Steam Engine History...

A steam engine is a heat engine that performs mechanical work using steam as its working fluid.[1]

Steam engines (heat engines using boiling water to produce mechanical motion) have a long history, going back at least 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 revolution, 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 wheels or windmills could be used. Significantly, this power source would later be applied to prime movers, mobile devices such as steam tractors and railway locomotives. Modern steam turbines generate about half of the electric power in the world using a variety of heat sources.


Steam engines are typically external combustion engines,[2]E.C.E.[›] although other external sources of heat such as solar power, nuclear power or geothermal energy may be used. The heat cycle is known as the Rankine cycle.

In general usage, the term 'steam engine' can refer to integrated steam plants such as railway steam locomotives and portable engines, or may refer to the machinery alone, as in the beam engine and stationary steam engine. Specialized devices such as steam hammers and steam pile drivers are dependent on steam supplied from a separate boiler.


Contents [hide]

1 Applications
1.1 Stationary applications
1.2 Transport applications
2 History
3 Basic operation of a simple reciprocating steam engine
4 Components of steam engines
4.1 Heat source
4.2 Boilers
4.2.1 Still engine
4.3 Motor units
4.3.1 Simple expansion
4.3.2 Compounding engines
4.3.3 Multiple expansion engines
4.3.4 Uniflow (or unaflow) engine
4.3.5 Turbine engines
4.3.6 Rotary steam engines
4.3.7 Jet type
4.3.8 Rocket type
4.4 Cold sink
4.5 Monitoring equipment
5 Advantages
6 Safety
7 Efficiency
8 Modern applications
9 See also
9.1 Steam museums
10 Notes
11 References
12 External links



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 motion 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 Revolution and saw widespread commercial use driving machinery in factories and mills, powering pumping stations 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 clock.

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 engines; notably this has made steam aircraft extremely rare. Similar considerations have meant that for small and medium-scale applications steam has been largely superseded by internal combustion engines or electric motors, 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 cogeneration processes and as a prime mover. This is becoming known as the Advanced Steam movement.

Steam engines can be classified by their application:


[edit] Stationary applications
Stationary steam engines can be classified into two main types:

Winding engines, rolling mill engines, steam donkeys, 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 stations, mills, factories and to power cable railways and cable tramways before the widespread use of electric power.
The steam donkey is technically a stationary engine but is mounted on skids to be semi-portable. It is designed for logging 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 engine is a stationary engine mounted on wheels so that it may be towed to a work-site by horses or a traction engine, rather than being fixed in a single location.


[edit] Transport applications
Steam engines have been used to power a wide array of transport appliances:

Marine: Steamboat, Steamship
Rail: Steam locomotive, Fireless locomotive
Agriculture: Traction engine, Steam tractor
Road: Steam wagon, Steam bus, Steam tricycle, Steam car
Construction: Steam roller, Steam shovel
Military: Steam tank (tracked), Steam tank (wheeled)
Space: Steam rocket
In many mobile applications internal combustion engines are more frequently used due to their higher power-to-weight ratio, steam engines are used when higher efficiency is needed and weight is less of an issue.

HISTORY
Main article: History of the steam engine

AeolipileThe history of the steam engine stretches back as far as the first century AD; the first recorded rudimentary steam engine being the aeolipile described by Hero of Alexandria.[3] In the following centuries, the few engines known about were essentially experimental devices used by inventors to demonstrate the properties of steam, such as the rudimentary steam turbine device described by Taqi al-Din[4] in 1551 and Giovanni Branca[5] in 1629.

The first practical steam-powered 'engine' was a water pump, developed in 1698 by Thomas Savery. It proved only to have a limited lift height and was prone to boiler explosions, but it still received some use for mines and pumping stations.

The first commercially successful engine did not appear until 1712. Incorporating technologies discovered by Savery and Denis Papin, the atmospheric engine, invented by Thomas Newcomen, 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 engine 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 vacuum generated by condensing steam instead of the pressure of expanding steam. Cylinders had to be large, as the only usable force acting on them was atmospheric pressure. 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 chain connecting the piston to the beam.

Around 1800, Richard Trevithick 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 motors and internal combustion engines 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 – overview
History of the steam engine – general history, concentrating on reciprocating engines
Steam turbine – the parallel development of turbine-type engines
Steam power during the Industrial Revolution
History of steam road vehicles