CoC Oral Exam Preparation (Part- I) – Machinery

Source: MAN Diesel (MAN-B&W-K98MC)

Cylinder liner wears:
1) Normal frictional wear: Due to metal to metal contact with high surface asperities under
marginal lubrication condition.
2) Abrasive wear: Due to presence of hard foreign particles from fuel, LO, and air.
3) Corrosive wear:Due to H₂SO₄ acid attack owing to sulphur within fuel. Only 0.1% of sulphur content causes corrosive wear, like hot and cold corrosion, and the rest carried away by exhaust gas. Sulphuric acid dew point = 120΄C to 160΄C.

Hot corrosion occurs at 460 – 570΄C.
Due to HCl acid attack, because of salts in air, charge air cooler leakage,
sea water in fuel and LO.

Other related causes:
1. Unsuitable liner material.
2. Incorrect ring clearance.
3. Misalignment of piston and liner.
4. Insufficient LO or improper arrangement of cylinder lubrication.
5. Cylinder oil having too low viscosity or alkalinity.
6. Cylinder oil containing abrasive particles.
7. Using of low sulphur fuel, in conjunction with high TBN cylinder oil.
8. Improper grade of fuel, and improper combustion.
9. Improper running-in, without high cylinder oil feed rate.
10. Overloading of engine.
11. Too low scavenge air temperature, leading to dew point corrosion.
Read more