Hypothetical LTD 4cyl Bellow SE Design

[skyfridge]

I like the idea of using bellows instead of pistons--yes, I have seen the youtube videos--though I haven't seen a model for bellow friction losses. It solves the sealing issue, and it seems that it would be much easier for a DIY build, maybe even with pressurized working fluid.

Since I don't have a bellow friction model, the first question would be about how the friction losses would compare with piston-cylinder friction losses.

The Stirling Thermal Power four-piston alpha design (illustrated at Stirling Engine Configurations) intrigues me. Here's the idea.

Mechanically link two bellows, one hot and one cold, to keep the two bellows 180° out. Imagine this pair as one piston. Each bellow does not directly exchange working fluid with the other of the pair.

Put the heat source exchanger in the dead volume of one bellow and the heat sink exchanger in the dead volume of the other bellow. Connect the source bellow of one pair through a regenerator to the sink bellow of the next pair and the sink bellow of the former to the heat bellow of the previous pair. Arrange it just like the 4cyl piston model, with each pair of bellows 90° out.

Instead of connecting the rods of the bellows to a crankshaft, put linear alternators on the rods.

With the alternator outputs rectified and combined (in series or parallel?) and the combined output connected to a load (battery, etc.) will the electrical resistance at each alternator replace the function of a flywheel?

With the only mechanical friction being in the bellow material, the linkage to keep the bellows of each pair 180° out and the linkage to keep the four pairs 90° out, can this arrangement have greater efficiency than the 4cyl piston model?

[skyfridge]

Sure, a swashplate would be awesome, but I haven't determined how to make one or if I have the skills to do so.

Also, instead of wondering if electomagnetic forces of the alternators could replace the function of a flywheel, maybe the muti-bellow arrangement and 90° linkage will do so?

Furthermore, I wonder about avoiding the use of a crankshaft to allow freedom of spatial arrangement of the bellows, though an arrangement that includes the other elements would be optimal.

[Ian S C]

I might be worth looking up free piston Stirling engines. I have one, the magnet that operates the linear alternator is repelled by a magnet placed under it, it is this or a mechanical spring that gives the return stroke, and acts as a flywheel would on a conventional engine.
Ian S C

[skyfridge]

Hi I an,

Thanks. I've seen the free piston configuration. Fabrication seems somewhat more complicated than what I'd like to tackle, but the spring/magnet mechanism did address my curiosity.

Linear alternators might not be my first choice afterall. I found a better description and illustration of the swashplate design, and it's looking much easier to accomplish. If I can put it together without welding or too much machining it will eliminate the 90° inter-pair linkage, and I could couple it to an off-the-shelf DC generator.

Now, I just need to determine how to make it all less lossy.

[Ian S C]

There is a photo of my free piston motor in my gallery, it's built as a GAMMA motor, water cooled, LPG fuelled.
Ian S C