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 transformed by a connecting rod and crank into rotational force for work. The term "steam engine" is normally applied to reciprocating engines, although some authorities have also referred to the steam turbine and devices such as Hero's aeolipile as "steam engines". The essential feature of steam engines is that they are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants, 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.
Steam-driven devices such as the aeolipile were known in the first century AD, and there were a few other uses recorded in the 16th century. In 1606 Jerónimo de Ayanz y Beaumont patented his invention of the first steam-powered water pump for draining mines. Thomas Savery is considered the inventor of the first commercially used steam powered device, a steam pump that used steam pressure operating directly on the water. The first commercially successful engine that could transmit continuous power to a machine was developed in 1712 by Thomas Newcomen. In 1764, James Watt made a critical improvement by removing spent steam to a separate vessel for condensation, greatly improving the amount of work obtained per unit of fuel consumed. By the 19th century, stationary steam engines powered the factories of the Industrial Revolution. Steam engines replaced sails for ships on paddle steamers, and steam locomotives operated on the railways.
Reciprocating piston type steam engines were the dominant source of power until the early 20th century. The efficiency of stationary steam engines increased dramatically until about 1922. The highest Rankine Cycle Efficiency of 91% and combined thermal efficiency of 31% was demonstrated and published in 1921 and 1928. Advances in the design of electric motors and internal combustion engines resulted in the gradual replacement of steam engines in commercial usage. Steam turbines replaced reciprocating engines in power generation, due to lower cost, higher operating speed, and higher efficiency. Note that small scale steam turbines are much less efficient than large ones.
, large reciprocating piston steam engines are still being manufactured in Germany.
History
Early experiments
One recorded rudimentary steam-powered engine was the aeolipile described by Hero of Alexandria, a Hellenistic mathematician and engineer in Roman Egypt during the first century AD. In the following centuries, the few steam-powered engines known were, like the aeolipile, essentially experimental devices used by inventors to demonstrate the properties of steam.A rudimentary steam turbine device was described by Taqi al-Din in Ottoman Egypt in 1551 and by Giovanni Branca in Italy in 1629. In 1601, Giambattista della Porta, described an apparatus by which the pressure of steam might be made to raise a column of water. The Spanish inventor Jerónimo de Ayanz received patents in 1606 for 50 steam-powered inventions, including a water pump for draining inundated mines. By 1615, Salomon de Caus developed a solar-powered atmospheric engine. Frenchman Denis Papin did some useful work on the steam digester in 1679, and first used a piston to raise weights in 1690.
Pumping engines
The first commercial steam-powered device was a water pump, developed in 1698 by Thomas Savery. It used condensing steam to create a vacuum which raised water from below and then used steam pressure to raise it higher. Small engines were effective though larger models were problematic. They had a very limited lift height and were prone to boiler explosions. Savery's engine was used in mines, pumping stations and supplying water to water wheels powering textile machinery. One advantage of Savery's engine was its low cost. Bento de Moura Portugal introduced an improvement of Savery's construction "to render it capable of working itself", as described by John Smeaton in the Philosophical Transactions published in 1751. It continued to be manufactured until the late 18th century. At least one engine was still known to be operating in 1820.Piston steam engines
The first commercially successful engine that could transmit continuous power to a machine was the atmospheric engine, invented by Thomas Newcomen around 1712. It improved on Savery's steam pump, using a piston as proposed by Papin. Newcomen's engine was relatively inefficient, and mostly used for pumping water. It worked by creating a partial vacuum by condensing steam under a piston within a cylinder. It was employed for draining mine workings at depths originally impractical using traditional means, and for providing reusable water for driving waterwheels at factories sited away from a suitable "head". Water that passed over the wheel was pumped up into a storage reservoir above the wheel.In 1780 James Pickard patented the use of a flywheel and crankshaft to provide rotative motion from an improved Newcomen engine.
