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.
Although a Stirling engine was used as early as 1818 to pump water in a quarry, steam engines (though still considered complex and potentially dangerous) remained the first choice for heavy applications. For light work such as pumping water for domestic use, air for church organs and powering toys, the hot air concept was an intriguing option.
Starting with an Essex engine
Until a chance conversation in the 1970s, engine enthusiast Wesley Bosch had never heard of hot air engines. But that was all it took for the Atwater, Minn., man. Wesley’s debut in hot air engines was an Essex engine that he bought from the estate of collector Harold Felt in 1985.
“Harold was just a young boy, 5 or 6, when a classmate brought the engine for show-and-tell at school,” Wesley says. “He admired it and kept after the boy about it. Finally he traded three Indian Head pennies and three Indian arrowheads for it.”
The engine was originally used to spin a postcard display at a drug store in nearby Willmar, Minn. Similar engines were widely used in varied retail applications, drawing the customer’s eye and interest. Essex engines were built in the early 1900s by W.H. Smith & Co., Buffalo, N.Y.
Ventilating fans were another good match for the Stirling hot air engine, which ran quietly and worked anywhere. When missionaries traveled to hot climates in undeveloped locations, a fan powered by a hot air engine helped provide relief from the heat.
The British-made Ky-Ko fan is a classic example. The fan could be dismantled and stored in a box when not in use. It ran on widely accessible kerosene, and it operated quietly. Wesley’s collection includes about 20 similar fans made all over the world.
Vintage fans are rarely found in good condition and typically need almost as much restoration work as the antique engines used to provide power to them. Three-quarters of the fans Wesley finds are missing guards; safety was not always a top priority a century ago.
In 1919, Lake Breeze Motor Co., Chicago, produced several models of fans designed for use with Stirling engines. To accommodate hoteliers, the company manufactured fans bearing the name of various hotels. Prices started at $22.
Pulling the load with a Sterling hot air engine
Stirling hot air engines made life easier on the farm and railroad, in hotels and factories, where pumping water was a never-ending chore. Hot air engines were the ideal power source for pumps because the engine did not need watching. Once the Stirling-type engine was started, it would pump water while other chores were tended to. Coal or wood provided the heat source.
Wesley has several Stirling-type engines specifically designed to pump water, including two Rider-Ericsson engines (5-inch and 8-inch), an English-made Robinson 7-inch rated at 1/4 hp and a 10-inch DeLamater-Ericsson manufactured by DeLamater Iron Works.
Hands-on hobby: collecting antique engines
Some hot air engine enthusiasts collect antique engines; others handcraft intricately detailed replica engines. Some replicas are working models; others are for display only. Among Wesley’s favorites is an engine built by George Tibert, Pisek, S.D. “I really like the linkage, the shape of the parts and the way everything fits so tightly together in a small space,” he says. Tibert machined all of the parts but did no polishing. “It was really rough,” Wesley says. “So I took it apart and polished everything. He said he figured I spent more time on it than he did. I worked on it so long that after a while I felt like I knew him.”
Another of Wesley’s favorites is one he made himself: an engine used to power fountains used in early fish aquariums. “Decades ago, aquariums were a status symbol in Germany. Before electricity, the water in fish aquariums had to be stirred by hand,” Wesley explains. “Louis Heinrici was the unrivalled market leader in these ‘salon fountains’ as they were referred to in 1880. His hot-air engine took care of the need to stir the water.”
Small hot air engines were also used to bring toys to life, particularly elegant, high quality toys. A treasured piece in Wesley’s collection is a miniature workshop produced by Jensen Steam Engine Mfg. Co., Jeannette, Pa., complete with a drill press, sharpeners, table saws and turning lathes. Wesley sometimes uses a German-made Carette hot air model engine to run the tools.
Wesley hosted a regional Stirling gathering in 2010. “Through this hobby, I have made so many new friends, not only in the U.S. but all over the world,” he says. “They tell me, ‘stop in any time, you are always welcome’ and my reply is the same to them.” FC
Curious? See a Stirling-powered Jost hot air fan and a Ky-Ko hot air fan in motion.
For more information:
–Contact Wesley Bosch via email at Wesley_bosch@yahoo.com.
–Stirling Engine Society
–Atwater (Minn.) Threshing Days, Sept. 8-9, 2012: The Atwater show serves as an unofficial regional gathering of hot air engine enthusiasts, including Wesley Bosch, who sets up an extensive display there.
Renae B. Vander Schaaf is a freelance writer living in northwest Iowa on an actual working farm. She enjoys writing about agriculture, rural life and history. Contact her at firstname.lastname@example.org.