User:John of Paris/sandbox 10

Invention and development

The laying of the foundations

Aeolipile

The first recorded steam-rotated device, the aeolipile, was described by Hero of Alexandria (Heron) in the 1st century AD, in his manuscript Spiritalia seu Pneumatica. Steam ejected tangentally from nozzles caused a pivoted ball to rotate; this suggests that the conversion of steam pressure into mechanical movement was known in Roman Egypt in the 1st century, although no useful function is evident and the device seems to have been used simply to demonstrate a mechanical principle.

More practical was the device described in 1551 by the Arab philosopher and astronomer, Taqi al-Din who exposed a method for rotating a spit by means of a jet of steam playing on rotary vanes around the periphery of a wheel. A similar machine is shown by Giovanni Branca an Italian engineer in 1629 for rotating a cylindrical escapement device that alternately lifted and let fall a pair of pestles working in mortars. Although these engines are often described as turbines, the steam flow was in no way concentrated by a casing, so much of its energy would have been dissipated in all directions leading to considerable waste; In early writings they were (perhaps more aptly) termed “mills”.

Commercial development of the steam engine, however, required an economic climate in which the developers of engines could profit by their creations. Classical, and later Medieval and Renaissance civilisations provided no such climate. Even as late as the 17th century, steam engines were created as one-off curiosities.The first machine was created by the Spanish inventor Jerónimo Ayánz de Beaumont, a patent that influenced Savery. The difficulty in breaking out of this situation is evident judging by the difficulties encountered by the Marquis of Worcester and later by his widow in gaining financial investment into the practical application of his ideas for the exploitation of steam power. In 1663, he published designs for, and installed a steam-powered device for raising water on the wall of the Great Tower at Raglan Castle (the grooves in the wall where the engine was installed were still to be seen in the 19th century). However, no one was prepared to risk money in this revolutionary new concept, and without backers the machine remained undeveloped.

Denis Papin's design for a piston-and-cylinder engine, 1680.

One of Denis Papin’s centres of interest was in the creating of a vacuum in a closed cylinder and in Paris in the mid 1670s he collaborated with the Dutch physicist, Huygens’ working on a piston engine in which air was driven out of a sealed cylinder by exploding gunpowder inside it, thus creating a partial vacuum. Observing the incompleteness of the vacuum produced by this means and on moving to England in 1680, Papin devised a version of the same cylinder that obtained a more complete vacuum by first boiling water inside the cylinder and then allowing it to cool and the steam to condense; in this way he was able to raise weights by attaching to the end of the piston rod a rope passing over a pulley. As a demonstration model the system worked, but in order to repeat the process the whole apparatus had to be dismantled and reassembled. Papin was aware that to make an the cycle rapidly repeat itself, the steam would have to be generated in separate purpose-built boiler and although he did envisage such a system, he did not take the project further, so all that can be said is that he invented the reciprocating steam engine conceptually and thus paved the way to Newcomen’s engine. Papin later designed a paddle boat driven by a jet playing on a mill-wheel in a combination of Taqi al Din and Savery's working principles; he is also credited with a number of significant devices, notably the safety valve.

Savery's attempt to develop a steam pump

The English engineer Thomas Savery continued Worcester’s technology, although it is by no means sure if Savery’s was an independent invention[7]. As with Worcester’s engine, a combination of the vacuum and pressure principles were used: the steam was first produced in a separate boiler and then transferred to a hollow pressure vessel onto which cold water was then sprayed in order to condense the steam. The vacuum thus formed drew the water from a well which was retained by closing a cock. The next charge of steam under pressure drove the water to a greater height, then the vessel was cooled once again, repeating the cycle. The the succession of vacuum and pressure could only raise water to a height of about 50 feet in all which was insufficient for draining deep mines, this in spite of the description of the apparatus in a pamphlet entitled the “Miner’s friend” specifying a succession of engines to be installed on ledges inside the shaft. Although Savery's patent of 2 July1698 claimed, in addition to "the raising of water", the ability to "occasion... motion to all sorts of mill-works" there is no evidence that they were used for any purpose other than pumping.

