Editing Stirling engine (section)

== History ==
{{rewrite|section|date=June 2021}}
[[File:Robert Stirling's engine patent.gif|thumb|Illustration from Robert Stirling's 1816 patent application of the air engine design that later came to be known as the Stirling Engine]]

=== Early hot air engines ===
[[Robert Stirling]] is considered one of the fathers of hot air engines, along with earlier innovators such as [[Guillaume Amontons]],<ref name="haeamontons-s01" /> who built the first working hot air engine in 1699.<ref>{{Cite web|url=http://hotairengines.org/primitive-air-engine/amontons-1699|title=Guillaume Amontons &#124; Hot Air Engines|website=hotairengines.org}}</ref>

Amontons was later followed by Sir [[George Cayley]].<ref name="haecayley1807-s01" /> This engine type was of those in which the fire is enclosed, and fed by air pumped in beneath the grate in sufficient quantity to maintain combustion, while by far the largest portion of the air enters above the fire, to be heated and expanded; the whole, together with the products of combustion, then acts on the piston, and passes through the working cylinder; and the operation being one of simple mixture only, no heating surface of metal is required, the air to be heated being brought into immediate contact with the fire.{{citation needed|date=July 2020}}

Stirling came up with a first air engine in 1816.<ref name="haestirling1816-s01" /> The principle of the Stirling Air Engine differs from that of Sir [[George Cayley]] (1807), in which the air is forced through the furnace and exhausted, whereas in Stirling's engine the air works in a closed circuit. The inventor devoted most of his attention to that.{{citation needed|date=July 2020}}

A {{convert|2|hp|adj=on}} engine, built in 1818 for pumping water at an Ayrshire quarry, continued to work for some time until a careless attendant allowed the heater to overheat. This experiment proved to the inventor that, owing to the low working pressure obtainable, the engine could only be adapted to low power for which there was, at that time, no demand.{{citation needed|date=July 2020}}

The Stirling 1816 patent<ref name="haestirling1816-s02" /> was also about an "[[economizer|economiser]]," which is the predecessor of the regenerator. In this patent (# 4081) he describes the "economiser" technology and several applications where such technology can be used. Out of them came a new arrangement for a hot air engine.{{citation needed|date=July 2020}}

With his brother James, Stirling patented a second hot air engine in 1827.<ref name="haestirling1827-s01" /> 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 pressurised to around {{convert|20|atm}}.{{citation needed|date=July 2020}}

The Stirling brothers were followed shortly after (1828) by Parkinson & Crossley<ref name="haeparkinson&amp;crossley" /> and Arnott<ref name="haearnott-s01" /> in 1829.{{citation needed|date=July 2020}}

These precursors, including Ericsson,<ref name="haeericsson" /> have brought to the world the hot air engine technology and its enormous advantages over the steam engine.{{citation needed|date=August 2023}} Each came with his own specific technology, and although the Stirling engine and the Parkinson & Crossley engines were quite similar, Robert Stirling distinguished himself by inventing the regenerator.{{citation needed|date=July 2020}}

Parkinson and Crossley introduced the principle of using air of greater density than that of the atmosphere and so obtained an engine of greater power in the same compass. James Stirling followed this same idea when he built the famous Dundee engine.<ref name="haestirling1842" />

The Stirling patent of 1827 was the base of the Stirling third patent of 1840.<ref name="haestirling1842patent-2" /> The changes from the 1827 patent were minor but essential, and this third patent led to the Dundee engine.<ref name="haestirling1842-2" />

