If you’re familiar with the inner workings of an internal combustion engine, you may have heard the term “cylinder liner.” But what exactly is a cylinder liner and what role does it play in an engine? In this article, we’ll explore the basics of cylinder liners and their importance in keeping your engine running smoothly.
What is a Cylinder Liner?
A cylinder liner is a cylindrical component that is inserted into an engine block to form a cylinder. In internal combustion engines, the cylinder liner provides a smooth surface for the piston to move back and forth and helps to maintain a tight seal between the piston and the cylinder wall.
Cylinder liners come in two main types: wet and dry. Wet liners are fully immersed in the engine coolant, which helps to transfer heat away from the engine and regulate its temperature. Dry liners are not in contact with the coolant and are used in engines that operate at high temperatures, such as diesel engines.
The material used for cylinder liners can vary depending on the type of engine and the operating conditions. Cast iron is a common material for wet liners, as it is durable and has good heat dissipation properties. For dry liners, a high-temperature-resistant material, such as aluminum or high-silicon cast iron, is often used to withstand the high temperatures generated during combustion.
One of the commonly used materials for cylinder liners is nickel-chromium iron, which is a type of cast iron that contains a specific composition of elements. The composition includes carbon, manganese, phosphorus, sulfur, silicon, nickel, and chromium.
To increase the wear resistance of the cylinder liners, a heat treatment process is used. The liners are heated to a temperature of 855°C to 865°C for 30 to 40 minutes and then rapidly cooled, or quenched, in oil. This type of heat treatment increases the hardness and toughness of the material, making it more resistant to wear and tear.
In engines that are subject to high levels of wear and tear, such as in heavy-duty vehicles, cylinder liners may be replaceable, allowing the engine to be rebuilt instead of replaced entirely. The cylinder liner is a critical component of an engine and plays a vital role in ensuring its efficiency and longevity.
The Functions Of Cylinder Liners
The strength, precision and uniformity of Cylinder Liners are important as they render these functions:
Serve as Sliding surface
Cylinder Liners form the inner wall of the cylinder, in direct contact to the piston rings that slide along the sleeve surface. Cylinder liners have excellent characteristics for a sliding surface as they are designed with high anti-galling properties.
Although the sliding surface is covered by a thin oil film for lubrication, the oil is retained, along with glaze that naturally forms in metal-to-metal contact. This causes less wear on the cylinder liner and the piston ring. Also, this natural lubrication allows for less consumption of oil as the engine runs.
Sealing Compressed Gas
As the engine works on compressed and rapidly expanding gas (combustion), sealing the chambers is a critical factor to keep engines running efficiently and safely.
This is where cylinder liners come in. The cylinder liners are manufactured with tight tolerances in order to prevent the compressed gas and combusted gas from escaping. Being in contact with high temperature and pressure, cylinder liners should be resistant to failure in such conditions.
Serve as Heat transfer
Since the cylinder liner is in direct contact with combustion, it receives heat and transfers it to the coolant.
Most engines have ‘dry liners’, which are designed to have contact with only the engine block. The engine block is then in contact with the coolant. A wet liner, on the other hand, is in direct contact with coolant along its external surface, providing a more efficient cooling.
Different Types Of Cylinder Liners
There are three basic types of cylinder liners: hot, dry, and finned. Each type has a different method of protecting the piston, but they are all made of high-grade materials like cast iron and ceramic-nickel plating.
#1. Dry Cylinder Liners.
Dry Type Cylinder Liner is the most common type of cylinder liner. It works under high pressure and temperature and hence has to be made up of cast iron and ceramic-nickel plating which are high-grade materials.
Dry Liners material Composition mostly includes Cast Iron and Ceramic-Nickel Compounds which gives it several features which are not achievable in Wet Liners.
A cylinder block with Dry Liners is more robust than its counterpart, wet liner liners. Dry liners are relatively thinner than Wet liners. Dry liner is not in direct contact with the coolant but protects Piston from wear and impurities.
Dry liner fits directly against the wall of the cooling jacket in the cylinder block.
Advantage of Dry Cylinder Liner is that its replacement is easy and it has no exposure to water jacket difficulty. Dry Liners can be used in almost all kinds of Engines.
The disadvantage of Dry Cylinder Liner is that the Cylinder block in which it is fitted is difficult to manufacture and heat dissipation is not quite efficient.
2. Wet Cylinder Liners.
Wet type Cylinders are made up of the same material as of Dry Type Cylinder Liner. Wet Liners interact with Engine coolant directly to protect the Piston.
Wet Liners have better heat dissipation and cooling than Dry-type Cylinder Liner. Wet Liners may have a cooling water space between the engine block and liner, or they may have integral cooling passages.
And in Wet liners which do not have integral cooling passages, the water jacket is formed by the liner and a separate jacket which is a part of the block. A static seal must be provided at both the combustion and crankshaft ends of the cylinders to prevent the leakage of coolant into the oil pan sump, or combustion space.
Generally, the seal at the combustion end of a liner consists of either a gasket under a flange or a machined fit. The wall of the Cylinder Liner must to strong enough to withstand the combustion pressure.
Advantage of Wet type Liner is that it is comparatively easy to manufacture, Cooling is more effective and longitudinal stress is relieved due to thermal expansion of liner.
Disadvantage of Wet type Liners is that its replacement is difficult and there is a risk of water leakage problems.
3. Air-cooled or Finned Cylinder Liners.
Air Cooled Cylinder Liners are made from a special “Shell Moulding Process” having wear-resisting, close-grained, iron casting to ensure long life and efficient cooling.
As the name suggests, Air air-cooled liners are specifically designed for Air-Cooled Engines. Air Cooled Liners are most commonly used in Automobiles. It’s working is the same as Dry Cylinder Liner but the cooling Medium in this scenario is air.
Heat dissipation of Air-Cooled Liner is carried through the mode of Forced convection with the help of its fins which is applied on its surface. Typically, the material of the Fin has a high thermal conductivity.
Advantages of Air Cooled/Finned type Cylinder Liner is that it is resistant to corrosion and it has very effective heat dissipation.
A disadvantage of an Air-Cooled Cylinder Liner is that it is designed to support an Air-Cooled Engine and thus cannot be installed in any coolant-based Mechanism.
Comparison of Dry and Wet Liners
- A wet liner can be easily replaced whereas a dry liner requires special tools because it is tight-fitted in the cylinder block.
- A wet liner is properly cooled as it comes in direct contact with the cooling water, whereas a dry liner does not come in direct contact with the cooling water. Hence the working temperature of a dry liner is more than a wet liner.
- A wet liner needs leak-proof joints so that the cooling water does not leak into the crankcase, whereas a dry liner has no such requirement.
- A wet liner does not require accurate finishing on the outside, whereas a dry liner needs accurate finishing.
- Finishing may be completed in a wet liner before assembly, whereas a dry liner needs finishing after assembly.
Materials for Cylinder Liners
The cylinder liner is made of special alloy cast iron, which has higher abrasion resistance compared to gray cast iron with flake graphite.
For cylinder liners, nickel-chromium iron has been popularly used. The nickel-chromium iron used contains carbon 3.5%; manganese 0.6%; phosphorous 1.5%; Sulphur 0.05%; silicon 2%; nickel 2%; and chromium 0.7%.
To increase the wear resistance, the liners are hardened by heating to 855°C–865°C for 30 to 40 minutes and then quenched in oil. By such heat treatment, the life of the liners is increased to three times as compared with grey iron or cast-iron cylinders.