An Encyclopedia of the History of Technology part 37 potx

PART TWO: POWER AND ENGINEERING
342
Sir George Cayley was the first to build an engine of Henry Wood’s type in
1807. Two other cycles that have been employed in external combustion
engines are one due to John Ericsson in 1826 and another named after Robert
Stirling, who patented an engine based on the cycle in 1816. Engines based on
the Wood, Ericsson and Stirling cycles were used quite extensively in the
nineteenth century because they did not need a steam boiler, which required
space and involved the danger of explosion. Although external combustion
engines were extinct by the early years of this century, engines based on the
Stirling cycle have experienced a substantial revival of interest beginning in the
late 1960s.
Stirling engine
The ideal Stirling cycle involves constant temperature heat addition and
removal, and constant volume heat addition and removal. It has an efficiency
equal to that of the Carnot cycle operating between the hot and cold reservoirs
of the Stirling cycle, but without the need to accommodate the very large
changes in volume of the working substance that are characteristic of the
Carnot cycle.
A particular feature of the Stirling engine is the use of two cylinders and
two pistons. One of these, the displacer piston, serves to transfer the working
substance between the hot and cold reservoirs, while the other, the power
piston, is connected to the surroundings by some appropriate means
(mechanical or electrical).
The practical Stirling engine differs from the thermodynamic ideal by
replacing the hot and cold reservoirs attached to the displacer cylinder by heat
exchangers located in the transfer connection between the two ends of the
displacer cylinder. A regenerator in the transfer connection is also added to
improve the thermodynamic efficiency.
APPENDIX
Heat engines and thermodynamics

A heat engine is a fixed mass of material, e.g. air, water or steam, called the
working substance, that undergoes a series of processes in such a way that it
converts heat into work. The processes are arranged so that the working
substance returns to its original state, i.e., it has undergone a cycle. The cycle is
also characteristic of a practical heat engine and in that case it is repeated as
often and as rapidly as the operator desires or is practical.
STEAM AND INTERNAL COMBUSTION ENGINES
343
The history of the heat engine is closely associated with the first and second
laws of thermodynamics. The first law states that energy can be neither created
nor destroyed so, in theory, all the chemical energy in the coal burnt to produce
steam could produce work in a steam engine. The engine would then be said to
be 100 per cent efficient. However, this is not observed in practice and Sadi
Carnot showed that it was impossible. Carnot also showed that if the heat was
supplied to the heat engine at a constant temperature T
h
(K or °R) and rejected
at a constant temperature T
c
(lower than T
h
), then the efficiency (
η
) of the heat
engine would be
η
=1-(T
c
/T
h

)
.
The corresponding heat engine cycle is called the
Carnot cycle. This result is important in the theory of thermal prime movers
because it indicates that the efficiency of a heat engine using the Carnot cycle
(and, by implication, any other cycle) is increased if T
c
is decreased, T
h
is
increased, or both. In practice the minimum available value for T
c
is 22°C (72
°
F),
so the goal of all heat engine designers is to increase T
h
and this is the common
thread that runs through the history of thermal power production. However, this
ambition has usually been frustrated by the inability to obtain materials that can
stand the elevated temperatures and pressures of the working substance.
The Carnot cycle is said to be an ideal cycle because all its processes are
reversible, that is, they occur infinitely slowly without friction, without fluid
turbulence, and heat exchange employs minute temperature differences.
Practical heat engines that are intended to work on a close approximation to
the Carnot cycle have impractical dimensions, so ideal cycles have been
defined that conform more nearly to the characteristics of the practical prime
mover. A particularly important group of such cycles are the air standard
cycles, which use air as the working substance. These are the ideal cycles
associated with the internal combustion engine and the gas turbine.

Reciprocating steam engines
The reciprocating steam engine comprises two essential parts: the cylinder and
the valve or steam chest. The cylinder has two ports at each end. These are
opened and closed while the piston moves from one end of the cylinder to the
other end, and back again, with the cycle of events repeated at each revolution
of the crankshaft.
The piston, which fits in the cylinder, is a circular disc with grooves around
its circumference, which hold spring rings in position (Figure 5.24). The latter
are free to expand outward and, thereby, fit the cylinder so tightly that steam
cannot leak past the piston. The piston is secured to the piston rod. On both
end faces of the cylinder there are a number of studs that pass through
corresponding holes in the cylinder covers so that the latter can be secured by
nuts screwed on to the studs. The rear cover has an opening for the piston rod
that is sealed by a stuffing box filled with packing held in place by the gland.
PART TWO: POWER AND ENGINEERING
344
A space is always left between the piston and the cylinder covers when the
piston is at either end of the cylinder to ensure that the piston does not strike
the cylinder cover.
The piston moves to and fro with a reciprocating motion and this linear
motion is converted into a circular one by a connecting rod, which is joined to
the piston rod at the crosshead. The latter slides on the guides or slidebars.
The connecting rod big-end is located at a distance, equal to half the piston
stroke, from the centre of the crank shaft.
The valve or steam chest has a plain flat surface machined parallel with the
axis of the cylinder in which there are three ports, the outer ones connected to
the corresponding ports in the cylinder, and the middle one the exhaust. Steam
Figure 5.24: The reciprocating engine (steam or internal combustion).
(a) Crosshead engine (double acting). Key: A cylinder head; B cylinder wall; C
piston ring; D piston; E piston rod; F gland; G crosshead guides; H crosshead; I

