Internal combustion engines are types of engines that use the reaction of a small explosion for energy. In this reaction, a type of fuel, such as gasoline, combines with air in a small space, called a combustion chamber. When the fuel is ignited by a spark, supplied by a spark plug, a small explosion occurs, expanding the air pressure in the combustion chamber violently. The pressure from the explosion is transferred to the pistons of the engine, which move, generating mechanical energy for the engine. A cylinder head is a vital part of an internal combustion engine, sitting above the cylinders and containing spark plugs and a portion of the combustion chamber.
Devices called cylinders are the portion of an internal combustion engine in which the pistons move. The pistons move incessantly while the engine is running, cycling as a result of the constant combustion of fuel in the combustion chambers. They are typically part of what is called an engine block, an arrangement of cylinders set all in a row. Engine blocks are composed of a molded heavy-duty metal, usually cast iron or aluminum. Due to the constant movement of the pistons within the cylinders, it is necessary to line the cylinders with a more wear-resistant lining, such as a harder metal.
The top portion of the engine block contains the cylinder head. It consists of the top of the combustion chamber, as well as the valves and spark plugs. It also has several internal passageways. These passageways are used to allow the fuel and air to reach the combustion chambers and for exhaust fumes to exit the combustion chamber and reach the exhaust valve. The passageways also allow for the flow of antifreeze to cool the engine. The engine block must be kept cool, due to the constant heat emitted by the internal combustion process.
