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Yea, I decided to go ahead and try a small model or two. Mostly what was holding me back is I had no real idea if any of my hair-brained modifications had any chance of working. I thought building one full size engine would be less work than building a bunch of test models first, but having something I could bring over to the neighbors house and show off would be kind of neat too, so why not.

Besides I haven't found out yet where I might get any 55 gallon drums around here.

I don't remember where I read about adding some water, but I read it somewhere. I've looked at like two dozen different sites so It would take a while to backtrack and try to find it at this point.

From what I've read about the difficulties of getting one of these things running, it will be something of a miracle if I can get this, as far as I know, "New" design to work.

I suppose I should have started out with a proven design, but where's the fun in that?

You (SScandizzo) got me to rethinking the whole Top Dwell idea.

I think I have been looking at this all wrong.

I do now remember something from Science class back in high school about thermodynamics. You can't capture "cold". There really isn't any such thing as "cold". COLD is just the absence of heat.

So do we really want a piping hot preheater parking itself in our Stirling Engine's COLD chamber, in an attempt to "capture" some "cold" that doesn't exist?

If cold is the absence of heat, then we would want to get that sucker outa there as quickly as possible after it has done it's job of delivering a blast of hot air. Right?

So what I'm figuring is a bottom "Dwell" of about 300 degrees of rotation. Then have that thing pop up like a jack in the box and immediately drop back down for another 300 degrees of the flywheels revolution, or something along those lines.

In order to produce "cold" which cant really be captured, since it doesn't exist, all we have to do is make the heat "absent" as soon as possible.

Also what would sucking all the heat out of the "preheater" do but waste all that precious heat that has been accumulated in the preheater! There is no gain in energy by sucking it out through the top of the chamber without it doing any work.

If we can get the "preheater" hot enough, and get it to deliver its heat fast enough, at a high RPM there won't really be any way to cool the "regenerator" down fast enough to do any good.

What I'm figuring is that it will transfer heat to the air in the chamber on both its way up and on it's way back down. This quick blast of heat might be more like the ignition of an internal combustion engine than a normal Stirling engine. This would make timing more critical than in a typical Stirling engine.

This morning I've been working on something else.

I was starting to make my insulating top for the "preheater/displacer/regenerator" thing and started using the bean can like a cookie cutter to cut this regenerator top somewhere near the size I wanted to fit inside the can.

After pressing the can down through the piece of insulation I saw the can nestled down there with insulation around it and got another idea.

The leftover ring of insulation could go around the base of the can to help keep the "preheater" chamber from dissipating heat out the sides of the can. We want to save that heat for doing some work.

Also the bottom of the bean can is recessed and what I had in mind for the completed engine was to set it on top of my wood stove.

I thought the recess in the bottom of the can would interfere with the metal to metal heat transfer between the top of the stove and the can, so I had been thinking about adding an aluminum base to the bottom of the can that would go up inside this recess in the can's base to help transfer heat from the stove to the can.

But this insulating ring would provide an opportunity to do something else as well.

The aluminum base, instead of fitting inside the can recess could be over-sized to capture more heat.

I had more or less discarded this idea though, as the aluminum extending beyond the can would probably just transfer whatever heat it picked up to the air above it rather than transferring it to the can. It might even take heat away from the base of the can and transfer it to the air!

But now with this ring of insulation, there would be no way for the base to transfer heat to the air, it would have to make it's way through the base of the can where it could be used to help power the engine as it wouldn't have anywhere else to go.

So I got a little side tracked this morning and built this insulating base out of the left over ring of insulation and an old aluminum pan of some sort that had big holes in the bottom.

I think the pan may have been for cooking Turkey inside another pan with holes in it so that grease would run down through the holes into the other pan.

Anyway, the holes came in handy for directing hot air to the bottom of the engine.

Scroll to the bottom of this page for new pictures.

http://members.tripod.com/prc_projects/photos_1.html

While putting the base together I gobbed it all up with blue silicone, which turned out to be completely unnecessary.

With the aluminum base fitted into a recess in the insulation ring the whole thing holds itself together pretty nicely, so I ended up wiping the silicone off as much as I could with some old newspaper.

