Steam engine

• 1. Introduction

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  The steam engine is a heat engine that turns the force of pressurized steam into mechanical work. Inside a cylinder, that pressure pushes a piston back and forth. A connecting rod and crank then convert the motion into rotational force. This simple chain of parts powered the factories of the Industrial Revolution, replaced sailing ships with paddle steamers, and put locomotives on the railways. Yet the idea was old long before any of that. A steam-driven device called the aeolipile was known in the first century AD, and a handful of other uses surfaced in the 16th century. The leap from curiosity to commercial machine took centuries of patents, explosions, and stubborn tinkering. Who first turned steam into money, and who made it efficient enough to change the world? Why did a device that once dominated all power eventually give way to electric motors and internal combustion? And how does a machine separate fire from the fluid it boils, yet still waste most of its heat? The answers run from a Hellenistic engineer in Roman Egypt to a German workshop still building large reciprocating engines today.

• 2. From Curiosity To Commerce

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  Hero of Alexandria, a Hellenistic mathematician and engineer in Roman Egypt, described the aeolipile during the first century AD. For centuries afterward, the few steam-powered engines that existed were 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 in which the pressure of steam might raise a column of water. The Spanish inventor Jeronimo de Ayanz received patents in 1606 for 50 steam-powered inventions, including a water pump for draining inundated mines. By 1615, Salomon de Caus had developed a solar-powered atmospheric engine. Denis Papin, a Frenchman, did useful work on the steam digester in 1679, and first used a piston to raise weights in 1690. The first commercial steam-powered device was a water pump, developed in 1698 by Thomas Savery. It used condensing steam to create a vacuum that raised water from below, then used steam pressure to lift it higher. Small engines worked well, but larger models were problematic, with very limited lift height and a tendency toward boiler explosions. Savery's engine drained mines, ran pumping stations, and supplied water to wheels powering textile machinery. One of its virtues was low cost. Bento de Moura Portugal improved the design to render it capable of working itself, as John Smeaton described in the Philosophical Transactions published in 1751. At least one Savery-type engine was still known to be operating in 1820.

• 3. The Piston And The Separate Condenser

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  Thomas Newcomen invented the atmospheric engine, also called the fire engine, around 1712. It was the first commercially successful engine that could transmit continuous power to a machine, improving on Savery's pump by adding a piston of the kind Papin had proposed. The engine worked by condensing steam under a piston to create a partial vacuum, with air pressure doing the pushing. It drained mine workings at depths that traditional means could not reach, and it pumped water back into reservoirs above factory waterwheels. Newcomen's engine was relatively inefficient and mostly used for pumping. Jacob Leupold described a two-cylinder high-pressure steam engine in 1720, published in his major work Theatri Machinarum Hydraulicarum, using two heavy pistons raised by steam pressure and returned by gravity. James Watt then developed an improved version of Newcomen's engine between 1763 and 1775, adding a separate condenser. By removing spent steam to a separate vessel for condensation, Watt greatly increased the work obtained per unit of fuel. Boulton and Watt's early engines used half as much coal as Smeaton's improved Newcomen design. Watt later modified his engine to provide rotary motion suitable for driving machinery, which let factories be sited away from rivers. In 1780, James Pickard patented the use of a flywheel and crankshaft to provide rotative motion from an improved Newcomen engine.

• 4. The High-Pressure Revolution

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  Watt's patent prevented others from making high-pressure and compound engines, and only after it expired in 1800 did the field open. Richard Trevithick, and separately Oliver Evans in 1801, introduced engines using high-pressure steam, with Trevithick obtaining his patent in 1802. Ewing noted that Watt's condensing engines were considered low pressure compared with the non-condensing high-pressure engines of the same period. High-pressure engines were far more powerful for a given cylinder size and small enough for transport applications. Trevithick and others developed the Cornish engine in the 1810s, a compound cycle engine that used high-pressure steam expansively and then condensed the low-pressure steam, making it relatively efficient. Its irregular motion and torque limited it mainly to pumping, and Cornish engines served mines and water supply until the late 19th century. The method of lessening energy loss in a very long cylinder came from British engineer Arthur Woolf, who in 1804 invented the compound engine and patented his Woolf high-pressure compound engine in 1805. In a compound engine, high-pressure steam from the boiler expands in a high-pressure cylinder, then enters one or more lower-pressure cylinders, spreading the temperature drop across several stages. This reduced the cylinder condensation and re-evaporation that dominated efficiency loss in reciprocating engines. Compounding became almost universal for marine engines after 1880, where reducing the weight of coal carried mattered most.

