If I want to make a Stirling engine as efficient as possible and run on a working gas of several thousand psi and not leak ,the free piston design would be the most inexpensive to make wouldnt it?Thanks.
A ideal Stirling is a free-piston design that runs on highly-pressurised hydrogen in the fully enclosed container. It has to be extremely hot on one end and extremely cold on the aother. Cylinders, displacer and piston are made from hard material with minimal heat conductivity and thermal expansion. The seams between cylinter and piston are machined to a high degree of precision, made from 'mutually-slippery' materials and contain no liquid lubricant.
thanks.perfect synopsis for me.Are there ceramic Stirling engines.Seems ideal.Iknow the heat shield material on the Space Shuttle in a dense form is actually harder than diamond.Would ceramic be perfect for one?
are fee piston designs any less or more efficient than the others?My gut makes me think theyd be less efficient although I hope not.I love the simplicity and seeming ruggedness of the design.
Theoretically free pistons are more efficient as less friction and move native timing of the displacer. In normal engines displacer is rigidly timed 90 degrees ahead of power piston. This is not the best regime as it starts compression midway through expansion cycle and vice versa. This reduces efficiency as the two cycles work against each other for a quarter of the time. Ringbom delays displacer movement till the pressure demands it (rather than rigidly 90 degrees), this is more efficient.
thank you very much!I was thinking my ideal Stirling engine would need to be along the idea until the pressure demands it.Thus,you also get max torque from this design as well?It never occured to me free piston was one way to do it.Well said!
I think thermoacustc stirling is more efficient and simple, he has no problem with connection with the crankshaft, or need a crankshaft. The efficiency of thermoacustc engines can be more than 45%.
True to a point. Stirling Engine of ANY design is the most efficient way to convert heat directly into mechanical energy known to man because it works on pure Carnot gas laws. However the maximum theoretical efficiency is about 36%, not quite 45, but still much better than steam or intenal combustion engines. SE potential efficiency is not an issue.
The issue is power density, ie the ratio of power output to the size/weight of the engine, it is here where SE loses out to steam and IC engines. And here the thermoacoustic design suffers especially. It is almost impossible to extract any decent power out of it unless it is the size of a house. The reason: it is hard to achieve a large temperature difference with this design due to the lack of active displacer/mixer. The acoustic waves don't vary temperature enough to produce significant power.
How does the displacer move if when there is no physical connection? I know it is by pressure inside the pressure vessel, but how is the movement facilitated?
Ringbom engines have the displacer push rod of a reasonably large diameter (8 mm in my case). That provides enough pushing area for the pressure inside to produce the sufficient force to move the push rod (syringe-style) and of course the displacer with it. The weight of the displacer and the push rod plays no part as it is compensated by the overhead spring whicj should be visible on the video. If it is not visible I may have to redo the video with a closeup.
I can understand how the pressure builds on the heat-half of the cycle. What causes the displacer to move to the cool side? Doesn't the displacer have to move before the pressure drops?
The displacer is moved to the coll side by the pressure buildup caused by an 'overdrove' due to the inertia of the flywheel which continues it's movement even after the expansion stroke is completed. Ie, once flywheel reached the bottom dead point due to the heat expansion of the air inside, it does not stop there but continues it's movement causing by now compression of the air which pushes the displacer rod 'out'. That moves the displacer to the cool side.
If I want to make a Stirling engine as efficient as possible and run on a working gas of several thousand psi and not leak ,the free piston design would be the most inexpensive to make wouldnt it?Thanks.
tomterahedrob 3 years ago
A ideal Stirling is a free-piston design that runs on highly-pressurised hydrogen in the fully enclosed container. It has to be extremely hot on one end and extremely cold on the aother. Cylinders, displacer and piston are made from hard material with minimal heat conductivity and thermal expansion. The seams between cylinter and piston are machined to a high degree of precision, made from 'mutually-slippery' materials and contain no liquid lubricant.
Naturally this design is hard to implement.
blg53 3 years ago
thanks.perfect synopsis for me.Are there ceramic Stirling engines.Seems ideal.Iknow the heat shield material on the Space Shuttle in a dense form is actually harder than diamond.Would ceramic be perfect for one?
tomterahedrob 3 years ago
In thermal sense yes. Not sure about it's mechanical properties or ability to keep machined shape to the high degree of precision though.
blg53 3 years ago
are fee piston designs any less or more efficient than the others?My gut makes me think theyd be less efficient although I hope not.I love the simplicity and seeming ruggedness of the design.
tomterahedrob 3 years ago
Theoretically free pistons are more efficient as less friction and move native timing of the displacer. In normal engines displacer is rigidly timed 90 degrees ahead of power piston. This is not the best regime as it starts compression midway through expansion cycle and vice versa. This reduces efficiency as the two cycles work against each other for a quarter of the time. Ringbom delays displacer movement till the pressure demands it (rather than rigidly 90 degrees), this is more efficient.
blg53 3 years ago
thank you very much!I was thinking my ideal Stirling engine would need to be along the idea until the pressure demands it.Thus,you also get max torque from this design as well?It never occured to me free piston was one way to do it.Well said!
tomterahedrob 3 years ago
I think thermoacustc stirling is more efficient and simple, he has no problem with connection with the crankshaft, or need a crankshaft. The efficiency of thermoacustc engines can be more than 45%.
fernandesilyt 2 years ago
True to a point. Stirling Engine of ANY design is the most efficient way to convert heat directly into mechanical energy known to man because it works on pure Carnot gas laws. However the maximum theoretical efficiency is about 36%, not quite 45, but still much better than steam or intenal combustion engines. SE potential efficiency is not an issue.
blg53 2 years ago
The issue is power density, ie the ratio of power output to the size/weight of the engine, it is here where SE loses out to steam and IC engines. And here the thermoacoustic design suffers especially. It is almost impossible to extract any decent power out of it unless it is the size of a house. The reason: it is hard to achieve a large temperature difference with this design due to the lack of active displacer/mixer. The acoustic waves don't vary temperature enough to produce significant power.
blg53 2 years ago
How does the displacer move if when there is no physical connection? I know it is by pressure inside the pressure vessel, but how is the movement facilitated?
16strings 4 years ago
Ringbom engines have the displacer push rod of a reasonably large diameter (8 mm in my case). That provides enough pushing area for the pressure inside to produce the sufficient force to move the push rod (syringe-style) and of course the displacer with it. The weight of the displacer and the push rod plays no part as it is compensated by the overhead spring whicj should be visible on the video. If it is not visible I may have to redo the video with a closeup.
blg53 4 years ago
I can understand how the pressure builds on the heat-half of the cycle. What causes the displacer to move to the cool side? Doesn't the displacer have to move before the pressure drops?
16strings 4 years ago
The displacer is moved to the coll side by the pressure buildup caused by an 'overdrove' due to the inertia of the flywheel which continues it's movement even after the expansion stroke is completed. Ie, once flywheel reached the bottom dead point due to the heat expansion of the air inside, it does not stop there but continues it's movement causing by now compression of the air which pushes the displacer rod 'out'. That moves the displacer to the cool side.
blg53 4 years ago
Cheers mate, I meant it. If there is any beauty in mechanical engineering this is it.
blg53 4 years ago
Poetry in motion, you said it. Well Done.
fuzzymonkey777 4 years ago