I made another ring of aluminum out of the same Turkey basting pan, or whatever the heck it was, to help direct some heat up the sides of the can as well. I'm not entirely sure this is a good idea. I may need to cut this side ring smaller or add another ring of insulation to cover it.

I'll probably be adding some sort of ring of cooling fins to the top part of the can. But...

I've been thinking instead, about adding some sort or cold zapper that would pop down. Kind of along the same lines as the preheater, but I haven't got anything specific clear in my head yet, some sort of heat scavenger. Something that could be controlled so as to get rid of the waste heat after it has done its job of powering the piston rather than just having the excess heat slowly dissipate.

I think there might be some advantage in it if the exact moment of cooling can be adjusted or "timed".

As it stands, cooling would already have begun DURING the heating phase, robbing the engine of some of that power before it has a chance to do any work.

Earlier someone said:

SScandizzo

Posted: Wed Nov 08, 2006 7:09 am Post subject:

-----------------------------------------------------------------
(....)

- Theoretically, you do NOT have to connect the displacer to the flywheel by linkage. The change in internal pressure can actually force out a secondary "piston" connected to the displacer. Look into Ringbom Stirlings for more information. (...)

I'm a bit puzzled in terms of how this might work.

Since the displacer is, in effect, the driving force of the engine, until it moved there would be no "change in internal pressure" to move the secondary piston to move the displacer.

Kind of like trying to get an egg before you have a chicken situation I would think.

You said "theoretically" so I'm wondering, are there any actual working engines using this principle?

In connection with what I've been thinking on; somehow isolating or delaying the COOLING phase until AFTER the heating phase has done it's work...

I'm thinking cooling should probably START at just about the time the hot "Jack in the box" has dropped back into his resting place at the bottom of the chamber.

I've run several Ideas in my imagination and haven't been able to clearly visualize any way for this to work. Well, actually I've thought of a dozen or so I suppose "in theory" - baffles, louvers, secondary cold chambers temporarily isolated from the main chamber in some way, cam driven, plunger driven, somehow attached to the displacer drive or having the piston rod extend THROUGH the piston into the displacer chamber, or some secondary cam or ratchet mechanism inside the chamber or cool water circulating around or through the chamber with some sort of flow regulator?

Something inside the chamber might work, but how to make it "adjustable" from the outside once the chamber is finally soldered or clamped shut? I don't want to have to disassemble the thing just to make adjustments I want to be able to make adjustments while the engine is running.

Some sort of screw adjustment on the outside extending into the chamber? An adjustable "stop" on the displacer rod, probably with yet another rod of some sort driving some louvers or something?

Anyway, the simplest thing I've been able to think of so far is something along the lines of what was mentioned earlier (quoted above).

The cooling should begin, in my estimation, precisely at the moment of maximum internal pressure. After that it's all down hill anyway. Accounting for some delay before the actual cooling begins, actuating the cooling "chamber"louvers or whatever should happen just a moment BEFORE peek pressure is achieved inside the chamber.

I'm imagining something very simple kind of like one of those plastic pop-up Turkey thermometer things that let you know when the Turkey is done, but along the lines of the secondary "piston" forced out by the change in internal pressure mentioned above but this "piston" consisting of little more than a sleeve attached to the cylinder and a "pin" about the same diameter as the displacer rod, but only about 3/4 's of an inch long.

This could somehow work against a spring or something. The spring tension could be adjusted by a screw so that the pin only moves when the desired internal pressure is reached.

The pin could tug a rod attached to something like the butterfly or choke valve inside a carburetor.

If the Hot Air inside the chamber can be set to swirling in some circular motion all that would be necessary is to open the butterfly to allow that circulating air to pass further up and through some cooling fins.

It seems like a lot to do, considering the device may have no effect on engine performance whatsoever, but we won't know until someone tries it, right?

I was also thinking some sort of "four stroke" engine with a heating cycle followed by a cooling cycle might work rather efficiently, but that is probably getting a bit beyond the little model I've already started.

To summarize, what I'm so far picturing is something functionally similar to a household well pump pressure regulator attached to the cylinder.

