Kerosene or

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Fio. I.I. I:acsi:nile reproduction of nti lulvcrtisinu piccc for a Stirling-engine ventilation fan. circ« 1900.

internal combustion engines. Nevertheless, by the time of the First World War. hot-air engines were no longer available commercially in large quantity, although production of machines for special purposes continued for many years.

One of the widest uses of hot-air engines in small sizes was to drive ventilating fans and water pumps. A facsimile reproduction of an advertising piece of 1900 is shown in F ig. 1.1. The production ol similar machines in substantial quantities was carried on in England to the late 1940s largely for export to tropical countries. The author has a fond vision of a missionary after a long day in the (iekl returning to his bungalow, pouring a mint julep, and relaxing on the stoep under the cooling breeze of his kerosene-driven Stirling engine.

Even today it is by no means unusual to come across hot-air engines. In 1971 for example a complete, new. and unused Bailey engine (circa 1902) of 3.6 kW (5 hp) rating, in its original factory packing was sold at a Welsh country-house auction. An Ericsson pumping engine was recently removed from a lakeside estate near Ottawa in Canada and refurbished fot exhibition in the foyer of an Ottawa machine works. In the United States one occasionally finds hot-air engines still fulfilling useful purposes.

There are many collections of historical engines. Perhaps the most extensive is that at the Ford Museum in Greenfield Village, Dearborn. Michigan. The Smithsonian Institute in Washington has a notable collection, as does the Science Museum in London, and the Museum of Technology in Paris. Three or four hot-air engines may be found operating daily on a routine basis at the Museum of Science and Technology in Birmingham, England. The Ericsson Museum in Philadelphia has many items and memorabilia of intense interest concerned with John Ericsson. There are also many private collections and in the U.S. Mid-West it is commonplace to see hot-air engines displayed alongside steam engines at county and state fairs.

High quality facsimile reproductions of old-time hot-air engine catalogues and other advertising pieces have recently been published by Alan G. Philips of Orlando, Florida, and by Robert Huxtable of Lansing, Michigan. Models of hot-air engines are still made in large numbers by amateur craftsmen and are also obtainable commercially from the sources listed in the back of this volume.


The present renaissance of interest in Stirling engines is due almost entirely to workers at the Philips Research Laboratory in Eindhoven. Work on small Stirling engines started there in the mid-1930s. The objective was to provide a small, quiet, thermally activated, electric-power generator for radios hi areas of the world without rcgulm power supplies. It is said the choice between steam and hot-air engines was made following a chance visit to the Museum of Technology in Paris by one of the technical directors of the laboratory where he saw some of the old hot-aii engines displayed. He believed, rightly, that modern materials and technology could elevate the hot-air engine to a performance undreamt of in earlier engines.

Work on Stirling engines continued during the German occupation in the Second World War and the first information about it was released soon after the war. Brilliant research and engineering resulted in the development of small generator sets far superior to any of the old hot-air engines. However, by the early 1950s the invention of the transistor ami improvements in dry batteries had eliminated the original need. Recognizing the significance of their work, though, the Philips engineers switched theii efforts to engines of higher powers, and the invention of the 'rhombic drive' and roll-sock seal led to the development of a family of single and multiple cylinder engines ranging in power up to hundreds of horsepower. This work has been reported periodically by Meijer (1969d> in a number of papers and more recently bv van Beukering and Fokker (1973).

In 1958 the General Motors Corporation of Detroit made a licensing agreement with Philips which continued until 1970. Percival (197-1) has given much interesting detail about the work done at General Motors in this period. They were concerned with Stirling engines for space and underwater power, vehicle and surface vessel propulsion, and stationary power.

Following relinquishment by General Motors of the licence agreement with Philips, the Ford Motor Co. of Detroit became licensees (in 1971) and alter some preliminary work and evaluation have embarked (in 1977) on a seven-year substantial ($IS0M) programme of development foi automotive Stirling engines funded by the U.S. Department of Energy.

