A
steam engine is a
heat engineA heat engine is a physical or theoretical device that converts thermal energy to mechanical output. The mechanical output is called work, and the thermal energy input is called heat. Heat engines typically run on a specific thermodynamic cycle...
that performs
mechanical workIn physics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI units of joules...
using
steamSteam is vaporized water. It is a transparent gas . At standard temperature and pressure, pure steam occupies about 1,600 times the volume of an equal mass of liquid water...
as its
working fluidThe working fluid in a machine is the pressurized gas or liquid which actuates the machine. Examples include steam in a steam engine, air in a hot air engine and hydraulic fluid in a hydraulic motor or hydraulic cylinder. More generally, a thermodynamic system consists of a system boundary across...
.
The idea of using boiling water to produce mechanical motion has a long history, going back about 2000 years. Early devices were not practical power producers, but more advanced designs producing usable power have become a major source of mechanical power over the last 300 years, enabling the
industrial revolutionThe Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, and transport had a profound effect on the socioeconomic and cultural conditions in the United Kingdom. The changes subsequently spread throughout Europe, North...
, beginning with applications for mine water removal using vacuum engines. Subsequent developments using pressurized steam and conversion to rotary motion enabled the powering of a wide range of manufacturing machinery anywhere water and coal or wood fuel could be obtained, previously restricted only to locations where
water wheelA water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, the development of hydropower. In the Middle Ages, waterwheels were used as tools to power factories throughout different counties. The alternatives were the windmill and human and animal...
s or windmills could be used. Significantly, this power source would later be applied to
prime moverPrime mover may mean:* A machine that transforms energy from thermal or pressure form to mechanical form; typically an engine or turbine.In philosophy and theology:* Prime Mover in the cosmological argument, as a "first cause" of existence...
s, mobile devices such as
steam tractorA steam tractor is a vehicle powered by a steam engine which is used for pulling.In North America, the term steam tractor usually refers to a type of agricultural tractor powered by a steam engine, used extensively in the late 1800s and early 1900s....
s and
railway locomotivesA steam locomotive is a locomotive powered by steam. The term usually refers to its use on railways, but can also refer to a "road locomotive" such as a traction engine or steamroller....
. Modern
steam turbineA 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 generate about 80 percent of the
electric powerElectric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work...
in the world using a variety of heat sources.
Steam engines are typically
external combustion engineAn external combustion engine is a heat engine where an working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work...
s,
although other external sources of heat such as
solar powerSolar energy, radiant light and heat from the Sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
,
nuclear powerNuclear power is power produced from controlled nuclear reactions. Commercial plants in use to date use nuclear fission reactions....
or
geothermalGeothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...
energy may be used. The heat cycle is known as the
Rankine cycleThe Rankine cycle is a thermodynamic cycle which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid. This cycle generates about 80% of all electric power used throughout the world, including virtually all solar thermal, biomass,...
.
In general usage, the term 'steam engine' can refer to integrated steam plants such as railway
steam locomotiveA steam locomotive is a locomotive powered by steam. The term usually refers to its use on railways, but can also refer to a "road locomotive" such as a traction engine or steamroller....
s and
portable engineA portable engine is a small steam engine, mounted on wheels or skids, which is used for driving machinery using a belt from its flywheel. It is not self-propelled and is towed to the work site by horses or bullocks, or even a traction engine. Portable engines were used mainly for driving...
s, or may refer to the machinery alone, as in the
beam engineA beam engine is a design of engine based on the principles of a first-class lever. A force is applied to one end of a beam, which is pivoted in the middle, and the lever action transfers the force to create work at the other end of the beam....
and
stationary steam engineStationary 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 , agricultural engines used for ploughing or...
. Specialized devices such as
steam hammerA steam hammer is a power-driven hammer used to shape forgings. It consists of a hammer-like piston located within a cylinder. The hammer is raised by the pressure of steam injected into the lower part of a cylinder and falls down with a force by removing the steam. Usually, the hammer is made to...
s and steam
pile driverA pile driver is a mechanical device used to drive piles into soil to provide foundation support for buildings or other structures. The term is also used in reference to members of the construction crew that work with pile-driving rigs....
s are dependent on steam supplied from a separate
boilerA boiler or steam generator is a device used to create steam by applying heat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure , but at pressures above this it is more usual...
.
Applications
Since the early 18th century steam power has been set to a variety of practical uses. At first it was applied to reciprocating pumps, but from the 1780s rotative engines (i.e. those converting
reciprocating motionReciprocating motion , also called reciprocation, is an up-and-down motion which repeats over and over again. It is found in a wide range of mechanisms such as reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes...
into rotary motion) began to appear, driving factory machinery. At the turn of the 19th century, steam-powered transport on both sea and land began to make its appearance becoming ever more dominant as the century progressed.
Steam engines can be said to have been the moving force behind the
Industrial RevolutionThe Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, and transport had a profound effect on the socioeconomic and cultural conditions in the United Kingdom. The changes subsequently spread throughout Europe, North...
and saw widespread commercial use driving machinery in factories and mills, powering
pumping stationPumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low-lying land, and the removal of sewage to processing sites.A pumping station...
s and transport appliances such as railway locomotives, ships and road vehicles. Their use in agriculture led to an increase in the land available for cultivation.
Very low power engines are used to power models and speciality applications such as the
steam clockA steam clock is a clock which is fully or partially powered by a steam engine. Only a few functioning steam clocks exist, most designed and built by Canadian horologist Raymond Saunders for display in urban public spaces...
.
The presence of several phases between heat source and power delivery has meant that it has always been difficult to obtain a power-to-weight ratio anywhere near that obtainable from
internal combustion engineThe 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 pressure gases, which are produced by the combustion, directly applies force to a movable...
s; notably this has made
steam aircraftSteam aircraft are aircraft that are propelled by steam engines. They were unusual devices because of the difficulty in producing a powerplant with a high enough power to weight ratio to be practical...
extremely rare. Similar considerations have meant that for small and medium-scale applications steam has been largely superseded by internal combustion engines or
electric motorAn electric motor uses electrical energy to produce mechanical energy, usually through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. Traction motors used on...
s, which has given the steam engine an out-dated image. However it is important to remember that the power supplied to the electric grid is predominantly generated using steam turbine plant, so that indirectly the world's industry is still dependent on steam power. Recent concerns about fuel sources and pollution have incited a renewed interest in steam both as a component of
cogenerationCogeneration is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat...
processes and as a prime mover. This is becoming known as the
Advanced SteamAdvanced steam technology reflects an approach to the technical development of the steam engine intended for a wider variety of applications than has recently been the case...
movement.
