Steam Power Fuel, Steam Propulsion, Steam Engines, Steam Locomotive
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Steam Power Fuel is used in a Steam engine which is an external combustion
heat engine that makes use of the heat energy that exists in steam, converting it
to mechanical work. Steam locomotives dominated rail traction from the mid 19th century until the mid 20th century. After that they were superseded by diesel and electric locomotives. Steam Propulsion and Steam Engines were used as the prime mover in pumping stations, locomotives, steam ships, traction engines, steam lorries and other road vehicles. |
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They were essential to the Industrial Revolution and saw widespread commercial use
driving machinery in factories and mills, although most have since been superseded
by internal combustion engines and electric motors.
Steam turbines, technically a type of steam engine, are still widely
used for generating electricity. About 86% of all electric power in the world is
generated by use of steam turbines.
A steam engine requires a boiler to heat water into steam. The expansion
of steam exerts force upon a piston or turbine blade, whose motion can be harnessed
for the work of turning wheels or driving other machinery. One of the advantages
of the Steam Power Fuel engine is that any heat source can be used to raise
steam in the boiler; but the most common is a fire fueled by wood, coal or oil or
the heat energy generated in a nuclear reactor.
Invention and Development
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The first recorded steam-powered device, the aeolipile, was described by Hero of
Alexandria (Heron) in 1st century Roman Egypt, 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. The device was used for some simple work, such as opening temple doors, but probably saw no other major uses. The first practical Steam Power Fuel Turbine was invented much later by Taqi al-Din, an Arab philosopher, astronomer, and engineer in 16th century Ottoman Egypt, 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. |
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A similar machine is shown by Giovanni Branca, an Italian engineer, in 1629 for
turning a cylindrical escapement device that alternately lifted and let fall a pair
of pestles working in mortars. The steam flow of these early steam turbines, however,
was not concentrated and much of its energy was dissipated in all directions and
would have led to a considerable waste of energy and are usually called "mills".
Commercial development of the Steam Power Fuel 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 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.
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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 an engine which drove out the air from a cylinder
by exploding gunpowder inside it. Realising 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 from boiling water and then allowing the steam to condense; in this way he was able to raise weights by attaching the end of the piston to 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 quickly saw that to make an automatic cycle the steam would have to be generated separately in a boiler; however as he did not take the project further all we can say is that he invented the reciprocating steam engine conceptually and thus paved the way to Newcomen's engine. Papin also designed a paddle boat driven by a jet playing on a mill-wheel in a combination of Taqi al Din and Savery's conceptions and; he is also credited with a number of significant devices such as the safety valve. |
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Early Industrial Engines
None of the foregoing developments were applied practically as a means of undertaking
any early useful task. Another early industrial Steam Power Fuel engine was
the "fire-engine", designed by Thomas Savery in 1698. This was a pistonless
steam pump, and apparently not very efficient.
It was thus Thomas Newcomen and his "atmospheric-engine" of 1712 that demonstrated
the first practical industrial Steam Power Fuel engine for which there was
a commercial demand. Together, Newcomen and Savery developed a beam engine that
worked on the atmospheric, or vacuum, principle. The first industrial applications
of the vacuum engines were in the pumping of water from deep mineshafts. In mineshaft
pumps the reciprocating beam was connected to an operating rod that descended the
shaft to a pump chamber.
The oscillations of the operating rod are transferred to a pump piston that moves
the water, through check valves, to the top of the shaft. Early Newcomen engines
operated so slowly that the valves were manually opened and closed by an attendant.
An improvement was the replacement of manual operation of the valves with an operation
derived from the motion of the engine itself, by lengths of rope known as potter
cord (Legend has it that this was first done in 1713 by a boy, Humphrey Potter,
charged with opening the valves; when he grew bored and wanted to play with the
other children he set up ropes to automate the process.)