James Stirling presented his engine to the Institution of Civil Engineers in 1845, <ref name="haestirling1842-S03" /> the first engine of this kind which, after various modifications, was efficiently constructed and heated, had a cylinder of {{convert|12|inch|cm|order=flip|abbr=off}} in diameter, with a length of stroke of {{convert|2|ft|cm|order=flip|round=5}}, and made 40 strokes or revolutions in a minute (40&nbsp;rpm). This engine moved all the machinery at the Dundee Foundry Company's works for eight or ten months, and was previously found capable of raising 320,000&nbsp;kg (700,000&nbsp;lbs) 60&nbsp;cm (2&nbsp;ft) in a minute, a power of approximately {{convert|21|hp|kW|order=flip|abbr=off}}.{{citation needed|date=July 2020}}
Finding this power insufficient for their works, the Dundee Foundry Company erected the second engine with a cylinder of {{convert|16|inch|cm|order=flip|abbr=off|round=5}} in diameter, a stroke of {{convert|4|ft|m|order=flip|abbr=off}}, and making 28 strokes in a minute. When this engine had been in continuous operation for over two years it had not only performed the work of the foundry in the most satisfactory manner but had been tested (by a friction brake on a third mover) to the extent of lifting nearly {{convert|687|t|lb|lk=on|abbr=off|sigfig=2}}, approximately {{convert|45|hp|kW|order=flip|abbr=off}}.{{citation needed|date=July 2020}}
<!--
This gives a consumption of {{convert|2.7|lb|kg|abbr=off|order=flip}} per horse-power per hour; but when the engine was not fully burdened, the consumption was considerably under {{convert|2.5|lb|kg|abbr=off|order=flip}} per horse-power per hour. This performance was at the level of the best steam engines whose efficiency was about 10%. After James Stirling, such efficiency was possible only thanks to the use of the economiser (or regenerator).{{citation needed|date=July 2020}}
-->

=== Invention and early development ===
The Stirling engine (or Stirling's air engine as it was known at the time) was invented and patented in 1816.<ref name="Sier-1999" /> It followed [[Hot air engine#History|earlier attempts at making an air engine]] but was probably the first put to practical use when, in 1818, an engine built by Stirling was employed pumping water in a [[quarry]].<ref name="Finkelstein-2001-2.2" /> The main subject of Stirling's original patent was a heat exchanger, which he called an "[[economiser]]" for its enhancement of fuel economy in a variety of applications. The patent also described in detail the employment of one form of the economiser in his unique closed-cycle [[hot air engine|air engine]] design<ref name="patent-1816" /> in which application it is now generally known as a "[[#Regenerator|regenerator]]". Subsequent development by Robert Stirling and his brother [[James Stirling (1800–1876)|James]], an engineer, resulted in patents for various improved configurations of the original engine including pressurization, which by 1843, had sufficiently increased power output to drive all the machinery at a [[Dundee]] iron foundry.<ref name="Sier-1995-93" />

A paper presented by James Stirling in June 1845 to the [[Institution of Civil Engineers]] stated that his aims were not only to save fuel but also to create a safer alternative to the [[steam engine]]s of the time,<ref name="Sier-1995-92" /> whose [[boiler]]s frequently exploded, causing many injuries and fatalities.<ref name="Nesmith-1985" /><ref name="Chuse-1992-1" /> This has, however, been disputed.<ref name="Organ-2008a" />

The need for Stirling engines to run at very high temperatures to maximize power and efficiency exposed limitations in the materials of the day, and the few engines that were built in those early years suffered unacceptably frequent failures (albeit with far less disastrous consequences than boiler explosions).<ref name="Sier-1995-94" /> For example, the Dundee foundry engine was replaced by a steam engine after three hot cylinder failures in four years.<ref name="Finkelstein-2001-30" />

=== Later 19th century ===
[[File:Ericsson hot air engine.jpg|thumb|upright|left|A typical late nineteenth/early twentieth-century water-pumping engine by the [[Rider-Ericsson Engine Company]]]]

Subsequent to the replacement of the Dundee foundry engine there is no record of the Stirling brothers having any further involvement with air engine development, and the Stirling engine never again competed with steam as an industrial scale power source. (Steam boilers were becoming safer and steam engines more efficient, thus presenting less of a target for rival prime movers). However, beginning about 1860, smaller engines of the Stirling/hot air type were produced in substantial numbers for applications in which reliable sources of low to medium power were required, such as pumping air for church organs or raising water.<ref name="Finkelstein-2001-2.4" /> These smaller engines generally operated at lower temperatures so as not to tax available materials, and so were relatively inefficient. Their selling point was that unlike steam engines, they could be operated safely by anybody capable of managing a fire. The 1906 Rider-Ericsson Engine Co. catalog claimed that "any gardener or ordinary domestic can operate these engines and no licensed or experienced engineer is required". Several types remained in production beyond the end of the century, but apart from a few minor mechanical improvements the design of the Stirling engine in general stagnated during this period.<ref name="Finkelstein-2001-64" />

