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steam engine, machine using steam power to perform mechanical work through the agency of heat.
(Read James Watt's 1819 Britannica essay on the steam engine.)
A brief treatment of steam engines follows. For full treatment of steam power and production and of steam engines and turbines, see Energy Conversion: Steam engines.

In a steam engine, hot steam, usually supplied by a boiler, expands under pressure, and part of the heat energy is converted into work. The remainder of the heat may be allowed to escape, or, for maximum engine efficiency, the steam may be condensed in a separate apparatus, a condenser, at comparatively low temperature and pressure. For high efficiency, the steam must fall through a wide temperature range as a consequence of its expansion within the engine. The most efficient performance-that is, the greatest output of work in relation to the heat supplied-is secured by using a low condenser temperature and a high boiler pressure. The steam may be further heated by passing it through a superheater on its way from the boiler to the engine. A common superheater is a group of parallel pipes with their surfaces exposed to the hot gases in the boiler furnace. By means of superheaters, the steam may be heated beyond the temperature at which it is produced by boiling water.

In a reciprocating engine, the piston and cylinder type of steam engine, steam under pressure is admitted into the cylinder by a valve mechanism. As the steam expands, it pushes the piston, which is usually connected to a crank on a flywheel to produce rotary motion. In the double-acting engine, steam from the boiler is admitted alternately to each side of the piston. In a simple steam engine, expansion of the steam takes place in only one cylinder, whereas in the compound engine there are two or more cylinders of increasing size for greater expansion of the steam and higher efficiency; the first and smallest piston is operated by the initial high-pressure steam and the second by the lower-pressure steam exhausted from the first.

In the steam turbine, steam is discharged at high velocity through nozzles and then flows through a series of stationary and moving blades, causing a rotor to move at high speeds. Steam turbines are more compact and usually permit higher temperatures and greater expansion ratios than reciprocating steam engines. The turbine is the universal means used to generate large quantities of electric power with steam.

The earliest steam engines were the scientific novelties of Hero of Alexandria in the 1st century ce, such as the aeolipile, but not until the 17th century were attempts made to harness steam for practical purposes. In 1698 Thomas Savery patented a pump with hand-operated valves to raise water from mines by suction produced by condensing steam. In about 1712 another Englishman, Thomas Newcomen, developed a more efficient steam engine with a piston separating the condensing steam from the water. In 1765 James Watt greatly improved the Newcomen engine by adding a separate condenser to avoid heating and cooling the cylinder with each stroke. Watt then developed a new engine that rotated a shaft instead of providing the simple up-and-down motion of the pump, and he added many other improvements to produce a practical power plant.

A cumbersome steam carriage for roads was built in France by Nicholas-Joseph Cugnot as early as 1769. Richard Trevithick in England was the first to use a steam carriage on a railway; in 1803 he built a steam locomotive that in February 1804 made a successful run on a horsecar route in Wales. The adaptation of the steam engine to railways became a commercial success with the Rocket of English engineer George Stephenson in 1829. The first practical steamboat was the tug Charlotte Dundas, built by William Symington and tried in the Forth and Clyde Canal, Scotland, in 1802. Robert Fulton applied the steam engine to a passenger boat in the United States in 1807.

Though the steam engine gave way to the internal-combustion engine as a means of vehicle propulsion, interest in it revived in the second half of the 20th century because of increasing air-pollution problems caused by the burning of fossil fuels in internal-combustion engines.

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Steam engine | Definition, History, Impact, & Facts

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Steam engine, machine using steam power to perform mechanical work through the agency of heat. In a steam engine, hot steam, usually supplied by a boiler, expands under pressure, and part of the heat energy is converted into work. Learn more about steam engines in this article.

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annimation on the fonctionnement of the Steam Engine:

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The discovery that steam could be harnessed and made to work is not credited to James Watt since steam engines used to pump water out of mines in England existed when Watt was born. We do not know exactly who made that discovery, but we do know that the ancient Greeks had crude steam engines. Watt, however, is credited with inventing the first practical engine. And so the history of the "modern" steam engine often begins with him.

James Watt

We can imagine a young Watt sitting by the fireplace in his mother's cottage and intently watching the steam rising from the boiling tea kettle, the beginning of a lifelong fascination with steam.

In 1763, when he was twenty-eight and working as a mathematical-instrument maker at the University of Glasgow, a model of Thomas Newcomen's steam pumping engine was brought into his shop for repairs. Watt had always been interested in mechanical and scientific instruments, particularly those which dealt with steam. The Newcomen engine must have thrilled him.

Watt set up the model and watched it in operation. He noted how the alternate heating and cooling of its cylinder wasted power. He concluded, after weeks of experimenting, that in order to make the engine practical, the cylinder had to be kept as hot as the steam which entered it. Yet in order to condense steam, there had some cooling taking place.

That was a challenge the inventor faced.

Invention of the Separate Condenser

Watt came up with the idea of the separate condenser. In his journal, the inventor wrote that the idea came to him on a Sunday afternoon in 1765 as he walked across the Glasgow Green. If the steam was condensed in a separate vessel from the cylinder, it would be quite possible to keep the condensing vessel cool and the cylinder hot at the same time.

The next morning, Watt built a prototype and found that it worked. He added other improvements and built his now famous steam engine.

Partnership with Matthew Boulton

After one or two disastrous business experiences, James Watt associated himself with Matthew Boulton, a venture capitalist, and owner of the Soho Engineering Works. The firm of Boulton and Watt became famous and Watt lived until August 19, 1819, long enough to see his steam engine become the greatest single factor in the upcoming new industrial era.