• 5. Steam On The Move

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  On the 21st of February 1804, the world's first railway journey took place when Trevithick's steam locomotive hauled 10 tonnes of iron, 70 passengers, and five wagons along the tramway from the Pen-y-darren ironworks near Merthyr Tydfil to Abercynon in south Wales. This was the first full-scale working railway steam locomotive, and its high-pressure steam reduced the engine's weight and raised its efficiency. Earlier groundwork had been laid by others. In 1784, the Scottish inventor William Murdoch built a model steam road locomotive, and steamboat pioneer John Fitch constructed an early working model of a steam rail locomotive in the United States, probably during the 1780s or 1790s. Trevithick visited the Newcastle area later in 1804, and the colliery railways of north-east England became the leading centre for locomotive development. He continued his own experiments with a trio of locomotives, concluding with the Catch Me Who Can in 1808. Four years later, Matthew Murray's successful twin-cylinder Salamanca ran on the rack-and-pinion Middleton Railway. George Stephenson built the Locomotion for the Stockton and Darlington Railway in 1825, the first public steam railway in the world, then built The Rocket, which won the Rainhill Trials in 1829. The Liverpool and Manchester Railway opened in 1830, using steam power exclusively for both passenger and freight trains. Mobile steam engines for roads became practical only after Trevithick's high-pressure work around 1800, and steam road vehicles became viable to produce commercially by the 1850s. Locomotives continued to be manufactured into the late twentieth century in places such as China and the former East Germany, where the DR Class 52.80 was produced.

• 6. The Engineer's Refinements

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  The Corliss steam engine, patented in 1849, marked the high point of the horizontal stationary engine. It was a four-valve counterflow engine with separate steam admission and exhaust valves and automatic variable steam cutoff. When Corliss was given the Rumford Medal, the committee declared that no one invention since Watt's time had so enhanced the efficiency of the steam engine. The design used 30 percent less steam and gave more uniform speed, making it well suited to manufacturing, especially cotton spinning. Speed control itself had a longer history. James Watt adopted the centrifugal governor in 1788, after his partner Boulton saw one on the equipment of a flour mill they were building. The governor could not hold a fixed speed, since it settled at a new constant speed in response to load changes, and it tended to oscillate whenever speed shifted. Engines fitted only with this governor were therefore unsuitable for constant-speed work such as cotton spinning, until variable steam cutoff improved control near the end of the 19th century. For analysis, the most useful instrument was the steam engine indicator, which traced cylinder pressure throughout the cycle on paper. Early versions were in use by 1851, but the most successful indicator was developed for high-speed engine maker Charles Porter by Charles Richard and exhibited at the London Exhibition in 1862. Engineers, mechanics, and insurance inspectors used it routinely, and it could be applied to internal combustion engines as well.

• 7. Turbines And The Long Decline

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  The final major evolution of steam engine design was the steam turbine, introduced in the late part of the 19th century. A turbine uses one or more rotors mounted on a drive shaft, alternating with fixed stators in the casing, the rotor blades catching steam to produce rotary motion directly. Turbines have fewer moving parts than reciprocating engines and need no connecting rod system, giving smoother rotation, lower maintenance, and less wear. They are generally more efficient than reciprocating piston engines for outputs above several hundred horsepower, though small-scale steam turbines are much less efficient than large ones. Turbines virtually replaced reciprocating engines in electricity generating stations early in the 20th century, where high speed suited generator service. Today most electric power comes from steam turbines, and in the United States 90 percent of electric power is produced this way using a variety of heat sources. The efficiency of stationary steam engines rose dramatically until about 1922, with the highest Rankine Cycle Efficiency of 91 percent and a combined thermal efficiency of 31 percent demonstrated and published in 1921 and 1928. Marine service saw turbines pioneered on the Turbinia, and they dominated large ship propulsion throughout the late 20th century. The dreadnought battleships and ocean liners adopted them where speed was essential, and the warship of 1905 was the first major one to replace the reciprocating engine with the then-novel turbine. Reciprocating engines did not vanish at once. Triple-expansion reciprocating engines drove the World War II Liberty ships, the largest number of identical ships ever built, with over 2700 constructed in the United States from a British original design.

• 8. Cycle, Efficiency, And What Remains

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  The Rankine cycle is the thermodynamic foundation of the steam engine, named after the Scottish polymath William John Macquorn Rankine. It uses the phase change of water, boiling to steam and condensing back to liquid, to convert heat into power, supplying heat externally to a closed loop and removing waste heat in a condenser. In the 1990s, Rankine steam cycles generated about 90 percent of all electric power used worldwide, including virtually all solar, biomass, coal, and nuclear power plants. The Carnot cycle sets the theoretical limit of efficiency, since the greater the temperature difference between two thermal reservoirs, the more efficient the engine. In steam turbines, entry temperatures are typically 565 degrees Celsius, the creep limit of stainless steel, with condenser temperatures around 30 degrees, giving a theoretical Carnot efficiency of about 64 percent against an actual 42 percent for a modern coal-fired station. The historical measure of efficiency was duty, the foot-pounds of work from burning one bushel of coal, defined as 94 pounds. The best Newcomen designs reached a duty of about 7 million, most closer to 5 million. Watt's low-pressure designs reached as high as 25 million and averaged about 17, a threefold improvement, while early Watt engines with high-pressure steam reached 65 million. A reciprocating engine exhausting to atmosphere typically reaches only 1 to 10 percent efficiency, while a modern large station with reheat and an economizer reaches the mid 40 percent range, the most efficient units approaching 50 percent. The reciprocating steam engine is no longer in widespread commercial use, yet large reciprocating piston steam engines are still being manufactured in Germany. In 2011, two German scientists at the University of Stuttgart revealed the world's smallest working steam engine, a micro-scale device operating on the principle of a Stirling engine.