Stirlingengineforum.com

This is modeled after the beta stirling engine animation. what I’ve added is to double the length of the cylinder. It is open at both ends. The two piston are connected like barbells. The connecting rod travels freely through the displacer, which is between the two pistons. The pistons share one heat source, in dead middle. The two cold sides are at each end of the cylinder.A firewall at dead center makes a seal on the displacer.One flywheel only. When one piston is knocking up the displacer, the other piston is in the deep cold end, and vise versa.Vacuum on one side pressure on the other side. This should compliment each others movement. I made a cardboard model it looks good to me. What do you think?
http://www.animatedengines.com/stirling.html




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Fullofhotair

10 out of 10 for lateral thinking but sadly it will not work and even if it were modified it could not be made.

As drawn, the air on each side of the 'firewall' remains in the hot volume at all times, for it to work the air must be displaced each 180deg of rotation to the cooled volume. If the displacer was split into two with a gap in the middle, then there would be displacement but the joining shaft would have to run in a 'sealed bearing' in the middle where the temperatures are highest. That still leaves the problem of how does the displacer/s attach to the displacer shaft through the piston connecting tube?

Nice try.

GeoffV

Geoff v;
How about a graphite bushing and a ceramic rod between the two displacers? Neither are good heat conductors.

Fullofhotair

Ceramic coef of expansion is about half that of graphite so it would be impossible to maintain a good seal as the temperature of the heater increases. Which still leaves the problem of attaching and sealing the displacer to the displacer rod through the piston tube. Furthermore as the alignment of the pistons and firewall bearing/seal is critical, any asymetric heating would cause the assembly to bend causing binding.

Even if you managed to surmount all the engineering difficulties you still finish up with a very long engine with massive imbalance so I really do have trouble understanding the point of this design?

GeoffV

Geoff v;
Iam hoping you can answer this question for me.This has really bugged me.If you have heat engines one on top of the other.They all have their hot end in a narrow chimney that is fired from below. How is the heat distributed? Heat rises so is each engine equally heated or does the first engine get most of the heat and the rest get progessively less?

Fullofhotair

In the arrangement you describe, the lowest heat exchanger will lower the gas temperature as it transfers heat from the flue gases so the next exchanger will see a lower temperature and so on.

GeoffV

Best way of getting the heat to the cylinders evenly, is with a ring burner, and for two hot ends, a burner with two holes, one for each hot end would be easy enough to make, even then it might be difficult to get exactly the same amount of heat in each cylinder. Although some of my favourate motors are horizontal, I prefer the motor to be vertical, with the hot end on top, I have a BETA motor, a free piston GAMMA, and an ALPHA with a Ross Yoke. The large horizontal motor (called 2nd motor in gallery), the large vertical with the hot end at the bottom, and a Ringbom motor, all have camp stove burners. The rest either have meths burners, or are designed as stove top fan engines. My idea is that heat rises, so it would be easier to cool a motor with the heat already at the top, my idea, not scientificly designed.
Geoff may differ, and I would be interested in which he thinks is best heat at top or bottom. Ian S C

It always seemed to me for an external heat engine to be at its most efficent the closer to ambient temp. the exhaust is the better.If you have 2 or three engines stacked and receiving the heat from the bottom of a narrow chimney your not throwing all that heat away.Even though the very top engine produces a lot less power they all could be connected like riders on a tandem bicycle.All the engines are horizontal but heated vertically. The cold end is away from the heat source except for conduction.

Fullofhotair

You are quite correct when you suggest that the heater exhaust should be as near ambient temperature as possible. Stacking engines on top of each other is not the most elegant way to achieve this as the coolest running engine would see so little heat that the efficiency would be very very low.

May I suggest a better way would be to transfer the residual heat from the exhaust gasses to the incoming burner air via a heat exchanger such that the burner air is preheated and the amount of fuel required, for a given temperature, is therefore minimised.

It's called a recuperator.

GeoffV