A compound engine is an

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...

that has more than one stage for recovering energy from the same

working fluid For fluid power, a working fluid is a gas or liquid that primarily transfers force, motion, or mechanical energy. In hydraulics, water or hydraulic fluid transfers force between hydraulic components such as hydraulic pumps, hydraulic cylinders, a ...

, with the exhaust from the first stage passing through the second stage, and in some cases then on to another subsequent stage or even stages. Originally invented as a means of making

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 trans ...

s more efficient, the compounding of engines by use of several stages has also been used on

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...

s and continues to have niche markets there. The stages of a compound engine may be either of differing or of similar technologies, for example: * In a

turbo-compound engine A turbo-compound engine is a reciprocating engine that employs a turbine to recover energy from the exhaust gases. Instead of using that energy to drive a turbocharger as found in many high-power aircraft engines, the energy is instead sent to ...

, the

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, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...

from the cylinders passes through a turbine, the two stages being dissimilar. * In a compound steam locomotive, the steam passes from the high-pressure cylinder or cylinders to the low-pressure cylinder or cylinders, the two stages being similar. * In a triple-expansion steam engine, the steam passes through three successive cylinders of increasing size and decreasing pressure. Such engines were the most common marine engines in the golden age of steam. These examples and

compound turbine A compound turbine is a steam turbine in which there are two casings, a high-pressure casing and a low-pressure casing, operating in concert to extract work from a single source of steam. The steam is partially expanded in the high-pressure casing, ...

s are the main but not the only uses of compounding in engines, see below.

Terminology

A compound engine uses several stages to produce its output. Not all engines that use multiple stages are called ''compound engines''. In particular, if an engine uses a later stage purely to extract energy from the exhaust for some other purpose, and notably for

turbo charging In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

, is not called a ''compound engine''. Similarly, proposed engines that use a

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 (e.g., a piston i ...

to drive a turbine would not be called ''compound engines'', as only the second stage produces output power. However, if a turbo compound engine is also

supercharged In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement. The current categorisation is that a supercharger is a form of forced induct ...

by feeding some of the shaft power back to the supercharger, as in some aircraft engines, it is still a compound engine. Usage of the terms ''supercharged'' and ''turbosupercharged'' has varied with time, for example the makers of the Wright R-3350 Duplex-Cyclone compound engine described it at the time as ''turbosupercharged''. It is however a compound engine, and a similar engine produced today would be described as ''supercharged'' rather than ''turbocharged''. The term compounding is a little less restrictive than ''compound engine''. Large

s are an application of compounding, as are the multiple rows of blades used in many

gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...

s, but neither is normally referred to as a compound engine. The several sets of blades in a single turbine are perhaps better thought of as similar in principle to the

uniflow steam engine The uniflow type of steam engine uses steam that flows in one direction only in each half of the cylinder. Thermal efficiency is increased by having a temperature gradient along the cylinder. Steam always enters at the hot ends of the cylinder and ...

than to compounding. Unlike the uniflow steam engine, which has found niche uses only, multiple row turbines have found enormous practical application. An engine that does not use compounding is referred to as a simple engine, particularly in the case of a

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

, or more precisely as a simple expansion engine, particularly in the case of a

marine steam engine A marine steam engine is a steam engine that is used to power a ship or boat. This article deals mainly with marine steam engines of the reciprocating type, which were in use from the inception of the steamboat in the early 19th century to their ...

. Note however that in the case of any

, ''simple engine'' can also be used to mean one that does not use a condenser to generate negative pressure and so improve efficiency. Use of separate condensers for this purpose is one of the key features that distinguishes the

Watt steam engine The Watt steam engine design became synonymous with steam engines, and it was many years before significantly new designs began to replace the basic Watt design. The first steam engines, introduced by Thomas Newcomen in 1712, were of the "at ...

of 1765 from the

Newcomen steam engine The atmospheric engine was invented by Thomas Newcomen in 1712, and is often referred to as the Newcomen fire engine (see below) or simply as a Newcomen engine. The engine was operated by condensing steam drawn into the cylinder, thereby creati ...

of 1712. No ambiguity arises in the case of a steam locomotive, as in a

condensing steam locomotive A condensing steam locomotive is a type of locomotive designed to recover exhaust steam, either in order to improve range between taking on boiler water, or to reduce emission of steam inside enclosed spaces. The apparatus takes the exhaust stea ...

the condenser is not there to increase efficiency, and may even reduce efficiency in order to conserve water and reduce emissions. So for example the

Metropolitan Railway A Class The Metropolitan Railway A Class and B Class were condensing steam locomotives built for the Metropolitan Railway by Beyer Peacock, first used in 1864. A total of 40 A Class and 26 of the slightly different B Class were delivered by 1885. Used ...

is in every sense a ''simple'' locomotive despite its condensers, and the term ''simple engine'' applied to steam locomotives always in practice means one that does not use compounding, again irrespective of its use of condensers. The terms ''simple expansion locomotive'' and ''simple expansion engine'' are sometimes applied to locomotives to remove any possible confusion.