When the pressure reaches a certain point a pin pops up.

Inside the chamber the other end of the pin pulls a butterfly valve open. thus allowing circulating air in the chamber to pass through some cooling fins that are otherwise isolated.

When pressure falls back down below a certain point, the pin returns to its original position closing the butterfly valve, now everything is set for another hot air blast.

A slightly more complicated version, might be some sort of rocker arm.

The "Pin" pops out pushing a rocker arm which drives a thinner rod down actuating the valve or louver or whatever it might be that temporarily prevents the cooling fins from working until the exact moment we actually want them to work.

The "outside" part of this mechanism could be sealed (if necessary) inside a little chamber attached to the outside of the displacer cylinder, and adjustments could be made by means of a screw which is accessible from the outside of the attached chamber, similar to a how a deep well water pump switch is activated from internal water pressure while regulated from the outside and being adjustable by the turn of a screw.

This may be a bit too much for me to attempt to incorporate into this little bean can, but if I can figure out a simple way to do it, I might just give it a try.

I'm not sure I'll have enough head room in this little can for all this though. I may have to swap the bean can out for a taller soup can.

The whole purpose of the displacer is to move the enclosed air from an external heat source to a heat sink. I think this is the genius of Stirling's design: there are no valves or complex passages.

Keep in mind that you probably want to keep your displacer as light as possible, since moving it (in conventional beta and gamma layouts) back and forth requires a change in momentum and is a source of friction. The more massive the displacer, the greater the loss of kinetic energy.

A Ringbom Stirling engine is a odd design: the displacer is not linked to the flywheel or power piston. Instead, a Ringbom uses the change in internal pressure to push the displacer. A shaft is connected on one end to the displacer and is exposed to the outside environment on the other end. Because the shaft takes up volume, the shaft will function almost like a second (smaller) power piston, moving out of the displacer cylinder when the internal temperature rises in order to help equalize the pressure on both sides. When the internal pressure decreases, due to the power piston moving to increase the internal volume, the displacer shaft is pulled back in due to the drop in internal pressure.

The above has a very important principle involved. There is a lag between change in volume and change in pressure. It takes some time (albeit a short time) for heat to increase the pressure in the system enough to affect the piston. This is why the displacer and power piston are out of phase. Many experiments have demonstrated that optimal linkage lies somewhere between 80 and 100 degrees. Ultimately, what is important is that the displacer lead the power piston so that the air inside the system has time to heat and expand before it moves the power piston. If the system were set-up so that maximum heating (displacer away from the hot side) was to occur at minimum volume (power piston at TDC) there is nowhere to go, in terms of heating, but down from that point. In other words, the system has peak power input before the piston has even had a chance to move. By the time the piston is at the halfway mark, the displacer has moved air away from the hot side and the pressure in the system would already begin to decrease.

While I certainly wouldn't discourage experimentation, I would recommend either obtaining or building a conventional Stirling that you could observe and perhaps tinker with for yourself. The basic design is incredibly elegant. While their is plenty of room for improvement, you may be surprised how well a straight-forward layout may suit your needs.

-Stefan

Thanks for all the very helpful clarifications and for the most part I agree with everything you say, however I'm not sure that the following statement applies to what I'm working on at this point:

Many experiments have demonstrated that optimal linkage lies somewhere between 80 and 100 degrees. Ultimately, what is important is that the displacer lead the power piston so that the air inside the system has time to heat and expand before it moves the power piston. If the system were set-up so that maximum heating (displacer away from the hot side) was to occur at minimum volume (power piston at TDC) there is nowhere to go, in terms of heating, but down from that point. In other words, the system has peak power input before the piston has even had a chance to move. By the time the piston is at the halfway mark, the displacer has moved air away from the hot side and the pressure in the system would already begin to decrease.

Technically my "displacer is not a displacer or even a regenerator and would not operate in the manner you describe here.

Aluminum is about the lightest metal available, except possibly titanium or some other metal I'm not aware of. Made without the rather heavy spacers I happened to use and without the big gob of JBWeld and with something lighter than a tin can as a housing, I think this could be made much lighter.