Low pressure engines

Newcomen "atmospheric" engine

Engraving of Newcomen engine. This appears to be copied from a drawing in Desaguliers' 1744 work: "A course of experimental philosophy", itself believed to have been a reversed copy of Henry Beighton's engraving dated 1717, believed to represent what is probably the second Newcomen engine erected around 1714 at Griff colliery, Warwickshire .)

It was Thomas Newcomen with his "atmospheric-engine"of 1712 who can be said to have brought together most of the essential elements established by Papin in order to develop the first practical steam engine for which there could be a commercial demand. This took the shape of a reciprocating beam engine installed at surface level driving a succession of pumps. The engine suspended by chains from one end of a rocking beam, worked on the atmospheric, or vacuum principle. [1].Such engines operated by admitting steam at extremely low pressure into the power cylinder. The inlet valve was then closed and the steam cooled, condensing it to a smaller volume of water and thus creating a vacuum in the cylinder. The upper end of the cylinder was open to the atmospheric pressure and lubricated by a layer of water maintained by a trickle feed. The pressure differential between atmosphere and vacuum displaced piston, to the bottom of the cylinder.

The piston was connected by a chain to the end of the great beam pivoted near its middle with the weighted force pumps connected by another chain to the opposite end of the beam which gave the pumping stroke by its own dead weight and provided the force to drive the water up pipes and to return the power piston to the top of the cylinder by force of gravity . The cooling water was sprayed directly inside the cylinder from a cistern that also provided the sealing water to the piston, the still-warm condensate running off into a hot well. The vacuum stroke gave sufficient power to lift and prime the pumps. Although inefficient and extremely heavy on coal, these engines enabled the raising of far greater volumes of water from greater depths than had been hitherto possible.

Watt reciprocating steam pump

James Watt's development of this engine as perfected and marketed from 1774 onwards in partnership and collaboration with Matthew Boulton, was able to improve efficiency through use of a separate condensing chamber immersed in a tank of cold water, connected to the working cylinder by a pipe and controlled by a valve. A small vacuum pump connected to the pump side of the beam drew off the warm condensate and delivered it to the hot well, at the same time helping to create the vacuum and draw the condensate out of the cylinder.

The development period was long and difficult, initially carried out by Watt at the University of Glasgow. In 1761 Professor Joseph Black proposed his 'theory of latent heat' which laid the foundations for the development of steam engine technology. Watt applied Black's theory to a model of the Newcomen engine that he had been given to repair. He soon realised that the repeated cooling and reheating of the working cylinder in the Newcomen engine was a source of inefficiency. This led to the development of the separate condenser that allowed the temperature of the cylinder to be maintained at a constant level. Watt's technology enabled the widespread commercial use of stationary steam engines. .

Humphrey Gainsborough produced a model condensing steam engine in the 1760s, which he showed to Richard Lovell Edgeworth, a member of the Lunar Society. Gainsborough believed that Watt had used his ideas for the invention; however the many accounts left by Watt explaining the succession of thought processes leading to the final design would tend to belie this.

Early Watt pumping engine.

Watt's ultimate development as marketed in Birmingham, England from 1774 onwards in partnership and collaboration with Matthew Boulton incorporated the separate condensing chamber immersed in a bath of cold water, communicating with the working cylinder beneath the piston by a pipe and controlled by a valve. A small vacuum pump connected to the pump side of the beam drew off the warm condensate and delivered it to the hot well, at the same time helping to create the vacuum and draw the condensate out of the cylinder. The hot well was also a source of pre-heated water for recycling to the boiler. A further radical change from the Newcomen engine was to close off the top of the cylinder and introduce low pressure steam above the piston and inside steam jackets that maintained cylinder temperature constant. On the upward return stroke, the steam on top was transferred through a pipe to the underside of the piston ready to be condensed for the downward stroke. Thus the engine thus no longer "atmospheric", the power stroke depending on the differential between the low-pressure steam and the partial vacuum. Sealing of the piston on a Newcomen engine had been achieved by maintaining a small quantity of water on its upper side. This was no longer possible in Watt's engine due to the presence of the steam, so sealing of the piston and its lubrication was obtained by using a mixture of tallow and oil. The piston rod also passed through a gland on the top cylinder cover sealed in a similar way.[2]

