There are three primary causes of cylinder liner wear: friction, corrosion, and abrasion.

• Frictional Wear: This type of wear happens due to the sliding contact between the piston rings and the cylinder liner surface. It's influenced by the materials used, surface finish, lubrication, and engine operating parameters like speed and load.
• Corrosion Wear: This is a major cause of wear, especially in engines running on heavy fuel oil (HFO) with high sulfur content. During combustion, sulfur forms acidic compounds. If the lubricating oil fails to neutralize these acids, they react with the cylinder liner, causing corrosive wear. This is particularly prevalent in the lower part of the liner where temperatures drop and acid condensation (dew point) occurs.
• Abrasive Wear: This mechanical wear is caused by hard, foreign particles in the combustion space. These particles can come from fuel additives, incomplete combustion, or wear debris from the engine itself.

Detection of abnormal cylinder liner wear is typically done through regular measurements. The most common method involves using a micrometer or a laser-based tool to measure the cylinder bore diameter at various points along its length and in different directions (fore-aft and athwartships). These measurements are then compared to previous readings to determine the wear rate. Visual inspections during overhauls can also reveal signs like scuffing or cloverleafing.

Excessive cylinder liner wear has several detrimental effects on engine performance and longevity.

• Cloverleafing: This is a specific pattern of corrosive wear that appears as worn regions midway between the cylinder ports and extending upwards. It's caused by inadequate acid neutralization or poor lubrication. When the liner wears down in these areas, the piston rings lose their support and can collapse, leading to a loss of compression.
• Scuffing: This occurs when the lubricating oil film breaks down, causing localized welding and tearing between the piston rings and the liner. Hard particles can exacerbate this. As the liner and rings wear, the piston skirt may also contact the liner, leading to severe scuffing.
• Loss of Compression: As the cylinder liner wears, the gap between the piston rings and the liner increases, leading to a loss of cylinder pressure. This results in reduced engine power and efficiency, increased fuel consumption, and higher exhaust temperatures.
• Increased Oil Consumption: The worn liner and rings allow excessive cylinder lubricating oil to pass into the combustion chamber, increasing oil consumption.

Consequences:

• Excessive blow-by and loss of compression.
• High lube oil consumption.
• Risk of piston seizure and engine failure.
• Reduced service life of liner and piston rings.

• Adequate lubrication: Cylinder oil must be supplied as per engine demand.
• Correct TBN: Cylinder oil must have sufficient TBN value to neutralise sulphuric acid.
• Proper feed rate: Ensure liner surface is completely wetted and oil film is maintained under firing conditions.
• Avoid prolonged slow steaming: Prevents loss of oil film in long-stroke engines.
• Regular inspection and cleaning: Prevent choking of oil quills and scavenge spaces.
• Good fuel treatment: To minimise abrasive particles.

The cylinder liner wear rate is calculated by measuring the increase in the cylinder bore diameter over a specific period. The formula for calculating the wear rate is:

$$Wear\:rate=\frac{Increase\:in\:diameter\left(mm\right)}{Operating\:hours\:\left(1000\:hours\right)}$$

To perform this calculation, you need two sets of accurate measurements taken at different times:

1. Measure the internal diameter of the cylinder liner at several points and in two directions (fore-aft and athwartships) at a known number of operating hours.
2. Repeat the same measurements after a known period of operation (e.g., 1000 hours).
3. Calculate the difference between the two measurements to find the increase in diameter.
4. Divide this increase by the number of thousands of hours operated to get the wear rate, typically expressed in millimeters per 1000 hours. A common acceptable wear rate is between 0.05 to 0.1 mm/1000 hours.