Some queries for my Stirling Engine system

[blitz000]

Thanks for the heads up for the power piston here is another one:
I have made quite a huge (in terms of its size) Stirling Engine and here are the following details

Displacer diameter: 590mm (about 2 ft)
Displacer stroke: 60mm (about 2.4 in)
Piston diameter: 105mm (about 4.1 in)
Piston stroke: 60mm

The system has two power pistons of the equal stroke and the same phase thus making this system a single acting but two power piston. (I've read it from a journal paper which is of the similar design, by Kongtragool and Wongwises a twin power piston. You can find their reports through Science Direct)

This is how the thermal system would look like in words
Steam from water -> Copper Plate -> Displacer Cylinder -> Power Piston -> Aluminum Plate -> Cold Water.
Hopefully you can imagine it. Meant to run as an Low Temperature Difference (LTD) System. Using atmospheric air as a running medium

I've done some calculation that it will produce power, although not much but it still would not run. Leaking from the many connections have been solved, and thus i'm afraid that the inertia/weight of the crankshafts and all will not make it run as most of the moving parts are steel.

Is there any pointers (more like a step by step guide) to check a Stirling Engine of such. Thank you.

[Ian S C]

blitz000, at a brief glance, it should work, you must have minimum friction, ball races for all bearings if possible, and if they are shielded, remove the shields, and wash out the grease. Use very light oil instead. Cut down as much weight as you can, then see if you can get rid of a bit more. The motor is not highly stressed, so great strength is not required. Experiment with the flywheel, it should not be too heavy, ie fairly light, but large diameter, for a motor that size a bike wheel might not be too far off. Ian S C

[blitz000]

I thank you for that comment. One last thing I would like to ask is about lubrication

I know that sometimes lubrication will foul up the heat transfer in the regenerator/displacer. But some how metal-metal (like you recommended Cast Iron-Cast Iron) would require some degree of lubrication. Should I run it dry or with some lubrication (if yes, what kind of lubrication would be good?)

[Ian S C]

blitz000, the reason for using cast iron is the fact that because it has an excess of free graphite, it is self lubricating to a degree. Thats why you get dirty black fingers when you work with it. I usually use a drop of very light oil when using cast iron and steel. To run with oil make the pistons with narrow shallow grooves around them to retain the oil. Oil is viscous, and creates drag, which is just another form of friction. If the oil gets in the hot end it gets cooked, and becomes gummy, even WD 40 will stick up a motor. Try to run the motor dry, if you have the pistons honed to the recomended fit, ie., they slide through the open cylinder under thier own weight, but stop when you block off one end of the cylinder. Ian S C

[Ferraccio]

Good evening,
I think that making a Power Stirling Engine is important do not lubricate, the limit is done from the running part' speed.
Sealings as e.g. solid Rulon, or Teflon coating (on carbon steel, stainless, or brass) , the rapport is 2 to 5, this meaning that when is lubricated the allowable speed is 5 m/sec, not lubricated is 2 m/sec. Also a good architecture have to reduce the loads (and for so friction stresses) on rubbing parts.
For higher loads and temperatures are allowable sintered metals self-lubricating (e.g.: bronze-graphite), on wich I've had good expereriences long time ago, (overall for non lubricated bearings) and I've seen that are well considered till now, as "composite material".
For power piston I think is very important do not have sealing system at all (as sealing rings), very tight construction tolerances give a good seal without other devices, overall if there aren't lateral loads.The loads are transferred to the cross heads.
The reason to avoid lubrication is clear: there is no oily material that is not tacky, and that did not carbonize in time at high temperatures, in air.
With an engine of this size is necessary to imagine continuous operation, without intervention.
Ferraccio

[Ferraccio]

The engine is clearly a Gamma architectture, with central displacer, and lateral power pistons, aligned.
I think the system is very good, becouse the dead spaces are reduced, if displacer and pistons are parallel superimposed, and for so near.
Ferraccio