In an internal combustion engine The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the, the cylinder head (often informally abbreviated to just head) sits above the cylinders A cylinder is the central working part of a reciprocating engine, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before precision features are machined into it. The cylinders may then be lined with sleeves or liners of some on top of the cylinder block The cylinder block or engine block is a machined casting containing cylindrically bored holes for the pistons of a multi-cylinder reciprocating internal combustion engine, or for a similarly constructed device such as a pump. It is a complex part at the heart of an engine, with adaptions to attach the cylinder head, crankcase, engine mounts, drive. It consists of a platform containing part of the combustion chamber The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber. This pressure can be used to do work, for example, to move a piston on a crankshaft or a turbine disc in a gas turbine. The energy can also be used to produce thrust when (usually, though not always), and the location of the poppet valves A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide. In most applications a pressure differential helps to seal the valve and in some applications also open it and spark plugs A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark. In a flathead engine A flathead engine or sidevalve engine is an internal combustion engine with valves placed in the engine block beside the piston, instead of in the cylinder head, as in an overhead valve engine. The design was common on early engine designs, but has since fallen from use, the mechanical parts of the valve train are all contained within the block, and the head is essentially a flat plate of metal bolted to the top of the cylinder bank Internal combustion piston engines are typically arranged with their pistons in rows, or 'planes', moving inside individual cylinders. This allows the engine block to be built from a single piece of machined metal. Engines sometimes have more than one row of pistons, each with their own block, referred to as cylinder banks with a head gasket A head gasket is a gasket that sits between the engine block and cylinder head in an internal combustion engine. Its purpose is to seal the cylinders to ensure maximum compression and avoid leakage of coolant or engine oil into the cylinders; as such, it is the most critical sealing application in any engine, and, as part of the combustion chamber, in between; this simplicity leads to ease of manufacture and repair, and accounts for the flathead engine's early success in production automobiles An automobile, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally for the and continued success in small engines, such as lawnmowers. This design, however, requires the incoming air to flow through a convoluted path, which limits the ability of the engine to perform at higher revolutions per minute Revolutions per minute is a unit of frequency of rotation: the number of full rotations completed in one minute around a fixed axis. It is used as a measure of rotational speed of a mechanical component (rpm), leading to the adoption of the overhead valve An overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine), and uses pushrods or rods to actuate rocker arms above the (OHV) head design, and the subsequent overhead camshaft Overhead camshaft, commonly abbreviated to OHC, valvetrain configurations place the engine camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters in a more direct manner compared to overhead valves and pushrods (OHC) design.
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Internally, the cylinder head has passages called ports or tracts Cylinder head porting refers to the process of modifying the intake and exhaust ports of an internal combustion engine to improve the quality and quantity of the air flow. Cylinder heads, as manufactured, are usually suboptimal due to design and manufacturing constraints. Porting the heads provides the finely detailed attention required to bring for the fuel/air mixture to travel to the inlet valves from the intake manifold In automotive engineering, an intake manifold or inlet manifold is the part of an engine that supplies the fuel/air mixture to the cylinders. An exhaust manifold or header collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple, for exhaust gasses Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. It is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle to travel from the exhaust valves to the exhaust manifold. In a water-cooled engine, the cylinder head also contains integral ducts and passages for the engines' coolant - usually a mixture of water and antifreeze Antifreeze is used in internal combustion engines and many other heat transfer applications, such as HVAC chillers and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from undergoing physical stresses and catastrophic deformation due to the expansion that occurs when water turns to ice. Most antifreezes are chemical - to facilitate the transfer of excess heat away from the head, and therefore the engine in general.
In the overhead valve (OHV) design, the cylinder head contains the poppet valves and the spark plugs, along with tracts or 'ports' for the inlet and exhaust gases. The operation of the valves is initiated by the engines camshaft An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata, water-raising machines, and water clocks such as the castle clock. The cam and camshaft later appeared in European mechanisms from at least the 14th century,, which is sited within the cylinder block The cylinder block or engine block is a machined casting containing cylindrically bored holes for the pistons of a multi-cylinder reciprocating internal combustion engine, or for a similarly constructed device such as a pump. It is a complex part at the heart of an engine, with adaptions to attach the cylinder head, crankcase, engine mounts, drive, and its moment of operation is transmitted to the valves pushrods An overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine), and uses pushrods or rods to actuate rocker arms above the, and then rocker arms Generally referred to within the internal combustion engine of automotive, marine, motorcycle and reciprocating aviation engines, the rocker arm is a reciprocating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it. One end is raised and lowered by the rotating lobes of the camshaft (either mounted on a rocker shaft - the rocker arms and shaft also being located within the cylinder head.