Rivals

Boulton and Watt, however, though they were pioneers, were not the only ones working on the development of the steam engine. They had rivals. One was Richard Trevithick in England. Another was Oliver Evans of Philadelphia. Independently, both Trevithick and Evans invented a high-pressure engine. This was in contrast to Watt's steam engine, where the steam entered the cylinder at only slightly more than atmospheric pressure.

Watt clung tenaciously to the low-pressure theory of engines all of his life. Boulton and Watt, worried by Richard Trevithick's experiments in high-pressure engines, tried to have the British Parliament pass an act forbidding high pressure on the grounds that the public would be endangered by high-pressure engines exploding.

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The Evolution of the Modern Steam Engine

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The discovery that steam could be harnessed and made to work is not credited to James Watt since steam engines used to pump water out of mines in England existed when Watt was born. We do not know exactly who made that discovery, but we do know that the ancient Greeks had crude steam engines.

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Did James Watt invent the steam engine?

How did James Watt contribute to the Industrial Revolution?

Is the watt named for James Watt?

James Watt, (born January 19, 1736, Greenock, Renfrewshire, Scotland-died August 25, 1819, Heathfield Hall, near Birmingham, Warwick, England), Scottish instrument maker and inventor whose steam engine contributed substantially to the Industrial Revolution. Watt was also known for patenting the double-acting engine and an early steam locomotive. He was elected fellow of the Royal Society of London in 1785.

Education and training

Watt's father, the treasurer and magistrate of Greenock, ran a successful ship- and house-building business. A delicate child, Watt was taught for a time at home by his mother; later, in grammar school, he learned Latin, Greek, and mathematics. The source for an important part of his education was his father's workshops, where, with his own tools, bench, and forge, he made models (e.g., of cranes and barrel organs) and grew familiar with ships' instruments.

Deciding at age 17 to be a mathematical-instrument maker, Watt first went to Glasgow, where one of his mother's relatives taught at the university, and then, in 1755, to London, where he found a master to train him. Although his health broke down within a year, he had learned enough in that time "to work as well as most journeymen." Returning to Glasgow, he opened a shop in 1757 at the university and made mathematical instruments (e.g., quadrants, compasses, scales). He met many scientists and became a friend of British chemist and physicist Joseph Black, who developed the concept of latent heat. In 1764 he married his cousin Margaret Miller, who, before she died nine years later, bore him six children.

While repairing a model Newcomen steam engine in 1764, Watt was impressed by its waste of steam. In May 1765, after wrestling with the problem of improving it, he suddenly came upon a solution-the separate condenser, his first and greatest invention. Watt had realized that the loss of latent heat (the heat involved in changing the state of a substance-e.g., solid or liquid) was the worst defect of the Newcomen engine and that therefore condensation must be effected in a chamber distinct from the cylinder but connected to it. Shortly afterward he met British physician, chemist, and inventor John Roebuck, the founder of the Carron Works, who urged him to make an engine. He entered into partnership with him in 1768, after having made a small test engine with the help of loans from Joseph Black. The following year Watt took out the famous patent for "A New Invented Method of Lessening the Consumption of Steam and Fuel in Fire Engines."

Meanwhile, Watt in 1766 became a land surveyor; for the next eight years he was continuously busy marking out routes for canals in Scotland, work that prevented his making further progress with the steam engine. After Roebuck went bankrupt in 1772, English manufacturer and engineer Matthew Boulton, the manufacturer of the Soho Works in Birmingham, took over a share in Watt's patent. Bored with surveying and with Scotland, Watt immigrated to Birmingham in 1774.

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After Watt's patent was extended by an act of Parliament, he and Boulton in 1775 began a partnership that lasted 25 years. Boulton's financial support made possible rapid progress with the engine. In 1776 two engines were installed-one for pumping water in a Staffordshire colliery, the other for blowing air into the furnaces of British industrialist John Wilkinson, the famous ironmaster. That year Watt married again; his second wife, Ann MacGregor, bore him two more children.

During the next five years, until 1781, Watt spent long periods in Cornwall, where he installed and supervised numerous pumping engines for the copper and tin mines, the managers of which wanted to reduce fuel costs. Watt, who was no businessman, was obliged to endure keen bargaining in order to obtain adequate royalties on the new engines. By 1780 he was doing well financially, though Boulton still had problems raising capital. In the following year Boulton, foreseeing a new market in the corn, malt, and cotton mills, urged Watt to invent a rotary motion for the steam engine, to replace the reciprocating action of the original. He did that in 1781 with his so-called sun-and-planet gear, by means of which a shaft produced two revolutions for each cycle of the engine. In 1782, at the height of his inventive powers, he patented the double-acting engine, in which the piston pushed as well as pulled. The engine required a new method of rigidly connecting the piston to the beam. He solved that problem in 1784 with his invention of the parallel motion-an arrangement of connected rods that guided the piston rod in a perpendicular motion-which he described as "one of the most ingenious, simple pieces of mechanism I have contrived." Four years later his application of the centrifugal governor for automatic control of the speed of the engine, at Boulton's suggestion, and in 1790 his invention of a pressure gauge, virtually completed the Watt engine.

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James Watt | Biography, Inventions, Steam Engine, & Facts

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James Watt, Scottish inventor whose steam engine contributed substantially to the Industrial Revolution. He was elected fellow of the Royal Society of London in 1785. Because of his contributions to science and industry, the watt, a unit of power in the International System of Units, was named for him.

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the Steam Engine

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https://www.britanica.com/technology/steam-engine
https://www.thoughtco.com/captivity-os-steam-1992676
https://www.livescience.com