Double-acting solar Gamma, twin rotary displacers
Posted: Tue Nov 21, 2017 6:01 pm
I've been reading about hot air engines for years, they are quite fascinating. So far, I've never taken that final step into building one yet. Although...I am closing in on a design that I feel might be worth actually trying out. I scan google and youtube about once a year to see if anything new has come up, and I'll try to credit those builders that have inspired parts of this.
Most proposals seem to focus on a large single engine, rather than two smaller ones in tandem, perhaps for the cost savings. However, I always liked the ability of tandem engines to have a more balanced pulse on the flywheel. Part of my interest in a double-acting power cylinder is that we can use a piston if we like (rather than a diaphragm), because any gas that leaks out past one side of the piston simply migrates some of the gas to the other side. With leakage being roughly equal in either direction, gas volumes on both sides would remain fairly equal over time. This allows the option of upgrading to Helium or Hydrogen later, although there is nothing wrong with building with air, especially in the prototyping stage.
Although I would construct the rotary displacers to be fairly balanced, I would prefer to plan on them being vertical, so the power piston is not fighting the weight of moving a displacer. For a conventional reciprocating-displacer Gamma, I would mount the displacer vertically, but...rotary displacers have grabbed my attention for now (partially because the displacer can be any weight, allowing it to act as the flywheel too.
VAWT auto-start...
Since the rotary displacers are vertical, its an easy arrangement to mount a Vertical Axis Wind Turbine above it (Google: Savonius). The problem with any kind of wind turbine is that...they only work if there is wind, plus...if you will be depending on them, you really need a 60-ft pole (or higher) to make the amount of energy harvested worth the effort...
After pondering a dozen half-baked self-starting schemes for a solar-heat Stirling, it occurred to me that a small VAWT near the ground has decent torque, but low RPMs...making it a weak option to generate 12V, BUT!...all it takes is an occasional breeze to make it spin a couple times. Within an hour of the sun rising, a solar Stirling with an attached VAWT would be spinning. If they were attached through a one-way clutch bearing (which I have used), once the VAWT has gotten the Stirling spinning after sunrise, the Stirling will continue spinning when there is no more air to spin the VAWT. Of course, any small breeze would allow the VAWT to help the Stirling spin a small generator, so it definitely sounds worthwhile to me.
Of course, having an auto-start system means that a large 'single' engine is an even more useful option, but I still like the idea of balanced forces on a double-acting power piston (or diaphragm).
Sooo...two vertical displacer cylinders side-by-side, rotary displacers in each, with a power cylinder on top using horizontal connecting rods. Here is a link to an example that is similar to what I envision (crank and piston located inside the sealed gas area):
http://www.bekkoame.ne.jp/~khirata/english/rot_se.htm
Here's a video of a working example of a rotary displacer, and this guy also adds two magnets to create a pneumatically-sealed rotary actuator to turn the external crank (a waste when used here, since the piston can leak, but...he could swap to a diaphragm in the future).
https://youtu.be/iZZ70nwU77c?t=36
If anyone is good at graphics or animations, I might be persuaded to pay for an example of this idea so I can better show what I mean?
Most proposals seem to focus on a large single engine, rather than two smaller ones in tandem, perhaps for the cost savings. However, I always liked the ability of tandem engines to have a more balanced pulse on the flywheel. Part of my interest in a double-acting power cylinder is that we can use a piston if we like (rather than a diaphragm), because any gas that leaks out past one side of the piston simply migrates some of the gas to the other side. With leakage being roughly equal in either direction, gas volumes on both sides would remain fairly equal over time. This allows the option of upgrading to Helium or Hydrogen later, although there is nothing wrong with building with air, especially in the prototyping stage.
Although I would construct the rotary displacers to be fairly balanced, I would prefer to plan on them being vertical, so the power piston is not fighting the weight of moving a displacer. For a conventional reciprocating-displacer Gamma, I would mount the displacer vertically, but...rotary displacers have grabbed my attention for now (partially because the displacer can be any weight, allowing it to act as the flywheel too.
VAWT auto-start...
Since the rotary displacers are vertical, its an easy arrangement to mount a Vertical Axis Wind Turbine above it (Google: Savonius). The problem with any kind of wind turbine is that...they only work if there is wind, plus...if you will be depending on them, you really need a 60-ft pole (or higher) to make the amount of energy harvested worth the effort...
After pondering a dozen half-baked self-starting schemes for a solar-heat Stirling, it occurred to me that a small VAWT near the ground has decent torque, but low RPMs...making it a weak option to generate 12V, BUT!...all it takes is an occasional breeze to make it spin a couple times. Within an hour of the sun rising, a solar Stirling with an attached VAWT would be spinning. If they were attached through a one-way clutch bearing (which I have used), once the VAWT has gotten the Stirling spinning after sunrise, the Stirling will continue spinning when there is no more air to spin the VAWT. Of course, any small breeze would allow the VAWT to help the Stirling spin a small generator, so it definitely sounds worthwhile to me.
Of course, having an auto-start system means that a large 'single' engine is an even more useful option, but I still like the idea of balanced forces on a double-acting power piston (or diaphragm).
Sooo...two vertical displacer cylinders side-by-side, rotary displacers in each, with a power cylinder on top using horizontal connecting rods. Here is a link to an example that is similar to what I envision (crank and piston located inside the sealed gas area):
http://www.bekkoame.ne.jp/~khirata/english/rot_se.htm
Here's a video of a working example of a rotary displacer, and this guy also adds two magnets to create a pneumatically-sealed rotary actuator to turn the external crank (a waste when used here, since the piston can leak, but...he could swap to a diaphragm in the future).
https://youtu.be/iZZ70nwU77c?t=36
If anyone is good at graphics or animations, I might be persuaded to pay for an example of this idea so I can better show what I mean?