Stirling Engines and their Role in the 21st Century

Robert Stirling - Pioneer of the Regenerative Heat Engine

What is a Stirling Engine? A Stirling engine is a machine which converts heat energy into mechanical power. In its simplest form you could burn some wood and pump water or generate electricity to run a PC for example. A wood powered computer - that's a novel idea! Stirling engines belong to a category of heat engines known as external combustion engines.  This means that the fuel is burnt outside of the engine cylinder - rather than inside the cylinder like an internal combustion engine  - the best example being the engine in a car. External combustion has certain advantages - you can use any fuel which you may have lying around, like wood waste in a sawmill, coffee bean husks, maize cobs, domestic refuse  as well as the more usual gaseous and liquid fuels. The other advantage is that you can control the amount of oxygen used in the combustion, and use the correct amount to get 100% combustion, which minimises the polluting waste products which occur during incomplete combustion. Stirling engines will work off any source of heat, so do not necessarily need combustion of fuel. Successful Stirlings have been demonstrated running on concentrated solar radiation, or the waste heat from industrial processes, such as glass making or steel smelting. Model Stirling engines are relatively easy to build, even out of bits of junk such as old tin cans or plumbing fittings. Low temperature difference (LTD) Stirlings will even run on the heat from your hand - sadly they do not produce much power. Stirling engines have been built in every size and shape imaginable from a tiny engine which will fit in a matchbox to an 800hp V12 monster intended for marine propulsion. Unfortunately, Stirling engines are not really suitable for putting into cars, unless they are used as in electric hybrid mode. There have however been Stirling powered vehicles, cars, buses, trucks and boats were all demonstrated in the 1960s. I have been interested in Stirling engines since 1976 when I saw my first hot-air engine in the scholol science lab. My interest was rekindled in 1990 when I happen across an article in "The Engineer" describing a Stirling being built in Hampshire. I strived to find out all I could and this eventually led to the formation of the Stirling Engine Society in 1997 -see opposite panel. 2016 is the Bicentenial of the patenting of the Stirling Engine.  I hope that Stirling engines will be commonplace by then.

The Stirling Engine Society The Stirling Engine Society was founded in January 1997, but existed in a somewhat unofficial from 1995. The society was formed by a group of model engineers and other Stirling enthusiasts, who were keen to see the development of the Stirling cycle engine into an everyday item. Stirling News is the quarterly newsletter sent out to all society members, and I was Editor for the first 10 editions from January 1995 to Winter 1998. Bob Sier has now taken over this role. If you are interested in becoming a member of the Stirling Engine Society please contact : The  Membership Secretary, Stirling Engine Society, P.O. Box 5909, Chelmsford, Essex. United Kingdom. CM1 2FG.

To download a recent copy of Stirling News - caution  1.7MB file - could take a while

Read Bob Sier's biographies of some of the Early Pioneers of Hot Air Engine Technology

This page is continued within "The Stirling Engineer's Notebook" an occasional e-journal reflecting some of the articles found in "Stirling News"- The Journal of the Stirling Engine Society - read more about the SES below.

I recommend visiting Koichi Hirata's Stirling Engine Page.

A recent article in the Guardian - Stirling Micro Combined heat and power - September 2000.

Early Developments The Stirling cycle engine is named after the Reverend Robert Stirling who lived in Scotland between 1790 and 1878. At the age of 26 he patented an idea for the reduction in consumption of fuel (coal and wood) for any industrial process which required a substance to be heated and cooled - examples were in the glassmaking, pottery  and brewing industries. He called this device the Economiser. In addition to a general patent to cover any heating and cooling process he also citied the example of an air engine which ran on the repetitive heating and cooling of air, making use of a specific form of the Economiser to reuse heat within the engine. This meant that if some of the waste heat could be reused, then less heat would be needed in the first place - which is how you could save fuel. Stirling proposed an engine which contained two moving pistons,   one being a loose fitting plunger known as the displacer and the other being like the piston in a steam engine with a leather sealing washer known as the power piston. The displacer moves to and fro in a cylinder (the displacer cylinder) which is heated at one end and kept cold with water or air cooling at the other end. The displacer is about three times as long as the diameter of the displacer cylinder, and about 3/4 of the length of the cylinde