Class 4 (4th Engineer) SSEP 📅 Aug 2022

Exam Question

State the causes of scavenge fire in a two-stroke engine and explain how the possibility of such an occurrence can be reduced. If a scavenge fire does occur what action should be taken? Discuss the use of CO2 and dry powder for extinguishing such a fire and describe a fixed installation for applying one of these chemicals. (16)

Reference Answer

### **1. Causes of Scavenge Fire**
A scavenge fire occurs when the three elements of the fire triangle (Fuel, Oxygen, Heat) are present in sufficient quantities within the engine's scavenge air space. The accumulation of combustible materials, combined with a source of ignition under faulty running conditions, leads to their combustion.
* **Fuel Sources:**
* **Unburnt/Partially Burnt Fuel Oil:** Caused by defective fuel injectors (e.g., dribbling, incorrect spray pattern, wrong pressure setting), allowing fuel droplets to impinge on the cooler cylinder liner walls, where they are scraped down by piston rings into the under-piston space.

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