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A hot air engine (historically called an air engine or caloric engine) is any
heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state ...
that uses the expansion and contraction of air under the influence of a temperature change to convert
thermal energy The term "thermal energy" is used loosely in various contexts in physics and engineering. It can refer to several different well-defined physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, ...
into
mechanical work In physics, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, for a constant force aligned with the direction of motion, the work equals the product of the force stren ...
. These engines may be based on a number of
thermodynamic cycles A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventua ...
encompassing both open cycle devices such as those of
Sir George Cayley Sir George Cayley, 6th Baronet (27 December 1773 – 15 December 1857) was an English engineer, inventor, and aviator. He is one of the most important people in the history of aeronautics. Many consider him to be the first true scientific aer ...
and
John Ericsson John Ericsson (born Johan Ericsson; July 31, 1803 – March 8, 1889) was a Swedish-American inventor. He was active in England and the United States. Ericsson collaborated on the design of the railroad steam locomotive ''Novelty'', which com ...
and the closed cycle engine of Robert Stirling. Hot air engines are distinct from the better known internal combustion based engine and steam engine. In a typical implementation, air is repeatedly heated and cooled in a
cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infi ...
and the resulting expansion and contraction are used to move a
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
and produce useful
mechanical work In physics, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, for a constant force aligned with the direction of motion, the work equals the product of the force stren ...
.


Definition

The term "hot air engine" specifically excludes any engine performing a
thermodynamic cycle A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventua ...
in which the working fluid undergoes a
phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...
, such as the
Rankine cycle The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines, such as steam turbines or reciprocating steam engines, allow mechanical work to be extracted from a fluid as it moves between a heat sour ...
. Also excluded are conventional
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal com ...
s, in which heat is added to the working fluid by combustion of fuel within the working cylinder. Continuous combustion types, such as
George Brayton George Bailey Brayton was an American mechanical engineer and inventor. He was noted for introducing the constant pressure engine that is the basis for the gas turbine, and which is now referred to as the Brayton cycle. Brayton's Ready Motor ...
's Ready Motor and the related
gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the direct ...
, could be seen as borderline cases.