Power was still limited by the low pressure, the displacement of the cylinder, combustion and evaporation rates and condenser capacity. Maximum theoretical efficiency was limited by the relatively low temperature differential on either side of the piston; this meant that for a Watt engine to provide a usable amount of power, the first production engines had to be very large, and were thus expensive to build and install.

Appearance of Watt rotative and double acting engines

Boulton & Watt, developed the reciprocating engine into the rotative type. Unlike the Newcomen engine, the Watt engine operated smoothly enough to be connected to a drive shaft—via sun and planet gears—to provide rotary power along with double acting condensing cylinders. The earliest example was build as a demonstrator and was installed in Boulton's factory to work machines for lapping or polishing buttons etc. For this reason it was always known as the "Lap engine"[3]. In early steam engines the piston is usually connected by a rod to a balanced beam, rather than directly to a flywheel, and these engines are therefore known as beam engines. This was in all essentials the steam engine that we know today.

"Strong steam"

As the 18th century advanced, the call was for higher pressures; this was strongly resisted by Watt who with some justification, mistrusted the materials resistance and the boiler technology of the day. The first known advocate of "strong steam" was Leupold in his scheme for an engine that appeared in encyclopaedic works from around 1725. Various projects for steam propelled vehicles or boats also appeared throughout the century one of the most promising being Nicolas-Joseph Cugnot's who demonstrated his "fardier" (steam wagon), in 1769. Whilst the working pressure used for this vehicle is unknown, the small size of the boiler gave insufficient steam production rate to allow the fardier to advance a few hundred metres at a time before having to stop to raise steam. Other projects and models were proposed, but as with William Murdoch, many were blocked by Boulton and Watt.

This did not apply in the USA and 1788, a steamboat built by John Fitch operated in regular commercial service along the Delaware river between Philadelphia PA and Burlington NJ, carrying as many as 30 passengers. This boat could typically make 7 to 8 miles per hour, and traveled more than 2,000 miles (3,200 km) during its short length of service. The Fitch steamboat was not a commercial success, as this travel route was adequately covered by relatively good wagon roads. In 1802 William Symington built a practical steamboat, and in 1807 Robert Fulton used the Watt steam engine to power the first commercially successful steamboat.

Oliver Evans in his turn was in favour of "strong steam" which he applied to boat engines and to stationary uses. He was a pioneer of cylindrical boilers; however Evans' engines did suffer several serious boiler explosions, which tended to lend weight to Watt's qualms.

The importance of raising steam under pressure (from a thermodynamic standpoint) is that it attains a higher temperature. Thus, any engine using high pressure steam operates at a higher temperature and pressure differential than is possible with a low pressure vacuum engine. The high pressure engine thus became the basis for most further development of reciprocating steam technology. Even so, around the year 1800, "high pressure" amounted to what today would be considered very low pressure, i.e. 40-50 psi (276 - 345 kPa), the point being that the high pressure engine in question was non-condensing driven solely by the pressure of the steam and once that steam had performed work, it was usually exhausted at higher-than-atmospheric pressure. The blast of the exhausting steam into the chimney could be exploited to create induced draught through the fire grate and thus increase the rate of burning, hence creating more heat in a smaller furnace, at the expense of creating back pressure on the exhaust side of the piston. The most important outcome was that engines could be made much smaller than previously for a given power output. There was thus the potential for steam engines to be developed that were small and powerful enough to propel themselves and other objects. As a result, steam power for transportation now became a practicality in the form of ships and land vehicles, which revolutionised cargo businesses, travel, military strategy, and essentially every aspect of society. The importance of raising steam under pressure (from a thermodynamic standpoint) is that it attains a higher temperature. Thus, any engine using high pressure steam operates at a higher temperature and pressure differential than is possible with a low pressure vacuum engine. The high pressure engine thus became the basis for most further development of reciprocating steam technology.