connecting rod; J crank-pin; K crank; L crank shaft.
(b) Trunk piston engine (single acting). Key: A cylinder head; B cylinder wall; C
piston rings; D gudgeon pin; E piston; F connecting rod; G crankpin; H crank; I
crankshaft.
STEAM AND INTERNAL COMBUSTION ENGINES
345
is supplied from the boiler through the pipe. The slide valve moves back and
forth on the machined surface and opens and closes the ports to admit and
release steam in accordance with the cycle of piston movements. This is
ensured by driving the valve by a crank, with the two connected through a
more or less complicated system of linkages known as the valve gear. (Modern
steam engines, particularly when working with high temperature steam, used
piston valves. Other important types are the Corliss valve, the poppet valve
and the drop valve.)
It is important to note that the valve does not admit steam throughout the
piston stroke, but only for a short period at the beginning. The pressure and
energy of the steam decreases as the piston completes its stroke and, in an ideal
engine with no friction, or other losses, the energy given up by the steam
appears as a moving force (work) at the piston rod. The steam is then said to
be used expansively. The same effect could be produced by admitting steam to
the cylinder throughout its stroke, but such non-expansive working would not
be as efficient as expansive working. This is clarified in Figure 5.25.
Figure 5.25: Effect of cut-off on the performance of the reciprocating steam
engine. In the diagram each square equals one unit.
Adapted with permission from C. S. Lake and A. Reidinger, ‘Locomotive Valves
and Valve Gears’ (Percival Marshall, London, n.d.).
PART TWO: POWER AND ENGINEERING
346
Steam turbines
The steam turbine converts the internal energy of the steam into rotary motion

by accelerating it to a high velocity in a specially shaped stationary passage
called a nozzle. The steam leaving the nozzle is then directed on to a row of
blades or buckets attached to a rotating wheel (see Figure 5.26). The flow
cross-section of the blade passages is specially designed to change the direction
of motion of the steam, and, in the reaction steam turbine, the pressure of the
steam. Because the linear speed of the blade increases with the radius, warped
twisted blades were introduced in the 1930s. This ensures that the steam is
incident on the blade at all radii with the minimum of losses due to turbulence
and friction.
The form of the stationary nozzle that accelerates the steam and directs it on
to the rotating blades depends on the desired speed of the steam at the nozzle
exit. De Laval discovered in 1888 that for very high steam speeds the nozzle
Figure 5.26: Principle of the steam turbine. Steam passes through the stationary
nozzle and is directed as a high velocity jet onto the blades attached to the
periphery of the rotating wheel. The steam experiences a drop in pressure as it
flows through the moving blades. The blades are so shaped that the steam,
which is flowing axially in this portion of the turbine, is turned (see the
enlargement). The change in steam direction and pressure (if employed) as the
steam passes through the moving blades imparts a force in the tangential
direction to the wheel that causes it to turn.
Reproduced with permission from W.G.Scaife, ‘The Parsons Steam Turbine’, in
Scientific American, vol. 152, no. 4 (1985), pp. 132–9.
STEAM AND INTERNAL COMBUSTION ENGINES
347
must have a converging-diverging form. The form of this nozzle is contrary to
expectation, in that it might be assumed that the continually decreasing cross-
section of a purely converging nozzle would be required to accelerate the
steam. However, the paradox arises from our everyday experience with
incompressible fluids, particularly water. Steam is a compressible fluid, that is,
its density depends on its pressure, whereas the density of water is, for

