Stirling Engine Thermodynamics

[Tom Booth]

.....Ya, survey says "opposing", lets get on the same page and use "with" then.

Well, if you want to get technical about it, the expanding gas is pushing against or in opposition to the inertia of the piston and crankshaft and whatever else is attached to it. Either way I think "against" is more appropriate than "with".

I didn't say anything about the displacer cooling down either. The air or gas cools down as a result of expending its own kinetic energy........but you did! "Rather the air in the displacer chamber, being heated and expanded to do work against the piston would cool down...." your words and you were clear this happens at this point. It doesn't. And don't come back with just the air there heats up, it just compounds your lack of understanding how these engines work.

LOL...

I think I know what I intended there, you are just reading it wrong. The subject of the sentence is "the air in the displacer chamber". Perhaps an additional comma would make the intended meaning clearer to you: "Rather the air in the displacer chamber, being heated and expanded to do work against the piston(, comma) would cool down...."

(i.e. the AIR is heated, the AIR expands, the AIR does work against the piston, the AIR cools back down as a result of expending kinetic energy to do work against the piston.)

Discount what way too easily ?........A flywheel isn't doing any appreciable work.

Not as much work. It's no longer blowing air around the room. I think that should be fairly obvious.

.........Unbelievable! No Tom, it is not obvious. You have to get some Stirling models and make the observation yourself someday.

Ummm... well, I built one. Without a fan. It didn't blow any air around the room.

Just because in a Senft engine the fan is incorporated into the engine it doesn't mean the extra work needed for the fan to push the air can be discounted any more than if a generator were permanently coupled to the crankshaft.

..............now you got lost as this relates to your theory. So this extra work will cool the engine how?

I think I've already made this abundantly clear. When a gas is made to do work it looses kinetic energy. For a gas, loosing kinetic energy is equivalent to loosing heat.

.........I'm sorry you haven't made any engines, but any build up of heat is not detrimental to a running model.

Really ?

Geez... I thought at a minimum it would reduce the temperature differential causing a loss of power output. I guess you consider overheating in a Stirling engine to be a good thing. Sorry, but I don't think you will find too many people who would agree with you on that one.

.........just a motivation, any luck on the "outside influence" question in Stirling that gets them running yet?

What "gets them running" was not the issue.

Your statement was: "The air does not work against a power piston". which was in direct response to my statement: "The gas in the displacer chamber is doing work against the piston reducing the temperature of the gas in the displacer chamber..."

I have no intention of going in search of some nonexistent reference in an effort to find support for your assertion.

The expanding gas in the displacer chamber doing work against the piston is the direct cause of the piston moving regardless of any indirect "outside influence".

[Longboy]

Well, if you want to get technical about it, the expanding gas is pushing against or in opposition to the inertia of the piston and crankshaft and whatever else is attached to it. Either way I think "against" is more appropriate than "with".

.....1)most people seeing the word "against" would say the expanding gasses stop the piston dead in its tracks.......2) the expanding gasses DO NOT push the piston at all in displacer Stirlings.

I think I know what I intended there, you are just reading it wrong. The subject of the sentence is "the air in the displacer chamber". Perhaps an additional comma would make the intended meaning clearer to you: "Rather the air in the displacer chamber, being heated and expanded to do work against the piston(, comma) would cool down...."
........Oh I see the subject and don't need the coma. What baffles everyone is this cool down when it sits above an open flame. I would think you would clear that up and note that, for your theorys sake, may happen elsewhere within the engine........thats if you understood how they work!
(i.e. the AIR is heated, the AIR expands, the AIR does work against the piston, the AIR cools back down as a result of expending kinetic energy to do work against the piston.)

...........Ya, this would be your theory. And you do not understand how a Stirling functions. You cannot support the theory. I know the heated air does not push, pull with or against the piston...........why don't you?

I think I've already made this abundantly clear. When a gas is made to do work it looses kinetic energy. For a gas, loosing kinetic energy is equivalent to loosing heat.