My theory or idea is to use this heating element in such a way that it maintains a temperature which is always much hotter than the air in the chamber regardless of its direction. Therefore it would, as long as it is exposed to the air in the chamber, be transferring heat to the air.

Therefore the point of highest pressure, or greatest expansion would be somewhere around the time that the "heating element" is back down at the hot end.

I'm assuming that it would be at this point that the piston should be near to what you describe as TDC.

In this design "maximum heating" would be when the "displacer-like heating element" had returned to the hot side, not as you describe: "away from the hot side" Therefore the timing would be quite different from the typical Stirling engine.

Getting the element "extra hot" to accomplish this might be achieved by means of the lengthy "dwell" of the element near the heat source and its rapid movement through the chamber and rapid return to its starting point at the "hot side".

Typically the displacer would take a rather leisurely stroll through the chamber and would therefor already have cooled down by the time it reached the cold end. If the pace could be picked up a bit it would probably still be giving off heat even on its return voyage back to its starting point at the hot end, especially if the heat sink at the cold end could be temporarily isolated while this was taking place.

Of course this idea just flowered in my head less than 24 hours ago I believe and has yet to be tested.

If a "straightforward" or conventional layout would suit my needs, no one would be happier about that than I would be. But if this were the case then why can't I just go to the hardware store tomorrow and pick up a Stirling generator?

I've read numerous posts in this forum and elsewhere that a Stirling engine, especially of the home grown variety would not be a suitable power source, in fact I've already been give much the same advice here, that I would be better off with a wind generator or photovoltaics.

On the other hand you may be perfectly correct as back in the 1800's someone COULD very well go out and buy a large "REAL" power producing Sterling Engine. With todays light weight materials I don't see why these things are not easier to come by. Though if you can afford to buy a yacht, then you can get one of very compact and efficient design, for a price.

But a "tin can" engine made to 55 gallon drum proportions would satisfy my needs as long as it could charge some 12 volt batteries.

Anyway, I've gone this far with the little "supercharged" bean can, it would be a shame not to follow through with it and see if it works as anticipated or not at all.

Don't you agree?

The whole purpose of the displacer is to move the enclosed air from an external heat source to a heat sink.

Granted that I am new to this game and probably don't know what I'm talking about, I will have to, at least in part, disagree with this statement.

Obviously moving air back and forth in the chamber is what the displacer does, but taking into consideration the overall purpose of a Stirling Engine, this is a little too simplistic an explanation.

The whole purpose is not to move the air from one end to the other but to extract energy in the process. That is, to introduce some resistance to this flow in order to extract energy, but not so much resistance as to bring the process to a complete halt.

This is true about any energy flow. Electricity for example is a flow of energy through a wire. By introducing "resistance" in one form or another, this energy can be extracted for various uses. If the resistance is too great however, the flow of energy comes to a stop and no energy can be extracted. Same situation with a water turbine or a steam engine or a wind turbine.

In each case there is a flow of something and a resistance to that flow which is used to extract some of the energy from the flow.

In this case we are talking about a flow of HEAT energy.

The HEAT is flowing from the heat source to the heat sink. The purpose of the Stirling engine is to introduce resistance to that flow in such a way as to extract some energy from the flow without stooping it.

The flow can be controlled and directed through certain channels by means of insulators. Without insulation on wires the energy in the wire would likely short out on something.

The exposed sides of a tin can are like exposed wires dissipating energy instead of forcing that energy to pass through our "resistor" which in this case is the air chamber or chambers through which this HEAT ENERGY is being forced to flow.

More rapid HEAT transfer passing through the chamber is like more VOLTAGE in a wire or faster water flowing over a water wheel or a stronger wind. A greater volume of heat transfer is like Higher Amperage or a greater volume of air or water directed at or through the appropriate "resistor" of whatever shape or form.

The means of extracting energy, our "resisting" in this case is the Stirling Engine itself. More specifically in this instance the resistor is the air which happens to expand as a consequence of "resisting" the flow of heat providing us with a means of extracting some energy. This expansion and contraction might be likened to the magnetic field around a wire through which there is a flow of electricity. The electricity does not power the motor directly but rather through the control of this electro-magnetic field.