On February 21, 1804 at the Penydarren ironworks at Merthyr Tydfil in South Wales, the first self-propelled railway steam engine or steam locomotive, built by Richard Trevithick, was demonstrated.

Trevithick's improvement to the Watt pumping engine

Trevithick pumping engine (Cornish system).

Around 1811 Richard Trevithick was required to update a Watt pumping engine in order to adapt it to one of his new large cylindrical Cornish boilers. Steam pressure above the piston was increased eventually reaching40 psi (0.28 MPa)

and now provided much of the power for the downward stroke; at the same time condensing was improved. This considerably raised efficiency and further pumping engines on the Cornish system (often known as Cornish engines) were built new throughout the 19th century, older Watt engines being updated to conform. Many of these engines were supplied worldwide and gave reliable and efficient service over a great many years with greatly reduced coal consumption. Some of them were very large and the type continued to be built right down to the 1890’s.

Simple expansion

This means that a charge of steam works only once in the cylinder. It is then exhausted directly into the atmosphere or into a condenser, but remaining heat can be recuperated if needed to heat a living space, or to provide warm feedwater for the boiler.

Compounding

As steam expands in a high pressure engine its temperature drops; because no heat is released from the system, this is known as adiabatic expansion and results in steam entering the cylinder at high temperature and leaving at low temperature. This causes a cycle of heating and cooling of the cylinder with every stroke which is a source of inefficiency.

A method to lessen the magnitude of this heating and cooling was invented in 1804 by British engineer Arthur Woolf, who patented his Woolf high pressure compound engine in 1805. In the compound engine, high pressure steam from the boiler expands in a high pressure (HP) cylinder and then enters one or more subsequent lower pressure (LP) cylinders. The complete expansion of the steam now occurs across multiple cylinders and as less expansion now occurs in each cylinder so less heat is lost by the steam in each. This reduces the magnitude of cylinder heating and cooling, increasing the efficiency of the engine. To derive equal work from lower pressure steam requires a larger cylinder volume as this steam occupies a greater volume. Therefore the bore, and often the stroke, are increased in low pressure cylinders resulting in larger cylinders.

Double expansion (usually known as compound) engines expanded the steam in two stages. The pairs may be duplicated or the work of the large LP cylinder can be split with one HP cylinder exhausting into one or the other, giving a 3-cylinder layout where cylinder and piston diameter are about the same making the reciprocating masses easier to balance.

Two-cylinder compounds can be arranged as:

• Cross compounds - The cylinders are side by side.
• Tandem compounds - The cylinders are end to end, driving a common connecting rod
• Angle compounds - The cylinders are arranged in a vee (usually at a 90° angle) and drive a common crank.

With two-cylinder compounds used in railway work, the pistons are connected to the cranks as with a two-cylinder simple at 90° out of phase with each other (quartered). When the double expansion group is duplicated, producing a 4-cylinder compound, the individual pistons within the group are usually balanced at 180°, the groups being set at 90° to each other. In one case (the first type of Vauclain compound), the pistons worked in the same phase driving a common crosshead and crank, again set at 90° as for a two-cylinder engine. With the 3-cylinder compound arrangement, the LP cranks were either set at 90° with the HP one at 135° to the other two, or in some cases all three cranks were set at 120°.

The adoption of compounding was common for industrial units, for road engines and almost universal for marine engines after 1880; it was not universally popular in railway locomotives where it was often perceived as complicated. This is partly due to the harsh railway operating environment and limited space afforded by the loading gauge (particularly in Britain, where compounding was never common and not employed after 1930). However although never in the majority it was popular in many other countries

Multiple expansion

An animation of a simplified triple-expansion engine.
High-pressure steam (red) enters from the boiler and passes through the engine, exhausting as low-pressure steam (blue) to the condenser.

