Exam Question
With reference to medium speed trunk piston engines:
(a) Explain the purpose of an anti-polishing ring (5)
(b) Describe how effective piston cooling is provided (5)
(c) Where is the thrust bearing fitted and why? (6)
Class 4 (4th Engineer)
MEKM
📅 Apr 2024
Reference Answer
### (a) Explain the purpose of an anti-polishing ring (5 marks)
The primary purpose of an anti-polishing ring, also known as a carbon cutting ring or fire ring, is to prevent 'bore polishing' or 'liner glazing' in medium-speed trunk piston engines. This ensures long-term engine reliability, maintains performance, and controls lubricating oil consumption.
**1. Mechanism of Bore Polishing:**
* During combustion, especially under varying loads or with certain fuel types, hard, abrasive carbon deposits can accumulate on the top land of the piston (the area between the top piston ring and the piston crown).
The primary purpose of an anti-polishing ring, also known as a carbon cutting ring or fire ring, is to prevent 'bore polishing' or 'liner glazing' in medium-speed trunk piston engines. This ensures long-term engine reliability, maintains performance, and controls lubricating oil consumption.
**1. Mechanism of Bore Polishing:**
* During combustion, especially under varying loads or with certain fuel types, hard, abrasive carbon deposits can accumulate on the top land of the piston (the area between the top piston ring and the piston crown).
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