Cylinder Heads & Parts

A cylinder in the central working part of an internal or external combustion engine, the space in which a piston travels. more...

Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or iron before precision features are machined into it. (Ceramics have also been tried, so far unsuccessfully.) The cylinders may then be lined with sleeves of some harder metal, or given a wear-resistant coating such as Nikasil. A cylinder's displacement, or swept volume, is its cross-sectional area (the bore) times by the distance the piston travels within the cylinder (the stroke). The engine displacement is the swept volume of one cylinder times the number of cylinders in the engine.

A piston is seated inside each cylinder by several metal piston rings which fit around its outside surface in machined grooves; typically two for compressional sealing and one to seal the oil. They are made of spring steel and make near contact with the hard walls of the sleeve, riding on a thin layer of lubricating oil which is essential to keep the engine from seizing up. This contact, and the resulting wear, explains the need for the hard lining on the inner surface of the cylinder. The breaking in of an engine is a process whereby tiny irregularities in the metals form congruent grooves. An engine job is a process in which the cylinders are machined out to a slightly larger diameter, and new sleeves and piston rings are installed.

Heat engines

Heat engines, including Stirling engines, are sealed machines using pistons within cylinders to transfer energy from a heat source to a colder reservoir, often using steam or another gas as the working substance. (See Carnot cycle.) The first illustration depicts a cross-section of a cylinder in a steam engine. The sliding part at the bottom is the piston, and the upper sliding part is a poppet valve that directs steam alternately into either end of the cylinder. Refrigerators and air conditioners are heat engines run in reverse, and the noise of the pistons moving inside cylinders is often a nuisance.

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