Table of Contents
A crankcase explosion happens when oil mist, formed at a hotspot inside the crankcase, reaches its lower explosion limit and ignites. This page explains the primary explosion, the more violent secondary explosion, and how the crankcase is kept safe.
Crankcase Explosion
What Is a Crank Case explosion
For an explosion of this type to happen inside the crankcase, there must be a hotspot and a presence of oil mist with satisfying conditions. inside the crankcase, there are many moving metallic parts with direct links to each other. if by some fault a hot spot develops in such place and it reaches 200’c, the oil flashing on it will vapourize. this Vapour will circulate the crankcase to its coolest part where it will condensate into white oil mist. when the concentration of this mist reaches 50mgl-1 it is at its lowest explosion limit. under operating conditions, at a temperature at 850’c, this oil mist will ignite causing Primary Explosion
Secondary explosion
The secondary explosion is that explosion that might happen in the crankcase after the primary explosion. when the primary explosion happens all the flame and gas are vented due to high pressure inside. when the pressure drop below 1 bar(atmospheric pressure) this will create a vacuum causing air to flood inside the crankcase resulting in another flammable mixture to be developed resulting in a secondary explosion.
Safety of Crankcase
- Oil mist detector
- C/C oil must be of high flashpoint
- C/C door should be of robust construction
- Crankcase breather
- Smothering gas connection
- Crankcase relief valve