Stirlingengineforum.com

Hello im a mechanical engineering student and im building a model stirling engine for my 2nd year project. I am now at the stage of starting the fabrication of my engine but before I start I thought it would be a good idea to put my design on this forum and get some feedback on my design by more experienced engine builders.

the engine im building is for educational purposes only so it only requires enough power to keep itself running. I decided to go for the gamma configuration. the displacer piston has a OD of 30mm and is 65mm long, the displacer cylinder has an ID of 34mm (which leaves a 2mm clearance between it and the displacer piston) and is 100mm long, the power piston has an OD of 25mm and both pistons have a 25mm stroke which gives a displacer/power pistion swept volume ratio of 1.43:1.(Is this okay?). All the moving parts will be running in bearings and will be acurately machined.

I'd like to hear some feedback on this engine before I start the build and constructive critcisim is very welcome, thanks.

Hi
Looks like a nice setup.
If its oriented like the drawing,you will have to heat it from above! How ?
If its lying down you have to compensate for more mecanical resistence from piston;you will need more heat.
When the power piston is vertical,it can be aligned to allmost float in the cyl.This is essential if you want to make a (very)LTD.
I will suggest you make the diplacer-piston 2mm smaller Ø,there will be less air resistence inside the displacer-cyl.
Also keep every moving part as light as possible.(pistons and conrods) Less moving weight=less counterweight=less mass to move.
Remembering each piston has to start-stop-turn 90-start-stop-turn 90-........
In my experience the heigth of the displacer-piston is most effective at 60% of the inside of the displacer-cyl.
I hope i misunderstand your drawing but it seems to me the timing is 180,it should be 90.
Good luck with your project,hope to see some pics. when it runs.
Jan
PS: as a mechanical engineering student you already know all off that,this just for everymans info

Thanks for the reply speedless.
The engine will not be orientated verticaly, it will be lying horizontaly and hope to use a homemade alcohol burner for the heat source, I hadnt considered the extra mechanical resitance caused by this but if it requires extra heat to get it running thats ok, il be happy if it runs at all (even if it takes a propane torch and some ice). You suggested that I make the displacer piston dia 2mm smaller, that would give me a 3mm gap between the displacer piston and the displacer cylinder, is that right?. And yes I do know that the timing should be 90 deg, I only orientated it that way in the drawing to show all the internal parts. Iv added some Solidworks CAD models of my engine.
NOTE: the connecting rods and flywheel in these models are not the final design, after I purchase the miniature bearings I will design the con-rods around them, they will be made from aluminium and will be designed to be as lightweight as possible.
Question
Can anyone give me any advice on the weight and size of flywheel that my engine will require? or will I just have to experiment?
Thanks in advance.

That is a well proven design, should run very well as long as the friction is low and the compression isn't too high. When completed, it should rotate many revolutions with a good flick of the flywheel (before you heat it)

...............Your flywheel diameter will be determined by where you locate the axle in the frame. Aluminum is easy to cut, cheap and lite. Brass easy to cut, costly and heavy. Material choice here will not be a factor in getting your engine running and a "T" framed Gamma is the most common configuration you see in videos. 2MM clearance (.080) is my minimum for displacer clearance and it should run with 3MM without any concern for rubbing inside the hot tube. A longer gland for the pushrod will help keep the displacer parrallel in the bore at 2MM for less chance of contact in the hot tube as the crankshaft imparts a perpendicular motion to the pushrod sliding in & out of the gland. You'll do fine with this layout.