......But you just continue to bring over facts in Thermodynamics and fail to match it with Stirling opperation. But when that heat is sustained (a working,running engine), How does a Stirling deal with this loss? Or is there no loss and the theory is defunct?

.........I'm sorry you haven't made any engines, but any build up of heat is not detrimental to a running model.


Really ?

Geez... I thought at a minimum it would reduce the temperature differential causing a loss of power output. I guess you consider overheating in a Stirling engine to be a good thing. Sorry, but I don't think you will find too many people who would agree with you on that one.

......Well you pick something up from my posts about how overheating looses the temp differential. And I would find many in agreement. For they know an overheated engine will not run but they see I was talking about a running engine where this heat build up is not an issue..........why didn't you see that? The heat builds up but the engine does not stall. Why doesn't the engine stall Tom???

What "gets them running" was not the issue.
......not for me but should be big time for you as you don't understand how a Stirling runs.
Your statement was: "The air does not work against a power piston". which was in direct response to my statement: "The gas in the displacer chamber is doing work against the piston reducing the temperature of the gas in the displacer chamber..."
........thats what we both said and disagree on thats what happens in Stirling.
I have no intention of going in search of some nonexistent reference in an effort to find support for your assertion.
(unbelievable!...........he's folding his tent and taking his ball home.) You come here, quote 4-5 authors, shout Thermodynamics and think thats the way it happens in Stirling, and is just too lazy to learn about these engines! (hand me a gernade and pull the pin please)!!!
The expanding gas in the displacer chamber doing work against the piston is the direct cause of the piston moving regardless of any indirect "outside influence".

......Now you are just mad at me. That would be a bold statement by someone too lazy to do the research and discover what makes the power piston move. When you bring your theory here Tom to the form, and someone calls you out about it, we would think you would have a fundemental understanding on the hows & whys Stirling engines work to hold up your end. When you are done shoveling snow spend an hour to find out! I know you are going to, cuzz you want me to eat a big fat can of "SHUT THE HELL UP"!:mrgreen:

[Tom Booth]

...the expanding gasses DO NOT push the piston at all in displacer Stirlings.(...) ...........Ya, this would be your theory. And you do not understand how a Stirling functions. You cannot support the theory. I know the heated air does not push, pull with or against the piston...........why don't you?

The expanding gas in the displacer chamber doing work against the piston is the direct cause of the piston moving regardless of any indirect "outside influence".

......Now you are just mad at me. That would be a bold statement by someone too lazy to do the research and discover what makes the power piston move. When you bring your theory here Tom to the form, and someone calls you out about it, we would think you would have a fundemental understanding on the hows & whys Stirling engines work to hold up your end.

I'm not mad at you. I actually find you rather amusing.

You have so far offered nothing in support of your continuing assertion variously phrased: "The air does not work against a power piston", "I know the heated air does not push, pull with or against the piston", "the expanding gasses DO NOT push the piston at all in displacer Stirlings."

I am genuinely quite baffled in regard to your insistence on this point.

I'll offer a few references in support of "My" wild theory, just for your personal edification:

"The Stirling cycle involves a series of events that change the pressure of the gas inside the engine, causing it to do work."

"Heat is added to the gas inside the heated cylinder (left), causing pressure to build. This forces the piston to move down. This is the part of the Stirling cycle that does the work."

"In part one of the cycle, the pressure of the heated gas pushing against the piston performs work."

"When the displacer is near the top of the large cylinder, most of the gas inside the engine is heated by the heat source and it expands. Pressure builds inside the engine, forcing the power piston up."

http://www.howstuffworks.com/stirling-e ... /printable

"The heated gas increases in pressure and pushes the power piston"

http://en.wikipedia.org/wiki/Stirling_engine

"In part one of the cycle, the pressure of the heated gas pushing against the piston performs work."