=== 20th-century revival ===
[[File:Philips Stirling engine.JPG|thumb|Philips MP1002CA Stirling generator of 1951]]

During the early part of the 20th century, the role of the Stirling engine as a "domestic motor"<ref name="Finkelstein-2001-34" /> was gradually taken over by [[electric motor]]s and small [[internal combustion engine]]s. By the late 1930s, it was largely forgotten, only produced for toys and a few small ventilating fans.<ref name="Finkelstein-2001-55" />

====Philips MP1002CA====
Around that time, [[Philips]] was seeking to expand sales of its radios into parts of the world where grid electricity and batteries were not consistently available. Philips' management decided that offering a low-power portable generator would facilitate such sales and asked a group of engineers at the company's research lab in [[Eindhoven]] to evaluate alternative ways of achieving this aim. After a systematic comparison of various [[prime mover (locomotive)|prime movers]], the team decided to go forward with the Stirling engine, citing its quiet operation (both audibly and in terms of radio interference) and ability to run on a variety of heat sources (common lamp oil&nbsp;– "cheap and available everywhere"&nbsp;– was favored).<ref name="Hargreaves-1991-28-30" /> They were also aware that, unlike steam and internal combustion engines, virtually no serious development work had been carried out on the Stirling engine for many years and asserted that modern materials and know-how should enable great improvements.<ref name="Philips-1947" />

By 1951, the 180/200 W generator set designated MP1002CA (known as the "Bungalow set") was ready for production and an initial batch of 250 was planned, but soon it became clear that they could not be made at a competitive price. Additionally, the advent of transistor radios and their much lower power requirements meant that the original reason for the set was disappearing. Approximately 150 of these sets were eventually produced.<ref name="Hargreaves-1991-61" /> Some found their way into university and college engineering departments around the world, giving generations of students a valuable introduction to the Stirling engine; a letter dated March 1961 from Research and Control Instruments Ltd. London WC1 to North Devon Technical College, offering "remaining stocks... to institutions such as yourselves... at a special price of £75 net".{{citation needed|date=July 2020}}

In parallel with the Bungalow set, Philips developed experimental Stirling engines for a wide variety of applications and continued to work in the field until the late 1970s, but only achieved commercial success with the "reversed Stirling engine" [[Applications of the Stirling engine#Stirling cryocoolers|cryocooler]]. They filed a large number of patents and amassed a wealth of information which they licensed to other companies and which formed the basis of much of the development work in the modern era.<ref name="Hargreaves-1991-77" />

====Submarine use====
In 1996, the Swedish navy commissioned three [[Gotland-class submarine]]s. On the surface, these boats are propelled by marine diesel engines; however, when submerged they use a Stirling-driven generator developed by Swedish shipbuilder [[Kockums]] to recharge batteries and provide electrical power for propulsion.<ref name="Kockums" /> A supply of liquid oxygen is carried to support burning of diesel fuel to power the engine. Stirling engines are also fitted to Swedish [[Södermanland-class submarine]]s, the [[Archer-class submarine]]s in service in Singapore, and the Japanese [[Sōryū-class submarine]]s, with the engines license-built by [[Kawasaki Heavy Industries]]. In a submarine application, the Stirling engine offers the advantage of being exceptionally quiet when running.{{citation needed|date=July 2020}}

===21st-century developments===
{{Further|Solar-powered Stirling engine}}
By the turn of the 21st century, Stirling engines were used in the dish version of [[Concentrated Solar Power]] systems. A mirrored dish similar to a very large satellite dish directs and concentrates sunlight onto a thermal receiver, which absorbs and collects the heat and using a fluid transfers it into the Stirling engine. The resulting mechanical power is then used to run a generator or alternator to produce electricity.<ref name="NREL_CSP" />

The core component of [[micro combined heat and power]] (CHP) units can be formed by a Stirling cycle engine, as they are more efficient and safer than a comparable steam engine. By 2003, CHP units were being commercially installed in domestic applications, such as home electrical generators.<ref name="BBC_CHP" />

In 2013, an article was published about [[scaling law]]s of free-piston Stirling engines based on six characteristic [[Dimensionless quantity|dimensionless groups]].<ref name="scaling" />