Stirlingengineforum.com

I’ve seen the idea thrown out but I’ve never seen a working model or a plan that looked like it might work. The basic setup is a conventional gamma. Flywheel, crankshaft, displacer all standard. The only change is there is no power piston. An enclosed fan similar to a centrifugal fan sets atop the engine with its shaft vertical and attached to the flywheel, crankshaft assembly. The timing is 90 deg. Offset by the crankshaft but it open and closes one way valves instead of being moved by the power piston .As the displacer rises the hot compressed working gas enters the turbine. As the displacer lowers the working gas is expelled. Would it have any advantages darn if I know? It would be different.

I think you guys aren't seeing this as I see it .If it was a gamma at some point the power piston would rise ,this is the exact time the valve would open ,letting the turbine spin. The valve would remain open up and until the piston fell. It would follow exactly a piston gamma ,only the turbine would spin ,not a piston move.

Hey mate,
Sometimes I personally find it hard to visualise what others are describing (and i guess, so can others), so maybe you could link us to some articles/images or something relevant, to help make your point.
I too am interested in hot air turbines and have been playing with some different ideas, for fun.
Here is the largest example of a Hot Air (temperature difference) engine that I've come across so far..



Its hard to argue with mother nature!

vamoose

It works almost like a power piston. The main difference is the 90deg offset runs the 2 one way valves .Instead of receiving power from the power piston. The power comes from the turning turbine. I don’t know if one valve would snap open while the other valve snapped shut or one opens by degrees as the other closes by same degrees.

http://imageshack.us/photo/my-images/856/gedc05362.jpg/

OK, I kind of get what your saying.
You might need somewhere for the gas to travel to, like another chamber or bladder or bellows, as the relative volume wants to expand and alternately contract as it heats and cools. This would help increase the amount of airflow through/past the turbine, I would think..
This chamber should be connected appropriately, relative to turbine and valve configuration.
eg. As the valve closes to the displacer it opens to the chamber and vice versa ..(the second valve does the same also, at the right moment, when timing dictates).
Maybe even a balloon might act as a chamber in a tin can design.

Also to extract any real power I would think the turbine/impeller 'blades' would need to be an extremely neat fit (small clearance) with the housing, so there is no significant 'blow by' of gas past the blades, but also no contact/friction loss as it turns.

There would be things to consider, like dead space resulting from the volume of the turbine for one and who knows what else.
I have no idea if it would work.
But am able to say that I can see what your getting at, interesting!
Or maybe i don't get it and have flown off on my own tangent , anyways..
Like always, there is only one real way to know if it will work, good luck!
vamoose

Vamoose
You totally understand it. I saw the same problem with gas pressure build in the turbine. Thats why I thought maybe one valve should open an equal degree to the other closing. Yes, I see What you mean, a lot of dead space .Maybe the dead space could also serve as an area for the regenerator ,by filling it with steel wool? Probably the smaller the tighter the turbine the better. Im still not quite clear how the valves would operate.

Vamoose
I just wanted to add this question to you. By having the valves open and close to equal degrees, do you think this would eliminate the need for the reserve bladder? When the out going one way valve is open 10% the return valve is closed 90%. When the out going valve is open to100% the return valve is open 100%. I just realized this isn't what I said earlier but is the way it would have to work. An entirely different timing set up than my original vision. Maybe some irregular cam shape for the valve timing conrod to attach to?

This might work for the valves. Think of the Watkins double action steam engine. The cylinder exit tube and the return tube come together divided by a small moving piston . One atop the other. The piston is timed to 90% off set by the (flywheel/turbine). There is only one conrod, working the piston. When one is open 10% the other is closed 90%.one open 50% the other closed 50%.One open 100% the other closed 0%.Back to simple design. The turbine could have a fan and shroud connected to one of its side by its shaft to move large quanities of air for cooling.

What if the turbine was on the side of the cylinder instead of at the top? The tubes to and from the turbine would then be in the right place for the regenerator. Steel wool could placed in them.

The idea now has changed to using pneumatic drill motor instead of a turbine. The engine will be a free piston design ,needing no timing to the displacer. The pneumatic drill will spin instead of a piston moving. The returning gas from the drill motor would be the same as the piston lowering. The pressure should change the same in both engines, if the two engines were doing equal work.

fullofhotair,
I'm not sure of the ratios to valve openings and 'what not', as I am only guessing at all this stuff, still I find it interesting and am interested in wherever this line of investigation ends up.
But like many of us on this forum I have my head space orientated in my own current line of thinking and ideas, so I can get a little muddle headed when I try to think outside my current box.

Still, I would like to add that I do recall reading about someone adapting a wankel rotary engine design into a hot air engine (this could be considered a type of turbine engine, in my opinion, at a stretch). So it might be worth you having a look into, and doing an internet search on the subject.
(Also, if I happen across a relevant link, I will post it.)
vamoose

The description the Sunpower site is not the same idea but it does utilize a turbine pump to drive a generator.

Preliminary Design of a 7 kWe Free-Piston Stirling Engine with Rotary Generator Output

http://www.sunpowerinc.com/library/pdf/ ... oc0080.pdf

A preliminary design for a linear motion free-piston Stirling engine / blower coupled to a rotary turbine /generator is described.

We have made something closer to what you have described. Stirlings that pump hot air to drive a turbine shaft connected to propellers for drones, kind of a hybrid gas turbine. The turbine is nothing more than a turbo charger. Unfortunately I can not provide details or pictures due to who the work is for but you should be able to deduce why there is more than one propeller as the Stirling piston is the valve in someway being more like a 2 cycle engine.

Aero
Thanks for the reply . You solved my problem with how to regulate the direction of flow. So you used a super charger I will look into that. Did the engine have high rpms and much torque?

The sterling engine will be a free piston design ,needing no timing to the displacer. The pneumatic drill will spin instead of a piston moving. The returning gas from the drill motor would be the same as the piston lowering.

Thanks,