Steam engines can be classified by their application:
Stationary applications
Stationary steam engineStationary 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 , agricultural engines used for ploughing or...
s can be classified into two main types:
- Winding engine
A winding engine is a stationary engine used to control a cable, for example to power a mining hoist at a pit head. Electric hoist controllers that have replaced proper winding engines in modern mining but use electric motors are also traditionally referred to as winding engines.Most proper winding...
s, rolling millA rolling mill is a machine or factory for shaping metal by passing it between a pair of work rolls.Rolling mills are often incorporated into integrated steelworks, but also exist as separate plants and can be used for other metals, and other materials....
engines, steam donkeySteam donkey, or donkey engine is the common nickname for a steam-powered winch, or logging engine widely used in past logging operations, though not limited to logging...
s, marine engines, and similar applications which need to frequently stop and reverse.
- Engines providing power, which rarely stop and do not need to reverse. These include engines used in thermal power stations and those that were used in pumping station
Pumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low-lying land, and the removal of sewage to processing sites.A pumping station...
s, millsA grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many different types of grinding mills and many types of materials processed in them. Historically mills were powered by hand , working animal, wind or water...
, factoriesA factory or manufacturing plant is an industrial building where workers manufacture goods or supervise machines processing one product into another. Most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production...
and to power cable railwayA cable railway is a steeply graded railway that uses a cable or rope to haul trains.-Introduction:...
s and cable tramwayA cable car or cable railway is a mass transit system using rail cars that are propelled by a continuously moving cable running at a constant speed. Individual cars stop and start by releasing and gripping this cable as required...
s before the widespread use of electric powerElectric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work...
.
The
steam donkeySteam donkey, or donkey engine is the common nickname for a steam-powered winch, or logging engine widely used in past logging operations, though not limited to logging...
is technically a stationary engine but is mounted on skids to be semi-portable. It is designed for
loggingLogging is the process in which certain trees are cut down for forest management and timber.In forestry the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard. In common usage...
use and can drag itself to a new location. Having secured the winch cable to a sturdy tree at the desired destination, the machine will move towards the anchor point as the cable is winched in.
A
portable engineA portable engine is a small steam engine, mounted on wheels or skids, which is used for driving machinery using a belt from its flywheel. It is not self-propelled and is towed to the work site by horses or bullocks, or even a traction engine. Portable engines were used mainly for driving...
is a stationary engine mounted on wheels so that it may be towed to a work-site by horses or a
traction engineA traction engine is a self-propelled steam engine 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 traction engine is to draw a load behind it...
, rather than being fixed in a single location.
Transport applications
Steam engines have been used to power a wide array of transport appliances:
- Marine: Steamboat
A steamboat or steamship, sometimes called a steamer, is a ship in which the primary method of propulsion is steam power, typically driving propellers or paddlewheels....
, Steamship
- Rail: Steam locomotive
A steam locomotive is a locomotive powered by steam. The term usually refers to its use on railways, but can also refer to a "road locomotive" such as a traction engine or steamroller....
, Fireless locomotiveA fireless locomotive is a type of locomotive designed for use under conditions restricted by either the presence of flammable material or the need for cleanliness...
- Agriculture: Traction engine
A traction engine is a self-propelled steam engine 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 traction engine is to draw a load behind it...
, Steam tractorA steam tractor is a vehicle powered by a steam engine which is used for pulling.In North America, the term steam tractor usually refers to a type of agricultural tractor powered by a steam engine, used extensively in the late 1800s and early 1900s....
- Road: Steam wagon
A steam wagon is a steam-powered road vehicle for carrying freight. It was the earliest form of lorry and came in two basic forms: overtype and undertype – the distinction being the position of the engine relative to the boiler...
, Steam busA steam bus is a bus powered by a steam engine. Early steam-powered vehicles designed for carrying passengers were more usually known as steam carriages, although this term was sometimes used to describe other early experimental vehicles too.-History:...
, Steam tricycleA steam tricycle is a steam-driven three-wheeled vehicle.-History:In the early days of motorised vehicle development, a number of experimenters built steam-powered vehicles with three wheels....
, Steam carA steam car is a car powered by a steam engine.- Technology :A steam engine is an external combustion engine , as opposed to an internal combustion engine...
- Construction: Steam roller
A steamroller is a form of road roller – a type of heavy construction machinery used for levelling surfaces, such as roads or airfields – that is powered by a steam engine...
, Steam shovelA steam shovel is a large steam-powered excavating machine designed for lifting and moving material such as rock and soil. It is the earliest type of power shovel.-Origins and development:...
- Military: Steam tank (tracked)
The Steam Tank was an early U.S. tank design of 1918 imitating the design of the British Mark IV tank but powered by steam.The type was designed by an officer from the U.S. Army's Corps Of Engineers. The project was started by General John A...
, Steam tank (wheeled)The Steam Wheel Tank was the official US Army name for the vehicle also known as the three-wheeled steam tank, the Holt Steam Tank and the Holt 150 Ton Field Monitor. It was an early U.S. produced tank built by the Holt Manufacturing Company sometime between late 1916 and early 1917. It was the...
- Space: Steam rocket
In these applications internal combustion engines are now used due to their higher
power-to-weight ratioPower-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...
, lower maintenance and space requirements .
History
The history of the steam engine stretches back as far as the first century AD; the first recorded rudimentary steam engine being the
aeolipileAn aeolipile , also known as a Hero engine, is a rocket style jet engine which spins when heated. In the first century AD, Hero of Alexandria described the device, and many sources give him the credit for its invention.The aeolipile he described is considered to be the first recorded steam engine...
described by
Hero of AlexandriaHero of Alexandria . was an ancient Greek mathematician who was a resident of a Roman province ; he was also an engineer who was active in his native city of Alexandria...
. In the following centuries, the few engines known about were essentially experimental devices used by inventors to demonstrate the properties of
steamSteam is vaporized water. It is a transparent gas . At standard temperature and pressure, pure steam occupies about 1,600 times the volume of an equal mass of liquid water...
