Exam Question

### (a) Sequence of a Crankcase Explosion
A crankcase explosion is a two-stage event initiated by the presence of a hotspot and the formation of a flammable oil mist within the engine's crankcase. The sequence, based on the provided reference, is as follows:
1. **Hotspot Formation**: An abnormal operating condition, such as a failing bearing, piston scuffing, or a piston blow-by, creates a localised area of very high temperature (a 'hotspot') within the enclosed crankcase.
2. **Oil Vaporization & Mist Formation**: Lubricating oil, which is continuously splashed and circulated within the crankcase, comes into contact with this hotspot. The oil rapidly vaporizes. This hot oil vapour then circulates to cooler regions of the crankcase, where it condenses into a fine, white, and highly flammable aerosol or 'oil mist'. For ignition, this mist must be within a specific flammable range, typically with particle sizes of 0.5 to 5 microns and a density of 30 to 50 mg/L.