The Steam Engine

So let’s get the “technical” bits out of the way first! In thermodynamics and engineering, an ‘engine’ is defined as “a system that converts heat to usable energy, particularly mechanical energy, which can then be used to do mechanical work”. The steam engine performs this mechanical work using steam as its working fluid and it 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 a rotational force for work. Steam engines are external combustion engines where the working fluid is separated from the combustion products. Easy, isn’t it!

An ‘aeolipile’ rotates due to the steam escaping from the arms. No practical use was made of this effect.

Although steam-driven devices were known as early as the above ‘aeolipile’ in the first century AD, with a few other uses recorded in the sixteenth 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, then James Watt made a critical improvement in 1764 by removing spent steam to a separate vessel for condensation, thus greatly improving the amount of work obtained per unit of fuel consumed.

Jacob Leupold’s steam engine.

The first commercial steam-powered device was a water pump, developed in 1698 by Thomas Savery. Small engines were effective, though larger models were problematic and were prone to boiler explosions. Savery’s engine was used in mines, pumping stations and supplying water to water wheels which powered textile machinery. Then in 1720 Jacob Leupold described a two-cylinder high-pressure steam engine and the invention was published in his major work “Theatri Machinarum Hydraulicarum”. The engine used two heavy pistons to provide motion to a water pump, where each piston was raised by the steam pressure and returned to its original position by gravity.

Early Watt steam pumping engine.

The next major step occurred when James Watt developed an improved version, developing his engine further and 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. But Watt’s designs were low pressure condensing engines and his patent prevented others from making high pressure and compound engines. Shortly after Watt’s patent expired in 1800, in 1801 Richard Trevithick and also (but separately) Oliver Evans, 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 (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. The Cornish engine was developed by Trevithick and others in the 1810s and it used high-pressure steam expansively, then condensed the low-pressure steam, making it relatively efficient. The Cornish engine design rather limited it to pumping, so they were used in mines and for water supply until the late nineteenth century. Early builders of stationary steam engines considered that horizontal cylinders would be subject to excessive wear, and as a result their engines were arranged with the pistons in a vertical position, but in time the horizontal arrangement became more popular, allowing compact, but powerful engines to be fitted in smaller spaces. The star of the horizontal engine was the Corliss steam engine, patented in 1849, which was a four-valve design with separate steam admission and exhaust valves and automatic variable steam cutoff. Corliss was given the Rumford Medal, an award bestowed by Britain’s Royal Society every alternating year for “an outstandingly important recent discovery in the field of thermal or optical properties of matter made by a scientist working in Europe”, and 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.

A steam powered road-locomotive.

As the development of steam engines progressed through the eighteenth century, various attempts were made to apply them to road and railway use. In 1784, William Murdoch, a Scottish inventor, built a model steam road locomotive. The first full-scale working railway steam locomotive was built by Richard Trevithick here in the United Kingdom and on 21 February 1804 the world’s first railway journey took place as Trevithick’s unnamed steam locomotive hauled a train along the tramway from the Pen-y-darren ironworks near Merthyr Tydfil to Abercynon in South Wales. The design incorporated a number of important innovations that included using high-pressure steam, which reduced the weight of the engine and increased its efficiency. Trevithick visited the Newcastle area later in 1804 and the colliery railways in north-east England became the leading centre for experimentation and development of steam locomotives. Trevithick continued his own experiments using a trio of locomotives, concluding with the ‘Catch Me Who Can’ in 1808 and in 1825 George Stephenson built the ‘Locomotion’ for the Stockton and Darlington Railway. This was the first public steam railway in the world and then in 1829, he built ‘The Rocket’ which was entered in and won the Rainhill Trials. The Liverpool and Manchester Railway opened in 1830, making exclusive use of steam power for both passenger and freight trains and the first experimental road-going steam-powered vehicles were built in the late eighteenth century, but it was not until after Richard Trevithick had developed the use of high-pressure steam that mobile steam engines became a practical proposition. The first half of the nineteenth century saw great progress in steam vehicle design, and by the 1850s it was becoming viable to produce them on a commercial basis, but 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 and steam road vehicles were used for many applications.

An early British horse-drawn fire engine with steam-powered water pump.

By the nineteenth century, stationary steam engines powered the factories of the Industrial Revolution. They also replaced sails on ships, giving us paddle steamers, whilst steam locomotives operated on the railways, with the latter continuing to be manufactured until the late twentieth century in places such as China and the former East Germany. Steam engines remained the dominant source of power until the early twentieth century, when advances in the design of the steam turbine, electric motors and internal combustion engines gradually resulted in the replacement of steam engines, with merchant shipping relying increasingly upon diesel engines, and warships on the steam turbine. The final major evolution of the steam engine design was in the use of steam turbines, starting in the late part of the nineteenth century. Steam turbines are generally more efficient than reciprocating piston type steam engines for outputs above several hundred horsepower, they have fewer moving parts and provide rotary power directly instead of through a connecting rod system or similar means. These steam turbines virtually replaced reciprocating engines in electricity generating stations early in the twentieth century, where their efficiency, higher speed appropriate to generator service and smooth rotation were advantages. Today most electric power is provided by steam turbines and were extensively applied for propulsion of large ships throughout most of the twentieth century. Although the old reciprocating steam engine is no longer in widespread commercial use, various companies are exploring or exploiting the potential of the engine as an alternative to internal combustion engines.