, such as the rudimentary
steam turbineA 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....
device described by
Taqi al-DinTaqi al-Din Muhammad ibn Ma'ruf al-Shami al-Asadi was a major Ottoman Turkish or Arab Muslim polymath: a scientist, astronomer and astrologer, engineer and inventor, clockmaker, physicist and mathematician, botanist and zoologist, pharmacist and physician, Islamic judge and mosque timekeeper,...
in 1551 and
Giovanni BrancaGiovanni Branca was an Italian engineer and architect, chiefly remembered today for what some commentators have taken to be an early steam engine.-Life:...
in 1629.
The first practical steam-powered 'engine' was a water pump, developed in 1698 by
Thomas SaveryThomas Savery was an English inventor, born at Shilstone, a manor house near Modbury, Devon, England.-Career:Savery became a military engineer, rising to the rank of Captain by 1702, and spent his free time performing experiments in mechanics...
. It proved only to have a limited lift height and was prone to
boiler explosionBoiler explosions are catastrophic failures of boilers. As seen today, boiler explosions are of two kinds. One kind is over-pressure in the pressure parts of the steam and water sides. The second kind is explosion in the furnace. Boiler explosions of pressure parts are particularly associated...
s, but it still received some use for mines and
pumping stationPumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low-lying land, and the removal of sewage to processing sites.A pumping station...
s.
The first commercially successful engine did not appear until 1712. Incorporating technologies discovered by Savery and
Denis PapinDenis Papin was a French physicist, mathematician and inventor, best known for his pioneering invention of the steam digester, the forerunner of the steam engine.-Life in France:...
, the atmospheric engine, invented by
Thomas NewcomenThomas Newcomen was an ironmonger by trade and a Baptist lay preacher by calling. He was born in Dartmouth, Devon, England, near a part of the country noted for its tin mines. Flooding was a major problem, limiting the depth at which the mineral could be mined...
, paved the way for the Industrial Revolution. Newcomen's engine was relatively inefficient, and in most cases was only used for pumping water. It was mainly employed for draining mine workings at depths hitherto impossible, but also for providing a reusable water supply for driving waterwheels at factories sited away from a suitable 'head'.
The next major step occurred when James Watt developed an improved version of Newcomen's engine.
Watt's engineThe Watt steam engine was the first type of steam engine to make use of steam at a pressure just above atmospheric to drive the piston helped by a partial vacuum...
used 75% less coal than Newcomen's, and was hence much cheaper to run. Watt proceeded to develop his engine further, modifying it to provide a rotary motion suitable for driving factory machinery. This enabled factories to be sited away from rivers, and further accelerated the pace of the Industrial Revolution.
Newcomen's and Watt's early engines were "atmospheric", meaning that they were powered by the
vacuumIn everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty," but in reality, no volume of space can ever be perfectly empty...
generated by
condensingCondensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase and the reverse of evaporation. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase, the change is called deposition...
steam instead of the
pressurePressure 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 :...
of expanding steam.
CylinderA 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...
s had to be large, as the only usable force acting on them was
atmospheric pressureAtmospheric pressure is defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above...
. Steam was only used to compensate for the atmosphere allowing the piston to move back to its starting position. Even if pressured steam had been available, it could not do any work (push) against the
chainIn most meanings chain is a sequence of connected links of some kind.Chain may refer to:* A physical, literal chain* Chain , unit of length* Gunter's chain, a unit of measurement...
connecting the piston to the beam.
Around 1800,
Richard TrevithickRichard Trevithick was a British inventor and mining engineer. His most significant success was the high pressure steam engine and he also built the first full-scale working railway steam locomotive...
introduced engines using high-pressure steam. These were much more powerful than previous engines and could be made small enough for transport applications. Thereafter, technological developments and improvements in manufacturing techniques (partly brought about by the adoption of the steam engine as a power source) resulted in the design of more efficient engines that could be smaller, faster, or more powerful, depending on the intended application.
Steam engines remained the dominant source of power well into the 20th century, when advances in the design of
electric motorAn electric motor uses electrical energy to produce mechanical energy, usually through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. Traction motors used on...
s and
internal combustion engineThe 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 pressure gases, which are produced by the combustion, directly applies force to a movable...
s gradually resulted in the vast majority of reciprocating steam engines being replaced in commercial usage, and the ascendancy of steam turbines in power generation.
See also
The history of steam engine development is a vast subject. The following articles cover aspects of steam engine development in greater detail:
- Timeline of steam power
See Steam engine, Steam power during the Industrial Revolution.Steam power developed slowly over a period of several hundred years, progressing through expensive and fairly limited devices in the early 1600s, to useful pumps for mining in 1700, and then to Watt's improved designs in the late 1700s...
– overview
- History of the steam engine
This article primarily deals with the history of the reciprocating-type steam engine.
The parallel development of turbine-type engines is described in the steam turbine article....
– general history, concentrating on reciprocating engines
- 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....
– the parallel development of turbine-type engines
- Steam power during the Industrial Revolution
During the Industrial Revolution, steam power replaced water power and muscle power as the primary source of power in use in industry. Its first use was to pump water from mines. The early steam engines were not very efficient, but a modified version created by James Watt gave engines the power...
- History of steam road vehicles
The history of steam road vehicles describes the development of vehicles powered by a steam engine for use on land and independent of rails; whether for conventional road use, such as the steam car and steam waggon, or for agricultural or heavy haulage work, such as the traction engine.The first...
Basic operation of a simple reciprocating steam engine
- Heat is obtained from fuel burnt in a closed firebox
- The heat is transferred to the water in a pressurised boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Overview:-Materials:...
, ultimately boiling the water and transforming it into saturated steam. Steam in its saturated state is always produced at the temperature of the boiling water, which in turn depends on the steam pressure on the water surface within the boiler.
- The steam is transferred to the motor unit which uses it to push on a piston
A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod...
sliding inside a cylinderA 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...
to power machinery.
- The used, cooler, lower pressure steam is exhausted to atmosphere.
Components of steam engines
There are two fundamental components of a steam engine: the
boilerA boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Overview:-Materials:...
or
steam generatorA boiler or steam generator is a device used to create steam by applying heat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure , but at pressures above this it is more usual...
, and the "motor unit", itself often referred to as a "steam engine". The two components can either be integrated into a single unit or can be placed at a distance from each other, in a variety of configurations.
Other components are often present; pumps (such as an
injectorAn injector, ejector, steam ejector or steam injector is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that draws in and entrains a suction fluid...
) to supply water to the boiler during operation, condensers to recirculate the water and recover the latent heat of vaporisation, and superheaters to raise the temperature of the steam above its saturated vapour point, and various mechanisms to increase the draft for fireboxes. When
coalCoal is a readily combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
is used, a chain or screw stoking mechanism and its drive engine or motor may be included to move the fuel from a supply bin (bunker) to the firebox.
Heat source
The heat required for boiling the water and supplying the steam can be derived from various sources, most commonly from burning combustible materials with an appropriate supply of air in a closed space (called variously
combustion chamber-Internal combustion engine: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...
, firebox). In some cases the heat source is a
nuclear reactorA nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate.The most significant use of nuclear reactors is as an energy source for the generation of electrical power and for the power in some ships...
or
geothermalGeothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...
energy.
Boilers
Boilers are
pressure vesselA pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is potentially dangerous and many fatal accidents have occurred in the history of their development and operation...
s that contain water to be boiled, and some kind of mechanism for
transferring the heat to the waterA heat exchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants,...
so as to boil it.
The two most common methods of transferring heat to the water according are:
- water-tube boiler
A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Water tube boilers are used for high-pressure boilers. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...
- water is contained in or run through one or several tubes surrounded by hot gases
- fire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
- the water partially fills a vessel below or inside of which is a combustion chamber or furnace and fire tubes through which the hot gases flow
Once turned to steam, some boilers use
superheatingIn physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...
to raise the temperature of the steam further. This allows for greater efficiency.
Motor units
A motor unit takes a supply of steam at high pressure and temperature and gives out a supply of steam at lower pressure and temperature, using as much of the difference in steam energy as possible to do mechanical work.
A motor unit is often called 'steam engine' in its own right. They will also operate on compressed air or other gas.
Simple expansion
This means that a charge of steam works only once in the cylinder. It is then exhausted directly into the atmosphere or into a
condenserA steam locomotive condensing apparatus differs in purpose from the usual closed cycle steam engine condenser, in that its function is primarily either to recover water, or to avoid excessive emissions to the atmosphere, rather than maintaining a vacuum to improve both efficiency and power...
, but remaining heat can be utilized if needed to heat a living space, or to provide warm feedwater for the boiler.
In most reciprocating piston engines the steam reverses its direction of flow at each
strokeReciprocating 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...
(counterflow), entering and exhausting from the cylinder by the same port. The complete engine cycle occupies one rotation of the crank and two piston strokes; the cycle also comprises four
events — admission, expansion, exhaust, compression. These events are controlled by valves often working inside a
steam chest adjacent to the cylinder; the valves distribute the steam by opening and closing steam
ports communicating with the cylinder end(s) and are driven by
valve gearThe valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...
, of which there are many types.
The simplest valve gears give events of fixed length during the engine cycle and often make the engine rotate in only one direction. Most however have a reversing mechanism which additionally can provide means for saving steam as speed and momentum are gained by gradually "shortening the
cutoffIn a steam engine, cutoff is the point in the piston stroke at which the inlet valve is closed.The point at which the inlet valve closes and stops the entry of steam into the cylinder from the boiler plays a crucial role in the control of a steam engine. Once the valve has closed, steam trapped in...
" or rather, shortening the admission event; this in turn proportionately lengthens the expansion period. However, as one and the same valve usually controls both steam flows, a short cutoff at admission adversely affects the exhaust and compression periods which should ideally always be kept fairly constant; if the exhaust event is too brief, the totality of the exhaust steam cannot evacuate the cylinder, choking it and giving excessive compression (
"kick back").
In the 1840s and 50s there were attempts to overcome this problem by means of various patent valve gears with separate variable cutoff valves riding on the back of the main slide valve; the latter usually had fixed or limited cutoff. The combined setup gave a fair approximation of the ideal events, at the expense of increased friction and wear, and the mechanism tended to be complicated. The usual compromise solution has been to provide
lap by lengthening rubbing surfaces of the valve in such a way as to overlap the port on the admission side, with the effect that the exhaust side remains open for a longer period after cut-off on the admission side has occurred. This expedient has since been generally considered satisfactory for most purposes and makes possible the use of the simpler
StephensonThe Stephenson valve gear or Stephenson link or shifting link is a simple design of valve gear that was widely used throughout the world for all kinds of steam engine. It was patented by George Stephenson but was actually invented by his employees....
,
JoyJoy valve gear is a type of locomotive valve gear, patented in 1870, where the movement is derived from a vertical link connected to the connecting rod. The vertical movement is translated into the horizontal movement required by the valve spindle by a die block moving in a slide which can be...
and Walschaerts motions.
CorlissA Corliss steam engine is a steam engine, fitted with rotary valves and with variable valve timing, invented by and named after the American engineer George Henry Corliss....
, and later,
poppet valveA 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...
gears had separate admission and exhaust valves driven by
trip mechanismsTrip valve mechanisms are a class of steam engine valve gear developed to improve efficiency. The trip mechanism allows the inlet valve to be closed rapidly, giving a short, sharp cut-off. The valve itself can be a drop valve or a Corliss valve....
or
camA cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...
s profiled so as to give ideal events; most of these gears never succeeded outside of the stationary marketplace due to various other issues including leakage and more delicate mechanisms.
- Compression
Before the exhaust phase is quite complete, the exhaust side of the valve closes, shutting a portion of the exhaust steam inside the cylinder. This determines the compression phase where a cushion of steam is formed against which the piston does work whilst its velocity is rapidly decreasing; it moreover obviates the pressure and temperature shock, which would otherwise be caused by the sudden admission of the high pressure steam at the beginning of the following cycle.
- Lead
The above effects are further enhanced by providing
lead: as was later discovered with the
internal combustion engineThe 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 pressure gases, which are produced by the combustion, directly applies force to a movable...
, it has been found advantageous since the late 1830s to advance the admission phase, giving the valve
lead so that admission occurs a little before the end of the exhaust stroke in order to fill the
clearance volume comprising the ports and the cylinder ends (not part of the piston-swept volume) before the steam begins to exert effort on the piston.
