubrication point.
12. If everything is found normal, inform bridge, start the engine and gradually increase speed. Outside feel over sequence to be carried out for satisfactory operation.
Crankcase safety devices
1) Breather pipe with flame trip 2) Oil mist detector 3) Crankcase relief doors. 4) Bearing temperature sensor 6) L.O return temperature sensor 7) Routine test on used L.O for viscosity, flash point and contamination.
An explosion occurs in the crankcase. For an explosion to occur there must be in the crankcase a mixture of oil mist and air in the ratio that is within the range of flammability.
In addition there must be a source of high temperature energy sufficient to initiate combustion. Explosion occurred. This source is called hot spot.
Cause of crankcase explosion
The normal content of crankcase is air. In this air there are oil globules (droplets) formed by the mechanical atomization of the oil as it s sprayed from the edge of the bearing and other places and as it is thrown about and churned by the quickly moving parts.
If a hot spot occurs the oil particles in the neighborhood will evaporate. This evaporation may cause the formation of a quantity of white condense oil mist in the cooler regions. The continual generation of heat at hot spot vaporization may proceed a space until the ratio of vapour to air lies within the range of flammability.
If hot spot can provide the necessary heat for ignition of vapour, a primary explosion may occur.
What is hot spot, and why occur ?
It is an overheated part, sufficient to initiate combustion.
A hot spot occur due to –
Failure of lube oil to bearing, sprockets and similar parts.
Hot gas blowing past the pistons may provide spark sufficient to cause an explosion in the trunk type pistons engine. (Hot spot temp: 280-400 °C Above the L.O flash point)
How will you know whether hot spot or not ?
1. By hand feel to crankcase door
2. Abnormal noise in crankcase. Irregular running engine
3. Bearing L.O temperature increase
4. Alarm will operate when it reach at oil mist concentration 2.5 – 5% LEL
5. Smelling & appearance of the dense oil mist when open breather pipe, drain cock.
How to prevent the crankcase explosion ?
To minimize the formation of explosive mixture.
To prevent the formation of hot spot in the crankcase.
a. The bearing should be in correct running clearance.
b. Lubricating oil should be adequately supplied to bearing , chain with sprocket wheels and other running parts
c. The piston with rings and cylinders should be in safe working limits.
d. Good fitting and efficient locking of working parts.
Action after detecting hot spot
01. Inform C/E & Bridge
02. Reduce the engine speed to reduce the heat generation
03. Increase lubrication to the running surfaces
04. Keep clear off crankcase relief door to prevent personnel injury, keep fire extinguisher ready 7 open skylight.
05. Inform bridge, stop engine, open indicator cocks, engage turning gear and turn engine with lub oil circulation continuing to prevent engine seizure.
06. After about 30 minutes or more when the engine is sufficiently cooled down , stop lub oil pumps and open crankcase door.
07. Try to locate the hot spot by hand feeling over and by observation
08. If the hot spot is located, prevent reoccurrence by making permanent repair
09. Make through inspection of crankcase.
10. Pay particular attention to hot bearings, piston, bottom end bolts, guides and piston rod around stuffing box.
11. Start lube oil pumps and check for proper flow of oil from every lubrication point.
12. If everything is found normal, inform bridge, start the engine and gradually increase speed. Outside feel over sequence to be carried out for satisfactory operation.
Crankcase safety devices
1) Breather pipe with flame trip 2) Oil mist detector 3) Crankcase relief doors. 4) Bearing temperature sensor 6) L.O return temperature sensor 7) Routine test on used L.O for viscosity, flash point and contamination.
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