1890s vintage triple-expansion (three cylinders of 26, 42 and 70 inch diameters in a common frame with a 42 inch stroke) marine engine that powered the SS Christopher Columbus

It is a logical extension of the compound engine above to split the expansion into yet more stages to increase efficiency. The result is the multiple expansion engine. Such engines use either three or four expansion stages and are known as triple and quadruple expansion engines respectively. These engines use a series of double-acting cylinders of progressively increasing diameter and/or stroke and hence volume. These cylinders are designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. As with the double expansion engine, where space is at a premium, two smaller cylinders of a large sum volume may be used for the low pressure stage. Multiple expansion engines typically had the cylinders arranged inline, but various other formations were used.

The images to the right show a model and an animation of a triple expansion engine. The steam travels through the engine from left to right. The valve chest for each of the cylinders is to the left of the corresponding cylinder.

The development of this type of engine was important for its use in steamships as by exhausting to a condenser the water can be reclaimed to feed the boiler, which is unable to use seawater. Land-based steam engines could exhaust much of their steam, as feed water was usually readily available. Prior to and during World War II, the expansion engine dominated marine applications where high vessel speed was not essential. It was however superseded by the British invention steam turbine where speed was required, for instance in warships and ocean liners. HMS Dreadnought of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.

Model of a triple expansion engine

S/S Ukkopekka Triple expansion steam engine

Uniflow (or unaflow) engine

Main article: Uniflow steam engine

This is intended to remedy the difficulties arising from the usual counterflow cycle mentioned above which means that at each stroke the port and the cylinder walls will be cooled by the passing exhaust steam, whilst the hotter incoming admission steam will waste some of its energy in restoring working temperature. The aim of the uniflow is to remedy this defect by providing an additional port uncovered by the piston at the end of its half-stroke making the steam flow only in one direction. By this means, thermal efficiency is improved by having a steady temperature gradient along the cylinder bore. The simple-expansion uniflow engine is reported to give efficiency equivalent to that of classic compound systems with the added advantage of superior part-load performance. It is also readily adaptable to high-speed uses and was a common way to drive electricity generators towards the end of the 19th century before the coming of the steam turbine.

Uniflow engines have been produced in single-acting, double-acting, simple, and compound versions. Skinner 4-crank 8-cylinder single-acting tandem compound [4] engines power two Great Lakes ships still trading today (2007). These are the Saint Marys Challenger,[5] that in 2005 completed 100 years of continuous operation as a powered carrier (the Skinner engine was fitted in 1950) and the car ferry, Badger.[6]

In the early 1950s the Ultimax engine, a 2-crank 4-cylinder arrangement similar to Skinner’s, was developed by Abner Doble for the Paxton car project with tandem opposed single-acting cylinders giving effective double-action. [7]

Turbine engines

Main article: Steam turbine

A steam turbine consists of an alternating series of rotating discs mounted on a drive shaft, rotors, and static discs fixed to the turbine casing, stators. The rotors have a propeller-like arrangement of blades at the outer edge. Steam acts upon these blades, producing rotary motion. The stator consists of a similar, but fixed, series of blades that serve to redirect the steam flow onto the next rotor stage. A steam turbine exhausts into a condenser that provides a vacuum. The stages of a steam turbine are typically arranged to extract the maximum potential work from a specific velocity and pressure of steam, giving rise to a series of variably sized high and low pressure stages. Turbines rotate at very high speed, therefore are usually connected to reduction gearing to drive another mechanism, such as a ship's propeller, at a lower speed. A turbine rotor is also capable of providing power when rotating in one direction only. Therefore a reversing stage or gearbox is usually required where power is required in the opposite direction.