practical purposes, independent of pressure. A fluid, as it passes through a
nozzle, experiences a decrease in pressure, so, if it is steam, its density
decreases. At first the density change is small and the velocity increase,
induced by the drop in pressure, is large. Since, for a constant mass rate of flow
at all points along the nozzle, the cross-sectional area is inversely proportional
to these two quantities, a decrease in nozzle cross-section is required. However,
at a point where the so-called critical pressure is reached in the nozzle, the
density starts to decrease much more rapidly with the decrease in pressure
along the nozzle, and, since the steam velocity is still increasing, the cross-
sectional area has to increase in order to accommodate the same mass rate of
flow. Hence, if the nozzle operates with an exit pressure less than the critical
pressure, it has the initial converging form followed by the diverging sections.
ACKNOWLEDGEMENTS
The author would like to thank Ian McNeil for the invitation to prepare this
chapter, and for his continued encouragement and patience during its
preparation. At the Rensselaer Polytechnic Institute: Mary Ellen Frank and
Susan Harris for assistance with the typing, the staff of the Folsom Library for
obtaining numerous papers and for facilitating the preparation of illustrations,
Professors F.F.Ling and M.Lai, chairman and acting chairman of the
Department of Mechanical Engineering, Aeronautical Engineering and
Mechanics.
FURTHER READING
Steam engines
Buchanan, R.A. and Watkins, G. The industrial archaeology of the stationary steam engine
(Allen Lane, London, 1976)
Dickinson, H.W. A short history of the steam engine, 2nd edn (Cass, London, 1963)
Hunter, L.C. A history of industrial power in the United States 1780–1930. Volume two:
steam power (University of Virginia Press for the Hagley Museum, Charlottesville,
VA, 1985)
Matschoss, C. Die Entwicklung der Dampf-Maschine, two vols. (Julius Springer, Berlin,

1908)
PART TWO: POWER AND ENGINEERING
348
Rolt, L.T.C. and Allen, J.S. The steam engine of Thomas Newcomen, (Moorland, Hartington
and Science History Publications, New York, NY, 1977)
Thurston, R.H. A history of the growth of the steam engine, Centennial Edition (Cornell
University Press, Ithaca, NY, 1939)
Steam turbines
Harris, F.R. ‘The Parsons centenary—A hundred years of steam turbines’, Proceedings of
the Institution of Mechanical Engineers, vol. 198, no. 9 (1984), pp. 183–224
Internal combustion engines
Büchi, A.J. Exhaust turbocharging of internal combustion engines, Monograph no. 1 (published
under the auspices of the Journal of the Franklin Institute, Lancaster, PA, 1953)
Cummins, C.L. Jr. Internal fire (Carnot Press, Lake Oswego, Oregon, 1976)
Delesalle, J. ‘Les Facteurs du progrés des diesel’, Entropie, vol. 21, no. 122 (1985), pp.
33–9
Hardy, A.C. History of motorshipping (Whitehall Technical Press, London, 1955)
Jones, J. ‘The position and development of the gas engine’, Proceedings of the Institution of
Mechanical Engineers, vol. 151 (1944), pp. 32–53
Mondt, J.R. ‘An historical overview of emission-control techniques for spark-ignition
engines’, Report No. GMR-4228 (General Motors Research Laboratories, Warren,
MI, 1982)
Norbye, J.P. The Wankel engine: design, development, applications (Chilton Book Co., Radnor,
Pa., 1971)
Pattenden, R.F.S. ‘Diesel engine research and development’, Chartered Mechanical
Engineer, vol. 9, January (1962), pp. 4–12
Ricardo, H.R. ‘Diesel engines’, Journal of the Royal Society of Arts, vol. 80 (1932), pp. 250–
62, 267–80
—— The high-speed internal combustion engine, 4th edn (Blackie, London, 1953)
Taylor, C.F. ‘Aircraft propulsion: a review of the evolution of aircraft power plants’,

Smithsonian report for 1962 (Smithsonian Institution, Washington, DC, 1962), pp.
245–98
Gas turbines
Baxter, A.D. ‘Air flow jet engines’, in O.E.Lancaster, (ed.), Jet propulsion engines, Vol.
XII, High Speed Aerodynamics and Jet Propulsion (Princeton University Press,
Princeton, NJ, 1959), pp. 29–53
Cox, H.R. ‘British aircraft gas turbines’, Journal of the Aeronautical Sciences, vol. 13,
(1946), pp. 53–87
Denning, R.M. and Jordan, T. ‘The aircraft gas turbine—status and prospects’, in Gas
turbines—Status and prospects, (ME Publications, New York, 1976), pp. 17–26
Keller, C. and Frutschi, H. ‘Closed cycle plants—Conventional and nuclear-design,
application operations’, in Gas turbine engineering handbook, Vol. II, (Gas Turbine
Publishers, Stamford, CT, 1976), pp. 265–83
STEAM AND INTERNAL COMBUSTION ENGINES
349
Meyer, A. ‘The combustion gas turbine: its history, development and prospects’,
Proceedings of the Institution of Mechanical Engineers, vol. 141, (1939), pp. 197–222
Moss, S.A. ‘Gas turbines and turbosuperchargers’, Transactions of the American Society of
Mechanical Engineers, vol. 66, (1944), pp. 351–71
Whittle, F. ‘The early history of the Whittle jet propulsion gas turbine’, Proceedings of the
Institution of Mechanical Engineers, vol. 152, (1945), pp. 419–35
External combustion engines
West, C.D. Principles and application of Stirling engines (Van Nostrand Reinhold, New York,
1986)