History

Steam

The oldest examples of compound engines are

compound steam engine A compound steam engine unit is a type of steam engine where steam is expanded in two or more stages. A typical arrangement for a compound engine is that the steam is first expanded in a high-pressure ''(HP)'' cylinder, then having given up he ...

s. In 1805

Arthur Woolf Arthur Woolf (1766, Camborne, Cornwall – 16 October 1837, Guernsey) was a Cornish engineer, most famous for inventing a high-pressure compound steam engine. As such he made an outstanding contribution to the development and perfection of th ...

patented the ''Woolf high pressure compound engine'' which used this principle. Compounding was particularly used on

stationary steam engine Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars ...

s, and on some but by no means all

s starting from the 1850s, particularly but not only in continental Europe. Three stage or

triple expansion 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 ...

reciprocating steam engines, with three cylinders of increasing bore in line, were particularly popular for

steamship A steamship, often referred to as a steamer, is a type of steam-powered vessel, typically ocean-faring and seaworthy, that is propelled by one or more steam engines that typically move (turn) propellers or paddlewheels. The first steamships ...

propulsion. "Doctor"

Alexander Carnegie Kirk Alexander Carnegie Kirk (16 July 1830 – 5 October 1892) was a Scottish engineer responsible for several major innovations in the shipbuilding, refrigeration, and oil shale industries of the 19th century. Kirk, born in Barry, Angus, receiv ...

, experimentally fitted his first triple expansion engine to a ship called ''Propontis'' in 1874. In 1881, Kirk installed a refined version of his engine in SS ''Aberdeen'' on

Clydeside Greater Glasgow is an urban settlement in Scotland consisting of all localities which are physically attached to the city of Glasgow, forming with it a single contiguous urban area (or conurbation). It does not relate to municipal government ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

. This ship proved the advantages of power and economy of the new engine, in commercial service between the United Kingdom and the

Far East The ''Far East'' was a European term to refer to the geographical regions that includes East and Southeast Asia as well as the Russian Far East to a lesser extent. South Asia is sometimes also included for economic and cultural reasons. The ter ...

. The first

warship A warship or combatant ship is a naval ship that is built and primarily intended for naval warfare. Usually they belong to the armed forces of a state. As well as being armed, warships are designed to withstand damage and are usually faster a ...

to be so equipped was the Spanish warship ''Destructor'', which was also built on Clydeside, and the first engine of this type used in ships of the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...

was designed by J. W. Reed, who also created the

Reed water tube boiler The Reed water tube boiler was a type of water tube boiler developed by J. W. Reed, manager of the engine works at Palmers Shipbuilding and Iron Company of Jarrow, England, where it was manufactured from 1893 to 1905. At this time, Palmer ...

. Other navies and commercial shipowners soon followed. Four-stage, or quadruple, expansion engines were also used. Several classes of steam locomotive have existed in both simple and compound form, most commonly when locomotives originally built as compound were converted to simple in order to gain power at the expense of efficiency, for example the majority of the

NZR X class The New Zealand X class was a pioneering class of eighteen 4-8-2 steam locomotives built for New Zealand Railways Department (NZR) and designed by A. L. Beattie that operated on the national rail network of New Zealand. In 1908, a heavy and pow ...

. Other conversions involved redesigning the details of the compounding, for example many compound locomotives designed by

Alfred de Glehn Alfred George de Glehn (15 September 1848 – 8 June 1936) was a notable English-born French designer of steam locomotives and an engineer with the Société Alsacienne de Constructions Mécaniques (SACM). His steam engines of the 1890s combined el ...

and state of the art in their day were modified by

André Chapelon André Chapelon (26 October 1892 – 22 July 1978) was a French mechanical engineer and designer of advanced steam locomotives. A graduate engineer of Ecole Centrale Paris, he was one of very few locomotive designers who brought a rigorous scien ...

to use his later scheme.

Internal combustion

Attempts have been made to build compound

s with high-pressure and low-pressure cylinders but these have not met with much success. Examples include: Deutz 1879, Forest-Gallice 1888, Connelly 1888, Diesel 1897, Bales 1897, Babled 1903, Butler 1904, Eisenhuth 1904-7, Abbot 1910. More recently, turbo-compounding has been applied to

Turbo compound engine A turbo-compound engine is a reciprocating engine that employs a turbine to recover energy from the exhaust gases. Instead of using that energy to drive a turbocharger as found in many high-power aircraft engines, the energy is instead sent to ...

s were extensively used as

aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...

s immediately after the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. Diesel turbo compound engines remain in use in trucks and agricultural machinery.http://www.demanddetroit.com/pdf/engines/2007-dd15-brochure.pdf retrieved 7 December 2012 ''Fifty free horsepower'' customer brochure

Examples

Turbo-compound engine A turbo-compound engine is a reciprocating engine that employs a turbine to recover energy from the exhaust gases. Instead of using that energy to drive a turbocharger as found in many high-power aircraft engines, the energy is instead sent to ...

s ** Truck and machinery engines ** Aircraft engines ***

Napier Nomad The Napier Nomad is a British diesel aircraft engine designed and built by Napier & Son in 1949. They combined a piston engine with a turbine to recover energy from the exhaust and thereby improve fuel economy. Two versions were tested, the c ...

