What is mechanizm to balance pressures?

[Aviator168]

In a pressurized stirling engine. The pressure of the crank case is the average of that when the gas is hot and cold; but things are never perfect. So when is mechanizm to keep them balanced? Anyone has a picture or graph depiction?

[Aviator168]

well? guess not that many people came by yet.

[Ian S C]

Don't worry, I'm thinking (perhaps we should worry), I think some motors have a bypass port that is exposed when the piston is at bottom dead centre. Others rely on leakage past the piston.
Ian S C

[Aviator168]

Have you noticed most of the stirling builders on youtube don't have it on their engines? This is holding their power/efficiency down. On the piston by pass mechanism. It is difficult to control timing and you don't want this happen on the hot side if the engine of alpha type.

[derwood]

Recently I have been trying to pressurize a thermal lag engine and have had similar questions. My engine will not run with an enclosed crank case. The only way I can get it to run is to greatly shorten the stroke. I think the problem is that the crank case pressure gets too high when the piston is at TDC and too low at BDC. I don't know of a regulator that would keep the crank pressure constant, especially at 1000 rpm. The goal is to simulate a higher atmospheric pressure. Under normal conditions with an open crank case, when the piston is at TDC you are basically compressing the world. This is not a problem since the world is so big. One way to fix this problem would be to have a very large crank case to absorb the change in pressure but this would take up a lot of space. In my case I am going to try an inline two cylinder with the pistons at 180 degrees. When one piston is at TDC the other is a BDC. In theory this should keep the crank case volume constant therefore keeping the pressure constant. This approach should work the same for an alpha with two cold cylinders and two hot cylinders sharing a single crank case.

[Aviator168]

There is no need to build a large crank case. For thermal lag engine, the pressure should be balanced at half of stroke and let the fly wheel carry the other half. As a matter of fact, too large a crank case can increase lost of efficiency.

[Ian S C]

Initially the complete engine both sides of the power piston are at unity, ie atmospheric both side, or what ever elevated pressure you have, the leakage of the piston would probably be enough, and once equalised the motor should run.
Ian S C

[H..Deep]

There are two methods of balancing the pressure that i know
1. Using a check valve.
A check valve is installed at the crankcase and it is connected with the compression space of the power piston favourably at TDC. This method helps to maintain the minimum buffer pressure.
2,. Using a cappilary tube.
Instead of the check valve a capilary tube is used rest all remains the same.This method is used to maintain the mean pressure bw the working space and the buffer space.

[Aviator168]

What about alpha engines?

[H..Deep]

I have never worked with alpha motor but i think these methods should also work with alpha motors. I followed a discussion on this forum about the use of snifter valve .
(http://stirlingengineforum.com/viewtopi ... =884#p3234)
https://www.youtube.com/watch?v=229RG-627es - Snifter valve for stirling

[Aviator168]

"A snifter valve is a check valve that maintains pressure inside the cylinders.
At the low pressure point in the cycle, if the internal pressure is less than the atmosphere
(or the crank case) it allows air to bleed in to the cylinders. And also in a pressurized
engine allows the cylinders to come up to pressure as the engine is pressurized."

I don't think this is correct. I did some simulation and calculation. The best place to put the valve is at the half way point of the cold cylinder.

[Ian S C]

a snifter valve can be fitted in the crown of the power piston, and with a bit of luck/good design, the pressure in an atmospheric motor can be kept at or above atmospheric pressure.
On a pressurised motor a transfer port similar to the one in a 2 stroke, although it only needs to be small.
Ian S C

[Aviator168]

Depends on what the designer wants. If he wants a little compression, the BDC of cold cylinder is where the transfer port will be. However, the compression energy comes from the fly wheel, and at the same time he's go more air to heat up with a more powerful next stroke. If he puts the transfer port at the middle of the cold cylinder, the part where the piston going from BDC to the middle of the cylinder is power by the external/crankcase pressure (like the fire eaters), and the engine also end up with less air to heat up. They both might end up with the same power output (need to measure this). To me, putting the transfer port at the BDC is a lot easier.

[Aviator168]

What about this type of stirling? Seem a bit difficult to keep the pressure in sync.


Edit. Never mind. Just figured it out.