A stronger "magnetic field", or the stronger the expansion and contraction of the air, the greater the potential horsepower.

The displacer's primary purpose then is not to move the air but to facilitate it's expansion and contraction so as to extract some energy as this expanding and contracting air forces movement in the piston.

For this to work, we don't really need a displacer at all. The displacer just helps speed up the process.

We could extract energy from an empty barrel sitting in the sun, though it would have a very lengthy cycle. Day=Hot==expansion Night=Cold=contraction. Our piston attached to the barrel would move imperceptibly slow, but it would move just the same so long as there was an air tight seal between the piston and cylinder wall.

What I've done here with this new design is throw out the book in regard to the rules about how a Stirling Engine is supposed to operate, and have gone back to fist principles and tried to devise a more efficient means of heating and cooling air in such a way as to extract some energy.

The "Thing", displacer, regenorator, preheator, heat element or whatever you want to call it is simply a device for heating air so that the air will rapidly expand. It's sole purpose is to heat the air and consequently cause the air to expand as rapidly and forcefully as possible. This is accomplished by providing a greater metal to air "surface area". As far as possible we want every molecule of air to come into contact with a hot metal surface. Most home built Stirling engines leave much to be desired in this respect I think. There is a lot of dead air space that could be more effectively heated by introducing more metal to air sutface area into the design.

Certainly the design I've come up with is not the ideal, and certainly not the only design possible for accomplishing this.

After this "thing" has done it's job of heating and expanding the air, in my opinion, it should simply get out of the way and if possible, completely isolates while the air is exsposed to a heat sink, which was also isolated during the heating process.

If the engine could be allowed to get hotter and hotter and hotter, theoretically we wouldn't need to get rid of the heat, just so long as we could keep expanding the air a little more each cycle, but practically speaking this would eventually cause a meltdown of the materials of which our engine is made.

Therefore, after the first expansion of air there has to be a return to the beginning. The hot air that has already done its job has to be cooled so the process might start over.

The problem as I see it is that in the typical Stirling engine design, the heating and cooling phase OVERLAP in that as Air is being "displaced" for the purpose of heating and expansion there are a lot of "leaks" or "short circuits" in the system where the maximum possible rate of expansion is being reduced or drained due to the fact that the air is still being "cooled" and contracted at one end of the system while we are attempting to heat and expand the air at the other end.

I'm all for simplicity and elegance, but my idea of introducing some sort of extra chambers or valves is an effort to patch up what appear to me to be "energy leaks" in the system robbing it of its horsepower. These leaks are like holes in the valves of an internal combustion engine, or broken piston rings or a scored cylinder allowing "plow by"

The engine may still run under such conditions but it will have been robed of its power.

Stirling may have been a"genius" but in my opinion the basic designs I've looked at seem an attempting to run a gas engine with burnt out valves.

The displacer itself is, as I see it, a kind of valve, though of a rather inefficient and "leaky" design.

Probably, in the end, this thing I'm working on should be called something other than a Stirling Engine though it is still based on Stirling Cycle principles of alternatively heating and cooling the air within a sealed chamber and extracting some of the energy from the resulting expansion and contraction through the attachment of a piston cylinder with a moveable piston that can work against the expanding and contracting air.

My purpose in this long winded explanation is not to be argumentative, but rather simply to make my reasoning on this project as transparent as possible.

If my reasoning is faulty, then I certainly want that pointed out to me, so keep the comments coming, even though it may appear I am being somewhat disagreeable in my response.

It may turn out, by experimenting and actually building this thing, that my reasoning is all wrong. I wouldn't doubt it. I've occassionally been wrong before.

Whatever way this little bean can experiment turns out, hopefully something will have been learned in the process.

Tom,

I think you may have blurred the purposes of the displacer and regenerator. While they can be physically the same component of the engine, they don't necessarily have to be. In fact, a regenerator is not necessary for a Stirling engine to produce power, it just improves its efficiency.

Examining Carnot's formula for efficiency:

(T(high)-T(low))/T(high)

Where T(high) represents the hotest temperature in the system and T(low) is the coolest temerature in the system, you will notice that it is the difference between the two temperatures that is most significant, not the high system temperature. What this means is that an engine may run at relatively low temperatures but be very efficient. This is what the Stirling engine accomplishes. Some engines have reached between 40% and 50% of theoretical.

