Class 4 (4th Engineer) MEKM 📅 Jul 2024

Exam Question

Make a diagrammatic sketch of a jacket cooling water system as applied to a two stroke main engine. Indicate the temperatures and pressures in the system. Describe in particular the flow of water from entry to the engine to outlet from the engine and sketch the more important joints in the system. (16)

Reference Answer

### **1. Jacket Cooling Water System: Objective and Principles**
The primary objective of the Main Engine Jacket Cooling Water (JCW) system is to maintain the optimal operating temperature of the cylinder liners, cylinder heads, and exhaust valve cages. This is critical for three main reasons:
* **Maintaining Lubricating Oil Properties:** Ensures the cylinder lubricating oil film on the liner surface has the correct viscosity for effective lubrication and sealing.
* **Preventing Cold Corrosion:** Keeps the liner surface temperature above the dew point of sulfuric acid (H₂SO₄), which forms from the sulfur in the fuel and water vapor from combustion. Failure to do so results in rapid, corrosive wear of the liner and piston rings.

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