Humphrey Gainsborough produced a model condensing Steam Power Fuel
engine in the 1760s, which he showed to Richard Lovell Edgeworth, a member
of the Lunar Society. In 1769 James Watt, another member of the Lunar Society,
patented the first significant improvements to the Newcomen type vacuum engine that
made it much more fuel efficient. Watt's leap was to separate the condensing phase
of the vacuum engine into a separate chamber, while keeping the piston and cylinder
at the temperature of the steam. Gainsborough believed that Watt had used his ideas
for the invention, but there is no proof of this.
Watt, together with his business partner Matthew Boulton, developed these patents
into the Watt Steam Power Fuel Engine in Birmingham, England. The increased
efficiency of the Watt engine finally led to the general acceptance and use of steam
power in industry. Additionally, 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. This was in all essentials the engine that we know today. In early
steam engines the piston is usually connected to a balanced beam, rather
than directly to a connecting rod, and these engines are therefore known as beam
engines.
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The next improvement in efficiency came with the American Oliver Evans and
the Briton Richard Trevithick's use of high pressure steam. Trevithick built
successful industrial high pressure single-acting Steam Power Fuel engines
known as Cornish engines. However, with increased pressure came much danger as engines and boilers were now likely to fail mechanically by a violent outwards explosion, and there were many early disasters. The most important refinement to the high pressure engine at this point was the safety valve, which releases excess pressure. Reliable and safe operation came only with a great deal of experience and codification of construction, operating, and maintenance procedures. |
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Nicolas-Joseph Cugnot demonstrated the first functional self-propelled steam
vehicle, his "fardier" (steam wagon), in 1769. Arguably, this was the first automobile.
While not generally successful as a transportation device, the self-propelled steam
tractor proved very useful as a self mobile power source to drive other farm machinery
such as grain threshers or hay balers. In 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. 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.
Reciprocating Engines
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Reciprocating engines use the action of steam to move a piston in a sealed chamber
or cylinder. The reciprocating action of the piston can be translated via a mechanical linkage into either linear motion, usually for working water or air pumps, or else into rotary motion to drive the flywheel of a stationary engine, or else the wheel(s) of a vehicle. Vacuum Engines Early Steam Power Fuel engines, or "fire engines" as they were at first called such as "atmospheric" and Watt's "condensing" engines, worked on the vacuum principle and are thus known as vacuum engines. Although Savery's patent of 2 July 1698 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. Such engines operate by admitting low pressure steam into an operating chamber or cylinder. The inlet valve is then closed and the steam cooled, condensing it to a smaller volume and thus creating a vacuum in the cylinder. The upper end of the cylinder being open to the atmospheric pressure operates on the opposite side of a piston, pushing the piston to the bottom of the cylinder. |
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The piston is connected by a chain to the end of a large beam pivoted near its middle.
A weighted force pump is connected by a chain to the opposite end of the beam which
gives the pumping stroke and returns the piston to the top of the cylinder by force
of gravity, the low pressure steam being insufficient to move the piston upwards.
In the Newcomen engine the cooling water is sprayed directly into the cylinder the
still-warm condensate running off into a hot well. Repeated and wasteful cooling
and reheating of the working cylinder was a source of inefficiency, however these
engines enabled the pumping of greater volumes of water and/or from greater depths
than had been hitherto possible.
Watt's version of this engine as developed and marketed from 1774 onwards in partnership
with Matthew Boulton, was meant to improve efficiency through use of a separate
condensing chamber immersed in a bath 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 hot well was also a source of pre-heated water for the boiler. Another radical
change 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 to be condensed for the downward stroke.
Thus the engine was 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 was 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.
Vacuum engines, although in general limited in their efficiency, were at least relatively
safe, use of very low pressure steam being preferable due to the primitive state
of 18th century boiler technology. Power was limited by the low pressure, the displacement
of the cylinder, combustion and evaporation rates and — where present — condenser
capacity. Maximum theoretical efficiency was limited by the relatively low temperature
differential on either side of the piston; this meant that for a vacuum engine to
provide a usable amount of power, the first industrial production engines had to
be very large, and were thus expensive to build and install.