History

The expansive property of heated air was known to the ancients.
Hero of Alexandria Hero of Alexandria (; grc-gre, Ἥρων ὁ Ἀλεξανδρεύς, ''Heron ho Alexandreus'', also known as Heron of Alexandria ; 60 AD) was a Greek mathematician and engineer who was active in his native city of Alexandria, Roman Egypt. He ...
's ''Pneumatica'' describes devices that might be used to automatically open temple doors when a fire was lit on a sacrificial altar. Devices called hot air engines, or simply ''air engines'', have been recorded from as early as 1699. In 1699,
Guillaume Amontons Guillaume Amontons (31 August 1663 – 11 October 1705) was a French scientific instrument inventor and physicist. He was one of the pioneers in studying the problem of friction, which is the resistance to motion when bodies make contact. He is ...
(1663–1705) presented, to the Royal Academy of Sciences in Paris, a report on his invention: a wheel that was made to turn by heat. The wheel was mounted vertically. Around the wheel's hub were water-filled chambers. Air-filled chambers on the wheel's rim were heated by a fire under one side of the wheel. The heated air expanded and, via tubes, forced water from one chamber to another, unbalancing the wheel and causing it to turn. See: * Amontons (20 June 1699
"Moyen de substituer commodement l'action du feu, à la force des hommes et des chevaux pour mouvoir les machines"
(Means of conveniently substituting the action of fire for the force of men and horses in order to move .e., powermachines), ''Mémoires de l'Académie Royale des Sciences'', pages 112-126. The ''Mémoires'' appear in the ''Histoire de l'Académie Royale des Sciences, année 1699'', which was published in 1732. The operation of Amontons' ''moulin à feu'' (fire mill) is explained on pages 123-126; his machine is illustrated on the plate following page 126. * For an account of Amontons' fire-powered wheel in English, see: Robert Stuart, ''Historical and Descriptive Anecdotes of Steam-engines and of Their Inventors and Improvers'' (London, England: Wightman and Cramp, 1829), vol. 1
pages 130-132
; an illustration of the machine appears on around the time when the laws of gasses were first set out, and early patents include those of
Henry Wood Sir Henry Joseph Wood (3 March 186919 August 1944) was an English conductor best known for his association with London's annual series of promenade concerts, known as the Proms. He conducted them for nearly half a century, introducing hundr ...
, Vicar of High Ercall near
Coalbrookdale Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. It lies within the civil parish called the Gorge. This is where iron ore was first sm ...
Shropshire (English patent 739 of 1759) and Thomas Mead, an engineer from Sculcoats Yorkshire (English patent 979 of 1791), the latter in particular containing the essential elements of a
displacer A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the ''working fluid'') between different temperatures, resulting in a net conversion of heat energy to mechanical work. More specif ...
type engine (Mead termed it the transferrer). It is unlikely that either of these patents resulted in an actual engine and the earliest workable example was probably the open cycle furnace gas engine of the English inventor
Sir George Cayley Sir George Cayley, 6th Baronet (27 December 1773 – 15 December 1857) was an English engineer, inventor, and aviator. He is one of the most important people in the history of aeronautics. Many consider him to be the first true scientific aer ...
It is likely that Robert Stirling's air engine of 1818, which incorporated his innovative ''Economiser'' (patented in 1816) was the first air engine put to practical work. The economiser, now known as the
regenerator Regenerator may refer to: * Regenerative heat exchanger, a type of heat exchanger * Regenerator (band), an independent record label set up in 2001 * Regenerator (''Resident Evil''), an enemy creature in the 2005 video game ''Resident Evil 4'' * ...
, stored heat from the hot portion of the engine as the air passed to the cold side, and released heat to the cooled air as it returned to the hot side. This innovation improved the efficiency of Stirling's engine and should be present in any air engine that is properly called a
Stirling engine A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the ''working fluid'') between different temperatures, resulting in a net conversion of heat energy to mechanical work. More specif ...
. Stirling patented a second hot air engine, together with his brother James, in 1827. They inverted the design so that the hot ends of the displacers were underneath the machinery and they added a compressed air pump so the air within could be increased in pressure to around 20 atmospheres. It is stated by Chambers to have been unsuccessful, owing to mechanical defects and to “the unforeseen accumulation of heat, not fully extracted by the sieves or small passages in the cool part of the regenerator, of which the external surface was not sufficiently large to throw off the unrecovered heat when the engine was working with highly compressed air.” Parkinson and Crossley, English patent, 1828 came up with their own hot air engine. In this engine the air-chamber is partly exposed, by submergence in cold water, to external cold, and its upper portion is heated by steam. An internal vessel moves up and down in this chamber, and in so doing displaces the air, alternately exposing it to the hot and cold influences of the cold water and the hot steam, changing its temperature and expansive condition. The fluctuations cause the reciprocation of a piston in a cylinder to whose ends the air-chamber is alternately connected. In 1829 Arnott patented his air expansion machine where a fire is placed on a grate near the bottom of a close cylinder, and the cylinder is full of fresh air recently admitted. A loose piston is pulled upwards so that all the air in the cylinder above will be made to pass by a tube through the fire, and will receive an increased elasticity tending to the expansion or increase of volume, which the fire is capable of giving it. He is followed the next year (1830) by Captain Ericsson who patented his second hot air engine. The specification describes it more particularly, as consisting of a “circular chamber, in which a cone is made to revolve on a shaft or axis by means of leaves or wings, alternately exposed to the pressure of steam; these wings or leaves being made to work through slits or openings of a circular plane, which revolves obliquely to, and is thereby kept in contact with the side of the cone.” Ericsson built his third hot air engine (the caloric engine) in 1833 "which excited so much interest a few years ago in England; and which, if it should be brought into practical operation, will prove the most important mechanical invention ever conceived by the human mind, and one that will confer greater benefits on civilized life than any that has ever preceded it. For the object of it is the production of mechanical power by the agency of heat, at an expenditure of fuel so exceedingly small, that man will have an almost unlimited mechanical force at his command, in regions where fuel may now be said hardly to exist". 1838 sees the patent of Franchot hot air engine, certainly the hot air engine that was best following the Carnot requirements. So far all these air engines have been unsuccessful, but the technology was maturing. In 1842, James Stirling, the brother of Robert, build the famous Dundee Stirling Engine. This one at least lasted 2-3 years but then was discontinued due to improper technical contrivances. Hot air engines is a story of trials and errors, and it took another 20 years before hot air engines could be used on an industrial scale. The first reliable hot air engines were built by Shaw, Roper, Ericsson. Several thousands of them were built.


