Class 4 (4th Engineer) MEKM 📅 Apr 2023

Exam Question

With reference to lubricating oil

(a) Explain why oil employed in the crankcase of a trunk piston engine differs in its properties from that employed in the crankcase of a crosshead engine; (6)

(b) List FOUR effects of bacterial attack on crankcase oil; (6)

Reference Answer

### (a) Differences in Lubricating Oil Properties: Trunk vs. Crosshead Engines (6 Marks)
The fundamental difference in lubricating oil requirements between trunk piston and crosshead engines stems from their basic design. A crosshead engine features a diaphragm and piston rod stuffing box, which effectively isolates the crankcase (containing the 'system oil') from the combustion space. In contrast, a trunk piston engine has no such separation, and the crankcase oil is directly exposed to the underside of the piston and combustion blow-by.
**Trunk Piston Engine Crankcase Oil:**
* **Function:** Serves a dual purpose: lubricating the bearings (main, crankpin, gudgeon pin) and cooling the piston. It is also inevitably exposed to combustion by-products.

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