Stirling engines are simple, easily constructed engines that are in theory able to run on virtually any source of heat, even at relatively low temperatures. They are best known for their potential to be more efficient than a gas or diesel engine or even as an alternative source of clean energy, but currently they have only been used in very specific and specialised applications. Although today the Stirling engine is most commonly used to power submarines, auxiliary power generators, large scale solar power, or as small models and toys, they have the potential to be developed for use in a much larger, successful market if the proper research is able to be applied.
The original Stirling engine was invented and patented by Robert Stirling on September 27, 1816 and first used in 1818 as a pumping device to push water into a quarry. Although it followed earlier attempts to produce an air engine, it was the first to be put to practical use. With help from his brother James, an engineer, the full patent for the invention and the fuel economiser was applied for. The device was not yet known as a Stirling Engine, that name was coined nearly one hundred years later by Dutch engineer Rolf Meijer to describe all types of closed cycle regenerative gas engines. The original Stirling engine is thought to have been produced to provide a safer alternative to the then-dangerous steam engine (due to high pressure boiler explosions). While the Stirling engine was never successfully employed for this purpose, by the beginning of the twentieth century it was being used as a safe and reliable source of low to medium power, mostly for pumping water and as cooling fan.
During the early 1900s, the Stirling engine was widely replaced as a domestic motor by the affordable electric motor, and soon after was largely unused for much besides small toys. By the 1930s, the Stirling engine was all but forgotten. However, around the same time, Philips began exploring alternate sources of energy in attempt to offer a quietly operating, cheap, and available option of radio to parts of the world without easily accessible sources of power or batteries. Although their attempts achieved only limited success, many Philips models made their way onto university and college engineering campuses, ensuring years of future exploration.
Early in 1983, Professor Ivo Kolin of the University of Zagreb, Croatia, demonstrated the very first low temperature differential Stirling engine to an amazed audience. This engine ran on a temperature difference of 100°C, which at the time was an astonishingly low figure. The demonstrated engine ran for a long time as the temperature differential lowered, eventually stopping when the difference dropped below 20°C. This feat was all the more remarkable when you consider the engine was constructed entirely with hand tools. The engine had no power piston and cylinder, instead relying on a rubber diaphragm to transmit the power from the square main chamber. A feature of this engine was the 'slip-link', a device for imparting an intermittent motion to the displacer inside the main chamber. At the low speed that this engine ran at, a dwell at each end of the displacer stroke was very beneficial. During the 1980's, Professor Kolin continued to refine his low temperature engines, still relying on a diaphragm but simplifying the original complex displacer drive mechanisms.
During the late 1980's and the early 1990's Professor Senft of the University of Wisconsin took up the idea of low temperature differential Stirling engines. The first models he produced were Ringbom engines, where there is no direct connection between the flywheel and the displacer, with the Ringbom engine being reliant on the changing pressure inside the main chamber to move the displacer back and forth. Professor Senft, working closely with Professor Kolin, continued working with Stirling engines, working out many of the design solutions that are used today in low temperature differential Stirling engines. In 1992 Professor Senft was asked to design and build a low temperature differential engine for NASA. This engine, called the N-92, was optimised for hand held operation, with a temperature difference as low as 6°C enough to power it. Professor Senft continues to work with Stirling Engines, and has written several books detailing the history and manufacture of Stirling engines.
The KS range of low temperature differential Stirling engines was designed and developed in England in 2002 by our design engineer Chris Guise. It was the first off-the-shelf low temperature differential Stirling engines available and has been in continual production ever since. The original KS90 was eventually developed into a wide range of affordable low temperature engines, including twin cylinder and Ross Yoke versions.
Contemporary use of the Stirling engine has been relatively limited. Typically, they are used in the commercial industry for very specialised products, such as the above-mentioned applicability for submarines or auxiliary power generators for use on yachts. Stirling engines have also found limited use as refrigerators and were even be used to power a few prototype cars in the 1970s. There are even a number of companies that have incorporated Stirling engines into central heating systems to generate effectively free electricaty from waste heat.
In addition to their commercial use, Stirling engines are frequently used as toy model kits, such as wide variety of models we currently have available. Small Stirling engines, such as our KS90, are proven so efficient that they have the ability to run on the surface of a warm hand or sunlit window.
Perhaps the Stirling engine's greatest promise is its potential to produce a wide range of access to greener energy. Because of its ability to run on almost any heat source, Stirling engines being used to harness alternative energy sources such as solar and geothermal power. In fact a number of companies now produce Stirling engines for waste heat recovery energy with the promise that they have the capacity to captured waste hear from industrial sites, commercial processes, or power generators and turn in into clean and renewable energy.
In the 1800s Stirling engines were discarded because of the quick advancements of steam engines. However the future for Stirling engines are looking very bright.
