The Stirling Motor

The Stirling Heat Engine

"The Stirling Heat Engine was the inspiration of the Reverend Robert Stirling from Cloag in Scotland. The Scottish vicars first engine, built in 1816 was a large affair with a cylinder 3.05 metres (10 ft) high and with a bore of 0.6 metres (2 ft). In 1876 Rev. Stirling wrote in a letter about his brother James, who had just died, "......These imperfections have been in great measure removed by time and especially by the genius of the distinguished Bessemer. If Bessemer iron or steel had been known thirty five or forty years ago there is scarce a doubt that the air engine would have been a great success...It remains for some skilled and ambitious mechanist in a future age to repeat it under favourable circumstances and with complete success...." Rev'd Dr. Robert Stirling (1790-1878) from "Stirling Engines" by G. Walker"

"The Stirling Engine was named by Dr. Rolf. J. Meijer who at that time was a project manager with Philips of Holland. Philips was struggling with creating a new name to call the 'Air' engine when there was no air inside the engine. This is because in an Air engine, the air inside the engine is called the 'working gas'. If you change the 'working gas' to a gas like Helium or Hydrogen, then it can no longer be called an 'Air' engine. The name Stirling Engine was chosen in honor of the inventor of the regenerator (economizer) and the engine that demonstrated its use.

The Stirling Engine's most basic configuration consists of two pistons each in its own cylinder. (Sometimes it is easier to envision these two cylinders as one long tube with the piston heads facing each other inside the tube (see the figure below)). Note that between these two pistons heads are the heater, cooler and regenerator. The regenerator (usually a block of woven wire) is in the center of this tube and the heater is between the regenerator and one piston (in red) while the cooler is between the regenerator and the other piston (in Blue). The volume attached to the 'heater' is the 'expansion space' where the hot gas pushes against the 'expansion piston'. The volume attached to the 'cooler' is the 'compression space'"... Stirling Engine Society - USA

Principle of the Stirling motor

"A Stirling engine is a closed-cycle, regenerative heat engine which uses an external combustion process, heat exchangers, pistons, a 'regenerator' and a gaseous working fluid contained within the engine to convert heat to mechanical work (motion). An important feature of the Stirling is the regenerator to store energy from the gas as it passes through on the way to the cooler (low temp. heat exchanger) and gives energy to the gas as the gas flows back through the regenerator going to the heater (high temp. heat exchanger). It is the regenerator that makes the Stirling Engine. There are two main categories of Stirling engines, the kinematic which has the pistons attached to a drive mechanism which determines the phase angles and converts the linear motion of the pistons to a rotary motion and the free piston which uses harmonic motion mechanics and usually planar springs to determine the cycle phases. There are hundreds of variations of types in these two categories. Particularly the kinematic is divided into Alpha (two pistons), Beta (piston and displacer in one cylinder) and Gamma (piston and displacer in separate cylinders). Then there are the double acting engines which are alpha engines in series. These can drive either a crankshaft drive or a swashplate drive ot a cousin, the wobble drive.(...) " more

SESUSA.org

"This site on the world wide web is dedicated to the Stirling engine. SESUSA.org continue to grow in numbers and accumulated knowledge made available on the web. SESUSA was established to exchange our knowledge, ask questions and express ideas regarding this unique engine." ... more

The Stirling and Hot Air Engine

"This site is being developed for:

• Collectors of vintage hot air engines
• Model Engineers who build Hot Air, Caloric, Stirling & Vacuum engines
• Study of external combustion regenerative air engines" ... more

The International Stirling Association

"Ever since its invention by Rev. Robert Stirling in 1816, the Stirling engine has been fascinating researchers and engineers with the singular thermo-dynamic features of its cycle, which has theoretical yields equaling and even exceeding those of the Carnot engine. However, the greater construction simplicity and specific power of internal combustion engines have prevented its diffusion, effectively confining it to niche uses and cryogenic applications. Over the last few years the problems related to environmental pollution and dwindling fossil fuel stocks have revived interest in the Stirling engine, which being based on external combustion, can be powered by alternative energy sources such as sun and biomass, thus offering a viable technological solution for micro-cogeneration units or remote generation of electricity." ... more

RobertStirlingEngine.com

"Stirling engine is the subject of theoretical studies and practical works in order to better know it, to improve its output and to increase its competitiveness facing other energy sources. This works enable the modelization of this engine, i.e. to put in equations the heat transfers, the flows of the fluids, to simulate certain configurations without having to build an engine... When one studies something at school or university, this promotes its introduction in everyday life. No doubt that will happen for the Stirling engine."

"A Stirling engine, how does it work ? For what is it used ? Who invented it and when ? Here are some questions which this site wishes to answer. It is open to all, it is popularizer but sometimes details specific points for the experts. This engine is also called 'hot-air engine' or 'external combustion engine'." ... more

Stirlingsteele.com

"Complete plans for the exciting Stirling-Steele Engine. This patented four cylinder Stirling based design is one of the best running hot air engines. 26 neatly comb bound pages of highly detailed drawings and instructions provide all necessary information to produce this modern compact version of Stirling Engine. Engine can be machined on a 6" lathe and small milling machine.

"My original four cylinder Stirling-Steele which was built in 1994 still runs great today! I have run this engine for more than 2000 hours without a component or engine failure. These little engines will turn up to 3000 RPM and produce up to 40 watts of shaft power. This is an excellent engine whether you are an experimenter of advanced heat engines or collector of fine precision machinery. Although a challenging project, it is also a most rewarding one." ... more

New Stirling Engine Design (one the right image)

"A three cylinder version of my new engine design. It has a closed crank case and can be pressurized. Its coaxial body allows for lots of outer surface area which is ideal for cooling. The hot caps at one end and the shaft exiting from the other makes this design a very attractive and easy to implement alternative." ... more "

Matteran Energy

"Matteran Energy has developed a thermal power plant capable of converting the energy in gentle warmth, (as differentiated from fiery heat) into electricity. Freely available warmth has been overlooked as a fuel until the invention of this power cycle. A scalable prototype has been developed in South Florida.

