Reciprocating engine - AbsoluteAstronomy.com

A reciprocating engine, also often known as a piston engine, is a heat engine

Heat engine

In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

that uses one or more reciprocating

Reciprocating motion

Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes...

piston

Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

s to convert pressure

Pressure

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

into a rotating motion

Circular motion

In physics, circular motion is rotation along a circular path or a circular orbit. It can be uniform, that is, with constant angular rate of rotation , or non-uniform, that is, with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of...

. This article describes the common features of all types. The main types are: the internal combustion engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

, used extensively in motor vehicles; the steam engine

Steam engine

A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...

, the mainstay of the Industrial Revolution

Industrial Revolution

The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...

; and the niche application Stirling engine

Stirling engine

A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work....

Common features in all types

There may be one or more pistons. Each piston is inside a cylinder

Cylinder (engine)

A cylinder is the central working part of a reciprocating engine or pump, 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 receiving precision machine work...

, into which a gas is introduced, either already hot and under pressure (steam engine

Steam engine

), or heated inside the cylinder either by ignition

Ignition system

An ignition system is a system for igniting a fuel-air mixture. Ignition systems are well known in the field of internal combustion engines such as those used in petrol engines used to power the majority of motor vehicles, but they are also used in many other applications such as in oil-fired and...

of a fuel air mixture (internal combustion engine

Internal combustion engine

) or by contact with a hot heat exchanger in the cylinder (Stirling engine

Stirling engine

). The hot gases expand, pushing the piston to the bottom of the cylinder. The piston is returned to the cylinder top (Top Dead Centre) either by a flywheel

Flywheel

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

or the power from other pistons connected to the same shaft. In most types the expanded or "exhausted

Exhaust gas

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. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle.It often disperses...

" gases are removed from the cylinder by this stroke

Stroke (engines)

Reciprocating motion, used in reciprocating engines and other mechanisms, is back-and-forth motion. Each cycle of reciprocation consists of two opposite motions: there is a motion in one direction, and then a motion back in the opposite direction. Each of these is called a stroke...

. The exception is the Stirling engine

Stirling engine

, which repeatedly heats and cools the same sealed quantity of gas.

In some designs the piston may be powered in both directions in the cylinder in which case it is said to be double acting.

In all types, the linear movement of the piston is converted to a rotating movement via a connecting rod

Connecting rod

In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....

and a crankshaft

Crankshaft

The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

or by a swashplate

Swashplate

A swashplate is a device used in mechanical engineering to translate the motion of a rotating shaft into reciprocating motion, or to translate a reciprocating motion into a rotating one to replace the crankshaft in engine designs.- Construction :...

. A flywheel

Flywheel

is often used to ensure smooth rotation. The more cylinders a reciprocating engine has, generally, the more vibration-free (smoothly) it can operate. The power of a reciprocating engine is proportional to the volume of the combined pistons' displacement.

A seal needs to be made between the sliding piston

Piston

and the walls of the cylinder

Cylinder (engine)

so that the high pressure gas above the piston does not leak past it and reduce the efficiency of the engine. This seal is provided by one or more piston ring

Piston ring

A piston ring is a split ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.The three main functions of piston rings in reciprocating engines are:...

s. These are rings made of a hard metal which are sprung into a circular groove in the piston head. The rings fit tightly in the groove and press against the cyinder wall to form a seal.

It is common for such engines to be classified by the number and alignment of cylinders and the total volume of displacement

Engine displacement

Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...

of gas by the pistons moving in the cylinders usually measured in cubic centimetres (cm³ or cc) or litre

Litre

pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...

s (l) or (L) (US: liter). For example for internal combustion engines, single and two-cylinder designs are common in smaller vehicles such as motorcycles, while automobiles typically have between four and eight, and locomotives, and ships may have a dozen cylinders or more. Cylinder capacities may range from 10 cm³ or less in model engines up to several thousand cubic centimetres in ships' engines.

The compression ratio

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...

is a measure of the performance in an internal-combustion engine or a Stirling Engine. It is the ratio between the volume of the cylinder, when the piston is at the bottom of its stroke, and the volume when the piston is at the top of its stroke.

