Stirlingengineforum.com

Hey all,

I'm issuing a wild thought alert!

I've been thinking of the old piston engines from bombers n P47's, those radials producing hundreds of HP. If one could heat the center of a purpose built radial Stirling, one could stack a lot of expansion chambers in a circle for more power. One central heating point could be shared more effectively, and focused light might be perfect for this. With proper fins, insulation from the hot end and air movement liquid cooling might not be needed. Lay that radial flat so the hot end can be formed like a stove to vent away damped for best transfer. Turbocharger bearings and cast iron take some serious heat, and a crank running in the hot end should work. If one built an intermediate temp diff engine it could run little hotter than internal combustion engine. Create a manifold to direct the heat across the very end of the displacers so that the end of the crank rests in an isolated high temp bearing. This bearing rest would be as isolated from heat as possible, and all the displacer glands would be ceramic. The con rods will be exposed within this bearing pocket/rest and an outside end cap/bearing/crank pass-through will enclose the workings. The power piston/cylinders could rest on the top side of the displacers, and share a second common crank throw. There would be only two throws for even a huge engine. The con rods would run on a common throw for all the displacers and all the con rods for the power pistons would run on a 90° offset throw . This outside cap would need be skeletonized to release as much latent heat as possible. I think this engine would make power, and no, it's not a DIY garage engine, at least for me. Perhaps a cast manifold isn't needed, but the bearing rest needs to be stiff to mount the displacers and support the crank.

Now, there's something I haven't heard of being tried. Anyone?

R

EDIT: I know there are nice radial Stirling engines but all I see are outside heated. Here's one.

http://www.youtube.com/watch?v=SX5XOpe8Eas&

I think having the bearing etc. in all that heat could cause a problem.What if you left the setup just as it was in the radial engines and put a heat sink just above the center with heat pipes running down to each cylinder.Like a teepee.That could be a good setup for a solar focus point.

theropod2, can,t see it as practical, a better way would be to lay the cylinders parallel, in a circle, and drive a swash plate, makes a very compact motor, there would be a fair bit of machine work required, although proberbly much less than the radial idea. One way the radial motor can be built is not as a Stirling Engine, but as a multi cylinder vaccuum, or flame licker motor, with the whole motor rotating, like the early rotary aircraft engines, the motor becomes its own flywheel, one of these say 2ft in diameter, with 6 or 8 cylinders could within the limits of this type of motor, be reasonably powerful. I say 6 or 8 cyl, but it could be any number. With an 4 stroke internal combustion engine, it must have an uneven number to get the correct timing. Ian S C

Theropod2,
I think its an inspired concept (at the least, its got my attention).
Not considering the possible problems/negatives for a moment, what I like about it is the flow of heat from a focused point, radially in an outward direction, to the colder surroundings (air, world, universe (entropy)). The heat is much more inclined to be turned into mechanical energy and not other losses, As its most likely path of escape is through a Carnot cycle and not an unwanted thermal conduction, or an exhaust escape.(there is no exhaust loss, if the heat is radiation/sun sourced (as long as you can insulate it from other paths of escape (there are ways))).
Using the Beta configuration that you indicated, is ideally suited for this particular design in my opinion. As opposed to the Alpha configured motor in the link, at least i think its an alpha, they call it an 8 cylinder. (This is also an impressive motor.)
Even though it would be hot in the middle, Sourcing all the parts would be a realistic possibility with modern materials and components that already exist.
Although it would be difficult to map out all the crank connections from the two throws, its very achievable if your that way inclined. There would be a reasonably finite limit to the number of radial cylinders you could have before you ran out of crank room.

I would love to see someone try to make this design, (it won't be me, as I’m still peddling around on my training wheels (with my hard hat on))

vamoose

While the amount of linkage required concerns me, the concept is definitely interesting. I could see this type of design being used to recoup heat losses from various industries. Water pipes, smoke stacks, etc are all usually round and dissipating heat. Creating a design that could wrap around these sources of heat could prove valuable if economically feasible.

I would imagine a cam activated linkage would work best. I'm thinking something like a gear with teeth that act as cams.

I was excited by Jerrys addition.I sort of see how the geared cam would work but not quite.The engine stays in place and the cam turns?How does the engine turn it? How is it connected?

Oops, Actually now I read your post properly I realise you probably meant using a Gamma setup. This Could work, as you have described, in my limited opinion.
(sorry sometimes I don’t absorb things strait away, I could still be wrong about what your describing. If we’re not on the same page then please just ignore my blabbing)

Also what about using Alpha setup with just 'one' common throw and having double acting pistons, With the cold half (power piston), that's at the top, of course. Then just tap/pipe (with relevant heat exchangers and regenerator) to a lower hot cylinder that is at 90 degrees in location and do the same all the way around. You may be able to tap off at slightly greater or lesser degrees, as 90deg isn't an absolute rule from what I’ve read, The degrees depends on number of cylinders you have and their relative radial location. (When I say double acting pistons, I mean like the ones NASA used in their experimental car engines)

Alternately one could consider the Beta setup as another option with the heat emanating from the piston and cylinder wall which are now a hot end (near the hub) in conjunction with multi piped (hot) heat exchanger, that then runs through a regenerator to the top of the displacer end and its heat exchanger (liquid cooled or air), that is now the cooling end. Maybe you could still use just two throws.

Hope some of this makes a bit of sense...

vamoose

I just dreamt of this engine running.The power pistons all faced out.The rods were inverted Vs .The cam was a flywheel around the waist heat source pipe.On the inside of the cam were waves not teeth.The rods were attached to this wavy track by wheels,like the cars on a rollercoaster are attached.When the power piston expanded the rod forced the fly wheel to turn so it could be at the highest point on the wave.The attached foot of the rod now was carried along by the spinning wave to take the power piston back down to the hot center.The gears were on the outside of the flywheel where an electrical generator was connected.I guess this configuration would be an alpha with all the clinders directly connected by their regenerator tubes.

You wave cam idea is a good description of what I was thinking of. Springs to keep the con-rods pushed against the cam, with the 90 degree offset achieved by placement of the con-rods on the wave cam. I think it's time to do a drawing to be sure we are thinking along the same lines.

You'v got to remember that to get a usable amount of power, you are looking for a heat source with at least 600*C, preferably nearer 1000*C, you can easily do that with solar power. Ian S C

What I was thinking about was a linear compound Alpha as the in the pic.
Except it is turned upside down with hot end at the bottom and coiled around the heat source.My drawing illustrates.Reading through different posts it seems like a lot of people look for a way to have the piston lull longer at the hot end to pick up more heat.With this wave cam all you have to do is shave off the bottom of the wave to get a good lull.
This is the URL to view PIX: http://profile.imageshack.us/user/fullofhotair/

http://youtu.be/nKGy08OVxyM
This radial steam engine has alot better rod connection than my inverted V idea.I was thinking if you wanted to go with a beta or gamma configuration you could have 2 wave guides maybe one on each side of the flywheel.One for the power piston and one for the displacer.

I like this discussion about an internal hot side surrounded by the working gas. has anyone considered an offset rotor inside of a cylinder? Like this http://www.youtube.com/watch?v=3pPDTqNWV5U, but with some sort of hot pipe or something in the middle (working gas compresses/expands in chambers separated by the moving walls).