Steam turbines provide direct rotational force and therefore do not require a linkage mechanism to convert reciprocating to rotary motion. Thus, 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 (about 86% of the world's electric production is by use of steam turbines) and to a lesser extent as marine prime movers. In the former, the high speed of rotation is an advantage, and in both cases the relative bulk is not a disadvantage. Virtually all nuclear power plants and some nuclear submarines, generate electricity by heating water to provide steam that drives a turbine connected to an electrical generator for main propulsion. A limited number of steam turbine railroad locomotives were manufactured. Some non-condensing direct-drive locomotives did meet with some success for long haul freight operations in Sweden, but were not repeated. Elsewhere, notably in the U.S.A., more advanced designs with electric transmission were built experimentally, but not reproduced. It was found that steam turbines were not ideally suited to the railroad environment and these locomotives failed to oust the classic reciprocating steam unit in the way that modern diesel and electric traction has done.

Rotary steam engines

It is possible to use a mechanism based on a pistonless rotary engine such as the Wankel engine in place of the cylinders and valve gear of a conventional reciprocating steam engine. Many such engines have been designed, from the time of James Watt to the present day, but relatively few were actually built and even fewer went into quantity production; see link at bottom of article for more details. The major problem is the difficulty of sealing the rotors to make them steam-tight in the face of wear and thermal expansion; the resulting leakage made them very inefficient. Lack of expansive working, or any means of control of the cutoff is also a serious problem with many such designs. By the 1840s it was clear that the concept had inherent problems and rotary engines were treated with some derision in the technical press. However, the arrival of electricity on the scene, and the obvious advantages of driving a dynamo directly from a high-speed engine, led to something of a revival in interest in the 1880s and 1890s, and a few designs had some limited success.

Of the few designs that were manufactured in quantity, those of the Hult Brothers Rotary Steam Engine Company of Stockholm, Sweden, and the spherical engine of Beauchamp Tower are notable. Tower's engines were used by the Great Eastern Railway to drive lighting dynamos on their locomotives, and by the Admiralty for driving dynamos on board the ships of the Royal Navy. They were eventually replaced in these niche applications by steam turbines.

Jet type

Invented by Australian engineer Alan Burns and developed in Britain by engineers at Pursuit Dynamics, this underwater jet engine uses high pressure steam to draw in water through an intake at the front and expel it at high speed through the rear. When steam condenses in water, a shock wave is created and is focused by the chamber to blast water out of the back. To improve the engine's efficiency, the engine draws in air through a vent ahead of the steam jet, which creates air bubbles and changes the way the steam mixes with the water.

Unlike in conventional steam engines, there are no moving parts to wear out, and the exhaust water is only several degrees warmer in tests. The engine can also serve as pump and mixer. This type of system is referred to as 'PDX Technology' by Pursuit Dynamics.

Rocket type

The aeolipile represents the use of steam by the rocket-reaction principle, although not for direct propulsion.

In more modern times there has been limited use of steam for rocketry—particularly for rocket cars. The technique is simple in concept, simply fill a pressure vessel with hot water at high pressure, and open a valve leading to a suitable nozzle. The drop in pressure immediately boils some of the water and the steam leaves through a nozzle, giving a significant propulsive force.

It might be expected that water in the pressure vessel should be at high pressure; but in practice the pressure vessel has considerable mass, which reduces the acceleration of the vehicle. Therefore a much lower pressure is used, which permits a lighter pressure vessel, which in turn gives the highest final speed.

There are even speculative plans for interplanetary use. Although steam rockets are relatively inefficient in their use of propellant, this very well may not matter as the solar system is believed to have extremely large stores of water ice which can be used as propellant. Extracting this water and using it in interplanetary rockets requires several orders of magnitude less equipment than breaking it down to hydrogen and oxygen for conventional rocketry.