The bore/stroke ratio

Stroke ratio

In a reciprocating piston engine, the stroke ratio, defined by either bore/stroke ratio or stroke/bore ratio, is a term which is used to describe the ratio between the diameter of the cylinder bore and the length of the piston stroke within its cylinders...

is the ratio of the diameter of the piston, or "bore", to the length of travel within the cylinder, or "stroke". If this is around 1 the engine is said to be "square", if it is greater than 1, i.e. the bore is larger than the stroke, it is "oversquare". If it is less than 1, i.e. the stroke is larger than the bore, it is "undersquare".

Cylinders may be aligned in line

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...

, in a V configuration

V 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...

, horizontally opposite

Flat engine

A flat engine is an internal combustion engine with multiple pistons that move in a horizontal plane. Typically, the layout has cylinders arranged in two banks on either side of a single crankshaft and is sometimes known as the boxer, or horizontally opposed engine. The concept was patented in 1896...

each other, or radially

Radial engine

The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...

around the crankshaft. Opposed-piston engines put two pistons working at opposite ends of the same cylinder and this has been extended into triangular arrangements such as the Napier Deltic

Napier Deltic

The Napier Deltic engine is a British opposed-piston valveless, two-stroke diesel engine used in marine and locomotive applications, designed and produced by Napier & Son...

. Some designs have set the cylinders in motion around the shaft, see the Rotary engine

Rotary engine

The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

.
In steam engines and internal combustion engines, valves are required to allow the entry and exit of gasses at the correct time in the piston's cycle. These are worked by cams or cranks driven by the shaft of the engine. Early designs used the D slide valve

D slide valve

The slide valve is a rectilinear valve used to control the admission of steam into, and emission of exhaust from, the cylinder of a steam engine.-Use:...

but this has been largely superseded by Piston valve

Piston valve

A piston valve is a device used to control the motion of a fluid along a tube or pipe by means of the linear motion of a piston within a chamber or cylinder.Examples of piston valves are:...

or Poppet valve

Poppet valve

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...

designs. In steam engines the point in the piston cycle at which the steam inlet valve closes is called the cutoff

Cutoff (steam engine)

In a steam engine, cutoff is the point in the piston stroke at which the inlet valve is closed. On a steam locomotive, the cutoff is controlled by the reverser....

and this can often be controlled to adjust the torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

supplied by the engine.

Internal combustion engines operate through a sequence of strokes which admit and remove gases to and from the cylinder. These operations are repeated cyclically and an engine is said to be 2-stroke

Two-stroke cycle

A two-stroke engine is an internal combustion engine that completes the process cycle in one revolution of the crankshaft...

, 4-stroke

Four-stroke cycle

A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...

or 6-stroke

Six stroke engine

The six-stroke engine is a type of internal combustion engine based on the four-stroke engine, but with additional complexity intended to make it more efficient and reduce emissions...

depending on the number of strokes it takes to complete a cycle.

In some steam engines, the cylinders may be of varying size with the smallest bore cylinder working the highest pressure steam. This is then fed through one or more, increasingly larger bore cylinders successively, to extract power from the steam at increasingly lower pressures. These engines are called Compound engines.

History

An early known example of rotary to reciprocating motion can be found in a number of Roman

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

saw mills (dating to the 3rd to 6th century AD) in which a crank and connecting rod mechanism converted the rotary motion of the waterwheel into the linear movement of the saw blades.

The reciprocating engine developed in Europe during the 18th century, first as the atmospheric engine then later as the steam engine

Steam engine

. These were followed by the Stirling engine

Stirling engine

and internal combustion engine

Internal combustion engine

in the 19th century. Today the most common form of reciprocating engine is the internal combustion engine running on the combustion of petrol, diesel, Liquefied petroleum gas (LPG) or compressed natural gas

Compressed natural gas

Compressed natural gas is a fossil fuel substitute for gasoline , diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill...

(CNG) and used to power motor vehicle

Motor vehicle

A motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...

s.

One of the most advanced reciprocating engines ever made was the 28-cylinder, 3500 hp Pratt & Whitney R-4360 "Wasp Major" radial engine which powered the last generation of large piston-engined planes before the jet engine and turboprop took over from 1944 onward. It had a total engine capacity of 71.5 litres (2.5 cu ft).