Integration of alternative sources of energy By Felix A. Farret, M. Godoy Simoes - Pg 442 Appendix C: The Stirling Engine

"Stirling engines are heat engines with gaseous working fluid. They are closed-cycle, which means that the gaseous working fluid is always inside of the engine. It is the gas that presses against the piston."

What Is a Stirling Engine? By Isabel Prontes
http://www.ehow.com/about_4661266_what- ... ngine.html

"the pressure of the heated gas pushing against the piston performs work"

http://www.hiddenmysteries.org/science/ ... rling.html

"The Stirling engine only makes power during the first part of the cycle... In part one of the cycle; the pressure of heated gas pushing against the piston performs work."

Pollution Less Engine S.R.K.R. ENGG. College Bhimavaram

"..a Stirling can use heat from nearly any source-open flame, solar, or nuclear-to heat an expandable gas working against a piston...

"A second piston, working out of phase with the power piston and called a displacer, squeezes the working gas from one end to the other so it may be cooled and re-heated to again expand against the piston."

Popular Science August 1974

[Tom Booth]

Now please, Mr, Longboy, with your vastly superior knowledge and experience, enlighten us as to your alternative theory in regard to what causes the piston to move and explain why little old me and all these other references are wrong, inapplicable, obsolete or whatever.

[Longboy]

Now please, Mr, Longboy, with your vastly superior knowledge and experience, enlighten us as to your alternative theory in regard to what causes the piston to move and explain why little old me and all these other references are wrong, inapplicable, obsolete or whatever

...........Well Tom I am truely sorry...............that you still don't know much about these engines! No prize for you. All these references you made here, THEY ARE CORRECT and I agree with them! Your problem is you read alot but just don't pay attention before you quote. All these refs, with illustrations or animated engines next to the text, talk about the ALPHA Stirling. And since this is not the engine you refer to you can't use it to make your case. Time to hit the books some more Tom! ( Doc, they accuse me of having vastly superior knowledge. "Well Longboy, take these two sticks of dynamite and place in your pillow case, lite the fuse, it'll all be over shortly". Thanks Doc, I knew I could count on you!

[Tom Booth]

....All these refs, with illustrations or animated engines next to the text, talk about the ALPHA Stirling. And since this is not the engine you refer to you can't use it to make your case.

On the contrary, most of the references are in regard to the Stirling Cycle which is applicable to all Stirling Engines. The Stirling Cycle is what defines a Stirling engine. Otherwise the quotes are about the displacer type Stirling specifically.

On the other hand, your statement: "The air does not work against a power piston" is wrong, regardless of what type of Stirling engine you might care to try and apply it to. It as a contradiction of basic Stirling principles in ANY Stirling engine.

You've insisted that I back up my statements and I've done so. It seems only fitting to insist that you back up yours, if you can.

[Longboy]

.....Then complete the Stirling cycle. If we can agree that the expanded air is pushing down on the power piston, what forces act to bring it back up to start it running?

your statement: "The air does not work against a power piston" is wrong,

I am just running against your use of that word "against" here! I say that doesn't happen. Thats just a stubborn sticking point. Could we further the debate by me saying that the hot gasses are pushing the piston down its bore? I think we can agree that is what happens regardless of what terms to use to describe this action. If I could get from you that "outside force" also acting on the power piston I would say you have it. If not I will complete the cycle in the next post.

[Tom Booth]

.....Then complete the Stirling cycle. If we can agree that the expanded air is pushing down on the power piston, what forces act to bring it back up to start it running?

If the expanding air has pushed the piston then it has already started running.

your statement: "The air does not work against a power piston" is wrong,

I am just running against your use of that word "against" here! I say that doesn't happen. Thats just a stubborn sticking point. Could we further the debate by me saying that the hot gasses are pushing the piston down its bore? I think we can agree that is what happens regardless of what terms to use to describe this action.

If you want to agree, that's fine. However, you had made your position on the issue abundantly clear previously:

"The air does not work against a power piston"

"I know the heated air does not push, pull with or against the piston"

"the expanding gasses DO NOT push the piston at all in displacer Stirlings."