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Around 1811 Richard Trevithick was required to update a Watt pumping engine
in order to adapt it to one of his new Cornish boilers. Steam pressure above the piston was increased eventually reaching 40 psi (2.8 bars) 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 Steam Power Fuel 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. |
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High Pressure Egines
In a high pressure engine, steam is raised in a boiler to a high pressure and temperature,
it is then admitted to a working chamber where it expands and acts upon a piston.
In "Cornish engines" steam pressure and vacuum are applied to the piston simultaneously.
As pressure is applied to the top of the piston, the steam from the previous cycle
is condensed to provide a vacuum below the piston. At the end of the stroke the
equilibrium valve opens to allow the steam above the piston to be transferred to
the lower part of the cylinder as the piston is lifted by the weight of the pump
end of the beam. The piston consequently reciprocates, much like in the vacuum engine.
The importance of raising steam under pressure (from a thermodynamic standpoint)
is that it attains a higher temperature. Thus, any engine using such steam operates
at a higher temperature differential than is possible with a low pressure vacuum
engine. After displacing the vacuum engine, the high pressure engine became the
basis for further development of reciprocating steam technology.
High pressure steam also has the advantage that engines can be much smaller for
a given power range, and thus less expensive. There is also the benefit that steam
engines then could be developed that were small enough and powerful enough to propel
themselves while doing useful work. As a result, steam power for transportation
became a practicality, most notably steam locomotives and ships, which revolutionised
cargo businesses, travel, military strategy, and essentially every aspect of society
at the time.
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Double-acting Engines The next major advance in high pressure Steam Power Fuel engines was to make them double-acting. In the single-acting high pressure engine above, the cylinder is vertical and the piston returns to the start—or bottom—of the stroke by the momentum of the flywheel (not shown). In the double-acting engine, Steam is admitted alternately to each side of the piston while the other is exhausting. This requires inlet and exhaust ports at either end of the cylinder (see the animated expansion engine below) with steam flow being controlled by valves. This system increases the speed and smoothness of the reciprocation and allows the cylinder to be mounted horizontally or at an angle. |
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Power is transmitted from the piston by a sliding rod—sealed to the cylinder to
prevent the escape of steam— which in turn drives a connecting rod via a sliding
crosshead). This in combination with the connecting rod converts the reciprocating
motion to rotary motion.
The inlet and exhaust valves have their reciprocating motion derived from the rotary
motion by way of an additional crank mounted eccentrically (i.e. off centre) from
the drive shaft. The valve gear may include a reversing mechanism to allow reversal
of the rotary motion.
A double-acting piston engine provides as much power as a more expensive 2-piston
single-acting engine, and also allows the use of a much smaller flywheel than what
would be required by a one-piston single-acting engine. Both of these considerations
made the double-acting piston engine smaller and less expensive for a given power
range.
Most reciprocating steam engines now use this technology, notable examples
including steam locomotives and marine engines. When a pair (or more) of
double acting cylinders, for instance in a steam locomotive, are connected
to a common driveshaft their crank phasing is offset by an angle of 90°. This is
called quartering and ensures that the engine will always start, no matter what
position the crank is in.
Some marine engines have used only a single double-acting cylinder, driving paddlewheels
on each side. When shutting down such an engine it was important that the piston
be away from either extreme range of its travel so that it could be readily restarted
(as there was not a second quartered piston to facilitate this).
Steam Distribution
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In most reciprocating piston engines the Steam reverses its direction of
flow at each stroke (counterflow), entering and exhausting from the cylinder by
the same port. The complete engine cycle occupies one rotation of the crank and two piston strokes; the cycle also comprises four events — admission, expansion, exhaust, compression. These events are controlled by valves often working inside a steam chest adjacent to the cylinder. |
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The valves distribute the steam by opening and closing steam ports communicating
with the cylinder end(s) and are driven by valve gear, of which there are many types.
The simplest valve gears give events of fixed length during the engine cycle and
often make the engine rotate in only one direction. Most however have a reversing
mechanism which additionally can provide means for saving steam as speed and momentum
are gained by gradually "shortening the cutoff" or rather, shortening the admission
event; this in turn proportionately lengthens the expansion period.
