A steam engine is a heat engine that performs mechanical work using steam as its working fluid.
Using boiling water to produce mechanical motion goes back over 2000 years, but early devices were not practical. The Spanish inventor Jerónimo de Ayanz y Beaumont patented in 1606 the first steam engine. In 1698 Thomas Savery patented a steam pump that used steam in direct contact with the water being pumped. Savery's steam pump used condensing steam to create a vacuum and draw water into a chamber, and then applied pressurized steam to further pump the water. Thomas Newcomen's ''atmospheric engine'' was the first commercial true steam engine using a piston, and was used in 1712 for pumping in a mine.
In 1781 James Watt patented a steam engine that produced continuous rotary motion. Watt's ten-horsepower engines enabled a wide range of manufacturing machinery to be powered. The engines could be sited anywhere that water and coal or wood fuel could be obtained. By 1883, engines that could provide 10,000 hp had become feasible. Steam engines could also be applied to vehicles such as traction engines and the railway locomotives. The stationary steam engine was a key component of the Industrial Revolution, allowing factories to locate where water power was unavailable.
Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be used. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In the cycle, water is heated and transforms into steam within a boiler operating at a high pressure. When expanded through pistons or turbines, mechanical work is done. The reduced-pressure steam is then condensed and pumped back into the boiler.
In general usage, the term ''steam engine'' can refer to either the integrated steam plants (including boilers etc.) such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine. Specialized devices such as steam hammers and steam pile drivers are dependent on the steam pressure supplied from a separate boiler. Reciprocating piston type steam engines remained the dominant source of power until the early 20th century, when advances in the design of electric motors and internal combustion engines gradually resulted in the replacement of reciprocating (piston) steam engines in commercial usage, and the ascendancy of steam turbines in power generation.〔 Considering that the great majority of worldwide electric generation is produced by turbine type steam engines, the "steam age" is continuing with energy levels far beyond those of the turn of the 19th century.
== History ==
History and modifications:
The Aeolipile (also known as a Hero engine) described by Hero of Alexandria in the 1st century AD is considered to be the first recorded steam engine. Torque was produced by steam jets exiting the turbine.
Thomas Savery, in 1698, patented first practical, atmospheric pressure, steam engine of one horse power (1 hp). It had no piston or moving parts but taps. It was a "fire engine", a kind of thermic syphon, in which steam was admitted to an empty container and then condensed. The vacuum thus created was used to suck water
from the sump at the bottom of the mine. The "fire engine" was not very effective and could not work beyond a limited depth of around thirty feet.
Thomas Newcomen, in 1712, developed first commercially successful piston steam engine of five horse power (5 hp). Its principle was to condense steam in a cylinder thus causing atmospheric pressure drive a piston and produce mechanical work.
James Watt, in 1781, patented steam engine that produced continued rotary motion and the power about 10 hp. It 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. It was an improvement of Newcomen’s engine.
Since the early 18th century, steam power has been applied 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 such as spinning mules and power looms. 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, mills and mines; powering pumping stations; and propelling transport appliances such as railway locomotives, ships, steamboats and road vehicles. Their use in agriculture led to an increase in the land available for cultivation. There has at one time or another been steam-powered farm tractors, motorcycles (without much success) and even automobiles as the Stanley Steamer.
The weight of boilers and condensors generally makes the power-to-weight ratio of a steam plant lower than for internal combustion engines.〔Lightweight steam turbines powered by decomposing high-test peroxide used neither boilers nor condensors, and were used in the V-2 and other rocket turbopumps, and torpedo propulsion.〕 For mobile applications steam has been largely superseded by internal combustion engines or electric motors. However most electric power is 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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』