In general, any freely-available thermal source, capable of providing a temperature differential of as little as 40 degrees Fahrenheit above or below ambient, can be used by Matteran's power plant for conversion into electricity, hydrogen fuel, refrigeration & air conditioning.

Today, these low-temperature energy sources are ignored as sources for power, because their temperatures are too low for efficient utilization by the only other known thermal power cycle: the Rankine cycle and its derivatives.

By eliminating the prime component of the Rankine cycle's inefficiency, the Matteran cycle more efficiently converts temperatures of 80-212 degrees Fahrenheit into electricity, hydrogen fuel, refrigeration & air conditioning.

Our industrial supporters, ConocoPhillips Petroleum, and GEA Heat Exchangers, provide modest assistance in their fields of expertise.

Contact Jeff Sterling to join forces as a leading supporter in the emergence of a whole new energy supply, and the technology we've developed to harness it." ... more

The fascinating world of Stirling engines
"Stirling engines have the most efficient cycle of any heat engine. That fact has enchanted, tantalized, and frustrated engineers and technology enthusiasts ever since the Philips electronics company began their efforts to develop power producing Stirling engines in the 1930s. As the years have passed since the 1930's two things have become clear to those who have thought carefully about Stirling engines. First, Stirling engines can do things that no other engines can do at all. Second, it doesn't make sense to develop Stirling engines to do things that other types of engines can do cheaply and well.

Stirling engines can be built that:
    - Are nearly silent at full power.
    - Run on any fuel from sunshine to cow manure.
    - Run for years without maintenance
    - Produce zero or very low emissions.
    - Are extremely efficient.

It is difficult to build Stirling engines that:
    - Are cheap
    - Start instantly
    - Can change power levels quickly and efficiently with a simple regulating mechanism.
    - Have a high power density

Of course, just because something is difficult doesn't mean that it's impossible. In fact, some of the world's most worthwhile projects have initially seemed difficult beyond all imagination. Fortunately or unfortunately developing a great Stirling engine and bringing it profitably to market has in the past seemed simple, straight forward and easy to some people. I assure you that it is not simple, it is not straight forward, and it certainly is not easy! My personal search for the right way to develop Stirling engines has led me to do unusual things like learn Russian, then travel to St. Petersburg Russia to look at Stirling engines. But wherever my search has led me, I have come to the conclusion that my job is to educate and teach people about clean green energy. It's the job of other people to develop power systems you can buy at a store." ... more

Kontax Stirling Engines

"Kontax Stirling Engines designs and manufactures a wide range of low and high temperature Stirling engines, thermo acoustic engines and wood burning stove fans. All design manufacture and assembly is carried out in our purpose built workshop in the beautiful Thames Valley in southeast England.

Our outstanding reputation has been built on high quality and attention to detail. Customers range from individual enthusiasts all the way up to corporate multi-nationals If you want a unique gift for a friend or relative or need a high quality corporate promotional item then you have come to the right place.

For corporate customers Kontax Stirling Engines is able to offer laser engraving of mottos and logos.

We also manufacture the KSF22 wood burning stove fan. If you have a wood burning stove you can put this Stirling engine powered fan on it and it will circulate the warm air from the stove around the room using only the heat from the stove.

Kontax Engineering Ltd is small specialist engineering company staffed by a team of highly skilled and dedicated engineers.

Kontax Stirling Engines have a clean, modern workshop where the parts used in our engines are manufactured by our skilled engineers." ... more

The Stirling and Hot Air Engine
"Engineers classify Stirling engines into three distinct types. The Alpha type engine relies on interconnecting the power pistons of multiple cylinders to move the working gas, with the cylinders held at different temperatures. The Beta and Gamma type Stirling engines use a displacer piston to move the working gas back and forth between hot and cold heat exchangers in the same cylinder.

Alpha Stirling
An alpha Stirling contains two separate power pistons in separate cylinders, one "hot" piston and one "cold" piston. The hot piston cylinder is situated inside the higher temperature heat exchanger and the cold piston cylinder is situated inside the low temperature heat exchanger. This type of engine has a very high power-to-volume ratio but has technical problems due to the usually high temperature of the "hot" piston and the durability of its seals.

Beta Stirling
A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel, pushes the power piston the other way to compress the gas. Unlike the alpha type, the beta type avoids the technical problems of hot moving seals.

Gamma Stirling
A gamma Stirling is simply a beta Stirling in which the power piston is mounted in a separate cylinder alongside the displacer piston cylinder, but is still connected to the same flywheel. The gas in the two cylinders can flow freely between them and remains a single body. This configuration produces a lower compression ratio but is mechanically simpler and often used in multi-cylinder Stirling engines.

Other Types
Changes to the configuration of mechanical Stirlingengines continue to interest engineers and inventors. Notably, some are in pursuit of the rotary Stirling engine; the goal here is to convert power from the Stirling cycle directly into torque, a similar goal to that which led to the design of the rotary combustion engine. No practical engine has yet been built but a number of concepts, models and patents have been produced. There is also a field of "free piston" Stirling cycles engines, including those with liquid pistons and those with diaphragms as pistons. An alternative to the mechanical Stirling engine is the fluidyne pump, which uses the Stirling cycle via a hydraulic piston. In its most basic form it contains a working gas, a liquid and two non-return valves. The work produced by the fluidyne goes into pumping the liquid.

A recent development of Stirling engines are the thermoacoustic stirling engine, which looks like the beta Stirling engines but without the displacer." ... more