The Cylinder Liner
Basically the cylinder liner is a hollow cylindrical shell which acts as the enclosure in which the combustion takes place. Of course the word hollow does not imply that it is weak in strength for it is under the fluid pressure due to combustion and hence must withstand the high level of hoop stress induced in it.
Another factor is the big temperature difference on the outside and inside (being in proximity of the combustion chamber) of the liner which tends to induce thermal stresses and the liner has to withstand those as well. Apart from the liner surface is also resistant to wear and corrosion.
The picture below shows the image of a typical cylinder liner which is resting on wooden blocks. As you can seen from the picture it is made up of quite thick material and the empty slots which we see towards the middle are known as scavenge ports which we will study later on.
Materials of Construction
Given the stringent requirements of strength and anti-corrosion property and provide a good surface for the piston rings to slide along its length, Cast Iron is the most widely used material mainly because of its lubricating properties which is a result of graphite present in its micro-structure.
Cast Iron is also porous in nature and this helps to prevent or minimize the risk of seizure of the piston during its operation and also is a remedial measure against extensive galling which takes place during piston motion.
Yet CI is not strong enough a material so it is not used in its pure form but alloyed with small quantities of elements such as Chromium, Copper or Nickel and such alloying is of the order of 5%.
Construction is done either by centrifugal casting in case of smaller liners and sand casting in case of larger liners. The inner surface of the cylinder liner is usually chrome plated to make it smooth but this smoothness also has its drawback that it does not allow oil to spread out properly thus affecting liner lubrication in a negative manner. This was rectified to a certain degree through the use of porous chrome honing.
We will take a look at the manufacturing of a specific cylinder liner in our next article.