Wednesday, June 3, 2009

My Model Stirling Engine

Check out the model stirling engine I bought from Kontax.

On a single cup of hot water, the flywheel turned for almost 3 hours! And on a single cup of ICE water, it turned in the opposite direction, for over 2 hours! Cool!

Stirling engines were invented in 1816, by the Scottish minister, Robert Stirling. They are technically, an external combustion engine, because the heat source is outside the piston chamber. It creates power from the differences between hot and cold, and will actually create more power on a cold day, than on a hot day.

Stirling engines are known to be very efficient, but I'm having a hard time finding reliable numbers on what the relevant efficiency range is. If you know, or find, good numbers on their efficiency, please let me know what they are.

The stirling engine must literally warm up. So, it cannot do fast starts and stops like an internal combustion engine (ICE). It is suited for long steady state operations. Another characteristic is that unlike an ICE, there have no: valves, intake, or exhaust. And so, they are very quiet. They also have fewer moving parts than an ICE, and so are more reliable. Because the heat source is outside the engine, any type of fuel can be used, such as: wood, natural gas, garbage. Even hot water, as in the case of the Kontax, if it was designed for that.

My current car generates a lot of waste heat, that you can really feel coming out from under the hood. I wondered if there was something wrong with it, but I was assured that was normal for that car.

On a long drive, I suddenly had the idea of a stirling engine that could capture the waste heat from the exhaust pipe. This could be used in hybrids. The waste heat could power a stirling engine, which would then be used to generate electricity.

Then I thought, why bother with an internal combustion engine (ICE) at all? In a hybrid, Instead of an ICE, why not just use a stirling engine to generate the electricity?

After I got back, I discovered that Dean Kamen, most well known for his invention of the Segway, is currently working on Stirling engine for use in hybrid automobiles.
Do great minds think alike? Can I compare myself to Dean Kamen?

And I’ve since found out that another company is also working on another heat exchanger that would work on the waste heat from the ICE.
They have a lot of calculations on their website, but I can’t seem to find a clear diagram of exactly how it all works. Even though they have patents:
the same website also talks about confidentiality agreements.

Considering how many ICE and electric motors manufacturers that exist, there are relatively few manufacturers of stirling engines around the world, and few places where the stirling is being used.

One place that the stirling engine is being used is in generating electricity at a solar energy plant in the Mojave desert. Mirrors reflect the sun’s heat onto one side of the stirling engine. The engine turns and generates electricity. All pollution free, and totally renewable. Very cool!

Another place stirling engines are being used is in Swedish submarines.

“The Stirling AIP system is practically vibration-free, silent and wakeless. Its infrared signature is very low.”

Stirling DK, from Denmark, manufactures a combined heat and power (CHP) unit for the home. The home is heated with biofuel such as wood chips, and the stirling engine generates electricity for the home at the same time.

The American company, Stirling Technology, manufactures a stirling engine for use in areas away from the power grid. It will supply 5 horsepower of shaft power at 650 RPM, and can be used to generate electricity, or pump water.

Ronald Steele has built a homemade stirling engine, and sells the plans for it here:

For more information on this very cool motor, check out these links:

Stirling Engine Society and cool Links:


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