Such high efficiency (note that this does not mean high power output) is possible, in part, because of the regenerator. The regenerator passively cools and heats the air around it depending upon which one has the higher heat level. This is another reason for the displacer: it move the air back and forth over the regenerative surface as the cycle progresses.

I actually like your example of the can sitting in the hot sun cooling in the evening. Theoretically, if we had a way of maintaining an engine that completed one cycle a day, there would be no need for components like a displacer. However, there would be absolutely no regenerative effect in this engine as once the chamber's pressure had been increased during the day, all of its heat would be lost at night.

The displacer, in its simplest form, can act as a regenerator by absorbing heat energy from the air that passes by it in one direction then releasing that heat energy back to the air as the air passes the other direction. The heating element that you are proposing doesn't seem to have this effect. It simply heats the air when present and allows the air to cool in its absence.

This isn't to suggest that your design won't work. As long as you are cycling between a high and low temperature and using the change in pressure to do work you should be able to generate useable power. That's the principle for all heat engines.

You asked earlier that if a conventional Stirling engine could suit your needs, why couldn't you just pick one up a the local hardware store. The answer, I think, has several parts. Internal combustion engines are well understood, cheap to manufacture, and generate large amounts of power for their size. Stirling engines, on the other hand, have not been as thoroughly researched, have greater cost demands on materials and workmanship, and generate far less power for their size. They are just not economically competitive at this time.

Nevertheless, you have been providing some great discussions for this forum, and whether it turns out to be a Stirling or not, I am looking forward to your progress!

-Stefan

Thanks again for taking the time to make those clarifications.

I have "blurred" the displacer and regenerator quite a bit, in terms of combining both functions in one unit.

That wasn't my idea, I saw an example of it on someones home built Stirling website some time ago, though I can't really say exactly where.

My basic goal, is to build an engine that can be powered from whatever heat source I have available. Generally a wood stove or the sun. but ultimately something that could turn a generator, whether it be a second hand car alternator or a custom built permanent magnet generator or alternator.

It would be nice if I could just go to the auto salvage and find a used alternator for it to turn, but a car alternator requires a very high RPM and at least about 8 horsepower behind it to charge a 12 volt battery, so that may be out of the question.

On the other hand, if a Stirling Engine has been built to power a submarine, I wouldn't rule out the possibility altogether that a home built engine might be able to achieve that kind of power, though possibly not the required RPM.

If I have to build a custom generator for it, that will have to be another learning experience. I know less about winding an armature or whatever it is you have to do than I know about Stirling Engines.

Today I think I came up with an answer to my problem regarding all the complicated valves and what not for "isolating the cold" while heating the air chamber.

Cold air falls and Hot air rises. I assume we can all agree on that.

Though that may not be true in an engine with a displacer working back and forth keeping the air agitated.

Since my "heating element" is not designed or intended to move or agitate the air or "displace" it but to simply heat the air as it is lifted through it, a simple partition of some sort might serve the purpose of keeping the hot air isolated from the "heat sink

The solution I kind of stumbled upon today, while I was actually trying to do something else, is laughably simple.

It is to have a double walled air chamber, which can be accomplished simply by sticking one can inside another larger can

The heating would take place in the center of the chamber through which the heating element is lifted and drooped back down.

If space is allowed for, or if holes are drilled in the top of the smaller can, the inside of which has just been heated. This hot air will begin to migrate over the top of the smaller can and pass down through the space between the two cans by natural convection.

If a small hole (say about 1/2 inch in diameter for my small model) is also made in the bottom of the smaller can, then this descending air may travel back up through this hole to the heating element chamber, to once again be pre-heated.

No extra valves, no extra moving parts, no extra linkage or rods or "stops" or pins or regulators, just natural convection. Your "displacer" in this case is nothing more than natural convection. Rising hot air and falling cold air perform their own displacement without any mechanical assistance whatsoever!

