Stirlingengineforum.com

I'm a bit confused as to how a pressurized stirling works. At the top of this page is an animation of an alpha engine: https://en.wikipedia.org/wiki/Stirling_engine

If this engine was pressurized where in the engine is the elevated pressure? Is the Hellium in the regenerator and in the generator side of both pistons or is the helium in the crank case and/or heat end? A description would be helpful. Thanks
Wellington

In the ALPHA motor shown the crankshaft would be enclosed and the whole engine pressurised, sometimes there is no crankshaft protruding, instead a generator is built inside the motor making sealing a bit easier. For engines up to 200 or 300psi air is OK, cheaper, and easier to manage, 1200psi or so an inert gas such as Argon is useful. Hydrogen, and to a lesser extent Helium have the problem that because of there small mollicular size they tend to leak through steel, and in the process make the steel brittle, not good on a pressure vessel.
Ian S C

Ian S C wrote:In the ALPHA motor shown the crankshaft would be enclosed and the whole engine pressurised, sometimes there is no crankshaft protruding, instead a generator is built inside the motor making sealing a bit easier. For engines up to 200 or 300psi air is OK, cheaper, and easier to manage, 1200psi or so an inert gas such as Argon is useful. Hydrogen, and to a lesser extent Helium have the problem that because of there small mollicular size they tend to leak through steel, and in the process make the steel brittle, not good on a pressure vessel.
Ian S C

So what does pressurisation do exactly? how and why does it produce more power?.
Wellington.

Unpressurised the working pressure is(about)30psi, and on heating can be double that, so the maximum pressure is 60 psi. Now put the pressure up to 200 psi, then heat it to double the temperature (Kelvin), and you are looking at 400 psi, it's also going to take more heat(not temperature) to heat the increased amount of gas, also the cooling system has got to be able to remove the extra heat.
Ian S C

Ian S C wrote:Unpressurised the working pressure is(about)30psi, and on heating can be double that, so the maximum pressure is 60 psi. Now put the pressure up to 200 psi, then heat it to double the temperature (Kelvin), and you are looking at 400 psi, it's also going to take more heat(not temperature) to heat the increased amount of gas, also the cooling system has got to be able to remove the extra heat.
Ian S C

Thanks Ian. So can a simple laminar flow/thermal acoustic engine like this one be pressurised if it was big enough?:
https://www.youtube.com/watch?v=Wbfc7n5qGIM
Wellington.

Sorry I'm not sure about pressurising a laminar flow motor. It's probably possible, someone else may know, or have tried it.
Ian S C

Would I be right in saying that when you pressurize an engine you get more power but less rpm?
Wellington.

In theory the crankcase and the swept space should have equal pressure if the engine is pressurized or not. If theory is right, then rpm should be decided by the pressurization's influence on engine power. So it seems that rpm and pressurization is not directly related.

Josephkaisner wrote:In theory the crankcase and the swept space should have equal pressure if the engine is pressurized or not. If theory is right, then rpm should be decided by the pressurization's influence on engine power. So it seems that rpm and pressurization is not directly related.

Thanks Joseph. I understand now that it can vary but in a general sense do you normally see a slowing of rpm when you increase pressure up to a given point? Wellington.

No, from what I read of these motors they tend to increase speed and power.
Ian S C

I agree with Ian.

How long till the increased pressure leaks out. These engines with shafts and conn rods are not air tight.

A lot of pressurised motors (including the Philips) have a small air pump to maintain pressure. Other than that, the design of air seals is a science in its self. The ideal way is to build a generator into the crankcase, the motor is started by running the generator as a motor from a battery, the battery then stays in the circuit and is charged by the generator, and gives a stable power supply.
Ian S C

Aha! Thanks, makes a lot of sense now.
So the only thing going from the pressurized vessel into atmospheric pressure is the wires?