Class 4 (4th Engineer) SSEP 📅 Jun 2025

Exam Question

(a) State the causes of scavenge fire in a two-stroke engine and explain how the possibility of such an occurrence can be reduced. (10)

(b) If a Scavenge fire does occur, what action should be taken?

Discuss the uses of CO2 and dry powder for extinguishing such a fire and describe a fixed installation for applying one of these substances. (10)

Reference Answer

### (a) Causes of Scavenge Fire and Prevention
A scavenge fire is the ignition of combustible materials that have accumulated in the scavenge air spaces of a two-stroke crosshead diesel engine. The fuel for the fire consists of a mixture of carbonized cylinder lubricating oil, unburnt fuel oil, and partial products of combustion deposited as a sludge.
#### Causes of Scavenge Fire
The conditions for a fire require fuel, oxygen (abundantly supplied by the scavenge air), and a source of heat or ignition. The primary causes relate to engine malfunctions that either increase the accumulation of fuel or provide an ignition source:

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