If necessary, and I suspect it will be to achieve the sort of power output I'm aiming for, The larger outer can can be outfitted with a yet Larger can serving as a water jacket.

In this way the entire central portion of the air chamber can be heated all at once throughout its full height from bottom to top and again from top to bottom.

Then while the heating element is "resting" in it's "dwell" position, the spent hoy air in the central part migrates to the outside, drawn there by the falling cold air, which is being cooled down by the water jacket.

The air circulates in a continuous loop. There would therefore be no, or very little loss due to air resistance at any point.

Heat the inside rapidly for expansion, then allow the air to cool somewhat more gradually by natural convection! There is no forceful displacement or agitation of the air.

I'm using an aluminum beer can for the inner wall, My original bean can for the outer wall and a coffee can for the water jacket.

I've been working on an animated GIF so as to illustrate what I am hoping will be the heat flow through this device. I've also gotten most of the parts cut out and ready for assembly but I won't be able to do any more tonight.

Tomorrow when it is light out, I may be able to take this outside again and take a few more pictures to upload.

I'm still not entirely certain what the timing will be, so my plan is to have a flywheel, or two, one for the piston and one for the heating element driver, (both on the same shaft) each with numerous holes drilled through for different positioning or different "timing".

I'm unable to think of any reason why this might not work.

Here is one frame of the animation with some arrows drawn in to show the convection currents. Hopefully this will provide a better idea of the concept. At this point, the element would have just finished heating the chamber and has returned to the bottom of the chamber for re-heating while in the "dwell" position.

Something not shown, that I'm intending to include as a kind of afterthought, is a sleeve of insulation around the outside of the central part of the air chamber to help isolate the hot inner part of the chamber from the cold outer part, probably made from the top of a Styrofoam egg carton. The gray squiggly line is part of the cold heat sink, helping to cool the air as it travels down the outside shell of the chamber. The other colored squiggly lines are meant to represent the hot and cold convection currents

Again, I just tacked this image to the end of the other photos that were already uploaded, so it will be necessary to scroll to the bottom of the page to view this

http://members.tripod.com/prc_projects/photos_1.html

I finally figured out at least one way to put a lid on this thing.

I took a second small Tuna-fish can, cut the bottom off and stuck a piece of foam insulation up in it.

When the "heating element is lifted, the lid should come off first exposing the hot fins inside the tuna can. then the lid lifts the rest of the element.

I had to rearrange the fastening system, and I'm going to have to go out and try to find some thin nuts and bolts to assemble it, but I think it should work.

There are a couple other ways of accomplishing this which would not add as much additional weight, but would take a considerable amount to work fashioning small parts. More so at least than drilling out a few extra holes.

When the element drops back down to the bottom, the lid should come down after it thus retaining and isolating the heating elements while the chamber above the element cools and the element inside the tuna can
heats up in preparation for the next cycle.

This should also eliminate the worry of the assembly coming apart, as it is no longer being lifted by a patch of JBWeld.

http://members.tripod.com/prc_projects/photos_1.html

I'm enjoying watching the wheels spin in your head Tom :) You no doubt are losing sleep at night (I know I do when I ponder Stirling designs) I see it's been cleared up about the displacer. The key note being not the heat or the cold, just how fast and efficient you can get the cycle between them running. The air must cycle hot, cold, hot... or the piston won't keep moving or fast enough to be useful. How quickly and how far the temp swings each cycle will determin the power. The displacer must (or some other means of air movement) move the air to make that happen. I think the biggest thing you have mentioned has been lack of surface area on the inside of the chamber. I see very possible gains there if done right. On the other hand, don't cause too much restriction of air flow in the process.

I also like the day / night cycle example although it would need to be very large to be useful. Maybe it could built pressure in a sealed tank and move a lot of water through a small turbine? Then on cool down, the flow would reverse. It would need some kind of valve system (not to mention two tanks, one hot and one cool or shaded) and timing control to wait for both peaks. Not a bad idea though.

Tying to visualize the air movement in this latest design, I've been thinking that this convection movement may turn out to work better than I ever imagined.

While the heating element remains stationary in the "dwell" position and with its lid on. The heat coming from beneath the element will have a tendency to rise. Also the cold air moving down the outer shell will have a tendency to push the heat into the element.