350
6

ELECTRICITY

BRIAN BOWERS
STATIC ELECTRICITY
The attractive power of lodestone, a mineral containing magnetic iron oxide,
was known to Lucretius and Pliny the Elder. The use of the magnetic compass
for navigation began in medieval times. A letter written in 1269 by Peter
Peregrinus gives instructions for making a compass, and he knew that it did
not point to the true North Pole. Knowledge of static electricity is even older,
dating back to the sixth century BC: Thales of Miletus is said to have been the
first to observe that amber, when rubbed, can attract light bodies.
The scientific study of electricity and magnetism began with William
Gilbert. Born in Colchester and educated at Cambridge, Gilbert was a
successful medical practitioner who became physician to Queen Elizabeth I in
1600. In that same year he also published his book De Magnete, which recorded
his conclusions from many years’ spare-time work on electrostatics and
magnetism, and, for the first time, drew a clear distinction between the two
phenomena.
In a very dangerous experiment the American statesman Benjamin Franklin
showed that a kite flown in a thunderstorm became electrically charged. His
German contemporary Georg Wilhelm Richmann was less fortunate: he was
killed trying the same experiment at St Petersburg in 1753.
Franklin also studied the discharge of electricity from objects of different
shapes. He suggested protection of buildings by lightning conductors and, in
the light of his discharge experiments, said that they should be pointed. The
value of lightning conductors was not fully accepted at first. Some argued
that they would attract lightning which would not have struck if the
conductor had not been there. Some people preferred ball-ended lightning
conductors to pointed ones. Among these was King George III, whose
reasoning seems to have been that since Franklin was a republican his science
must be suspect too.
ELECTRICITY

351
The distinction between conductors and insulators; the fact that there were
two forms of static electricity, later called ‘positive’ and ‘negative’; and the
principle of storing electric charges in a Leyden jar—a capacitor formed by a
glass jar coated with metal foil inside and out—were all worked out during the
eighteenth century. Most electrical experiments at that time used electricity
produced by frictional electric machines. There were many designs of such
machines, but typically a globe or plate of glass or other non-conducting
material was rotated while a cloth rubbed its surface.
The discovery of the electric current, about 1800, did not end the story
of static electricity. Two important machines of the nineteenth century were
Armstrong’s hydro-electric machine and the Wimshurst machine. William
Armstrong was a solicitor and amateur scientist who founded an
engineering business in Newcastle upon Tyne. His attention was drawn to
a strange effect noticed by an engine driver on a colliery railway. The
driver experienced ‘a curious pricking sensation’ when he touched the
steam valve on a leaking boiler. Armstrong found that the steam, issuing
from a small hole, became electrically charged. He then built a machine
with an iron boiler on glass legs and a hard-wood nozzle through which
steam could escape. He found the steam was positively charged, and he
then made a larger machine which was demonstrated in London producing
sparks more than half a metre long. This ‘hydro-electric machine’, as he
called it, established Armstrong’s scientific reputation. A War Office
committee on mines suggested in 1857 that Armstrong’s machine, with its
very high voltage output, could be used for detonating mines. In practice
magneto-electric machines were soon available, and Armstrong’s machine
never saw practical use.
During the nineteenth century numerous machines were made which
multiplied static electric charges by induction and collected them in Leyden
jars or other capacitors. Best known was the Wimshurst machine, made in

1883 by James Wimshurst, a consulting engineer to the Board of Trade.
CURRENT ELECTRICITY
An electric current, as opposed to static charges, was first made readily
available in 1800 as a result of the work of the Italian Alessandro Volta who
later became Professor of Natural Philosophy at the University of Pavia. He
was following up work done by his fellow-countryman Luigi Galvani,
Professor of Anatomy at the University of Bologna. Galvani had been
studying the effects of electric discharges from frictional machines on the
muscles of dead frogs. In the course of this work he noticed that a muscle
could be made to twitch with the aid of nothing more than two pieces of
different metals. Galvani thought the source of the phenomenon he had