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Cylinder liner Material
1) The liner can be manufactured using a superior material to the cylinder block. While the cylinder block is made from a grey cast iron.
2) the liner is manufactured from a cast iron alloyed with chromium, vanadium and molybdenum. (cast iron contains graphite, a lubricant. The alloying elements help resist corrosion and improve the wear resistance at high temperatures.)
Does high peak pressure affect the liner
For high peak pressure, the liner must be made thicker at the top to accommodate the higher hoop stresses, and prevent cracking of the material.
If the thickness of the material is increased, then it stands to reason that the working surface of the liner is going to increase in temperature because the cooling water is now further away. Increased surface temperature means that the material strength is reduced, and the oil film burnt away, resulting in excessive wear and increased thermal stressing.
the solution is to bring the cooling water closer to the liner wall, and one method of doing this without compromising the strength of the liner is to use tangential bore cooling.
Holes are bored from the underside of the flange formed by the increase in liner diameter. The holes are bored upwards and at an angle so that they approach the internal surface of the liner at a tangent. Holes are then bored radially around the top of the liner so that they join with the tangentially bored holes.
Factors that contribute to liner wear
The main factors that contribute to liner wear can be one or more of the following:
- Friction
– 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
Other factors that can either increase or reduce the rate of wear include the cylinder working pressure, temperature, and maintenance of piston rings, combustion efficiency, and any contamination from air or fuel.
- Abrasion
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.
- Corrosion
Corrosion occurs mainly in engines burning heavy fuels, particularly those with a 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.
Sulphuric acid corrosion may be caused in the lower part of the liner if the jacket cooling water temperature is too low. This may allow vapors present after combustion to condense. The moisture formed absorbs any sulphur present to form sulphuric acid. This can be prevented by maintaining jacket temperature above the corresponding dew point.
Water vapor will be present from the combustion of hydrogen together with any water present in the fuel. It may be increased if water passes from the charged air cooler.
- Adhesion
Adhesion or scuffing is a form of local welding between particles of the piston rings and liner rubbing surface, resulting in a rapid wear.
This is exacerbated if the lubrication oil film between piston rings and liner is reduced due to excessive temperature, insufficient supply or incorrect distribution of oil, and piston blow-by.
Engines operating on some low sulphur grades of fuel oil may also be prone to scuffing damage.
- 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.
- Micro-seizure
Appearance: micro seizure resembles abrasive wear since the characteristic marks run axially on the liner surface.
Causes: this is due to irregularities in the liner and piston rings coming into contact during operation. They occur as a result of breakdown of lubrication due to an insufficient quantity of lube oil, insufficient viscosity, or excessive loading.
Effects: this results in instantaneous seizure and tearing takes place on the liner surface and on the piston rings surface.
Micro-seizure may not be destructive; indeed it often occurs during a running in period. However, it does become destructive if it is allowed to continue.
How Can Cylinder Liner Wear be Minimised?
Cylinder wear can be minimised by carrying out the following steps:
1) By avoiding any ingress of water inside the liner by properly treating the fuel oil.
2) By maintaining the correct grade of cylinder oil.
3) By supplying correct feed rate with load change dependent lubrication system
4) By avoiding ingress of moisture from the charge air.
5) By maintaining proper jacket water temperature.
6) By supplying good quality purified fuel oil inside the combustion chamber
7) By properly maintaining the fuel injector and fuel system for correct atomization and injection of fuel inside the chamber
8) By doing regular scavenge port inspection for early detection of piston ring wear and liner surface wear9) By doing proper running in of new liner as prescribed by the engine maker
10) By honing the wear liner surface to retain oil in the small pocket avoiding scuffing and other problemsHow to Measure Cylinder Liner Bore Wear?
Cylinder liner ovality has to be gauged at regular intervals as specified in the maintenance manual. The records of gauging are kept for each cylinder and wear rate is calculated.
Procedure:
- After engine is shut down and cooled, open the cylinder head and remove the piston
2. Cover the stuffing box hole to avoid debris falling inside crankcase
3. Remove the liner ring and clean the carbon deposits from top surface of the liner
4. Insert a ladder and carefully inspect the liner surface before gauging
5. 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
6. 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 cylinder liner ovality is checked.
A liner diameter measuring instrument ( a type of micrometer) along with a standard template rod is used to measure liner dimensions. Generally while taking the measurement the temperature of the liner and micrometer should be kept at the same temperature.
If the temperature exceeds than that of the liner or vice versa then the readings have to be corrected by multiplying the value with the correction factor and deducting the value obtained from the reading taken. The reading obtained at the end will be the correct reading.
The wear rate will be different inside the liner. The wear will be more in the top one-third part as combustion takes place there and temperatures and pressure are also very high at the top.
How to Calculate Cylinder Liner Wear Rate and Ovality?
For calculating the cylinder liner wear rate, the current reading is compared with the last taken reading.
Suppose, for a liner of 800 mm bore, the position 1 latest reading (for P-S) comes out to be 841.81. The last recorded reading for position 1 (P-S) is 841.45. Hence the wear for this position in P-S direction is 0.36.
Now the position 1 latest reading (for F-A) comes out to be 841.78. The last recorded reading for position 1 (F-A) is 841.45. Hence the wear for this position in F-A direction is 0.33.
To calculate the ovality, the F-A wear rate is deducted from P-S wear rate, which will be 0.03.
Similarly, cylinder liner wear rate and cylinder liner ovality for all positions are calculated in a similar manner.
Liner surface: It looks like a fine finish, but on a microscopic scale it is undulating to allow for rapid running-in and to provide a key for L.O which carries away metal particles from running-in process.
The process of honing rectifies the shape of the liner, returning it to circular shape, it also removes scuffed areas and restores the surface cross pattern.
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