But the heat will have nowhere to go. Or will it?

It seems to me that at this point, the rising hot air will have a tendency to transfer it's heat to the metal fins inside the element and the metal will act like a heat sponge allowing the hot air entering the element to cool and contract, though the heat will not be lost as it will have been absorbed into the metal on the same principal as a "regenerator".

In a sense then the heat will be "pumped" into the air chamber in controlled increments but at relatively higher temperatures than what would normally be possible as there will be little mixing between hot and cold air as would occur with normal displacer movement.

When the top comes off and the element is exposed and rises through the chamber this accumulated heat will be released back into the chamber and the air re-exspanded.

Thats the theory anyway. Whether it will work in actual practice remains to be seen.

I still only have a general vague idea about the timing that will be necessary, and have as yet done no work on exactly what form the flywheel assembly or mounting will take though I have a few ideas in mind, it seems I never end up with exactly what I set out to do.

I'm wondering if I should be optimistic and include a power take-off of some form :smile:

I'm still thinking about what I read about adding a small amount of water to the displacer chamber to improve the performance of the engine.

Though, on the site I was reading, no explanation was given as to why this might be true, I'm inclined to think that HUMID air would increase the temperature differential on the following theory of operation:

When HOT and HUMID air is introduced into a cold chamber there would tend to be some condensation (Phase Change). This condensing water would decrease the air temperature and pressure of the air more so than dry air alone. When reheated, the water would tend to evaporate and the reverse would be true.

If in addition to a very small amount of water, some SMOKE were introduced to the chamber, the water would have something immediate in the air to condense upon, forming a cloud within the chamber, thus the very small amount of water might remain suspended in the air rather than condensing on the chamber walls.

If a small amount of water were added, just enough to create a humid environment but remain suspended in the air, I don't see that this would have much of a damaging effect, especially if the parts exposed to the humid air were made of some non-corrosive material.

If all works well, you can determine the timing of the system by moving your heating element by hand and watching the response from the power piston.

Cartech: I like the reverse flow idea for the passive solar engine! I would still want to avoid valves and such if possible, but at least you've found a way to get a second phase out of the thing.

Tom: I'm beginning to suspect that your regenerator is going to function in a more traditional way than you may have intended: as a displacer. Ultimately, you're working model will clear much of this up, so keep building! I look forward to your success no matter what form it manifests.

-Stefan

I've been somewhat stalled in this Stirling Engine Project.

After thinking about it for a while, some of the ideas that at first seemed they might work have, on further contemplation, started to look like they don't make much sense, like having the water jacket surrounding the entire engine, including the heat chamber. There doesn't seem to be a whole lot of logic in that.

I came up with this rough sketch of a possible modification, with the water jacket on top for rapid cooling and an insulated heat chamber on bottom for heat retention.

http://members.tripod.com/prc_projects/photos_1.html

Bottom of page.

This would still rely on convection, to some degree, but with the convection in the cold area isolated from the convection in the hot area.

Otherwise, I think I've gotten together most, if not all of the parts and pieces I'll need to finally put this thing together.

I'm inclined however to think that the first
Solar design, with the flat plate type heating chamber on top was an all around better arrangement and probably much easier to build.

The extremely simple and easy to build looking design illustrated on this website looks like something I might be able to utilize for this backyard project as well:

http://physeeks.dyndns.org:8000/Stirlin ... -body.html

I'm wondering what sort of power output one could expect to get from such a contraption if something like 55 gallon barrels were utilized instead of mere soda-pop cans.

I like the water cans idea. Looks easy to make and if done on a bit larger scale than coffee cans you could mess with stroke etc. I could also use a better bearing than wire through aluminum. Doesn't sound like it's of much use if the RPM is that low though. It would need serious torque if it's to be useful. Not sure if I get how the connecting rods are being kept in line, that too would be important. No real seals or tight fitting needed. Just make all the bearings low friction and it would be fun to watch though. Might just be the back yard power plant your looking for. BTW, Northern tool sells a wind generator for about 700.00 USD. Looks perfect to charge batteries.