I might also emphasize one of my previous references:

"The Stirling engine only makes power during the first part of the cycle... In part one of the cycle; the pressure of heated gas pushing against the piston performs work."

Pollution Less Engine S.R.K.R. ENGG. College Bhimavaram

If you want to "complete the cycle" that's fine, but irrelevant.

In regard to some of your previous comments and questions i.e. why don't some model Stirling engines overheat and stall, I can only surmise that you are referring to display models or conversation pieces that by design have their heat input severely limited so that they are impossible to overheat.

Typically, these are beautifully constructed, finely crafted, very interesting to look at but completely useless in terms of power production.

On the other hand you have model Stirlings that are scaled down versions of larger Power producing engines. These engines are designed so as to maximize heat intake as it is the heat converted into work that produces the power for these workhorses. If they are not provided with some work to do, they overheat.

[Longboy]

If the expanding air has pushed the piston then it has already started running

........Or I just touched the brake, and the car already is stopped. Things happen between that time. Engine is not going anywhere yet. What happens in the Stirling cycle Tom?

Quote:
"The air does not work against a power piston"

"I know the heated air does not push, pull with or against the piston"

"the expanding gasses DO NOT push the piston at all in displacer Stirlings."


I might also emphasize one of my previous references:

.........This rehash isn't going to help because it all relates to your word "against". (and I see my word "push" here so you got me)!

If you want to "complete the cycle" that's fine, but irrelevant.

..........I would use that line too if I didn't know the Stirling cycle. I get that alot by those who would blow it off using words like "irrelevant". If you can't explain what happens in the Stirling cycle I understand.

In regard to some of your previous comments and questions i.e. why don't some model Stirling engines overheat and stall, I can only surmise that you are referring to display models or conversation pieces that by design have their heat input severely limited so that they are impossible to overheat.

.......Surmise? We are on the same page Tom, its MODEL ENGINES! I wouldn't have jumped into this topic if you never mentioned models. Heat input is adjustable regardless of design of the engine. Who wants to cook their engine by not limiting heat input? You openned up the topic refering to Stirling models. I was refering to your words in the upcoming qoute...........

If heat is being converted into work then the more work the engine is made to perform the cooler it should run. Maybe the problem with many model Stirling engines overheating is that they are being run without a load of any kind and therefore the heat, rather than being transfered to the load on the engine to do work is just building up and causing the engine to overheat.

No. I don't buy into that there are many models that don't run for this reason. Running models don't tend to overheat by not driving acessorys. Of items that prevent a running engine, problems in models relate to radiator capacity and design for our discussion. That heat has to be carried away to maintain the differential and physical distance, isolation and/or insulation contribute (Gamma). You can speed up a model but that doen't inpart a power increase to the point of helping your theory.

..........constructed, finely crafted, very interesting to look at but completely useless in terms of power production.

........I wish you would have openned up this topic with that line in there somewhere. Cuzz I think we are talking model engines by your own words! I talked about their low torque output so putting your theory to test on a model unlikely!

Perhaps this is already a known fact but for me it is something of a new realization and I'm wondering if anyone with more knowledge and experience in this area might be able to confirm or refute this supposition.

Modeling Stirling engines is my backround. I'm trying but had to find out if you have down the Stirling cycle. Saying the pressure working against ( or pushing down upon)the power piston and the engine runs is incomplete. Any teacher in school would hand you the paper back and tell you to complete the explanation of the Stirling cycle. Responding with "irrelevant" shows you don't have it. Atmospheric pressure pushes the power piston back up the bore. The internal air has cooled down at this point, its pressure is now below atmospheric. Cooler air takes less volume, the power piston moving up its bore decreases that volume. The engine runs!

On the other hand you have model Stirlings that are scaled down versions of larger Power producing engines. These engines are designed so as to maximize heat intake as it is the heat converted into work that produces the power for these workhorses. If they are not provided with some work to do, they overheat.