Other licences were granted by Philips to United Stirling AB of Malmo. Sweden (in 1968) and to a West German consortium of the two diesel engine companies MAN and MWM (1967). United Stilling is ;> consortium of Swedish interests, principally Kockums, the great Swedish shipbuilders of Malmo, and FFW, a Swedish government company oriented to defence interests. In the early 1970s there was substantial cooperative effort between Philips and the European licensees in the development of transport-vehicle engines, and marine and underwater power systems. Later, the European licensees chose to follow a more independent path.

Zacharias (1974) has provided an interesting account of developments at MAN/MWM. Since about 1974, they have ceased much public discus sion iȒ their activities. However, it is understood that their programme of development is continuing unabated with concentration of effort on engines of 370 kW (500 hp) to 740 kW (1000 hp) for underwater power systems.

The Swedish group, United Stirling, concerned primarily in the early days with heavy-vehicle engines, have expanded their interests to the passenger car field. They did some work in cooperation with Ford but in 1978 a second substantial ($100M) programme for automotive Stirling engines was initiated in the United Stales by the Department of Energy and involving the two United States companies Mechanical Technology, Inc. of Latham, New York, and American Motors Corp.. Detroit, Michigan, in partnership with United Stirling of Sweden. Hallare and Rosenqvist (1977) have provided an interesting historical review of the United Stirling work.

To manage these two automotive programmes, the Stirling Fngine Project Office was established at the National Aeronautics and Space Administration (NASA) Lewis Research Centre, Cleveland, Ohio and to develop competence in the field an independent programme of study and development was started at NASA Lewis about 1975.

The External Combustion Bngine Project was initiated by the LJ.S. Department of Energy in 1977 to demonstrate the use of 370 kW (500 hp) to 1480 kW (2000 hp) Stirling engines burning coal and other 'alternative' fuels with high efficiency, including municipal, industrial, and agricultural wastes. Management for this programme is the responsibility of the Argonne National Laboratory. Illinois.

In the early 1960s William Beale, a professor at the Ohio University, Athens. Ohio, invented the free-piston Stirling engine and with remarkably single-minded purpose brought the device into commercial production in the farm ú£ 'á small demonstration engine in the early 1970s. Further development followed with substantial funding to perfect a gas-fired air-conditioning pump unit now in the final pre-production stages. Beale's company. Sunpower Inc., in association with M.T.I., Latham, N Y. is engaged in producing free-piston Stilling engines for other applications, notably as nuclear-fuelled space power plants and as solar-powered electric generators.

The General F.lectric Company in the United States is also developing Beale-type free-piston Stirling engines and are also said to be in the process of acquiring a Philips licence.

Substantive work on miniature engines for artificial hearts has been funded for over a decade by the United States National Institutes of Health. Cardiovascular Devices Branch, Department of Health. Education. and Welfare, Bethesda. Maryland. This broad investigative pro-

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separate Stirling engine developments ¡it the Donald Douglas Laboratories, Richland, Washington, at the Aerojet Liquid Rocket Co., Sacramento, California, and at the Thermo-electron Corp., Waltham, Massachusetts. A separate programme of Stirling engine artificial heart development is being carried out jointly by Westinghouse and Philips, funded by the U.S. Department of Energy.

Research oil Stirling engines for solar, space, and underwater power, and the development of a basic laboratory research engine is in progress ■'it the California Institute of Technology, .let Propulsion Laboratory, Pasadena, California.

At the Atomic Energy Research Establishment. Harwell, England, a free-piston Stirling engine was developed in the early 1970s and is believed to be in commercial production as both a radioisotope or fossil-fuelled electric-power generator for navigation aids or other remote unattended locations requiring low-power electric supplies.

The Swedish company FFW, a parent of L'nited Stirling, has developed a 10 kW (13.6 hp) power generator for recreational vehicles and other uses and is said to be planning to introduce the unit commercially in the United States in 1978 through the Stirling Power Systems Corp. of Ann Arbor. Michigan.

