Cylinder liners are critical components of marine diesel engines, playing a crucial role in the engine’s performance and longevity. These liners are designed to provide a durable and reliable surface for the engine’s pistons to move against, withstand high temperatures and pressures, and resist corrosion and wear.
In this blog post, we’ll explore the importance of cylinder liners in marine diesel engines and how they work. We’ll discuss different types of cylinder liners, such as wet and dry liners, and their advantages and disadvantages.
We’ll also cover common issues that can arise with cylinder liners, such as scuffing, wear, and cracking, and how to diagnose and address these issues. We’ll provide tips on how to maintain cylinder liners, such as proper lubrication, coolant, and cleanliness, to extend their lifespan and ensure optimal engine performance.
Whether you’re a marine diesel engine mechanic or a vessel owner, this post will provide you with valuable insights into cylinder liners, their function, and how to maintain them for optimal engine performance and longevity.
Cylinder Liners of Diesel Engines
In this Post we will discuss the following on Cylinder Liners of Diesel Engines.
- Cylinder liner function,
- Properties of Cylinder liner material,
- Types of cylinder liners,
- Cylinder liner manufacturing process,
- Difference between cylinder liner and sleeve.
The post will be useful for the readers to understand the basics of Cylinder liner.
Functions of Cylinder Liner
A Liner is cylindrical part located in cylinder block of an engine. Cylinder liner forms the part of combustion chamber in which combustion of fuel occurs. The piston in cylindrical shape reciprocates in the space created by cylinder liner.
The cylinder liner is manufactured separately from the cylinder block for the following reasons.
- Separately manufacturing process of cylinder liner will allow the use of superior material to the cylinder block. The liner is manufactured from a cast iron alloyed with chromium, vanadium, and molybdenum. The alloying elements help resist corrosion and improve the wear resistance of the liner at high temperatures.
- The cylinder liner will wear out at certain operating hours of use and, therefore, need to be replaced. The cylinder block will run up to the engine life unless there is some accident in the engine.
- The cylinder liner will expand more and is free to expand diametrically and lengthwise. If the Cylinder Block and Cylinder liner were cast as one piece, unacceptable thermal stresses would cause a fracture.
Functions of Anti polishing/ Flame Ring
Flame ring installed in the cylinder liner top part performs the following functions.
- Scrapes carbon deposits
- Removes the excessive lubricating oil on piston crown
- Reduces the lubricating oil consumption.
For the following listed reasons, cylinder liners are manufactured separately.
- Due to the reciprocating movement of the piston, the cylinder liner will wear and will need replacement.
- At the operating temperature, the cylinder liner is hotter than the jacket/cylinder blocks. Hence the expansion of the liner will be more than the expansion of the jacket. If the cylinder liner were not made separately, then undesirable thermal stresses would occur, causing fracture of the material?
Difference between Cylinder Liner and Sleeve
Sleeves are mainly used for the repairs of the damaged block. Cylinder Liners are used in an engine that is fitted in the cylinder block.
Types of Cylinder Liners
- Dry Type Cylinder liner
- Wet Type of Cylinder Liner
Dry Type Cylinder liner
The walls of the dry type liner are thin. As a result, the liner is shrunk in the cylinder block, built with fins and cooled by air, usually used small engines. In a Dry-type liner, Water doesn’t circulate around the liner, for cooling. Instead, the liner is tightly fitted in the cylinder block.
Wet Type cylinder line
A wet-type cylinder liner directly contacts the cooling Water, which circulates around the liner for cooling purposes. The circulating Water controls the piston rings and liner temperature. Wet liners will have the cooling surface between the engine cylinder block and the liner. In some cases, there are integral cooling spaces.
In wet-type cylinder liners not provided with the integral cooling passages, the water jacket is built by the liner and separate jacket. A stationary seal is provided at both the combustion and crankshaft end of cylinders to arrest the coolant leakage into the oil sump or combustion chamber
Typically the seal towards the combustion chamber end is either a metallic tom back gasket or finely machined surface. On the sump side, neoprene rubber rings are provided for sealing purposes. linear expansion of the cylinder liner will be provided by this arrangements. The walls of the cylinder liners of the wet type are strongly built to withstand the working pressure of the combustion process.
Material of Construction
Cylinder liner is manufactured with better material than that of the cylinder block. The cylinder block is manufactured with grey cast iron, and the Cylinder liner is made of centrifugally cast iron copper vanadium alloyed for better lubrication properties due to graphite, corrosion resistance, and wears resistance at high temperatures.
Material Composition for large bore Cylinder liners
Cast iron with , Carbon-3.00%, Magnese-1.00%, Silcon-0.70%, Sulphur-0.10%, Phosphorus- 0.25%, Vanadium- 0.15%,
- Sand Casting
- Centrifugal Casting.
Sand Casting; – This process is adopted for the manufacture of large slow-speed Engines. This process enhanced wearing properties due to the best grain flow formed in casted material—better graphitization enhancing lubricating properties due to steady cooling rate.
Centrifugal Casting- This process is adopted for Medium and high-speed engines. Robust liner, consistent structure, low wearing quality (due to fast cooling rate) is achieved with this process.
Following activities are undertaken during the liner manufacturing process.