...........I have not seen where these classic engines (Heinrici, Robinson, etc.) were problematic in not doing a job and just idling. Any particular reason anyone would light them up anyway if no work needed to be done? With your proposal that Stirling would run cooler if doing more work, as in models overheating for this reason, my thoughts are more likely the engine would run at higher temps. More heat energy needed to do more work and the engine would not dissapate this increased heat to the point of cooler running.

[Tom Booth]

If the expanding air has pushed the piston then it has already started running

........(...)Engine is not going anywhere yet.

So you believe that, although the expanding hot air pushes against the piston, the piston stubbornly refuses to move ?

This would seem to be your assertion, based on your previous comments: "I know the heated air does not push, pull with or against the piston" ; "the expanding gasses DO NOT push the piston at all..." etc.

If you want to "complete the cycle" that's fine, but irrelevant.

..........I would use that line too if I didn't know the Stirling cycle. I get that alot by those who would blow it off using words like "irrelevant". If you can't explain what happens in the Stirling cycle I understand.

The question brought up in this thread is (or was); as a result of the expanding air or gas doing work to push the piston, does the air or gas loose energy and drop in temperature. Yes or no. What does or doesn't happen during the rest of the cycle is largely irrelevant.

You have asserted repeatedly that the expanding gas does not push, pull or otherwise influence the piston "at all". That the engine "is not going anywhere" as a result. This is another issue, (for you at least, apparently) relating to the expanding gas doing or not doing any work to push the piston. Again, what does or doesn't happen in the rest of the cycle is irrelevant as to this second issue you have manufactured.

..........constructed, finely crafted, very interesting to look at but completely useless in terms of power production.

........I wish you would have openned up this topic with that line in there somewhere. Cuzz I think we are talking model engines by your own words!...

I mentioned model engines in passing, but the question of an expanding hot gas loosing heat and getting colder as a result of giving up its kinetic energy to do work is a question that primarily relates to engines, large or small, model or otherwise that have some potential for performing some work. Such display models, which by design, have no such capacity, do not fit into that category, though the theory would still apply in principle.

The principle, which is the topic of this discussion, if true, would apply to any Stirling engine. The discussion is not limited to model engines.

Atmospheric pressure pushes the power piston back up the bore.

And please explain how atmospheric pressure pushes the piston "back up the bore" if, as you have asserted, the piston has not moved down the bore as a result of the expanding gas pushing it down the bore in the previous phase. (i.e. "Engine is not going anywhere yet")

With your proposal that Stirling would run cooler if doing more work, as in models overheating for this reason, my thoughts are more likely the engine would run at higher temps. More heat energy needed to do more work and the engine would not dissapate this increased heat to the point of cooler running.

Thank you for your opinion.

But the question is, would the engine run cooler if it were performing some work, assuming a fixed heat input, such as a steady burning candle or the focal point of a parabolic solar reflector.

"More heat energy needed to do more work" would not make either the sun or the candle burn brighter so as to satisfy the engines increased appetite. Rather, the additional heat needed to meet the the added work load would be drawn from the excess heat that would have otherwise been dissipated to the heat sink causing the engine to overheat. (theoretically).

Lets say that an array of solar powered Stirling engines are out in the desert, connected to the power grid feeding energy to a city. It had been a hot sunny day and everyone had their air conditioners going. A storm passes over the city (but not the desert) cooling things off, so everyone turns off their air conditioners. Now the engines are running at full tilt, but the power load has dropped. The power grid can no longer accommodate the
energy output from the solar array. The generators connected to the Stirling engines have less of a load and so turn easier. The Stirling engines turning the generators now have less of a load and begin freewheeling. Less heat is converted into work but the heat input from the sun has remained constant so the engines begin to overheat.

If this is not a problem then I fail to understand why someone would be applying for a patent for a device intended to solve just such a problem as previously noted:

"When powering a Stirling engine with solar energy from a mirror array, the solar energy supplied to the engine is substantially constant, and so the load must be maintained at a sufficient level to use all the solar energy supplied by the mirror array. If the load drops, the engine very quickly overheats and is damaged.

