Why Cylinder Liners are Used

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Why are Cylinder Liners a very important component in an engine? Do all engines have cylinder liners? In this article, we discuss why cylinder liners are used: its functions and importance, and how it came about.

Cylinder liners are one of the core parts of an engine. They primarily serve as protection against an engine’s wear and tear. The cylinder liner is a thin cylindrical component installed in the cylinder block, and is in direct contact with the fuel combustion process.

Also known as cylinder sleeves, the liners are precisely manufactured in order to guide the piston assembly, thus efficiently converting the fuel’s combustion into mechanical energy.

Moreover, we expound more on Cylinder Liner’s functions below.
What is the Function of Cylinder Liners?

In our previous post on How are Cylinder Liners Made, we discuss the complexity of manufacturing Cylinder Liners, and the important aspects that are needed in creating them. 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.

There are three primary reasons why cooling engines is important:

Improve volumetric efficiency: Having cooler engines will allow more air to go in the cylinder. Having more air means higher output and better combustion.

Prevent erratic ignition: Especially for gasoline engines with spark-type ignition, having cooler temperature can prevent air-fuel mixtures to burn prematurely. This causes knocking sounds in your engine, and worse, may lead to overheating and deterioration of components.

Ensure engine reliability: Overheating an engine can cause various issues when it is not prevented. Reaching a temperature higher than allowed can cause softening and deformation of components. Light engines having aluminum components are prone to this issue since aluminum can soften when temperature reaches above 200°C.

Protect engine block from wear and tear

Photo credit: Ceramizer

Cylinder Liners provide protection to engine blocks as they “receive” the wear, rather than the engine block. With this, in case of wear, the cylinder liner is easier and more economical to replace, rather than the whole engine block.

For engines that have no cylinder liners, the cylinder is repaired by boring out the cylinder existing in order to create a new smooth surface, and then replacing the piston and piston rings with larger ones.

However, another technique is sleeving: boring the cylinder and then installing a new sleeve to compensate for the larger hole created by boring.

VIDEO: https://www.youtube.com/watch?v=5_7PtvziB-Q
A Brief History of Cylinder Liners

Earlier engines have been fully made in cast iron for several reasons. Iron was one of the strongest metals, and it was also easy and cheap to manufacture. As these engines were made in full cast iron, there was no need for cylinder liners.

These were used for a long time, although aluminum engine blocks were already started to be produced in the early 1960’s. These engine blocks were made with a lighter material- aluminum, but installed with durable cast iron liners. Aluminum engine blocks were very rare that only 2% of the car population has aluminum engine blocks installed.

Beyond the 1990’s, manufacturers started to migrate into aluminum engines as rules on emissions and fuel consumption became tighter. This pushed manufacturers to find ways to reduce the vehicles’ weight and create more efficient engines.

Today, aluminum engine blocks cover almost two thirds of all manufactured engine blocks and still continues to increase.
Types of Cylinder Liners
There are several types of Cylinder Liners, each having advantage and disadvantages:
Dry Cylinder Liners
Dry cylinder liners are the most common type, and are thinner than wet liners. They are not in direct contact engine coolant, however it is installed with a very close fit, providing protection from heat and impurities.

Pros:
Easy replacement as this is the most common type
No exposure to water jacket difficulty which compromises strength
Can be used in almost all kinds of Engines.
Cons:
Cylinder block in which it is fitted is difficult to manufacture and
Inefficient heat dissipation

Wet Cylinder Liners
Wet cylinder liners come in direct contact with engine coolant. Some wet cylinder liners are fitted with small openings that disperse heat and impurities.

Pros:
comparatively easy to manufacture
More efficient cooling
Cons:
replacement can be more difficult
risk to water leakage issues

Finned Cylinder Liners
Finned cylinder liners are designed for the air-cooling.These liners are manufactured with small fins which allows air around the cylinder to provide cooling.

Pros:
Resistant to corrosion and it has
Very effective heat dissipation.
Cons:
Only works for Air Cooled Engines
Cannot be installed in coolant based engines
Conclusion
The emergence of cylinder liners has been a great innovation in the design of engines. Its discovery provided a boost in efficiency, economy and sustainability. For a vehicle user, this component may seem negligible, but the function of the cylinder sleeves gives our car engine more efficient combustion and longer service life.

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