- Rough Machining
- Hydro Test ( 7 bars)
- Ports forming
- Final machining of the internal and external surface
- Honing the internal surface- (surface finish approximately to 3.5lm)
- Surface treatment
Surface Finish Treatment
Surface finish treatment is given to the inner surface of the liner for the piston rings to seat wholly and quickly so that the engine doesn’t use oil. The surface finish should fulfill the Piston ring manufacturer’s standards and maintain the excellent cross-hatch marks on the working surface to retain the lubricating oil and make the lubricating oil available to piston rings.
Types of Stress in Liners
Liners are subjected to following stresses.
- Mechanical stress – pressure:- In Supercharges engines firing pressure is about 90 to 100 bar and with the latest design this pressure is about 130 bars. The firing pressure in natural aspirated engines is 75 to 80 Bars. Firing pressure produces longitudinal and circumferential stress. Longitudinal stress is hoop stress and is twice of circumferential stress and hence is taken in to consideration.
- Thermal stress – temperature: – Temperature ingredient across the liner is produced due to the resistance to heat flow through liner wall metal. The inner wall of liner expands more than the outer wall. The thermal stress will increase in proportion to the liner wall thickness.
Cylinder Liner Failures
1. Crack through the Liner flange due to unequal or extra tightening of cylinder heads
2. Inadequate support causing hoop stress crack
3. New piston ring hitting the wear ridge causing circumferential Crack.
4. Flame intrusion causing a crazy crack
5. Cracks across the port bar due to overloading, unsatisfactory cooling, scavenge fire, poor installation of rubbing sealing ring.
Cylinder Liner Repair Chart
Cylinder Liner Wear
- Abrasion is caused by hard particles produced due to lubricating oil film breakage.
- Acidic combustion products causing corrosion
- Metal to metal contact due to boundary lubrication causing scuffing break down.
- Hard particles derived from airborne dirt, ash contents carbon from combustion due to worn piston rings.
- Cold corrosion due to the sulfur turning into Acid at dew point.
The procedure of Cylinder Liner Removal
Follow the proper method for the removal of the liner. Cylinder liner will be damaged for not adopting the prescribed procedure and recommended tools by the engine manufacturer.
- Remove the piston and connecting rod
- Mark identification mark concerning cylinder block.
- Loosen the cylinder shoes of the cylinder liner lifting tool
- Put the shoes of the device at the bottom edge of liner
- Jack up the cylinder liner by turning the nut clockwise.
- Remove and discard the sealing ring (Tom’s back ring).
- Remove the cylinder liner lifting tool
- Remove and dump the cylinder sealing rings.
Important Note;- Always store or place the cylinder in a vertical direction. Else there may be a distortion of the liner. Also, note that the liner marking for the refitting in the unit’s exact location has been removed.
Cylinder liner cleaning procedure
Clean the liner with the following procedure.
- Clean the liner properly by using the recommended detergents ,hot water and cleaning brush.
- Rinse the cleaned liner with steam or hot water
- Dry the liner with dry compressed air.
- Smear the bore of the liner with fresh engine oil.
- Wait for 10 minutes for oil work into the working surface.
- Wipe the cylinder bore with the clean paper towel
- Repeat the step 4 through 6 in case the black residue is observed on the towel
Inspection of Liner
Points to be observed while inspecting the cylinder liner
- Check the cylinder liner for cracks, fretting, and scoring.
- Scavenge ports opening with sharp edges,
- Formation of the edge at the top dead center position
- Liner surface with mechanical friction wear impressions and abrasive wear.
- Blow-by dark areas.
- Acidic and cold corrosion marks on the surface
- Lubrication opening with cracks and damages.
- Glazing of liner surface with a diminished indication of honing marks.
- Lube oil flow from lubrication ports
- Gauging of Liner bore for ovality and wear.
- Replace the Liner in case of any cracks, fretting, and scoring is detected.
- Inspect the cylinder liner for any cavitations erosion as per the below figure.
Gauging of the Cylinder liner
Gauging of the cylinder liner is to be carried out at regular
intervals mentioned in the OEM manual. Maintain the Record of measurement in
the format shown below for future reference and wear rate calculation.
Inspect the liner thoroughly after proper cleaning. The temperature of the Liner bore measuring gauge and Liner should be identical.
In case of temperature difference exceeds or vice versa, then the following multiplying factor will be used.
Liner gauging report format
CYLINDER LINER HONING
In the course of continuous operation, Cylinder liners will be subjected to wear and tear. This wear is uniformly scattered. The highest wear develops between the turnaround points of the top and bottom piston rings. Generally, scuffing marks are observed at the area of the top piston reversal point. Most of the cylinder liners will be oval over long engine running hours.
Lubricating oil consumption will increase with the the additional effect of wear
A new cylinder liner received from the factory will have cross-hatch markings honed on the working surface. This roughness retains the lubricating oil required to maintain a uniformly distributed oil film between the piston rings’ turnaround points.
If the surface of the liner becomes glazed over a period of operation, the piston ring will easily break the oil film and cause extensive wear to the liner. The excess oil will not be retained and pass to the combustion chamber and burn off instead.
After gauging the liner, if the wear is found within the prescribed limits by the manufacturer, it will be possible to recondition the liner. This repair is possible by Honing process in the workshop.
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We hope you enjoyed our blog on the Cylinder Liners of Diesel Engines. It is a very important part of the engine, but we know that many people are not entirely sure what they do. In this blog, we have covered these parts and included a few helpful tips to help you out. If you have any questions, please don’t hesitate to reach out to us at https://marinediesel.co.in/contact-us/. Thank you for reading, we would love to hear from you!