Compounding engines
As steam expands in a high pressure engine its temperature drops; because no heat is released from the system, this is known as
adiabatic expansionIn thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid. The term "adiabatic" literally means impassable, coming from the Greek roots ἀ- , διὰ- , and βαῖνειν ; this etymology corresponds here to an...
and results in steam entering the cylinder at high temperature and leaving at low temperature. This causes a cycle of heating and cooling of the cylinder with every stroke which is a source of inefficiency.
A method to lessen the magnitude of this heating and cooling was invented in 1804 by British engineer
Arthur WoolfArthur Woolf 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 the Cornish Engine.Woolf left Cornwall in 1785 to work for Joseph Bramah's engineering works in London...
, who patented his Woolf high pressure compound engine in 1805. In the compound engine, high pressure steam from the boiler expands in a high pressure (HP) cylinder and then enters one or more subsequent lower pressure (LP) cylinders. The complete expansion of the steam now occurs across multiple cylinders and as less expansion now occurs in each cylinder so less heat is lost by the steam in each. This reduces the magnitude of cylinder heating and cooling, increasing the efficiency of the engine. To derive equal work from lower pressure steam requires a larger cylinder volume as this steam occupies a greater volume. Therefore the bore, and often the stroke, are increased in low pressure cylinders resulting in larger cylinders.
Double expansion (usually known as compound
) engines expanded the steam in two stages. The pairs may be duplicated or the work of the large LP cylinder can be split with one HP cylinder exhausting into one or the other, giving a 3-cylinder layout where cylinder and piston diameter are about the same making the reciprocating masses easier to balance.
Two-cylinder compounds can be arranged as:
Cross compounds
- The cylinders are side by side.
Tandem compounds
- The cylinders are end to end, driving a common connecting rod
Angle compounds - The cylinders are arranged in a vee (usually at a 90° angle) and drive a common crank.
With two-cylinder compounds used in railway work, the pistons are connected to the cranks as with a two-cylinder simple at 90° out of phase with each other (quartered).
When the double expansion group is duplicated, producing a 4-cylinder compound, the individual pistons within the group are usually balanced at 180°, the groups being set at 90° to each other. In one case (the first type of
Vauclain compoundThe Vauclain compound was a type of compound steam locomotive that was briefly popular around 1900. Developed at the Baldwin Locomotive Works, it featured two pistons moving in parallel, driving a common crosshead and controlled by a common valve gear using a single, complex piston valve.The...
), the pistons worked in the same phase driving a common crosshead and crank, again set at 90° as for a two-cylinder engine.
With the 3-cylinder compound arrangement, the LP cranks were either set at 90° with the HP one at 135° to the other two, or in some cases all three cranks were set at 120°.
The adoption of compounding was common for industrial units, for road engines and almost universal for marine engines after 1880; it was not universally popular in railway locomotives where it was often perceived as complicated. This is partly due to the harsh railway operating environment and limited space afforded by the
loading gaugeA loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...
(particularly in Britain, where compounding was never common and not employed after 1930). However although never in the majority it was popular in many other countries.
Multiple expansion engines
It is a logical extension of the compound engine (described above) to split the expansion into yet more stages to increase efficiency. The result is the multiple expansion engine. Such engines use either three or four expansion stages and are known as triple
and quadruple expansion engines respectively. These engines use a series of double-acting cylinders of progressively increasing diameter and/or stroke and hence volume. These cylinders are designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. As with the double expansion engine, where space is at a premium, two smaller cylinders of a large sum volume may be used for the low pressure stage. Multiple expansion engines typically had the cylinders arranged inline, but various other formations were used. In the late 19th century, the Yarrow-Schlick-Tweedy balancing 'system' was used on some marine triple expansion engines. Y-S-T engines divided the low pressure expansion stages between two cylinders, one at each end of the engine. This allowed the crankshaft to be better balanced, resulting in a smoother, faster-responding engine which ran with less vibration. This made the 4-cylinder triple-expansion engine popular with large passenger liners (such as the
Olympic classThe Olympic-class ocean liners were a trio of ocean liners built by the Harland & Wolff shipyard for the White Star Line in the early 20th century. Although the three were the largest and most luxurious of their time, two were lost early in their careers: in the infamous disaster on the morning of...
), but was ultimately replaced by the virtually vibration-free turbine (see below).
The image to the right shows an animation of a triple expansion engine. The steam travels through the engine from left to right. The valve chest for each of the cylinders is to the left of the corresponding cylinder.
The development of this type of engine was important for its use in steamships as by exhausting to a condenser the water can be reclaimed to feed the boiler, which is unable to use
seawaterSeawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every of seawater has approximately of dissolved salts...
. Land-based steam engines could exhaust much of their steam, as feed water was usually readily available. Prior to and during
World War IIWorld War II, or the Second World War , was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis...
, the expansion engine dominated marine applications where high vessel speed was not essential. It was however superseded by the British invention
steam turbineA 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....
where speed was required, for instance in warships, such as the dreadnought battleships, and
ocean linerAn ocean liner is a ship designed to transport people from one seaport to another along regular long-distance maritime routes according to a schedule. Liners may also carry cargo, mail, and may sometimes be used for other purposes .Cargo vessels running to a schedule are sometimes referred to as...
s.
HMS DreadnoughtThe sixth HMS Dreadnought of the Royal Navy was a battleship that revolutionised naval power when she entered service in 1906. Dreadnought represented such a marked advance in naval technology that her name came to be associated with an entire generation of battleships, the "dreadnoughts", as well...
of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.
Uniflow (or unaflow) engine
This is intended to remedy the difficulties arising from the usual counterflow cycle mentioned above which means that at each stroke the port and the cylinder walls will be cooled by the passing exhaust steam, whilst the hotter incoming admission steam will waste some of its energy in restoring working temperature. The aim of the uniflow is to remedy this defect by providing an additional port uncovered by the piston at the end of each stroke making the steam flow only in one direction. By this means, thermal efficiency is improved by having a steady temperature gradient along the cylinder bore. The simple-expansion uniflow engine is reported to give efficiency equivalent to that of classic compound systems with the added advantage of superior part-load performance. It is also readily adaptable to high-speed uses and was a common way to drive electricity generators towards the end of the 19th century before the coming of the steam turbine.
