Heyday of the Stirling Hot Air Engine

By Renae Vander Schaaf
Published on November 18, 2011
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Engine enthusiast Wesley Bosch with his Ky-Ko hot air fan.
Engine enthusiast Wesley Bosch with his Ky-Ko hot air fan.
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Wesley built this replica of a Lake Breeze fan.
Wesley built this replica of a Lake Breeze fan.
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Reverend Dr. Robert Stirling
Reverend Dr. Robert Stirling
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This reproduction “salon fountain” is powered by a hot air engine.
This reproduction “salon fountain” is powered by a hot air engine.
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Watering the herd: Hot air engines found a ready audience in specialized applications – like pumping water in remote locations, as shown in this 1903 ad. The engines were dependable, required little maintenance and could be left unattended for long periods.
Watering the herd: Hot air engines found a ready audience in specialized applications – like pumping water in remote locations, as shown in this 1903 ad. The engines were dependable, required little maintenance and could be left unattended for long periods.
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The compact complexity of this Tibert engine makes it one of Wesley’s favorites.
The compact complexity of this Tibert engine makes it one of Wesley’s favorites.
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Tibert engine back view.
Tibert engine back view.
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Wesley restored this Jost radio fan in his basement workshop.
Wesley restored this Jost radio fan in his basement workshop.
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Radio fan produced by Jost Engineering Co. Wesley suspects the “radio” name has more to do with the word “radial” than with an actual radio.
Radio fan produced by Jost Engineering Co. Wesley suspects the “radio” name has more to do with the word “radial” than with an actual radio.
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This five-inch (piston) Rider-Ericsson hot air-style pumping engine was manufactured in about 1907.
This five-inch (piston) Rider-Ericsson hot air-style pumping engine was manufactured in about 1907.
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Essex engine with a turntable and gear reduction. On top of the turntable: a Carette engine dating to about 1911. This Essex was patented in 1902 by W.H. Smith & Co., Buffalo, N.Y.
Essex engine with a turntable and gear reduction. On top of the turntable: a Carette engine dating to about 1911. This Essex was patented in 1902 by W.H. Smith & Co., Buffalo, N.Y.

Almost 200 years ago, in 1816, a 26-year-old Presbyterian minister in Scotland patented a revolutionary external combustion engine. The closed-cycle Stirling hot air engine was designed as a safe, economical and efficient alternative to steam. Although the hot air engine never achieved success in industrial applications, Robert Stirling’s invention met the needs of low-power domestic applications from the 1860s to the early 1900s.

How Stirling engines work

The Stirling engine receives its heat supply through the cylinder walls or a heat exchanger in contact with the heat source. Alternately heating and cooling the air causes expansion and contraction, which creates the power stroke that moves the piston. Every Stirling engine has a sealed cylinder with one part hot and the other cold. The working gas inside the engine (which is often air, helium or hydrogen) is moved by a mechanism from the hot side to the cold side. When the gas is on the hot side, it expands and pushes up on a piston. When it moves back to the cold side, it contracts.

Stirling’s “Heat Economizer” (basically, a heat exchanger) is one of the earliest examples of engines operating with the heat regeneration principle. To prevent heat waste, gas flowed through a porous material such as steel wool or tubing.

Stirling’s invention was well ahead of its time. About eight years later, in 1824, Nicolas Leonard Sadi Carnot of France discovered that heat could not be transmitted from a cold object to a warm one, and that the efficiency of an engine relies on the amount of heat it is capable of employing.

Existing materials posed another major problem. Because the power produced by a Stirling engine is directly related to the extremes between heat and cold, extremely hot air was needed for efficient operation. Metals commonly available in the early 1800s, however, could not withstand such heat.

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