"...Thus when overheating is detected the mirror segments are moved out of focus to reduce the amount of energy received, such as when the load on a Stirling engine drops.

http://www.wipo.int/pctdb/en/wo.jsp?IA= ... SPLAY=DESC

If this is true, in principle, that given a constant heat input, having a load on a Stirling engine keeps it running cooler, then the principle should apply to any Stirling engine, including model Stirlings running on the steady heat input from a tea candle.

Certainly someone might vary the heat input in one way or another or cool the overheating engine by some other means, (usually by the application of some ice cubes) but that is not the issue.

[Tom Booth]

Tom,

At the risk of upsetting an already tipping cart of apples I think you're confusing terms here.

Like which terms in particular ?

Don't get upset with us for trying to show what's going on inside the COMPLETE engine cycle.

Who's upset ?

If you go back and read my first post in this thread, I've already given a very brief outline of the basic complete Stirling cycle. I see no need to go into exhaustive detail in regard to a subject everybody is already well aware of.

I am by no means an expert on the thermodynamics involved, but I don't think one needs to be to understand the principles involved.

A rash assumption.

The displacer is being acted upon in a Stirling engine by the heat and cold during the complete cycle.

I think you would need to specify what type of Stirling engine you are referring to here. In general, the displacer isn't acted upon by anything other than the crankshaft which is driven by the power piston which is driven by the expanding gas. The momentum imparted to the crankshaft and flywheel carries the engine and all its various working parts, including the displacer, through the rest of the cycle. Unless you are talking about a free displacer type engine. In that case, it seems to me, the displacer is driven primarily by pressure changes.

The power piston is not, at least to the extent you are suggesting.

"Is not" what ? "being acted upon... by the heat and cold" ?

I have not stated or suggested, nor do I believe that the power piston is "acted upon" directly by temperature changes of any sort.

The air or gas is made to expand by the application of heat and contract by transferring that heat to the heat sink as I've already stated from the start. The pressure changes due to the expansion and contraction of the gas act upon the piston.

The power piston is being acted upon by the EXTERNAL air pressure in its inward stroke. Without a free flow of atmosphere on the external side of the power piston the engine WILL NOT RUN.

Unless you are talking about a modern pressurized engine. I would not consider highly pressurized nitrogen for example "a free flow of atmosphere".

When the power piston is moved outward it creates a low pressure situation within the sealed container of the engine.

Right. Just like when I blow up a balloon. The high pressure makes the balloon expand and the resulting expansion of the balloon creates a low pressure inside the balloon. brilliant! LOL...

This low pressure allows the already expanding heated air to expand further

Even more interesting. The expanding heated air expands even further due to its low pressure. astounding!

Good thing I've got you guys with such critical thinking to correct my sloppy thinking.

and increases the effect on the displacer during its heat induced movement phase.

heat induced movement phase.

And the movement of the displacer has nothing to do with the momentum of the flywheel.

I'll assume again you are referring to a free displacer type engine.

The question brought up in this thread is (or was); as a result of the expanding air or gas doing work to push the piston, does the air or gas loose energy and drop in temperature. Yes or no. What does or doesn't happen during the rest of the cycle is largely irrelevant.(edit: in regard to that question)

No, Tom, it is highly relevant, and I attempt to show why above. One cannot isolate on part of the Stirling cycle from the others and still expect to have a working engine.

Certainly one needs a full cycle for a working engine. So what.

One can examine any one part of that cycle one chooses.

That heat is shed by means of radiation.

And none whatsoever by being converted into work.

Thanks for your opinion.

The load on a Stirling engine has very little to no effect on heat transfer

No, not "heat transfer" directly.

However, if some of the heat is converted into work, then this would effect the amount of heat remaining which would then need to be dissipated by heat transfer to the heat sink.