The largest reciprocating engine in production at present, but not the largest ever built, is the Wärtsilä-Sulzer RTA96-C

Wärtsilä-Sulzer RTA96-C

The Wärtsilä RT-flex96C is a two-stroke turbocharged low-speed diesel engine designed by the Finnish manufacturer Wärtsilä. It is currently considered the largest reciprocating engine in the world, designed for large container ships, running on heavy fuel oil...

turbocharged two-stroke diesel engine of 2006 built by Japan’s Diesel United, Ltd. It is used to power the largest modern container ships such as the Emma Mærsk

Emma Mærsk

Emma Mærsk is the first container ship in the E-class of eight owned by the A. P. Moller-Maersk Group. When she was launched in 2006, Emma Mærsk was the largest container ship ever built...

. It is five stories high (13.5 m (44.3 ft)), 27 metres (88.6 ft) long, and weighs over 2300 metric ton in its largest 14 cylinders version producing more than 84.42 MW (114,800 bhp). Each cylinder has a capacity of 1820 litres (64.3 cu ft), making a total capacity of 25480 litres (899.8 cu ft) for the largest versions.

Engine capacity

For piston engines, an engine's capacity is the engine displacement

Engine displacement

, in other words the volume swept by all the pistons of an engine in a single movement. It is generally measured in litre

Litre

s (L) or cubic inches (c.i.d. or cu in or in³) for larger engines, and cubic centimetres (abbreviated cc) for smaller engines. All else being equal, engines with greater capacities are more powerful and provide greater torque at lower speed (rpm) and consumption of fuel increases accordingly, although power and fuel consumption are affected by many factors outside of engine displacement.

Other modern non-internal combustion types

Reciprocating engines that are powered by compressed air, steam or other hot gases are still used in some applications such as to drive many modern torpedoes or as pollution-free motive power. Most steam-driven applications use steam turbine

Steam turbine

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

s, which are more efficient than piston engines.

The French-designed FlowAIR vehicles use compressed air stored in a cylinder to drive a reciprocating engine in a pollution-free urban vehicle.

Torpedoes may use a working gas produced by high test peroxide

High test peroxide

High-test peroxide or HTP is a high -concentration solution of hydrogen peroxide, with the remainder predominantly made up of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with no remaining liquid water...

or Otto fuel II

Otto fuel II

Otto fuel II is a monopropellant used to drive torpedoes and other weapon systems. It is not related to the Otto cycle.-Properties:This distinct-smelling, reddish-orange, oily liquid is a mixture of three synthetic substances: propylene glycol dinitrate , 2-nitrodiphenylamine, and dibutyl...

, which pressurise without combustion. The 230 kg (507.1 lb) Mark 46 torpedo

Mark 46 torpedo

Designed to attack high-performance submarines, the Mark 46 torpedo is the backbone of the U.S. Navy's lightweight ASW torpedo inventory, and is the current NATO standard. These aerial torpedoes, such as the Mark 46 Mod 5, are expected to remain in service until the year 2015...

, for example, can travel 11 km (6.8 mi) underwater at 74 km/h (46 mph) fuelled by Otto fuel without oxidant.

Miscellaneous engines

There are a large number of unusual varieties of piston engines that have various claimed advantages, many of which see little if any current use:

Free-piston engine
Free-piston engine
A free-piston engine is a linear, 'crankless' internal combustion engine, in which the piston motion is not controlled by a crankshaft but determined by the interaction of forces from the combustion chamber gases, a rebound device and a load device A free-piston engine is a linear, 'crankless'...
Swing-piston engine
Swing-piston engine
A swing-piston engine is a type of internal combustion engine in which the pistons move in a circular motion inside a ring-shaped "cylinder", moving closer and further from each other to provide compression and expansion. Generally two sets of pistons are used, geared to move in a fixed...
IRIS engine
IRIS engine
The IRIS Engine is a design for a new type of internal combustion engine. Its inventors say that engines constructed using this design can be smaller, lighter and significantly more efficient than traditional engines of comparable horsepower and displacement...
Bourke engine
Bourke engine
The Bourke Engine was designed by Russell Bourke in the 1920s, as an improved two-stroke engine. Despite finishing his design and building several working engines, the onset of World War II, lack of test results, and the poor health of his wife compounded to prevent his engine from ever coming...

External links

HowStuffWorks: How Car Engines Work
Reciprocating Engines at Infoplease
Piston Engines US Centennial of Flight Commission

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Common features in all types

History

Engine capacity

Other modern non-internal combustion types

Miscellaneous engines

See also

External links