In the overhead camshaft (OHC) design, the cylinder head contains the valves, spark plugs and inlet/exhaust tracts just like the OHV engine, but the camshaft is now also contained within the cylinder head. The camshaft may be seated centrally between each offset row of inlet and exhaust valves, and still also utilizing rocker arms (but without any pushrods), or the camshaft may be seated directly above the valves eliminating the rocker arms and utilizing 'bucket' tapets.
Implementation
The number of cylinder heads in an engine is a function of the engine configuration Engine configuration is an engineering term for the layout of the major components of a reciprocating piston internal combustion engine. These components include cylinders, pistons, crankshaft and camshaft(s). An inline or straight engine Usually found in four- and six-cylinder configurations, the straight engine, or inline engine is an internal-combustion engine with all cylinders aligned in one row, with no offset. They have been used in automobiles, locomotives and aircraft, although the term in-line has a broader meaning when applied to aircraft engines; see Inline engine has only one cylinder head. A V engine (or Vee engine) A V engine, or Vee engine is a common configuration for an internal combustion engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft. The Vee configuration generally reduces the overall engine length, height and weight compared to usually has two cylinder heads, one for each cylinder bank Internal combustion piston engines are typically arranged with their pistons in rows, or 'planes', moving inside individual cylinders. This allows the engine block to be built from a single piece of machined metal. Engines sometimes have more than one row of pistons, each with their own block, referred to as cylinder banks of the 'V'. However, Volkswagen Group Volkswagen Group is a German automobile manufacturing group; and according to figures published by economic research firm Global Insight in November 2009, is the largest automobile maker in the world by vehicle production. Its parent company Volkswagen Aktiengesellschaft, (FWB: VOW3) sometimes referred to as VW AG or VWAG, develops vehicles and, for instance, produces a specific type of compact narrow angle V engine called the VR6 engine The VR6 engine is an internal combustion engine configuration, consisting of six cylinders. It was developed and is produced by Volkswagen Group. It is similar to a V engine, but with the cylinders offset and tilted from each other by either 10.6° or 15°, instead of the more common 45°, 60°, or 90°, where the angle between the cylinder banks is so narrow that it utilises a single head. A flat engine A flat engine is an internal combustion engine with multiple pistons that all move in the horizontal plane. The most popular and significant layout has cylinders arranged in two banks on either side of a single crankshaft, generally known as "boxers". There is a widely-used but technologically less significant form consisting of a (basically a V engine, where the angle between the cylinder banks is now 180 degrees) has two heads.
Some engines, particularly medium- and large-capacity diesel engines A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. This is in contrast to spark ignition engines such as a petrol engine (known as a gasoline engine in North America) or gas engine (using a built for industrial, power generation and traction purposes (trucks A truck or lorry (British English) is a motor vehicle designed to transport cargo. They vary greatly in size, power and configuration, with the smallest being mechanically similar to an automobile. Commercial trucks can be very large and powerful, and may be configured to mount specialized equipment, such as in the case of fire trucks and concrete, locomotives A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th century to distinguish, heavy equipment Heavy equipment refers to heavy-duty vehicles, specially designed for executing construction tasks, most frequently, ones involving earth moving. They are also known as construction equipment, earth movers, engineering vehicles, or just plain equipment. They usually comprise five equipment systems: implement, traction, structure, power train, etc.) have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders. Such a design also allows engine manufacturers to easily produce a 'family' of engines of different layouts and/or cylinder numbers without requiring new cylinder head designs.
The design of the cylinder head is key to the performance and efficiency of the internal combustion engine, as the shape of the combustion chamber, inlet passages and ports (and to a lesser extent the exhaust) determines a major portion of the volumetric efficiency Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More specifically, volumetric efficiency is a ratio of what quantity of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static and compression ratio The compression ratio of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber; from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines of the engine.
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References
External links
- Cylinder head - design and manufacturing processes video
- Assembly of Ford 3d Duratec HE Engine - video showing construction and operation of four cylinder internal combustion engine courtesy of Ford Motor Company
Categories: Engine technology
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