An industrial boiler used for a stationary steam engine.

For safety reasons, just about all steam engines are equipped with mechanisms to monitor the boiler, such as a pressure gauge and a sight glass, which is usually a a transparent tube through which the operator of a tank or boiler can observe the level of liquid contained inside, to monitor the water level. Many engines, both stationary and mobile, are also fitted with a governor to regulate the speed of the engine without the need for any human interference. The most useful instrument for analysing the performance of steam engines is the steam engine indicator. There is much more than can be said on the intricacies of how steam engines work, but I have no intention of detailing them here. Suffice to say that land-based steam engines could exhaust their steam to atmosphere, as feed water was usually readily available. Prior to and during World War I a design of engine dominated marine applications where high vessel speed was not essential, but it was superseded by the British invention of a steam turbine where speed was required, for instance in warships such as the ‘Dreadnought’ battleships and ocean liners. HMS Dreadnought, constructed in 1905, was the first major warship to replace the proven technology of the standard steam engine with the then-novel steam turbine.

A rotor of a modern steam turbine used in a power plant.

A steam turbine consists of one or more rotors (rotating discs) mounted on a drive shaft, alternating with a series of stators (static discs) fixed to the turbine casing. The rotors have a propeller-like arrangement of blades at the outer edge. Steam acts upon these blades, producing rotary motion. Turbines are only efficient if they rotate at relatively high speed, therefore they are usually connected to reduction gearing to drive lower speed applications, such as a ship’s propeller. But in the vast majority of large electric generating stations, turbines are directly connected to generators with no reduction gearing and typical speeds are from 3,000 to 3,600 revolutions per minute, but in nuclear power applications the turbines typically run at half these speeds. Steam turbines provide direct rotational force and therefore do not require a linkage mechanism to convert reciprocating to rotary motion so they produce smoother rotational forces on the output shaft. This contributes to a lower maintenance requirement and less wear on the machinery they power than a comparable reciprocating engine. The main use for steam turbines is in electricity generation and in the 1990s about 90% of the world’s electric production was by use of steam turbines. However, the recent widespread application of large gas turbine units and typical combined cycle power plants has resulted in reduction of this percentage to the 80% regime for steam turbines. In electricity production, the high speed of turbine rotation matches well with the speed of modern electric generators, which are typically direct connected to their driving turbines.

‘Turbinia’ at speed – the first steam turbine-powered ship.

In marine service, pioneered on the ‘Turbinia’, steam turbines with reduction gearing (although the Turbinia has direct turbines to propellers with no reduction gearbox) dominated large ship propulsion throughout the late twentieth century, being more efficient (and requiring far less maintenance) than reciprocating steam engines. In recent decades, reciprocating diesel engines and gas turbines have almost entirely supplanted steam propulsion for marine applications. Virtually all nuclear power plants generate electricity by heating water to provide steam that drives a turbine connected to an electrical generator. Nuclear-powered ships and submarines either use a steam turbine directly for main propulsion, with generators providing auxiliary power, or else employ turbo-electric transmission, where the steam drives a turbo generator set with propulsion provided by electric motors. A limited number of steam turbine railway locomotives were manufactured and some non-condensing direct-drive locomotives did meet with some success for long haul freight operations in Sweden and for express passenger work here in Britain, but were not repeated. Elsewhere, notably in the United States, more advanced designs with electric transmission were built experimentally, but not reproduced. It was found that steam turbines were not ideally suited to their railroad environment and these locomotives failed to oust the classic reciprocating steam unit in the way that modern diesel and electric traction has done.

With all of the above there is the need for safety. Steam engines possess boilers and other components that are pressure vessels which contain a great deal of potential energy. As a result, steam escapes and boiler explosions can and have in the past caused great loss of life. Whilst variations in standards may exist in different countries, stringent legal, testing, training, care with manufacture, operation and certification is applied to ensure safety. The steam engine contributed much to the development of thermodynamic theory, however, the only applications of scientific theory that influenced the steam engine were the original concepts of harnessing the power of steam and atmospheric pressure and knowledge of properties of heat and steam. The experimental measurements made by Watt on a model steam engine led to the development of the separate condenser. Watt independently discovered latent heat, which was confirmed by the original discoverer Joseph Black, who also advised Watt on experimental procedures. Watt was also aware of the change in the boiling point of water with pressure. Otherwise, the improvements to the engine itself were more mechanical in nature. Though thermodynamic concepts did give engineers the understanding needed to calculate efficiency, which aided the development of modern high-pressure and temperature boilers as well as the steam turbine. A modern, large electrical power station, producing several hundred megawatts of electrical output with steam reheat, economiser etc. will achieve efficiency in the mid 40% range, with the most efficient units approaching 50% thermal efficiency. It is also possible to capture the waste heat using cogeneration in which the waste heat is used for heating a lower boiling point working fluid or as a heat source for district heating via saturated low-pressure steam. In the twentieth 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. Happily 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, but apart from interest by many steam enthusiasts around the world, the occasional replica vehicle as well as experimental technology, no steam vehicles are in regular production at present.

This week… Empathy.
We can rarely experience things in the same way as another but we can empathise, even in silence, with them. Knowing that you are there, that they are not alone, can be enough. A few have said that to understand another person, you must swim in the same water that drowned them. But I believe that if you cannot swim, you can at least be a lifeline which others can hold on to and trust.

Click: Return to top of page or Index page

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: