In a

reciprocating engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...

, the cylinder is the space in which a

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...

travels. The inner surface of the cylinder is formed from either a thin metallic liner (also called "sleeve") or a surface coating applied to the engine block. A piston is seated inside each cylinder by several metal

piston ring A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine. The main functions of piston rings in engines are: # Sealing the combustion chamber so that there is mini ...

s, which also provide seals for compression and the lubricating oil. The piston rings do not actually touch the cylinder walls, instead they ride on a thin layer of lubricating oil.

Steam engines

The cylinder in a

steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be tr ...

is made pressure-tight with end covers and a piston; a valve distributes the steam to the ends of the cylinder. Cylinders were cast in cast iron and later in steel. The cylinder casting can include other features such as valve ports and mounting feet.

Internal combustion engines

The cylinder is the space through which the

travels, propelled to the energy generated from the combustion of the air/fuel mixture in the combustion chamber. In an

air-cooled engine Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. In all combustion engines, a great percentage of the heat ge ...

, the walls of the cylinders are exposed to the airflow, to provide the primary method of cooling to the engine. Most air-cooled engines have cooling fins on the cylinders and each cylinder has a separate case in order to maximise the surface area available for cooling. In engines where the cylinders are removable from the engine block, a removable single cylinder is called a jug. For motorcycle engines, a "reverse cylinder engine" is where the intake ports are on the front side of each cylinder, and the exhaust ports are on the rear side of each cylinder.

Cylinder liners/sleeves

Cylinder liners (also known as sleeves) are thin metal cylinder-shaped parts which are inserted into the

engine block In an internal combustion engine, the engine block is the structure which contains the cylinders and other components. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attach ...

to form the inner wall of the cylinder. Alternatively, an engine can be 'sleeveless', where the cylinder walls are formed by the engine block with a wear-resistant coating, such as

Nikasil Nikasil is a trademarked electrodeposited lipophilic nickel matrix silicon carbide coating for engine components, mainly piston engine cylinder liners. Development Nikasil was introduced by Mahle in 1967, and initially developed to allow Wankel ...

or plasma-sprayed bores. During use, the cylinder liner is subject to wear from the rubbing action of the

s and piston skirt. This wear is minimized by the thin oil film which coats the cylinder walls and also by a layer of glaze which naturally forms as the engine is run-in. On some engines, the cylinder liner is replaceable, in case it becomes worn or damaged. On engines without replaceable sleeves, the cylinder can sometimes be repaired by boring out the existing liner to produce a new smooth and round surface (although the diameter of the cylinder is slightly increased). Another repair technique is 'sleeving' the cylinder— boring it and then installing a sleeve in the extra space created by the boring. Most engines use 'dry liners', where the liner is surrounded by the engine block and does not make contact with the coolant. However, cylinders with 'wet liners' are used in some water-cooled engines, especially French designs. The wet liners are formed separately from the main casting so that liquid coolant is free to flow around their outsides. The advantage of wet liners is better cooling and a more even temperature distribution, however this design reduces the rigidity of the engine.

References

{{Automotive engine, state=expanded Engine technology

Steam engines

Internal combustion engines

Cylinder liners/sleeves

See also

References