The inlet valves may be driven by a double cam system whose phasing and duration is controllable; this allows adjustments for high torque and power when needed with more restrained use of steam and greater expansion for economical cruising.
Uniflow engines have been produced in single-acting, double-acting, simple, and compound versions. Skinner 4-crank 8-cylinder single-acting tandem compound engines power two
Great LakesThe Great Lakes are a collection of freshwater lakes located in eastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth. They are sometimes referred to as the "Third...
ships still trading today (2007). These are the Saint Marys Challenger, that in 2005 completed 100 years of continuous operation as a powered carrier (the Skinner engine was fitted in 1950) and the car ferry, .
In the early 1950s the Ultimax engine, a 2-crank 4-cylinder arrangement similar to Skinner’s, was developed by
Abner DobleAbner Doble , was an American mechanical engineer who built and sold steam-powered automobiles. His father was William Ashton Doble, inventor of the Doble water wheel, and his grandfather and namesake was the founder of the Abner Doble Company.Abner Doble began apprenticing at his family's factory...
for the Paxton car project with tandem opposed single-acting cylinders giving effective double-action.
Small uniflow steam engines have been made as conversions of two-stroke internal combustion engines, by feeding the cylinder with steam via a "bash valve" in the spark plug hole which is knocked open by the piston reaching the top of its stroke.
Turbine engines
A steam turbine consists of an alternating series of one or more rotating discs mounted on a drive shaft, rotors
, and static discs fixed to the turbine casing, stators. The rotors have a propeller-like arrangement of blades at the outer edge. Steam acts upon these blades, producing rotary motion. The stator consists of a similar, but fixed, series of blades that serve to redirect the steam flow onto the next rotor stage. A steam turbine often exhausts into a surface condenser that provides a vacuum. The stages of a steam turbine are typically arranged to extract the maximum potential work from a specific velocity and pressure of steam, giving rise to a series of variably sized high and low pressure stages. Turbines are only effective if they rotate at very high speed, therefore they are usually connected to reduction gearing to drive another mechanism, such as a ship's propeller, at a lower speed. This gearbox can be mechanical but today it is more common to use an alternator/generator set to produce electricity that later is used to drive an electric motor. A turbine rotor is also only capable of providing power when rotating in one direction. Therefore a reversing stage or gearbox is usually required where power is required in the opposite direction.
Steam turbines provide direct rotational force and therefore do not require a linkage mechanism to convert reciprocating to rotary motion. Thus, they produce smoother rotational forces on the output shaft. This contributes to a lower maintenance requirement and less wear on the machinery they power than a comparable reciprocating engine.
The main use for steam turbines is in
electricity generationElectricity generation is the process of creating electricity from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...
(about 80% of the world's electric production is by use of steam turbines) and to a lesser extent as marine prime movers. In the former, the high speed of rotation is an advantage, and in both cases the relative bulk is not a disadvantage; in the latter (pioneered on the
TurbiniaTurbinia was the first steam turbine powered steamship. Built as an experimental vessel in 1894, and easily the fastest ship in the world at that time, Turbinia was demonstrated dramatically at the Spithead Navy Review in 1897 and set the standard for the next generation of steamships, the...
), the light weight, high efficiency and high power are highly desirable.
Virtually all
nuclear powerNuclear power is power produced from controlled nuclear reactions. Commercial plants in use to date use nuclear fission reactions....
plants generate electricity by heating water to provide steam that drives a turbine connected to an
electrical generatorIn electricity generation, an electrical generator is a device that converts mechanical energy to electrical energy. The reverse conversion of electrical energy into mechanical energy is done by a motor; motors and generators have many similarities...
.
Nuclear-powered ships and submarinesNuclear marine propulsion is propulsion of a ship powered by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships .-Power plants:...
either use a steam turbine directly for main propulsion, with generators providing auxiliary power, or else employ
turbo-electricA turbo-electric transmission uses electric generators to convert the mechanical energy of a turbine into electric energy and electric motors to convert it back into mechanical energy to power the driveshafts....
propulsion, where the steam drives a turbine-generator set with propulsion provided by electric motors. A limited number of
steam turbine railroad locomotivesA steam turbine locomotive is a steam locomotive which transmits steam power to the wheels via a steam turbine. Numerous attempts at this type of locomotive were made, mostly without success...
were manufactured. Some non-condensing direct-drive locomotives did meet with some success for long haul freight operations in
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
and for
express passenger work in BritainThe Turbomotive was a modified Princess Royal Class steam locomotive designed by William Stanier and built by the London, Midland and Scottish Railway in 1935. It used turbines instead of cylinders...
, but were not repeated. Elsewhere, notably in the U.S.A., more advanced designs with electric transmission were built experimentally, but not reproduced. It was found that steam turbines were not ideally suited to the railroad environment and these locomotives failed to oust the classic reciprocating steam unit in the way that modern diesel and electric traction has done.
Rotary steam engines
It is possible to use a mechanism based on a
pistonless rotary engineA pistonless rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does, but instead uses one or more rotors, sometimes called rotary pistons...
such as the
Wankel engineThe Wankel engine is a type of internal combustion engine which uses a rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that is...
in place of the cylinders and
valve gearThe valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...
of a conventional reciprocating steam engine. Many such engines have been designed, from the time of James Watt to the present day, but relatively few were actually built and even fewer went into quantity production; see link at bottom of article for more details. The major problem is the difficulty of sealing the rotors to make them steam-tight in the face of wear and thermal expansion; the resulting leakage made them very inefficient. Lack of expansive working, or any means of control of the
cutoffIn a steam engine, cutoff is the point in the piston stroke at which the inlet valve is closed.The point at which the inlet valve closes and stops the entry of steam into the cylinder from the boiler plays a crucial role in the control of a steam engine. Once the valve has closed, steam trapped in...
is also a serious problem with many such designs.
By the 1840s it was clear that the concept had inherent problems and rotary engines were treated with some derision in the technical press. However, the arrival of electricity on the scene, and the obvious advantages of driving a dynamo directly from a high-speed engine, led to something of a revival in interest in the 1880s and 1890s, and a few designs had some limited success.
