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Significant Scots
Robert Stirling


Robert Stirling, inventor of the Stirling engine, was born at Gloag, Methvin, Perthshire on 25 October, 1790 and was the third of a family of eight children. His father was Patrick Stirling, son of Michael Stirling of Threshing Machine fame and his mother was Agnes Stirling, daughter of Robert Stirling, farmer in the Cromlix, Dunblane.

In 1850 the simple and elegant dynamics of the engine were first explained by Professor McQuorne Rankine. Approximately one hundred years later, the term "Stirling engines" was coined by Rolf Meijer in order to describe all types of closed cycle regenerative gas engines. Perhaps his most important invention was the "regenerator" or "economizer" as he called it. This is used today in Stirling engines and many other industrial processes to save heat and make industry more efficient. 

Stirling engines are unique heat engines because their theoretical efficiency is nearly equal to their theoretical maximum efficiency, known as the Carnot Cycle efficiency. Stirling engines are powered by the expansion of a gas when heated, followed by the compression of the gas when cooled. The Stirling engine contains a fixed amount of gas which is transferred back and forth between a "cold" end (often room temperature) and a "hot" end (often heated by a kerosene or alcohol burner). The "displacer piston" moves the gas between the two ends and the "power piston" changes the internal volume as the gas expands and contracts.

Stirling engines are being studied at NASA for use in powering space vehicles with solar energy!

Robert was a bright lad and, from 1805 to 1808, attended Edinburgh University, where he studied Latin, Greek, Logic, Mathematics and Law. His younger brother James was later to attend at the age of 14 and became a Civil Engineer of some fame.

Robert enrolled as a student of Divinity at Glasgow University in November 1809 and completed five sessions. He was a model student there. On 15th November 1814, he was enrolled at Edinburgh University as a Student of Divinity, where again his conduct was exemplary. In 1815, Robert Stirling was examined by the Presbytery of Dunbarton and, after the usual tests, found competent to preach the Gospel, a license being issued to this effect on 26th March, 1816. In 1816, he was presented by the Commisioners of the Duke of Portland to the second charge of the Laigh Kirk, Kilmarnock. He
appeared before the Presbytery of Irvine, who unanimously agreed on his suitability and, after satisfactory execution of varied trials had him ordained Minister of the Second Charge of Laigh Kirk on 19 September, 1816.

At an early age, Robert had been introduced to engineering by his father, Patrick Stirling, who had assisted his own father, Michael, in the maintenance of his threshing machines, and had always shown a keen interest in anything mechanical, and in particular in sources of power for machinery. On 27th September, 1816, he applied for a patent for his now well famed engine. He had his patent enrolled on 20 Jan 1817. He had been working on this engine for several years before moving to Kilmarnock, and his research continued there.

In Kilmarnock, he met up with a certain Thomas Morton, with similar interests in new ideas. He was the son of a brick manufacturer, who had served an apprenticeship as a turner and wheelwright, and then set up in this business on his own account. He was responsible for several innovations including a new improved carpet loom. He also erected a novel observatory at Morton place, in the year 1818.

When the two men got together, Rev. Robert arranged with Morton for the use of premises at Morton Place, where his experiments continued. These were specially built for them. Stirling was to use them for some 20 years. His experiments embraced more than the Stirling Heat Engine. He was, like Morton, also interested in astronomy and was not long in acquiring the skills which Morton could give him in the manufacture of lenses. His brother James closely followed the experiments and encouraged
his brother greatly in his research.

Robert Stirling was married, on 10 Jul 1819, to Jean Rankin, daughter of William Rankin, wine merchant in Kilmarnock, and Jean McKay. She was born at Kilmarnock on 27 Jun 1800. Their family turned out to be as inclined to engineering as the father.

Patrick Stirling, born 29 Jun 1820, became a famous Railway Locomotive Engineer.
Jane Stirling, born 25 Sep 1821, fed ideas of her own to her bothers.
William Stirling born 14 Nov 1822, was a Civil Engineer and Railway Engineer in South America. Robert Stirling, born 16 Dec 1824, was a Railway Engineer in Peru.
David Stirling, born 12 Oct 1828, followed in his father's footsteps and became the Minister of Craigie, Ayrshire.
James Stirling, born 02 Oct 1835, was another well known Railway Engineer.
Agnes Stirling, born 22 Jul 1838, was a gifted artist whose talents were confined to the family.

Robert Stirling was a gifted speaker and was beloved by his flock. He died at Galston on 06 Jun 1878, leaving a heritage in his engine which has yet to see its full potential.

