Robert Stirling (25 October 1790 – 6 June 1878) was a Scottish clergyman and engineer. He invented the Stirling engine and was inducted into the Scottish Engineering Hall of Fame in 2014.
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Early life
Robert Stirling was born at Cloag Farm, a location in Scotland near the village of Methven, Perthshire. A member of the Dublane side of the Stirling family, Robert was born to Patrick and Agnes Stirling. He was one of eight children that Patrick and Agnes shared.
His grandfather was Michael Stirling, most famously known for his invention of the threshing machine. Robert's father, Patrick, also spent time experimenting and innovating with industrial agricultural equipment.
Though Robert, like his father and grandfather, had a natural inclination for engineering, he began attending Edinburgh University in 1805 at the age of fifteen to study divinity in hopes of becoming a minister. His brother James, who would play a major role in Stirling's future engineering endeavours, also attended Edinburgh at the age of 14.
He finished his studies at University of Edinburgh and continued in November 1809 to study at Glasgow University where, according to Keith Laidler, he studied the classics, philosophy, theology and mathematics, but probably very little science. In 1814, he returned to Edinburgh University studying divinity for a final time.
Robert was licensed to preach in the Church of Scotland in 1816 by the Presbytery of Dumbarton. In September 1816, the commissioner of the Duke of Portland granted Stirling the title of Minister as the second charge for the Laigh Kirk parish in Kilmarnock. Finally, in February 1824, Stirling was appointed as the minister of nearby Galston Parish Church where he continued his ministry until 1878.
In July 1819, Robert Stirling married Jane Rankine. Together, they had seven children, five sons and two daughters.
Engineering and science
History
Robert Stirling is considered as one of the fathers of hot air engines. Few before him ventured to build air engines, Guillaume Amontons being the first one to build a working hot air engine in 1699.
Amontons was followed in 1807 by George Cayley whose engine 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.
Stirling came up with a first patent for an air engine in 1816. The principle of the Stirling Air Engine differs from Cayley's, in which the air is forced through the furnace and exhausted, whereas in Stirling's engine the air works in a closed circuit. It was to it that the inventor devoted most of his attention. A 2 hp (1.5 kW) Stirling hot air 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 become overheated. This experiment proved to the inventor that, owing to the low working pressure obtainable, the engine could only be adapted to small powers for which there was at that time no demand.
The Stirling 1816 patent was also about an "Economiser", 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. In 1818, one engine was built to pump water from a quarry in Ayrshire, but due to technical issues, the engine was abandoned for a time.
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 atm (2,000 kPa; 290 psi).
The two Stirling brothers were followed shortly after in 1828 by Parkinson & Crossley and in 1829 and Arnott. These precursors, to whom John Ericsson should be added, have brought to the world the hot air engine technology and its enormous advantages over the steam engine. Each of them 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, the first example of a Regenerative heat exchanger.
Hot air engine
Robert Stirling's best known invention is the heat engine now referred to as the Stirling engine. In 1816 the Stirling brothers applied for a patent in both Scotland and England for a device they invented, a Heat Economiser. The function of this invention was to store and release heat as air circulated through its mechanisms. This differed from most heat engines which used steam as their method of storing and releasing energy.
While in Kilmarnock, he collaborated with another inventor, Thomas Morton, who provided workshop facilities for Stirling's research. By 1818 Stirling had incorporated this Heat Economiser into a piston engine that created a closed cycle heat engine, which was powered by air, a contrast to the steam engines that were predominant at the time. This updated version of the heat engine was used to pump water from a quarry. Stirling's heat engine was able to run well but was limited by the weaker metals available at the time. Due to the flimsiness of the materials used, the air vessels were eventually crushed by the high pressure of the heated air.
In 1824 Stirling sought to improve the efficiency of the heat engine by attempting to separate the air present in the economizer. This was done by making the plungers in the air engine from thin plates of metal. This was to improve airflow and offer better heating and cooling of the engine. Although this idea received a patent, it was ultimately unsuccessful in improving the heat engine's overall efficiency.
In 1840 Stirling received another patent for the heat engine after altering the design in a new attempt to increase durability. The improvements added by Stirling included the addition of rods or plates in the passage through which hot air travelled to the cold section of the engine. By having these surfaces, the air was able to be cooled to a lower temperature when travelling from the hot section of the engine to the cold section of the engine. Additionally, Stirling added cupped leather collars around the piston rods to seal gaps and minimize the leakage of air from the engine. After developing these improvements, Stirling built two of these heat engines to use at an iron foundry he managed in Dundee. One of these air engines was started in March 1843 where it ran until December 1845 when an air vessel failed. The air vessel failure could be attributed to the metals being unable to withstand the high temperatures at which the engine was running. After replacing the air vessel a couple times, the air engine was dismantled in 1847 after Stirling left the Dundee iron foundry.
Personal life and death
On 10 July 1819, Stirling married Jane Rankine at Kilmarnock. They had seven children:
Patrick Stirling, born 29 June 1820, became a locomotive engineer
Jane Stirling, born 25 September 1821, housewife
William Stirling born 14 November 1822, became a civil engineer and railway engineer in South America
Robert Stirling, born 16 December 1824, became a railway engineer in Peru.
David Stirling, born 12 October 1828, became the Minister of Craigie, Ayrshire
James Stirling, born 2 October 1835, became a locomotive engineer
Agnes Stirling, born 22 July 1838, became an artist
Rev. Robert Stirling died in Galston, East Ayrshire on 6 June 1878. He is buried in Galston Cemetery where a new gravestone was erected in December 2014 by public subscription, replacing the original stone which was in a ruined state. It was rededicated on Sunday 3 May 2015.
Honours
On 11 January 1840, Stirling was awarded the title Doctor of Divinity by the University of St. Andrews for his excellence in ministry.
On 3 October 2014 Stirling was inducted into the Scottish Engineering Hall of Fame.