planning fro large solar gamma stirling engine

[asimations]

I made a small ltd gamma stirling engine that runs with solar heat provided its lower plate is cooled with cold water or ice. You can see the video http://www.youtube.com/watch?v=rVA11giUIpk. Now i have plans to build a larger engine that yield useful energy to charge a battery atleast of 12v. This will be multi cylinder engine. I want to post few pics of its plan i made on a graphic software.I dont now where to post the pics.

here the graphics

solar1.jpg (24.2 KiB) Viewed 13802 times

[asimations]

well i found the pics and posted I need help regarding the power it can generate. The size of displacer cylinder will be around 10 inches dia, 14 inches height, . I want to run a dc motor of car blower to charge the battery or may be the car alternator. There is no problem of sunlight in my place its plenty and blazing hot in summer. Cooling will be provided by water.

[jimlarsen]

It looks like a design that will run, but I am skeptical about having enough power for your goals.

There is no real advantage to having such a tall displacer. It is adding more weight that you don't need, and causing a little additional dead airspace inside the pressure chambers.

I suspect that the generators you mention may create more load than this engine can turn. But I may be wrong. I have built several solar engines, but they are all smaller than what you describe.

If you really need to charge a battery, a solar panel is a simpler solution. But if you want to build a solar Stirling to do it, that is great too. The design you have illustrated will not start on its own, so it won't work if unattended.

[jimlarsen]

Another thing. With multi-cylinder engines you will want to set the displacers to be opposed to each other along the crankshaft. Each drive piston is then phased 90 degrees behind that displacer. This balances the engine very nicely. In your drawings you show them all moving in unison.

[asimations]

thanks for ur reply and advice. I saw a multicylinder engine in which all pistons in same phase and all displacers in same but 90 degrees out of phase to pistons. But i may take your advice to work on this kinda configuration. Manual start is what I believe right now but may be I can use the same motor to start engine that will charge the battery. Cost is the main thing that make me consider the making of this engine. My question is, "how to find the power that it will generate?".

[Ian S C]

Jims right about the phasing of the cylinders, as it is it would run in the fashon of a single cylinder motor.
I would then start by turning the motor over, crank at he bottom, displacers at the top, then you need a very large reflector, because if you want power out, you need lots of heat in, you will proberbly need a water cooling jacket at the cold end. You'd be pushing it to drive an automotive alternator, I'v go one driven by a little Villiers 2 stroke, and it struggles to produce 300 watts at 12 volts, I think it runs at about 2500rpm, or maybe 3000rpm. Ian S C

[onecycleDan1990]

I think someone has figured this out already. Namely Bill Gross from Idealabs. His team built a low pressure or unpressurized (presumably) gamma engine with plain heat exchangers that produced 250 watts continuous electric output, which would likely imply at least a 500 watt mechanical output engine allowing for generator losses and especially the very large turn down ratios in solar thermal machines. It is shown in a video on TED Talks. The concentrator array is far too complicated for any amateur whatsoever to replicate, and the linkage would be difficult to build. The engine looks to be between 200 and 400 cc displacement, and probably spins at a modest speed. A home builder could probably replicate the gas circuit itself closely, use a crank-slider or scotch yoke instead of the unique linkage of the original, and improvise a simpler heat source.

here is a link to a long but interesting video, which is currently the only images I know of of the inside of this engine:

http://www.ted.com/talks/bill_gross_on_new_energy.html

[hephaestus]

Bill Gross got unnecessarily complicated...

Yes you can use his petal system... But a 4x8 solar water heater is going to get you the same or better results...

Part of what's drawn me here was looking for a way to turn a planned passive solar water heater system into a full on active system solar water heater. The "off grid" consultants answer was to use PV with battery... I didn't much like that since the powers not linearly connected... Sun goes away, heat doesn't instantly go away; this bothers me...

Where I'm personally looking at - is using 'existing' solar water heaters to feed heat to the engine (and acts as a battery - does hold heat; thus the power's available long after the sun goes down), I like less maintenance so adding water/ice etc to the bottom doesn't work for me - thus trying to find some design info on ammonia absorption systems, so the heat from the solar provides cooling as well.

The engine design for me is still open, temptation is to run a gamma style system - but a multi cylinder alpha (I was eyeballing that post about the dalhousie? grad students version - would be easily scaled out to a 2/4 cylinder by mirroring it on a combined crankshaft) makes more sense to me in terms of separation and layout. I could be nuts, but the alpha makes more mechanical sense to me...

[jimlarsen]

Where I'm personally looking at - is using 'existing' solar water heaters to feed heat to the engine (and acts as a battery - does hold heat; thus the power's available long after the sun goes down)

I like that idea! I hadn't thought of that before. Use a large collector to feed a "normal" sized engine. I had always thought in terms of scaling up the entire engine. This way you just scale up the collector. It would not be as hot as a parabolic reflector, but it would be efficient.

[asimations]

one more thing i would like to know is "what metal should i use to make the top plate to catch the heat" should it be aluminium copper or steel. Or steel above the aluminium to lose less heat from above into environment. copper would be costly i guess.

[jimlarsen]

Aluminum is the traditional choice, so long as it can tolerate the temperatures and pressures of your design. Aluminum is a good conductor and is relatively cheap. Copper is a slightly better conductor, but is more expensive.

[Ian S C]

Copper will also stand a lot more heat than aluminium, a good solar consentrator, on a good day should be able to melt the aluminium.Stainless steel will over come the over heating problem, and as the metal is thin, conductivity is not a problem (the heat only has to go through a few thou).
If you go the aluminium way, the best finish on it is black anodised, not black paint, as the paint actually works as an insulator.
I used a Fresnel lens to run one of my engines, and the heat from the sun actually etched a line across the stainless steel displacer cylinder, but the engine produced more power than when it was running on LPG. The lens was a large one, designed to be put in front of a TV screen. Ian S C

[jaket]

I think the same principles go for stirling that work for gasoline engines. If you want power, you just cannot increase the single cylinder size as it cannot rev high enough and the single cylinder causes vibration as the piston is so big.

with stirling design it's even more important to keep the single cylinder small, because the air is easier to heat up in small cylinder as all the air is close to the heat.(in small cylinders the heat is never far away).

problem with too many cylinders is mostly friction so there is some sort of balance of optimum cylinder size.

for power, I would go for high revolutions as stirling engine torgue is quite small, so the faster you can run it the more work you get out of it.

to charge a 12volt battery, straight solarpanel works best. of course that won't work in dark;)

[Ian S C]

Jaket, the old engines often had pistons of 8" or more, admittably the revs were low. Have a look at Vile Fly's V twin compressor convertion, he's doing it the right way by making the hot end in the form of multiple tubes, this aids heating in a larger cylinder. As balance goes, at least the piston, and other moving parts can be made lighter than a similar sized IC engine because there is no explosive force, but the hot air engine creates its power by gradual expansion, then contraction, so that there are less stresses in the engine, and if you want balance, a 4 cylinder alpha motor is proberbly the best, proberbly a swash plate drive. You could have 6 or 8 cylinders in this type of motor. Ian S C

[asimations]

kindly post the address of you tube movie