As a result of public concern about noise, air pollution, and energy conservation there has in recent years been increasing interest in Stirling engines. Ihis is manifest irt the soaring number of papers published annually, a total of 70 in 1977. and in 1978. 25 at the 13th Intersociety Energy Conversion Engineering Conference alone. Many original and innovative developments to the theory and practice of Stirling engines are being made in an increasing number of industrial companies, universities, and government research establishments in North America, Europe, South Africa, and elsewhere. A directory of the known Stirling engine activities was prepared in 1978 by William Martini (Martini 197Sa) and is reproduced in abbreviated form herein.

Stirling engines operate well as cooling engines. The possibilities of this were recognized as early as 1834, by John llerschel, and in 187(i Alexander Kirk described a refrigerating machine that had been in use for ten years. However, it was not until the late 1940s that serious effort was directed to the commercial development of Stirling-cycle cooling engines. Again, this was undertaken by the Philips Company at Eindhoven under the direction of Dr. J. Köhler. I lie-first cooling engine (an air liquefier) was introduced in 1953. Since that time, further research has resulted in the development of a variety of cryogenic cooling engines, covering a wide range of cooling capacities, and lias led to the manufac ture of associated equipment for cryogenic research and industrial applications. So far. Stirling-cycle cooling engines have proved more suitable for the cryogenic (extremely low temperature) range, rather than the higher temperature range (of domestic and industrial interest) which is dominated, at present, by T'reon' vapour-compression refrigerating machines.

Other manufacturers have entered the small (and miniature) cryogenic cooling engine market, including Malakar l.abs. Inc., Hughes Aircraft Co., Texas Instruments, and the Martin Marietta Corp. in the United States. These companies, together with North American Philips Inc. (who specialize in miniature cryogenic coolers), have as their principal interest the provision of small cooling engines for electronic applications, mainly in infra-red detection equipment for a variety of military and civil purposes.

Other reciprocating regenerative cryogenic cooling engines have been developed, principally the Collins helium liquefier, by A. D. Little Inc., and a variety of GilTord-McMahon machines. All these machines have valves and, in accordance with the definition adopted earlier, must be classified as Ericsson-cycle machines. 1'his is not to suggest that such machines are unimportant. The development, by Samuel Collins at M.I.T., of a relatively inexpensive and reliable expansion-engine, capable of liquefying helium, was among the most significant advances in cryogenic engineering, opening up the possibilities of helium research on a broad front. The future benefits of this research in terms of superconducting electric-power transmission and miniaturized electronics are incalculable.

Early in the composition of this present work the decision was made to abandon the concept of a single volume embracing the Stirling engines for both power generation and cooling applications. The mass of information available is simply too great for adequate compression in a single volume. Furthermore, the readers of one are rarely interested in details of the other, thus it seemed sensible, in fact became inevitable, that separate volumes were required, one for Stirling engines used for power purposes and another for the cooling application. This book is the one dealing with power applications. A companion volume is in preparation for the cooling engines.


At this time (1978) the future prospects of the Stirling engine appear brighter than ever before. In independent surveys of alternative automotive propulsion systems, the Stirling engine always emerges as a Favoured unit with high potential for development. The characteristics of low noise, low levels of emission products, multifucl capacity, lone life, coiimarahlo size and weight, good partload performance, and favourable torque characteristics combine to form an impressive challenge to internal combustion engines. For this reason the United States Government has seen fit to underwrite the cost of a comprehensive seven-year development programme for automotive Stirling engines carried out by two independent, competent, and capable engineering teams. However the spark-ignition and compression-ignition engines in their variety of forms are formidable opponents so long as the distillate fuels, gasoline or diesel oil, remain available in relative plenty. As these supplies decline, a move to the all-electric economy will become inevitable. Perhaps it is in these circumstances that the Stirling engine, with thermal battery charged overnight, will emerge to become the dominant automotive propulsion system of the future.

Its use for stationary power generation in a broad power spectrum appears virtually assured. It is likely to find increasing use in heat pumps and refrigeration systems. An excellent start has been made on Stirling-engine artificial hearts, ll will likely remain the dominant system for small and intermediate size cryogenic and low temperature refrigeration systems.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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