Running the coffee cup engine on sunshine

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george.henderson
Posts: 2
Joined: Sat Apr 06, 2002 7:26 am
First Name: George
Last Name: Henderson

Running the coffee cup engine on sunshine

Post by george.henderson »

I am interested in sharing experiences of running the coffee cup
engine on sunlight. I shall start by saying what I did and hope to
hear from others who may have followed a similar path or may have
succeeded with a completely different approach.

To get the engine to run on solar radiation, the solar energy must
be directed to raise the temperature of the bottom plate well above
that of the crankcase. If you simply orient the engine with its
bottom plate facing the sun, there is some of the desired effect but
the exposed perimeter of the crankcase also absorbs solar radiation
causing some unwanted temperature rise at the other side of the
cylinder. I first tried to maximise the radiation absorbed by the
bottom plate and to minimise that absorbed by the crankcase by
painting the bottom plate matt black and covering the exposed
perimeter of the crankcase around the bottom plate with aluminium
cooking foil. This showed some benefit but not enough to make the
engine run in the rather weak sunshine in which I tried it. (But it
might be sufficient in a sunnier place)

The next step was to minimise heat loss from the bottom plate by
applying a transparent cover enclosing an air gap. In other words,
I was trying to turn it into a miniature flat-plate solar
collector. I found a very simple way of doing this. I took a piece
of rigid foam polystyrene packaging in the form of a board about 2
cm thick and cut a square just a little bigger than the base of the
engine crankcase. I then traced the outline if the round bottom
plate and cut a hole through the polystyrene to give a push fit over
the cylinder and stretched a clear plastic sheet over one side
fixing it with staples. When pushed over the cylinder, it shields
the bottom of the crankcase from the sun, insulates the edge of
cylinder and provides an air gap reducing convective heat loss from
the bottom plate. It works well, even in the relatively weak
sunshine that we have had here in England between showers in the
last two days.
chris___9640
Posts: 1
Joined: Wed Jun 12, 2002 2:03 am
First Name: Chris
Last Name: Eaton

Response to Running the coffee cup engine on sunshine

Post by chris___9640 »

Hi George,

I am only a complete beginner to the whole world of Stirling Engines, but I do find the whole concept facinating. Over the years I have "dabbled" in a number of different technologies from a hobby perspective. One of these was the subject of "Solar Cooking". I think that if you follow this link;

http://solarcooking.org/funnel.htm

you may be able to find some inspiration. I made the funnel cooker myself. It is cheap and easy to construct. Scaled-up slightly, and with more attention to materials etc I think that you may be able to get some satisfying results. The need for a huge parabolic dish is totally overated. If you are trying to power your house - you gotta have a big dish. If you want to power just a few devices (maybe a water pump or a few lights or battery charger) then I don't think that you need to fill your back yard.

The original author of the Solar Funnel Cooker (Professor Steven Jones) used it in Utah with reasonable success. I have used it in Borneo (Brunei actually). It is very hot here, with lots of ambient sunshine per day. It cooked my food in minutes (about 13 mins to be precise).

I think that a solar powered Stirling is a definate possibility for Borneo.

Have you looked much at Rotary Stirling Engines?
The animations on the website:

http://www.trochilicengines.com/animations/

look interesting.

If the outer edges of the "Rotor Pistons" on these Rotary designs were magnetised and a coil was wound around the "cool" end of the casing (cylinder) then I think that a combined "Rotary Stirling / Electrical Generator" could be produced all in one shell. This would reduce losses considerably because there would be no requirement for an external drive shaft. The "Output" power is transmitted Magnetically through the casing to the coils.

If the rotors (magnets) were made from a ceramic, or a high temperature Samarium-Cobalt, then the operating temperature of the rotor could be extended to approx 550°F. However, that would push the cost of the device through the roof and could only be considered by a company that was prepared to mass-market the device.

I would like to start a forum for Rotary-Stirlings. Do you think that there would be much interest?

Bye for now
Chris Eaton
george.henderson
Posts: 2
Joined: Sat Apr 06, 2002 7:26 am
First Name: George
Last Name: Henderson

Response to Running the coffee cup engine on sunshine

Post by george.henderson »

The solar cooker is interesting. It needs more power and higher temperatures than the coffee-cup engine but the idea of concentrating the solar radiation could work very well, especially if significant output power were to be required. With the coffee- cup engine, the few watts of incoming radiation directly falling on its base is sufficient to make it run. What my simple attachment does is to reduce to heat loss from the bottom plate and the shield the top plate (crankcase) from the incoming radiation. Increasing the radiation level by using a reflector could have the same effect.

I have seen the description of the rotary Stirling engine but do not know enough about it to say whether or not it might be more efficient than other designs. Also, I do not know how much interest there would be in a forum on them. You might find other configurations interesting, especially the 'free piston' type which has few moving parts. See www.sunpower.com/technology/index.html for a list of publications including many on the free-piston engine.


weaver_r
Posts: 2
Joined: Tue Sep 03, 2002 3:44 am
First Name: Richard
Last Name: Weaver

Response to Running the coffee cup engine on sunshine

Post by weaver_r »

I did it a couple years ago.

Check this out:
http://www.stirlingengine.com/file-stor ... ion_id=175
weaver_r
Posts: 2
Joined: Tue Sep 03, 2002 3:44 am
First Name: Richard
Last Name: Weaver

Response to Running the coffee cup engine on sunshine

Post by weaver_r »

I am informed that some things on this site has been fixed so that a login isn't necessary. I uploaded the page to a different location. View it at:
http://www.stirlingengine.com/users/Ric ... ingUL.html

Rich
jem
Posts: 1
Joined: Fri May 02, 2003 11:21 pm
First Name: Jeno E.
Last Name: Mozes

Response to Running the coffee cup engine on sunshine

Post by jem »

I've done this at our summer fair and was interviewed by tv reporter for doing it.

1. Get a nice cool cup of lemondade (ice water would work fine also). make sure it is filled to the top so the bottm plate of your Stirling engine touches the cool lemonade (water).

2. Place the Stirling engine on top of the cup like a cover.

3. Wait a few moments for the sun to heat the top and the lemonade to do it's trick then give it a crank and voila and engine that runs on the summer sun and lemonade. Doesn't get any better than that!!! (Unless you get thirsty in which case the engine's out of luck).
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