Click here to see a Stirling engine that runs of a cup of coffee

From the book "Stirling Cycle Engines" by Andy Ross

Everywhere, it seems, interest is picking up in the Stirling engine. The prestigious Jet Propulsion Lab recently reported that the Stirling is one of the two most promising alternative automobile engines for the future, offering silence, long life, improved mileage, and greatly reduced pollution. Ford Motor Company announced it has installed an experimental Stirling in a sedan for testing as part of its current research effort on the Stirling. The Energy Research and Development Administration recently entered an eight year $110 million contract with Ford for development of a Stirling automobile engine. In Sweden, work is said to be progressing very well toward the development of a Stirling suitable for delivery vans and other vehicles.

By no means is all of the current interest in this old engine related to powering road vehicles. In Athens, Ohio a great deal of development work is being done on a Stirling powered heat pump for home heating. In this application, gas or other fuel is used to run a small Stirling engine, which in turn drives a conventional heat pump to heat or cool a home. This may seem like a complicated way to provide heat when compared with the conventional method of simply burning the gas and using that heat directly. But the fact is that the Stirling heat pump approach provides a great deal more heating for the same amount of gas, because it makes a more efficient use of the high temperature flame of the gas. Even at today’s gas prices, it is anticipated that such devices could pay for themselves in gas bill savings in three or four years.

In Holland, where the revival of interest in the Stirling engine first began about forty years ago, air liquifying machines based on the Stirling cycle are being produced and sold world-wide.

In India, South America, and other places around the world, the Stirling is receiving attention as a potential power source for pumping irrigation water and doing other farm chores; because, unlike the gasoline engine, it can use almost any combustible substance for fuel, including sticks and straw. As the price of oil continues to rise, the multifuel capacity of the Stirling becomes one of its most important virtues.

Nor is all the current interest in the Stirling solely for utilitarian purposes; hobbyist Norris Bomford spent several years developing a Stirling engine to propel his graceful rowing skiff over the lakes and rivers of England. The engine, which pushes his craft at a gentle three to four miles per hour, is so quiet that builder Bomford can indulge in his two favorite recreations at the same time — boating and listening to classical music on a portable record player.

Many other hobbyists in England and North America have discovered for themselves the intriguing challenges presented by designing and building their own small Stirling engines. The first international power competition for these model engines has been held in London, under the auspices of the well-known Model Engineer magazine, and it promises to become an annual event.

What is a Stirling?

What is a Stirling engine? Like the gasoline, diesel, and jet engines with which we are all familiar, the Stirling is a heat engine; that is, an engine that derives its power from heat. But unlike those other engines, the Stirling obtains its heat from outside, rather than inside, the working cylinders. In this respect, the Stirling is similar to that charming old workhorse of the industrial revolution, the steam engine.

This difference, between external and internal combustion, is one of the main reasons for the widespread current interest in the Stirling. An internal combustion engine, that is an engine that burns its fuel inside its working cylinders or chambers like the gasoline, diesel, or gas turbine engine, is generally rather particular about its fuel. A gasoline engine may be modified to run on hydrogen, methane, or propane; but it will not run on salad oil, straw, coal, or peat. When one thinks of a small gasoline engine, one tends to think of it as a self-contained little powerpak; perhaps it would be more appropriate to think of it as a power plant with an oil refinery attached to it!

Of the three internal combustion engines mentioned, the gas turbine is probably the most omnivorous with respect to fuel; yet even it is limited indeed when compared to the Stirling. Quite literally, any source of heat, as long as its temperature is high enough, will do to power a Stirling. This last statement is no doubt true of any other externally heated engine, like the steam engine, but interest has focused on the Stirling as the externally heated engine of choice because it holds the promise of making the most power for a given supply of heat (or fuel) of the practical alternatives presently known.

Thus, the Stirling can directly use concentrated solar energy, or it can burn kerosene, coal, straw, wood, sawdust, cardboard, discarded Christmas trees, or any other combustible substance imaginable.

It can also use stored heat. Certain salts give off great amounts of heat for their weight in the process of cooling from their liquid to their solid state. With a salt such a lithium fluoride, this change of state occurs at a high temperature, in the neighborhood of 1550F, which is an excellent temperature for the hot end of a Stirling engine. When space-age techniques of thermal insulation are employed in conjunction with these salts, it has been found that a very good thermal storage battery can be made from which to run a Stirling engine. This is similar to the electric motor-storage battery system, except heat is stored instead of electricity. The thermal battery-Stirling system is superior, however, in that it can be recharged (electrically reheated) much faster and it can store over eight times more shaft power per pound than a lead-acid battery.

But even when it is burning a conventional fuel, such as gasoline or diesel fuel, a Stirling has an important advantage resulting from its basic design. That is, its combustion takes place against hot surroundings at atmospheric pressure, and not against cooled cylinder walls at elevated pressures as is the case in the gasoline engine. Combustion under the conditions in the Stirling produces practically no carbon monoxide or unburned hydrocarbons, and the level of nitrogen oxides is also relatively low. In terms of these three pollutants, the Stirling is about the cleanest heat engine imaginable, and this accounts for the present interest in the engine by automakers.


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