Of the few designs that were manufactured in quantity, those of the Hult Brothers Rotary Steam Engine Company of Stockholm, Sweden, and the spherical engine of
Beauchamp TowerBeauchamp Tower was an English inventor and railway engineer who is chiefly known for his discovery of full-film or hydrodynamic lubrication.-Early life:...
are notable. Tower's engines were used by the
Great Eastern RailwayThe Great Eastern Railway was a pre-grouping British railway company, whose main line linked London Liverpool Street to Norwich and which had other lines through East Anglia...
to drive lighting dynamos on their locomotives, and by the
AdmiraltyThe Admiralty was formerly the authority in the United Kingdom responsible for the command of the Royal Navy. Originally exercised by a single person, the office of Lord High Admiral was from the 18th century onward almost invariably put "in commission", and was exercised by a Board of Admiralty.In...
for driving dynamos on board the ships of the
Royal NavyThe Royal Navy of the United Kingdom is the oldest of HM Armed Forces . From the beginning of the 18th century until well into the 20th century, it was the most powerful navy in the world, playing a key part in establishing the British Empire as the dominant world power from 1815 until the early...
. They were eventually replaced in these niche applications by steam turbines.
Jet type
Invented by Australian engineer
Alan BurnsProfessor Alan Burns is a professor in the Computer Science Department at the University of York. He has been at the University of York since 1990, and held the post of Head of Department from 1999 until 30 June 2006, when he was succeeded by John McDermid....
and developed in Britain by engineers at Pursuit Dynamics, this underwater
jet engineA jet engine is a reaction engine that discharges a fast moving jet of fluid to generate thrust in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets and pump-jets...
uses high pressure steam to draw in water through an intake at the front and expel it at high speed through the rear. When steam condenses in water, a shock wave is created and is focused by the chamber to blast water out of the back. To improve the engine's efficiency, the engine draws in air through a vent ahead of the steam jet, which creates air bubbles and changes the way the steam mixes with the water.
Unlike in conventional steam engines, there are no moving parts to wear out, and the exhaust water is only several degrees warmer in tests. The engine can also serve as pump and mixer. This type of system is referred to as 'PDX Technology' by Pursuit Dynamics and has been applied to
food technologyFood technology, or Food tech for short is the application of food science to the selection, preservation, processing, packaging, distribution, and use of safe, nutritious, and wholesome food....
problems.
Rocket type
The
aeolipileAn aeolipile , also known as a Hero engine, is a rocket style jet engine which spins when heated. In the first century AD, Hero of Alexandria described the device, and many sources give him the credit for its invention.The aeolipile he described is considered to be the first recorded steam engine...
represents the use of steam by the rocket-reaction principle, although not for direct propulsion.
In more modern times there has been limited use of steam for rocketry—particularly for rocket cars. The technique is simple in concept, simply fill a pressure vessel with hot water at high pressure, and open a valve leading to a suitable nozzle. The drop in pressure immediately boils some of the water and the steam leaves through a nozzle, giving a significant propulsive force.
It might be expected that water in the pressure vessel should be at high pressure; but in practice the pressure vessel has considerable mass, which reduces the acceleration of the vehicle. Therefore a much lower pressure is used, which permits a lighter pressure vessel, which in turn gives the highest final speed.
There are even speculative plans for interplanetary use. Although steam rockets are relatively inefficient in their use of propellant, this very well may not matter as the solar system is believed to have extremely large stores of water ice which can be used as propellant. Extracting this water and using it in interplanetary rockets requires several orders of magnitude less equipment than breaking it down to hydrogen and oxygen for conventional rocketry.
Cold sink
As with all heat engines, a considerable quantity of waste heat is produced at relatively low temperature. This must be disposed of.
The simplest cold sink is simply to vent the steam to the environment. This is often used on
Steam locomotiveA steam locomotive is a locomotive powered by steam. The term usually refers to its use on railways, but can also refer to a "road locomotive" such as a traction engine or steamroller....
s, but is typically very inefficient.
Steam locomotive condensing apparatusA steam locomotive condensing apparatus differs in purpose from the usual closed cycle steam engine condenser, in that its function is primarily either to recover water, or to avoid excessive emissions to the atmosphere, rather than maintaining a vacuum to improve both efficiency and power...
can be employed to improve efficiency.
Alternatively, sometimes the 'waste heat' is useful in and of itself, and in those cases very high overall efficiency can be obtained; for example
combined heat and powerCombined Heat and Power may refer to:* Cogeneration* Combined Heat and Power Solar...
(CHP) uses the waste heat/steam for
district heatingDistrict heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...
. This is highly efficient.
Where CHP is not being used steam turbines in power stations virtually all use surface condensers as a cold sink for their cycles. The condensers are cooled by water flow from oceans, rivers, lakes, and often by cooling towers which evaporate water to provide cooling energy removal. The resulting condensed hot water output from the condenser is then put back into the boiler via a pump.
Monitoring equipment
For safety reasons nearly all steam engines are equipped with mechanisms to monitor the boiler, such as a pressure gauge and a
sight glassA sight glass or water gauge is a transparent tube through which the operator of a tank or boiler can observe the level of liquid contained within.-Liquid in tanks:...
to monitor the water level.
Advantages
The strength of the steam engine for modern purposes is in its ability to convert heat from almost any source into mechanical work, unlike the internal combustion engine.
Similar advantages are found in a different type of external combustion engine, the
Stirling engineA Stirling engine is a heat engine that operates 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....
, which can offer efficient power (with advanced regenerators and large radiators) at the cost of a much lower power-to-size/weight ratio than even modern steam engines with compact boilers . These Stirling engines are not commercially produced, although the concepts are promising.
Steam locomotives are especially advantageous at high elevations as they are not adversely affected by the lower atmospheric pressure. This was inadvertently discovered when steam locomotives operated at high altitudes in the mountains of South America were replaced by diesel-electric units of equivalent sea level power. These were quickly replaced by much more powerful locomotives capable of producing sufficient power at high altitude.
For road vehicles, steam propulsion has the advantage of having high torque from stationary, removing the need for a clutch and transmission, though start-up time and sufficiently compact packaging remain a problem.
In Switzerland (Brienz Rothhorn) and Austria (Schafberg Bahn) new rack steam locomotives have proved very successful. They were designed based on a 1930s design of
Swiss Locomotive and Machine WorksSwiss Locomotive and Machine Works were a railway equipment manufacturer based in Winterthur in Switzerland. Much of the world's mountain railway equipment was constructed by them....
