Cylinder liner, in which the compression of air and the combustion of fuel/air mixture takes place inside the cylinder liner, so it forms part of the combustion chamber.
It must provide adequate strength and fatigue life,
readily transfer heat,
resist avrasion and corrosion,be able to retain a film of lubricating oil on working surfaces, and have rate of thermal expansion compatible with adjacent parts.
It must maintain low wear rates and friction losses from the sliding motion of piston rings under fluctuating pressure and temperature.
To meet these requirements for Limited intial cost, liners are cast in pearlitic grey cast iron to which alloying elements such as vanadium and Titanium are added to enhance strength,wear and corrosion Resistance.
Chromium plating of internal surface can be carried out to reduce urea and corrosion further. The Chrome must either be deposited as a porous structure or else be etched to retain lubrication. Chrome plated liners have extended life but initial cost is Greater.
chromium plated piston ring must not used with plated Liners.
The upper end of the liners forms a flange of sufficient strength to support it.This flange is secured between the cylinder cover and the jacket or engine entablature,leaving the lower end of the liner free for thermal expansion. The liner thickness must give adequate strength to resist the internal gas load but is limited by necessary to transfer heat rapidly to reduce the thermal stress. Thickness may be reduced towards the lower end where pressure and temperature are less, but External Flanges and bossing may be added to accomodate seal rings, lubricator connection etc.
In large two stroke engine liners, Scavenge air ports will be cut or cast in near the lower end. Engines using loop or Cross scavenge system will also need exhaust ports.All port edge are shaped to direct the flow.cylinder liners in four -stroke engine requires no ports and are of more simple shape.
Fig:-2-stroke cylinder liner
To remove excess heat, limit thermal stress and maintain a surface temperature at which an oil lubrication film can be retained,liners require an external cooling system.