The more heat left over which is not converted into work, the more heat there is that needs to be dissipated.

Perhaps you would care to give your opinion in regard to the statements made in the patent application previously noted:

"When powering a Stirling engine with solar energy from a mirror array, the solar energy supplied to the engine is substantially constant, and so the load must be maintained at a sufficient level to use all the solar energy supplied by the mirror array. If the load drops, the engine very quickly overheats..."

If as you say: "The load on a Stirling engine has very little to no effect on heat transfer", what is this guy talking about ?

Do you suppose he and I are suffering from the same ignorance or delusion?

If as you say, you are "by no means an expert on the thermodynamics", can you really say with confidence that this patent is worthless and based on a fallacy rather than acute observation and experience, along with a thorough understanding of the thermodynamic principles involved, which you confessedly lack ?

[Longboy]

So you believe that, although the expanding hot air pushes against the piston, the piston stubbornly refuses to move ?

This would seem to be your assertion, based on your previous comments: "I know the heated air does not push, pull with or against the piston" ; "the expanding gasses DO NOT push the piston at all..." etc.

This isn't helping Tom. Explained my use of these lines already. We have a running engine, the power piston recipricates cause the Stirling cycle is completed.

The question brought up in this thread is (or was); as a result of the expanding air or gas doing work to push the piston, does the air or gas loose energy and drop in temperature. Yes or no. What does or doesn't happen during the rest of the cycle is largely irrelevant.

......Already answered, its a part of Thermo law.

You have asserted repeatedly that the expanding gas does not push, pull or otherwise influence the piston "at all". That the engine "is not going anywhere" as a result. This is another issue, (for you at least, apparently) relating to the expanding gas doing or not doing any work to push the piston. Again, what does or doesn't happen in the rest of the cycle is irrelevant as to this second issue you have manufactured.

This issue is totally yours now. And I only deal with running engines. This is a sticking point with you that I already addressed being related to your repeated use of "against". Time to drop it!

And please explain how atmospheric pressure pushes the piston "back up the bore" if, as you have asserted, the piston has not moved down the bore as a result of the expanding gas pushing it down the bore in the previous phase. (i.e. "Engine is not going anywhere yet")

....That would be because the Stirling cycle, which is IRRELEVANT to you, has not happened. You do want questions answered or debated based on a running engine......are you conflicted Tom? If you have to have someone explain the importance of atmopheric pressure in Stirling then you still haven't got it and this debate goes nowhere. 3rd time in same post, you run back to what I said. Try to warm up to the idea that we have a "running" engine now to play your theory upon!

But the question is, would the engine run cooler if it were performing some work, assuming a fixed heat input, such as a steady burning candle or the focal point of a parabolic solar reflector.

....... I would say steady loads upon an engine would result in steady operating temps. A Stirling engine not driving an accessory (load) runs cooler because less input heat is needed for the Stirling cycle (running). Not because more heat is dispersed through its radiator or directed to help drive a load.

Rather, the additional heat needed to meet the the added work load would be drawn from the excess heat that would have otherwise been dissipated to the heat sink causing the engine to overheat. (theoretically).

.........If drawing a load and the engine runs with this load you cannot equate this heat as being "excess". It would be........"operational" heat load. I don't know if in industrial Stirling engines this radiated heat can be recaptured/ recycled to contribute to its heat input. I think this conflicts with Thermodynamics. If so this would mean less virgin energy to continue the process of pulling the load. If engine is pulling this load and continues to run, there is no overheating.

Lets say that an array of solar powered Stirling engines are out in the desert, connected to the power grid feeding energy to a city. It had been a hot sunny day and everyone had their air conditioners going. A storm passes over the city (but not the desert) cooling things off, so everyone turns off their air conditioners. Now the engines are running at full tilt, but the power load has dropped. The power grid can no longer accommodate the
energy output from the solar array. The generators connected to the Stirling engines have less of a load and so turn easier. The Stirling engines turning the generators now have less of a load and begin freewheeling. Less heat is converted into work but the heat input from the sun has remained constant so the engines begin to overheat.

