Tiny Stirling Engine

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NickG:
Thanks for the interest guys.

Is still have a couple of issues to sort out with the design. The crankshaft on mine is turned from a piece of solid brass - it might be a bit heavy but I can balance the assembly later by adding mass to 1 side of the flywheel. Hopefully, as my cc is larger, the engine will have enough about it to turn it over. It shouldn't be difficult to machine but I'll have to do things in the right order as it will not have much structural integrity once I start cutting the journals. The other problem doing it from solid is how do you get the big ends on?! Jan's plans suggest putting small slit at the end of the con rod into the big end hole, the rod is that thin you can simply bend it, push it over the crank journal and it'll spring back - I don't really like the sound of that so was racking my brains to think of something else - I can't think of something simple so it seems Jan's idea is a good one.

You're right about all the materials Olli. The displacer is supposed to be balsa wood (I know, the colour is wrong!) but I might have to see what else I have that's suitable - might have some balsa somewhere. I think the flywheel in the vid looks like acrylic. I've found some plastic for my displacer cylinder - top off sun cream, might work, might not, if not I'll have to do what Chris suggested and go around tesco's with my digi vernier :lol:

Ade kindly sent me the graphite for the piston so I'll be attempting that.

I'm not sure what an Alpha type engine is Olli - I was up to speed on this sort of stuff but have forgotten, would have to read up again! Is it the type where the displacer makes a seal too rather than allowing the air around it? I think you need a lot of heat for them and they usually have a low ratio of swept volumes to keep everything as efficient as possible? Or am I thinking of something else?

I'll have to get on with the drawings later but I won't post them until I know it works!

Nick

madjackghengis:
Hi Nick, interesting build, funny you should only have three projects going, are you ever going to be a serious modeler? :poke: A beta Stirling is one where the power piston runs in the same cylinder as the displacer, and is probably the most efficient, it certainly is in large scale. An alpha type is one with a separate displacer cylinder and power cylinder, with the two connected, and easiest to make LTDs since they tend to have large diameter displacer cylinders, and short strokes, with long stroke, hence high torque power pistons, to make them work well at low differentials. I only know this because I'm starting one of each at the moment, and am still gathering materials. :hammer: mad jack

NickG:
Hi Madjack,

:lol: I said I wasn't including the larger projects, mainly because it just depresses me - can I never finish anything?! I might as well mention them now though, they include the refurbishment of a 3 1/2" gauge locomotive (same as Stew's as it happens), refurbishment of a 4 1/2" scale wallis & stevens simplicity Steam Roller, building of a 5" gauge sweet pea locomotive and not a model but the restoration of a 1989 Ford Escort RS Turbo - all work in progress but haven't done much with any of them for a long time. Every time I look at any of them more seriously, I find something that makes them become an even larger project :doh:

Thanks for explaining the different stirling cycle engines. I have made 1 stirling so far to my own design, it was an alpha type engine with the cylinders at 90 degrees to each other enabling use of the same crank.

I remember coming across another type of engine though, I can't remember the designation, still two cylinders but they both have air tight pistons - can't quite remember how they work, willhave to have a look. THink there is a regenerator in the middle and somehow both pistons provide a power stroke?

Nick

Brass_Machine:
Wow that is a tiny Sterling. Best of luck on this one Nick. I know I will be watching.

Eric

madjackghengis:
Hi Nick, there is a "Ringbom" Stirling, which has a piston which moves just the displacer, and has a separate power piston which moves according to the pressure differential, and there is a "resonance" or "acoustic resonance" type where it has a single piston, a heat chamber with good insulation from the cylinder and piston with the cylinder well cooled, and relies on a "resonating pressure pulse" established by the heat raising the pressure, and the power piston setting up a pulse, which will settle into driving the piston at the resonant frequency of the pressure wave in the closed cycle, as it alternates between pressure and temperature change, as per the first law of thermodynamics, I believe, which says in a closed system, the pressure of a gas will be directly proportional to the relative temperature, so the piston changing the volume allows the temperature to turn into pressure when the volume is reduced, and pushes the piston out, which increases the volume, allowing the air to cool, with the excess heat carried off by the mass of the cylinder, piston and the rest of the "cool" end of the engine, which takes it below its original pressure, so it expands faster when all the air is pushed into the hot end, and raising the pressure again. The phase shift takes place in the transfer of the heat to pressure, and the change of pressure with the "loss" of heat when the piston has been moved, and has lowered the pressure by increasing the volume, and at the same time, losing some of the energy of the heat also through transfer, causing the resonant effect which acts in place of a displacer. This engine seems to work by applying the same principle of a "hydraulic ram", pumping system which uses the inertia of running water to establish a resonance, and pump by just changing the pressure in a closed chamber with valves to bleed off excess water, and keep a resonating pressure change continuing and the inertia of the water actually doing the pumping. There is a video of this form of single piston Stirling among the videos available at the beginning of this post. It has taken a lot of mind bending to get around this idea and make it make sense, but having seen it work, it must make sense. :loco: mad jack

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