Applications

Steam engines can be classified by their application:

Stationary engines

Stationary steam engines can be classified into two main types:

• Winding engines, rolling mill engines, steam donkeys, (marine engines) and similar applications which need to frequently stop and reverse.
• Engines providing power, which stop rarely and do not need to reverse. These include engines used in thermal power stations and those that were used in mills, factories and to power cable railways and cable tramways before the widespread use of electric power. Very low power engines are used to power model ships and speciality applications such as the steam clock.

The steam donkey is technically a stationary engine but is mounted on skids to be semi-portable. It is designed for logging use and can drag itself to a new location. Having secured the winch cable to a sturdy tree at the desired destination, the machine will move towards the anchor point as the cable is winched in.

Vehicle engines

Steam engines have been used to power a wide array of types of vehicle:

• Steamboat and steamship
• Land vehicles:
  • Steam locomotive
  • Steam car
  • Steam roller
  • Steam shovel
  • Traction engine
  • Steam aircraft

Advantages

The strength of the steam engine for modern purposes is in its ability to convert heat from almost any source into mechanical work. Unlike the internal combustion engine, the steam engine is not particular about the source of heat. Most notably, without the use of a steam engine it would be more difficult to harness nuclear energy for useful work, as a nuclear reactor does not directly generate either mechanical work or electrical energy—the reactor itself simply heats or boils water. It is the steam engine which converts the heat energy into useful work. Steam may also be produced without combustion of fuel, through solar concentrators. A demonstration power plant has been built using a central heat collecting tower and a large number of solar tracking mirrors, (called heliostats). (see Whitecliffs Project[8])

Similar advantages are found in a different type of external combustion engine, the Stirling engine, which can offer efficient power (with advanced regenerators and large radiators) at the cost of a much lower power-to-size/weight ratio than even modern steam engines with compact boilers.

Steam locomotives are especially advantageous at high elevations as they are not adversely affected by the lower atmospheric pressure. This was inadvertently discovered when steam locomotives operated at high altitudes in the mountains of South America were replaced by diesel-electric units of equivalent sea level power. These were quickly replaced by much more powerful locomotives capable of producing sufficient power at high altitude.

In Switzerland (Brienz Rothhorn) and Austria (Schafberg Bahn) new rack steam locomotives have proved very successful. They were designed based on a 1930s design of Swiss Locomotive and Machine Works (SLM) but with all of today's possible improvements like roller bearings, heat insulation, light-oil firing, improved inner streamlining, one-man-driving and so on. These resulted in 60 percent lower fuel consumption per passenger and massively reduced costs for maintenance and handling. Economics now are similar or better than with most advanced diesel or electric systems. Also a steam train with similar speed and capacity is 50 percent lighter than an electric or diesel train, thus, especially on rack railways, significantly reducing wear and tear on the track. Also, a new steam engine for a paddle steam ship on Lake Geneva, the Montreux, was designed and built, being the world's first full-size ship steam engine with an electronic remote control[9]. The steam group of SLM in 2000 created a wholly-owned company called DLM to design modern steam engines and steam locomotives.

Efficiency

Main article: thermodynamic efficiency

The efficiency of an engine can be calculated by dividing the number of joules of mechanical work that the engine produces by the number of joules of energy input to the engine by the burning fuel. The rest of the energy is dumped into the environment as heat.

No pure heat engine can be more efficient than the Carnot cycle, in which heat is moved from a high temperature reservoir to one at a low temperature, and the efficiency depends on the temperature difference. Hence, steam engines should ideally be operated at the highest steam temperature possible (superheated steam), and release the waste heat at the lowest temperature possible.

In practice, a steam engine exhausting the steam to atmosphere will have an efficiency (including the boiler) of 1% to 8%, but with the addition of a condenser and multiple expansion engines the efficiency may be greatly improved to 25% or better. A power station with steam reheat, etc. will achieve 30% to 42% efficiency. Combined cycle in which the burning material is first used to drive a gas turbine can produce 50% to 60% efficiency. It is also possible to capture the waste heat using cogeneration in which the residual steam is used for heating. It is therefore possible to use about 90% of the energy produced by burning fuel—only 10% of the energy produced by the combustion of the fuel goes wasted into the atmosphere.

