Which design is the most efficient Stirling Engine?

Discussion on Stirling or "hot air" engines (all types)
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yeehi
Posts: 5
Joined: Fri Jan 26, 2018 3:34 am

Which design is the most efficient Stirling Engine?

Post by yeehi » Fri Jan 26, 2018 3:43 am

Of all the possible engine designs, which is the most efficient in converting the temperature differential into motion?

Bang per buck, which gas and metals result in the greatest power from the components?

yeehi
Posts: 5
Joined: Fri Jan 26, 2018 3:34 am

Re: Which design is the most efficient Stirling Engine?

Post by yeehi » Sat Jan 27, 2018 2:53 am

There is a difference between efficiency and power.

The Alpha configuration apparently has a better power-to-weight ratio than the Beta, because the Alpha has two pistons.

The gas inside the chamber provides better power if it has a lower specific heat capacity. Helium is good for that. (One must additionally consider the effects of leakage and corrosion at high temperatures.)

The lubricant must not be susceptible to combustion and explosion at higher temperatures. Graphite is suggested as a low friction material inside the chamber.

Having a material that poorly conducts heat is beneficial for separating the hot from cold gases. Steel was preferred to aluminium because of this.

For greater efficiency, some device that could capture some of the heat as it moved from the hot to the cold chamber is beneficial. A material like steel wool can help.

These answers are not very good, but they are better than nothing, I hope!

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Which design is the most efficient Stirling Engine?

Post by Ian S C » Sat Jan 27, 2018 3:44 am

yeehi, that's all basicly correct. To increase the efficiency and power out put, pressurization is the key, and once you exceed about 200 psi, a change of gas to something innert is required, at 1200psi Argon is ok and much cheaper than the Helium required for higher pressures.
For a home built motor, minimum friction is essential, and a careful choice of materials is required, ie., low friction for piston and cylinder, glass cylinder and graphite piston, steel or cast iron cylinder with a cast iron piston. and I have a motor with a brass cylinder and Teflon/PTFE piston.
For the hot end, the hot cap is best in stainless steel, and the same for the displacer.
If a separate regenerator is to be used, stainless steel foil has been found to be the best, wire and steel wool tend to break up and the bits get in places they shouldn't.
After all that an efficient means of heating, and at least as important cooling is required. It is said that it is easy to get the heat into the motor, the hard bit is getting it out.
Ian S C

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