***

Wright R-3350 Duplex-Cyclone The Wright R-3350 Duplex-Cyclone is an American twin-row, supercharged, air-cooled, radial aircraft engine with 18 cylinders displacing nearly . Power ranged from 2,200 to over 3,700 hp (1,640 to 2,760 kW), depending on the model. ...

which was produced in both simple and compound versions and which in compound configuration powered many post

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

aircraft including the

Lockheed Constellation The Lockheed Constellation ("Connie") is a propeller-driven, four-engined airliner built by Lockheed Corporation starting in 1943. The Constellation series was the first pressurized-cabin civil airliner series to go into widespread use. Its press ...

http://www.enginehistory.org/Wright/Kuhns/CurtissWrightTC18/TurboCompounds.shtml retrieved 9 December 2012http://www.superconstellation.org/TechnicalInformation/motor/motor-en.html retrieved 9 December 2012 ***

Dobrynin VD-4K The Dobrynin VD-4K was a Soviet six-bank, 24-cylinder, turbo-compound, inline engine developed after the end of World War II. It was superseded by turboprop engines before it could be widely used. Development The VD-4K, originally designated as ...

aircraft engine *

Compound steam engine A compound steam engine unit is a type of steam engine where steam is expanded in two or more stages. A typical arrangement for a compound engine is that the steam is first expanded in a high-pressure ''(HP)'' cylinder, then having given up he ...

s **

Compound locomotive A compound locomotive is a steam locomotive which is powered by a compound engine, a type of steam engine where steam is expanded in two or more stages. The locomotive was only one application of compounding. Two and three stages were used in shi ...

s (see also :Compound locomotives) *** LMS Compound 4-4-0 ***

NZR A class (1906) The NZR A class were a class of steam locomotives built in 1906 with a 4-6-2 wheel arrangement for the New Zealand Railways Department (NZR). The class should not be confused with the older and more obscure A class of 1873. They were designed b ...

*** LMS 6399 Fury *** Württemberg Tssd ***

Bavarian S 3/6 The Class S 3/6 steam locomotives of the Royal Bavarian State Railways (later Class 18.4-5 of the Deutsche Reichsbahn) were express train locomotives with a 4-6-2 Pacific (Whyte notation) or 2'C1' (UIC classification) wheel arrangement. Of al ...

*** Some

Mallet locomotive The Mallet locomotive is a type of articulated steam railway locomotive, invented by the Swiss engineer Anatole Mallet (1837–1919). The front of the locomotive articulated on a bogie. The compound steam system fed steam at boiler pressur ...

s, particularly the original designs ***

Nilgiri Mountain Railway X class The X class is a metre gauge 0-8-2RT rack and pinion compound locomotive used by the Nilgiri Mountain Railway in the Nilgiri Hills of southern India. They are used on the section between Coonoor and Mettupalayam, where the steepest gradient is ...

** Cross-compound steam-driven air compressor, eg Westinghouse 8 1/2" 150-D, used on many large American locomotives **Many

traction engine A traction engine is a steam engine, steam-powered tractor used to move heavy loads on roads, plough ground or to provide power at a chosen location. The name derives from the Latin ''tractus'', meaning 'drawn', since the prime function of any t ...

s **Most reciprocating

s *** Two triple-expansion steam engines were fitted to each of the three

Olympic-class ocean liner The ''Olympic''-class ocean liners were a trio of British ocean liners built by the Harland & Wolff shipyard for the White Star Line during the early 20th century. They were (1911), ''Titanic'' (1912) and (1915). All three were designed to be ...

s including

RMS Titanic RMS ''Titanic'' was a British passenger liner, operated by the White Star Line, which sank in the North Atlantic Ocean on 15 April 1912 after striking an iceberg during her maiden voyage from Southampton, England, to New York City, United ...

(1912), driving the wing propellers. These engines were typical of the era. In the Olympic class, further compounding was achieved by using the exhaust steam from these engines to drive a low-pressure

steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...

driving a smaller central propeller. This scheme had been pioneered by

SS Laurentic (1908) SS ''Laurentic'' was a United Kingdom of Great Britain and Ireland, British Transatlantic crossing, transatlantic ocean liner that was built in Belfast, Ireland, and launched in 1908. She is an early example of a ship whose propulsion combined ...

. * Rolls Royce R6 compound

Wankel engine The Wankel engine (, ) is a type of internal combustion engine using an Eccentric (mechanism), eccentric rotary combustion engine, rotary design to convert pressure into rotating motion. It was invented by German engineer Felix Wankel, and desi ...

http://www.der-wankelmotor.de/Motoren/Rolls-Royce/rolls-royce.html (in

German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

) retrieved 7 December 2012

References

{{steam engine configurations Engine technology

Terminology

History

Steam

Internal combustion

Examples

See also

Theory

Inventors and designers

Similar technology

References