Crankcase explosion occurs due to the ignition of oil mist. The temperature inside the crankcase is quite high. Certain parts of the crankcase will be higher still. These are called hotspots. For example, certain bearings may have higher temperature. Certain regions of the piston can be hotter due to some abnormality. Leaks can occur in the combustion chamber (crankcase blowby). This can contain sparks which can ignite the oil mist.
Oil mist is formed when oil reaches the hot areas of the crankcase and gets vapourised. As the vapour drifts in the crankcase, it can get condensed into a white mist once it reaches the relatively cooler areas. This white mist is highly atomised. When this mist comes in contact with a hot surface, it can ignite causing the explosion.
Preventing Crankcase explosions
- Monitor the oil mist levels in large engines continually using oil mist detectors.
- Monitor the temperature of the engine and connecting rod bearings.
- Do not operate the engine above its rated load.
- Perform specified maintenance regularly
Some of the indications of an explosion are
- Change in the engine speed.
- Unusual Noise.
- Sudden increase in the temperature of the exhaust.
- Increase in the load.
- Smell of the oil mist in the engine room.
When any of the indications are noticed,
- the fuel and air supply should be cut off.
- the engine should be stopped and allowed to cool.
- Do not open the crankcase doors until the engine has cooled.