However, as one and the same valve usually controls both steam flows, a short cutoff
at admission adversely affects the exhaust and compression periods which should
ideally always be kept fairly constant; if the exhaust event is too brief, the totality
of the exhaust steam cannot evacuate the cylinder, choking it and giving excessive
compression ("kick back"). In the 1840s and 50s there were attempts to overcome
this problem by means of various patent valve gears with separate variable cutoff
valves riding on the back of the main slide valve; the latter usually had fixed
or limited cutoff.
The combined setup gave a fair approximation of the ideal events, at the expense
of increased friction and wear, and the mechanism tended to be complicated. The
usual compromise solution has ever since been to provide lap by lengthening rubbing
surfaces of the valve in such a way as to overlap the port on the admission side,
with the effect that the exhaust side remains open for a longer period after cut-off
on the admission side has occurred.
This expedient has since been generally considered satisfactory for most purposes
and makes possible the use of the simpler Stephenson, Joy and Walschaerts motions.
Later, poppet valve gears had separate admission and exhaust valves driven by cams
profiled so as to give ideal events; nevertheless most of these gears never succeeded
in ousting conventional gears due to various other issues including leakage and
more delicate mechanisms.
Compression
Before the exhaust phase is quite complete, the exhaust side of the valve closes,
shutting a portion of the exhaust steam inside the cylinder. This determines the
compression phase where a cushion of steam is formed against which the piston does
work whilst its velocity is rapidly decreasing; it moreover obviates the pressure
and temperature shock, which would otherwise be caused by the sudden admission of
the high pressure steam at the beginning of the following cycle.
Lead
The above effects are further enhanced by providing lead: as was later discovered
with the internal combustion engine, it has been found advantageous since the late
1830s to advance the admission phase, giving the valve lead so that admission occurs
a little before the end of the exhaust stroke in order to fill the clearance volume
comprising the ports and the cylinder ends (not part of the piston-swept volume)
before the steam begins to exert effort on the piston.
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.
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Multiple Expansion 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. |
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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 image to the right shows a model and an animation of a triple expansion Steam
Power Fuel 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 Steam Power Fuel 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.
Uniflow (or Unaflow) 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 engines
power two Great Lakes ships still trading today (2007). These are the Saint Marys
Challenger, 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.
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.
Steam Turbine Engines
A Steam Turbine Engine 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 Turbine Engines 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.
Other Engines
Other types of steam engine have been produced and proposed, but have not
been nearly so widely adopted as reciprocating or turbine engines
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 Engines
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 Engines
The aeolipile represents the use of Steam by the rocket-reaction principle,
although not for direct Steam 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 Power Fuel 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 Power Fuel engines have been used to power a wide array of types of
vehicle:
- Steamboat and Steamship.
- Land vehicles:
- Steam Locomotive
- Steam Car
- Steam Lorry
- Steam Roller
- Steam Shovel
- Traction Engine
- Steam Aircraft
- Steam Locomotive
Advantages
The strength of the Steam Power Fuel 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 nuclear energy
could not be harnessed 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).
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 Power Fuel 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. The steam group of SLM in 2000 created a wholly-owned
company called DLM to design modern steam engines and steam locomotives.
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.
Business Tips
Some tips on how to avoid business failure:
- Don't underestimate the capital you need to start up the business.
- Understand and keep control of your finances - income earned is not the same as
cash in hand.
- More volume does not automatically mean more profit - you need to get your pricing
right.
- Make sure you have good software for your business, software that provides you with a good reporting picture of all aspects of your business operations.
See More Information On:
-
ShopMateWeb Online Cloud Based Business Database Application
-
ShopMate Desktop Automotive Database Software
-
ShopMate Desktop Modules Explained - Screen Shots
-
AzureMate Desktop Cloud Data Storage Explorer Software
-
Software Downloads and Installations
-
MotoShop Automotive Database Software
-
Accountancy - Accounting Theories
-
Ideas for Business - Business Tips
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