Commercial Manufacturers

Hot engines found a market for pumping water (mainly to a household water tank) as the water inlet provided the cold required to maintain the temperature difference, though they did find other commercial uses. * Hayward, Tyler & Co of London. Engines for pumping water and working Punkahs c1876-1883. * Hayward-Tyler & Co of London. Domestic water supply (Rider's patent) c1888-1901. * W.H. Bailey & Co, Salford. Engines for pumping domestic water and operating stable machinery c1885-1887 * Adam Woodward & Sons, Ancoats, Manchester. Robinson's patent. c1887 * Norris & Henty, London. Resellers of 'Robinson' type pumping engines. c1898-1901 * C.H. Delamater & Co, Delamater Iron Works, New York. 'Rider' and 'Ericsson' type engine. 1870s-1898 * Rider Engine Company, Walden, New York. 1879-1898 * Rider-Ericsson Engine Company, Walden, New York. 1898-


Thermodynamic cycles

A hot air engine
thermodynamic cycle A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventua ...
can (ideally) be made out of 3 or more
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management * Business process, activities that produce a specific s ...
es (typically 4). The processes can be any of these: *
isothermal process In thermodynamics, an isothermal process is a type of thermodynamic process in which the temperature ''T'' of a system remains constant: Δ''T'' = 0. This typically occurs when a system is in contact with an outside thermal reservoir, and ...
(at constant temperature, maintained with heat added or removed from a heat source or sink) *
isobaric process In thermodynamics, an isobaric process is a type of thermodynamic process in which the pressure of the system stays constant: Δ''P'' = 0. The heat transferred to the system does work, but also changes the internal energy (''U'') of t ...
(at constant pressure) * isometric / isochoric process (at constant volume) *
adiabatic process In thermodynamics, an adiabatic process (Greek: ''adiábatos'', "impassable") is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. Unlike an isothermal process ...
(no heat is added or removed from the working fluid) **
isentropic process In thermodynamics, an isentropic process is an idealized thermodynamic process that is both adiabatic and reversible. The work transfers of the system are frictionless, and there is no net transfer of heat or matter. Such an idealized process ...
,
reversible adiabatic process In thermodynamics, an isentropic process is an idealized thermodynamic process that is both adiabatic and reversible. The work transfers of the system are frictionless, and there is no net transfer of heat or matter. Such an idealized process ...
(no heat is added or removed from the working fluid - and the
entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodyna ...
is constant) * isenthalpic process (the
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...
is constant) Some examples (not all hot air cycles, as defined above) are as follows: Yet another example is the Vuilleumier cycle.


See also

*
Stirling engine A Stirling engine is a heat engine that is operated by the cyclic compression and expansion of air or other gas (the ''working fluid'') between different temperatures, resulting in a net conversion of heat energy to mechanical work. More specif ...
* Thermoacoustic hot air engine * Manson-Guise Engine * Flame-licker engine *
Carnot heat engine A Carnot heat engine is a heat engine that operates on the Carnot cycle. The basic model for this engine was developed by Nicolas Léonard Sadi Carnot in 1824. The Carnot engine model was graphically expanded by Benoît Paul Émile Clapeyron in ...
* Timeline of heat engine technology


References


External links


Introduction to Stirling-Cycle Machines
(Select the desired biography)
Apparatus for the Method of Heat Differentiation
Vuilleumier patent
Inquiry into the Hot Air Engines of the 19th Century
{{DEFAULTSORT:Hot Air Engine Engines