The reason for varying efficiencies is because of the thermodynamic rule of the Carnot Cycle. The efficiency is the absolute temperature of the cold reservoir over the absolute temperature of the steam, subtracted from one. As the temperature changes in seasons, the efficiency changes with it, unless the cold reservoir is kept in an isothermal state. It should be noted that the Carnot Cycle calculations require absolute temperatures.

One source of inefficiency is that the condenser causes losses by being somewhat hotter than the outside world, although this can be mitigated by condensing the steam in a heat exchanger and using the recovered heat, for example to pre-heat the air being used in the burner of an external combustion engine.

The operation of the engine portion alone is not dependent upon steam; any pressurized gas may be used. Compressed air is sometimes used to test or demonstrate small model "steam" engines.

Unconventional engines

In the 2007 international scrapheap challenge, which pitted British and American engineers against each other to construct paddle-boats in the spirit of Isambard Kingdom Brunel, the British team chose to power their paddles via use of a scratch built steam engine. This engine, rather than using a mechanical linkage to control the steam feed to the pistons, utilised scavenged microswitches and solenoid valves in an electrical system believed by the scrapheap presenters to be the first such functional system ever attempted. The paddle-steamer - thus constructed - was racing against the American diesel version. Both were making similar headway until a catastrophic loss of pressure halted their attempt.

See also

• Timeline of steam power
• Steam power during the Industrial Revolution
• Boiler
• Valve gear
• Compound locomotive
• Live steam
• Steam clock
• Steam car
• Steamboat
• Reciprocating engine
• Heat Regenerative Cyclone Engine

Steam Fairs

UK

• Carter's Steam Fair - touring vintage fairground, including several rides powered by steam engines
• Great Dorset Steam Fair - 5-day annual show in England - specialises in showing engines being used in their original context: heavy haulage, threshing, ploughing, sawing, road making, etc

USA

• Antique Gas & Steam Engine Museum - Bi-Annual show in Vista, CA, Specializing in farm equipment, engines, and machinery from 1850-1950

Steam museums

See also: List of pumping stations, many of which are, or were, steam-powered.

UK

• Bolton Steam Museum
• Crofton Beam Engines (Movie of Crofton engines operating)
• Hollycombe Steam Collection
• Kempton Park Steam Engines
• Kew Bridge Steam Museum

Canada

• Ontario Agricultural Museum in Milton, Ontario
• Steam Era in Milton, Ontario

External links

• Interactive Animation – (in German)
• Titanic's Triple Expansion Engines on Titanic-Titanic.com
• Howstuffworks - "How Steam Engines Work"
• Animated engines - Illustrates a variety of steam engines
• A history of the growth of the steam-engine
• Uniflow engines
• Steam powered lawn mower
• Rotary steam engines
• Beauchamp Tower's spherical steam engine
• Miniature live steam site
• Steamboat revival on Lake Geneva
• New Scientist jet steam engine article
• Dual pistons with linear generator as microCHP
• An art project underway that aims to build a steam powered Victorian house on tractor treads
• A short movie of a mill engine under steam at Barnoldswick, Lancashire, England
• Steam Engineering Tutorials
• A history of the growth of the steam engine Cornell University Library Historical Monographs Collection. {Reprinted by} Cornell University Library Digital Collections

Steam museums

• Bancroft Mill Engine[10], Barnoldswick. Movie of engine operating here [11]
• Country Living Museum in Dudley, Staffs UK: full-size working replica of the first Newcomen atmospheric engine of 1712.
• Newcomen Engine House, Dartmouth, Devon, England, UK
• Hamilton Museum of Steam and Technology in Hamilton, Ontario. An old municipal pumphouse dating to 1860 with its original two Woolf Compound Rotative Beam Engines, one of which still operates.

Cats and IW links suppressed

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