(SLM) but with all of today's possible improvements like roller bearings, heat insulation, light-oil firing, improved inner streamlining, one-man-driving and so on. These resulted in 60 percent lower fuel consumption per passenger and massively reduced costs for maintenance and handling. Economics now are similar or better than with most advanced diesel or electric systems. Also a steam train with similar speed and capacity is 50 percent lighter than an electric or diesel train, thus, especially on rack railways, significantly reducing wear and tear on the track. Also, a new steam engine for a paddle steam ship on Lake Geneva, the Montreux, was designed and built, being the world's first full-size ship steam engine with an electronic
remote controlRadio control is the use of radio signals to remotely control a device. The term is used frequently to refer to the control of model vehicles from a hand-held radio transmitter...
. The steam group of SLM in 2000 created a wholly owned company called DLM to design modern steam engines and steam locomotives.
Safety
Steam engines possess boilers and other components that are pressure vessels that contain a great deal of potential energy. Steam escapes and
boiler explosionBoiler explosions are catastrophic failures of boilers. As seen today, boiler explosions are of two kinds. One kind is over-pressure in the pressure parts of the steam and water sides. The second kind is explosion in the furnace. Boiler explosions of pressure parts are particularly associated...
s (typically
BLEVEBLEVE , is an acronym for boiling liquid expanding vapor explosion. This is a type of explosion that can occur when a vessel containing a pressurized liquid is ruptured. Such explosions can be extremely hazardous....
s) can and have caused great loss of life in the past. While variations in standards may exist in different countries, stringent legal, testing, training, care with manufacture, operation and certification is applied to try to minimise or prevent such occurrences.
Failure modes include:
- over-pressurisation of the boiler
- insufficient water in the boiler causing overheating and vessel failure
- pressure vessel failure of the boiler due to inadequate construction or maintenance.
- escape of steam from pipework/boiler causing scalding
Steam engines frequently possess two independent mechanisms for ensuring that the pressure in the boiler does not go too high; one may be adjusted by the user, the second is typically designed as an ultimate fail-safe.
Lead
fusible plugA fusible plug is a threaded metal plug, usually of bronze, brass or gunmetal, with a tapered hole drilled completely through its length. This hole is sealed with a metal of low melting point, usually lead or tin. It is screwed into the crown sheet of a steam engine firebox, typically extending...
s may be present in the crown of the firebox. If the water level drops, such that the temperature of the firebox crown increases significantly, the
leadLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
melts and the steam escapes warning the operators, who may then manually drop the fire. Except in the smallest of boilers the steam escape has little effect on dampening the fire. The plugs are also too small in area to lower steam pressure significantly, depressurizing the boiler. If they were any larger, the volume of escaping steam would itself endanger the crew.
Efficiency
The efficiency of an engine can be calculated by dividing the energy output of mechanical work that the engine produces by the energy input to the engine by the burning fuel.
No heat engine can be more efficient than the
Carnot cycleEvery thermodynamic system exists in a particular state. When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred. In the process of going through this cycle, the system may perform work on its...
, in which heat is moved from a high temperature reservoir to one at a low temperature, and the efficiency depends on the temperature difference. For the greatest efficiency, steam engines should be operated at the highest steam temperature possible (
superheated steamA superheater is a device used to convert saturated steam into dry steam used for power generation or processes. There are three types of superheaters namely: radiant, convection, and separately fired...
), and release the waste heat at the lowest temperature possible.
In practice, a steam engine exhausting the steam to atmosphere will typically have an efficiency (including the boiler) in the range of 1% to 10%, but with the addition of a condenser and multiple expansion, it may be greatly improved to 25% or better.
A mega watt electrical power station with steam reheat, economizer etc. will achieve up to 50% thermal efficiency.
It is also possible to capture the waste heat using
cogenerationCogeneration is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat...
in which the waste heat is used for heating a lower boiling point working fluid or as a heat source for district heating via saturated low pressure steam. By this means it is possible to use as much as 85-90% of the input energy.
Modern applications
Although the reciprocating steam engine is no longer in widespread commercial use, various companies are exploring or exploiting the potential of the engine as an alternative to internal combustion engines.
The company Energiprojekt AB in
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
has made progress in using modern materials for harnessing the power of steam. The efficiency of Energiprojekt's steam engine reaches some 27-30% on high-pressure engines. It is a single-step, 5-cylinder engine (no compound) with superheated steam and consumes approx. 4 kg of steam per kWh.
Steam museums
- See also: List of pumping stations, many of which are, or were, steam-powered.
UK
- Bolton Steam Museum
Bolton Steam Museum is a museum in Bolton, Greater Manchester, England, which houses a variety of preserved steam engines. It is owned and run by the Northern Mill Engine Society .-Overview:...
- Bressingham Steam and Gardens - Gardens, Steam railways and museum of steam vehicles
- Crofton Beam Engines
- Hollycombe Steam Collection
The Hollycombe Steam Collection is a collection of steam-powered vehicles, rides and attractions based at Liphook in Hampshire. The collection includes fairground rides, a display farm and two railways.- History :...
- Kempton Park Steam Engines
The Kempton Park Steam Engines are two large triple-expansion steam engines, dating from 1926-1929, at the Kempton Park waterworks, Middlesex, London. Each engine is of a similar size to that used in RMS Titanic and rated at about 1008hp...
- Kew Bridge Steam Museum
Kew Bridge Steam Museum houses a museum of water supply and a collection of water pumping steam engines. The museum is an Anchor Point of ERIH, The European Route of Industrial Heritage...
US
- The New England Wireless and Steam Museum
Canada
- Ontario Agricultural Museum
The Country Heritage Park is located in Milton, Ontario and recreates rural life in the 1800s in Ontario...
in Milton, OntarioMilton is a town in Southern Ontario, Canada, part of the Greater Toronto Area, located 40 km west of Toronto on Highway 401, and is the western terminus for the Milton line commuter train and bus corridor operated by GO Transit...
- Steam Era
Steam Era is a festival held every Labour Day Weekend in the Town of Milton, Ontario featuring historic steam tractors....
in Milton, Ontario
Further reading
External links