In 1720, Jacob Leupold described a two-cylinder high-pressure steam engine. The invention was published in his major work "Theatri Machinarum Hydraulicarum". The engine used two heavy pistons to provide motion to a water pump. Each piston was raised by the steam pressure and returned to its original position by gravity. The two pistons shared a common four-way rotary valve connected directly to a steam boiler.
The next major step occurred when James Watt developed an improved version of Newcomen's engine, with a separate condenser. Boulton and Watt's early engines used half as much coal as John Smeaton's improved version of Newcomen's. Newcomen's and Watt's early engines were "atmospheric". They were powered by air pressure pushing a piston into the partial vacuum generated by condensing steam, instead of the pressure of expanding steam. The engine cylinders had to be large because the only usable force acting on them was atmospheric pressure.
Watt developed his engine further, modifying it to provide a rotary motion suitable for driving machinery. This enabled factories to be sited away from rivers, and accelerated the pace of the Industrial Revolution.
High-pressure engines
The meaning of high pressure, together with an actual value above ambient, depends on the era in which the term was used. For early use of the term Van Reimsdijk refers to steam being at a sufficiently high pressure that it could be exhausted to atmosphere without reliance on a vacuum to enable it to perform useful work. states that Watt's condensing engines were known, at the time, as low pressure compared to high pressure, non-condensing engines of the same period.Watt's patent prevented others from making high pressure and compound engines. Shortly after Watt's patent expired in 1800, Richard Trevithick and, separately, Oliver Evans in 1801 introduced engines using high-pressure steam; Trevithick obtained his high-pressure engine patent in 1802, and Evans had made several working models before then. These were much more powerful for a given cylinder size than previous engines and could be made small enough for transport applications. Thereafter, technological developments and improvements in manufacturing techniques resulted in the design of more efficient engines that could be smaller, faster, or more powerful, depending on the intended application.
The Cornish engine was developed by Trevithick and others in the 1810s. It was a compound cycle engine that used high-pressure steam expansively, then condensed the low-pressure steam, making it relatively efficient. The Cornish engine had irregular motion and torque through the cycle, limiting it mainly to pumping. Cornish engines were used in mines and for water supply until the late 19th century.
Horizontal stationary engine
Early builders of stationary steam engines considered that horizontal cylinders would be subject to excessive wear. Their engines were therefore arranged with the piston axis in vertical position. In time the horizontal arrangement became more popular, allowing compact, but powerful engines to be fitted in smaller spaces.The acme of the horizontal engine was the Corliss steam engine, patented in 1849, which was a four-valve counter flow engine with separate steam admission and exhaust valves and automatic variable steam cutoff. When Corliss was given the Rumford Medal, the committee said that "no one invention since Watt's time has so enhanced the efficiency of the steam engine". In addition to using 30% less steam, it provided more uniform speed due to variable steam cut off, making it well suited to manufacturing, especially cotton spinning.
Road vehicles
The first experimental road-going steam-powered vehicles were built in the late 18th century, but it was not until after Richard Trevithick had developed the use of high-pressure steam, around 1800, that mobile steam engines became a practical proposition. The first half of the 19th century saw great progress in steam vehicle design, and by the 1850s it was becoming viable to produce them on a commercial basis. This progress was dampened by legislation which limited or prohibited the use of steam-powered vehicles on roads. Improvements in vehicle technology continued from the 1860s to the 1920s. Steam road vehicles were used for many applications.In the 20th century, the rapid development of internal combustion engine technology led to the demise of the steam engine as a source of propulsion of vehicles on a commercial basis, with relatively few remaining in use beyond the Second World War. Many of these vehicles were acquired by enthusiasts for preservation, and numerous examples are still in existence. In the 1960s, the air pollution problems in California gave rise to a brief period of interest in developing and studying steam-powered vehicles as a possible means of reducing the pollution. Apart from interest by steam enthusiasts, the occasional replica vehicle, and experimental technology, no steam vehicles are in production at present.