Belgian Waffles

An exhibition on the Stirling engine (the 1st in Ireland) is planned for this summer in cooperation with Sonairte (http://sonairte.ie). More details will come soon in this website. Stay tuned!

Why this exhibition?

As an engineer, I was very intrigued when I discovered this simple technology that is old (almost 200 years old) and yet so modern (somewhere even futuristic) in the same time. The more I got to learn about it the more I found it attractive.

Personally what struck me the most is its versatility : you can run it using any source of heat which makes it great for the developing countries where people can not have access to electricity or petroleum products..

Here are some of the advantages that convinced me to think that this technology is worthy of interest and will gain more and more popularity as it will get known by the public by large.

Its main advantages are the following:

• The silence of operation : The combustion is continuous outside of the cylinders (as opposed to the internal combustion engines likes the cars' ones). In addition, its design is such as the engine is easy to balance and generates few vibrations. They can be built to run without an air supply (they are for example used for air-independent propulsion in submarines).
• The high efficiency : Almost 40% while internal combustion engine (car's engine) are around 30-35%. It is possible to make it work in co-generation or CHP (combined heat and power generation), the overall efficiency can be higher than 90%. You can find more details on the Irish CHP association (they mention the Stirling technology)
• The multitude of possible “hot sources” : Whatever can produce heat can run this engine : combustion of various gases, wood, sawdust, husk, waste, solar or geothermic energy...
• The ecological aptitude to respond to the environmental requirements on air pollution. It is indeed easier to achieve a complete combustion in this type of engine.
• Reliability and easy maintenance: : The technological simplicity makes it possible to have engines with a very great reliability and requiring little maintenance.
• An important lifetime. Because of its “rusticity”, It is very robust engine and require less maintenance and less lubricants than other engines.
• Reversibility : If instead of giving heat to make the Stirling run, we can induce this Stirling to run thanks to another engines, this Stirling becomes then a heat pump : it absorbs the heat of its environment (causing the temperature to drop). This principle is used to produce very low temperature in industry.

Rice-husk-powered Stirling engine (India)used to pump water up

Back to the future

This technology is back again into the limelight because of its numerous advantages that are rediscovered by the scientific community and that are more appreciated nowadays that they were.

For example, when used in solar application, you can reach efficiency (conversion of heat into electricity) of more than 30%.In comparison photovoltaic panels have a poor performance, about 15%.

By the way:Ireland is one of the world leader in this type of technology!! Learn more here.

Another example : the Stirling technology is (again) interesting the NASA. It is planned to use this technology to produce electricity. Here is picture of this high tech-battery.

If you are curious, here is a short article about this project with a nice animation of this Stirling-battery:

History

The Stirling engine was invented by Reverend Robert Stirling in 1816. He was a Scottish minister. At that time, Stirling engines were recognized as a safe engine that could not explode like steam engines of that era often did.

A Stirling engine in the early days

Since then, many kind of Stirling engines were manufactured with a view to increasing the output and the efficiency. Its popularity raised and spread around the world. Its fame started to fade only when the Otto engine (invented by N. Otto in 1877) and Diesel engine (invented by R. Diesel on 1893) appeared in the market.

Stirling Engine was studied again in the early 20th century, when PHILIPS Corporation started to research on Stirling engine as the power source of portable generator in the late 1930.Philips was seeking to expand sales of its radios into areas where electricity was unavailable and the supply of batteries uncertain. They improved greatly the efficiency of this old technology and many patents were logged. But Philips stopped the researches in the 1950's with the avent of the transistor.

But Since then, the Stirling engines never disappeared completely and were studied in Europe and America. The engine started to develop rapidly with the effect of oil-shock in 1973.

Now, Stirling engine is studied across the world. For examples, Solar Stirling engine, hot spring Stirling engine, underwater Stirling engine, air-conditioning Stirling system, Stirling refrigerator.

How it works?

Very schematically :you need a hot end and cold end to make it work.simple!

If you heat up the air in a cylinder with a burner, the air contained inside gets warmer and expands. This expansion can push a piston (symbolised by the green rectangle).
If you cool down the cylinder for example by projecting water (symbolised by the purple hose in the drawing hereunder), the air cools down and the piston can be back to its initial position.

By repeating the 2 actions continuously, you can get a regular motion as the following:

Such an engine would work but with a lot of difficulties: kindle the burner, extinguish it, sprinkle the cylinder, stop the cooling... with many successive thermal shocks.

What if instead of warming and cooling the whole cylinder, we force the air to travel from a hot area (Hot end) to a cold area (cold end)?

Let's warm up continuously the upper part of the cylinder (symbolised by the burner) and cool down the lower part with the sprinkler. We have now 2 distinct ends : a hot one and cold one.
How to move the air now from the hot end to the cold end?
The Reverend Stirling introduced an artifice providing a solution to this problem: the displacer. The displacer's job is to move the air from a hot end (where the burner is)to the cold end  (bottom part of the cylinder)and vice versa.

When the displacer (grey rectangle) is moved down, the air is pushed to the upper part of the cylinder and is not in contact with the cold end. When there, the air can warm up, expand and move the piston down. When the displacer is moved up, he pushes the air to the lower colder end where the air can cool down and contract (which allows the piston to move back again).
The repetition of these movements induce the following cycle :

simple, no?

What can you see at the exhibition? 

There will be different Stirling engines in different shapes such as:

helicopters powered by candels

fans

tricycles

solar Stirling engine

water pump

cars powered by a stirling engine and remotely controlled....

There will be also some rare items that are cousins of the Stirling engines : the Ericsson engines and the Manson engines. They are related because they are all part of the hot air engines family (as opposed to the Steam engines).

I will not speak about these 2 other types of engines here (there will be a film to clarify everything) but I will just say that the Manson is worth seeing (it is my favourite) because it is the most simple engine never been conceived!

You will understand what I mean when you will see it.

There will be also one Fluidyne : simple tube that uses the same principle as the Stirling engine and allows to pump up water.

Kids will love watching these little wonders! The adults will look at them in awe and will surely (as I once did) try to to guess how it works.

It is definitely an outing for all the family. You will enjoy it an learn something in the same time.What else can you expect from an exhibition?

If you want to have an idea of what a Stirling engine is, just pay a visit to Sonairte one of these days : I lent them a Stirling engine and it is displayed in their reception.It will be showcased there till the exhibition.

By the way, the exhibition is held Sunday 25t of July. This day is also the day for the farmer market in Sonairte. It will be another reason to come that day!

And last but no least : the exhibition is FREE.

See you there!!!