11.Types of liner wear

Types of wear in cylinder liner:

1) Friction.

2) Corrosion.

3) Abrasion

4) Scuffing or Adhesion

5) Clover leafing

6) Micro-seizure

Frictional Wear:

Frictional wear takes place between the sliding surfaces between the cylinder liner and piston rings, and can somewhat controlled by adequate cylinder lubrication, but is also affected by:

• Materials of construction
• Surface finish
• Choice of cylinder lubrication
• Piston speed
• Engine load

Corrosion wear:

Corrosion occurs mainly in engines burning heavy fuels, particularly those with high sulphur content. It is caused by the acid formed during combustion, and this may be neutralized by the use of high alkaline cylinder oil. The production of acids will be more if sulfur content is more, leading to the formation of sulphuric acid. Sulphuric acid is formed due to absorption of the condensate or moisture present inside the combustion space with sulphur. This can be prevented by maintaining jacket temperature above the corresponding dew point

Clover leafing

Clover leafing is a form of wear on cylinder liners due to high sulphur content in the fuel oil. Clover leafing takes place between each pair of lubricating quills.

Cylinder oil is injected with maximum alkalinity from the quills and as it passes down, the alkalinity reduces and acidity increases. This results in acidic etching on the liner surface in the form of leaf scales along the sides of lubricating quills.

Sulphuric acid corrosion is found more in the lower part of the liner as the temperature of jacket water is very low. Corrosion due to sulphur will be high due to the presence of water in fuel and condensate in the air. This wear is generally seen between the quills. The wear near the quills enlarge and gives a characteristic of the clover leaf shape to the wear pattern. This phenomenon is called clover leafing.

Abrasion wear:

Abrasion is caused from metal particles, both from the splintering of piston rings and fuel oil, ash being present in some heavy fuels, along with catalytic fines that will act as an abrasive. These hard particles act as an abrasive material between the piston rings and the cylinder liner causing liner abrasive wear.

Adhesion/Scuffing wear or Micro seizure:

Adhesion or scuffing or micro seizure is a form of local welding between particles of the piston rings and liner due to failure of lubrication oil film between piston rings and liner, insufficient supply or incorrect distribution of oil, and piston blow-by.

How Cylinder Liner Wear is measured:

• The cylinder liner wear is measured by a standard template, which consists of strategically positioned holes, wherein the micrometer is placed and the readings are taken.
• The readings are taken for both port starboard and forward aft positions. This is done because the wear is not same in both direction and the ovality is checked.
• The wear rate will be different in the liner. The wear will be more in the top one third parts as combustion takes place there and temperatures and pressure is also very high at the top.
• An approximate normal wear rate of the liner is about 0.1 mm per 1000 running hours.
• The wear rate increases if the engine is overloaded. Generally the liner has to be replaced when the wear is about 0.6-0.8% of the bore diameter or as per the manufacturer’s recommendation.