If this is not a problem then I fail to understand why someone would be applying for a patent for a device intended to solve just such a problem as previously noted:

........I haven't seen the patent but in a pratical view, if there is no call for for more kilowatts, why would you continue to dirrect the sun on these engines to the point of overheating them anyway? Is this patent for some kind of monitoring gear that can move the mirrors away from the engines at the time they begin to overheat? Is it explained why they overheat with reduced load? Patents are filed for the usual reasons anyway. Cost, time, efficiencys. Other wise expressed as "less, less, more!

If this is true, in principle, that given a constant heat input, having a load on a Stirling engine keeps it running cooler, then the principle should apply to any Stirling engine, including model Stirlings running on the steady heat input from a tea candle.

I would say an increased but constant heat input is needed by a Stirling to drive a load and its radiator capacity should be adequate to disperse this increased heat input to prevent an overheat condition.

[Tom Booth]

Tom,

At the risk of upsetting an already tipping cart of apples...

Tom,

I really was only trying to help. I see the above response as mean-spirited, and the bold portions highlight my findings. Think whatever you want. I'm done here.

RS

I apologize,

Mr "longboy" has been making rather hostile and abusive comments towards me throughout - to the effect that I have no right coming to this forum to present my ideas without first having a basic grasp of Stirling engine principles... (which I see he has since gone back and edited out - understandably so - since he has thoroughly demonstrated his own lack of such understanding).

My response to you was not mean spirited, just over-defensive and perhaps miss-directed.

Again, my apologies.

[Longboy]

Mr "longboy" has been making rather hostile and abusive comments towards me throughout - to the effect that I have no right coming to this forum to present my ideas without first having a basic grasp of Stirling engine principles... (which I see he has since gone back and edited out - understandably so - since he has thoroughly demonstrated his own lack of such understanding).

.....Try to relax over there Tom....have a doughnut! I do understand there are those who come to the forum without the Stirling cycle understanding. You have been accommodated here. Others have read this thread and see my proding and razzing to get from you the Stirling cycle was in vain. None of my razzes on you have been edited out. All my "self depreciating" text is still there too! If you want me to tone it down I can do that. My last post yesterday shows signs of that. Do you have anymore about that patent issue?

[Tom Booth]

Mr Longboy,

From our earlier discussion:

If the engine is not doing work, then the heat will gradually build up and result in a gradual reduction in the temperature differential and consequently a reduction in torque.

.............That does not happen! Not for the reason of not doing work. You are not considering all the factors that go into the build of a Stirling engine that prevents this scenario.

On the other hand, if the engine is given some work to do at the start, then there should be more heat being converted into work, less heat build up, a gradual increase in temperature differential and a consequent gradual increase in torque.

...........You can't back that conclusion up!

Lets see:

Here are some basic operating instructions for a Stirling Engine developed for use in third world countries by VITA Technologies:

It briefly explains the principle I have outlined above, using slightly different wording, but the basic principle is the same. I have highlighted the pertinent material:

Typical operating instructions are as follows:

1. Make sure the engine is in good operating condition and
the hopper is full of fuel.

2. Start a fire in the burner with kindling (e.g., wood shavings,
dried leaves), and operate the air blower by hand
until the interior of the burner is sufficiently hot to
receive and ignite the fuel from the fuel feed.

3. Hand operate the combustion air blower and the fuel auger
until the heater head of the engine reaches a moderate
temperature (about 300[degrees]C). The engine is now ready to
start.

4. Turn the flywheel over, and the engine should begin to run
on its own power immediately (easy starting is one of the
best features of this engine).

5. Allow a short time for the engine to pressurize itself and
to drive the burner until it is at full operating pressure
and temperature. During this time, the engine will gradually
grow stronger and more capable to do work. The load
can be increased as the engine grows stronger.This happens
automatically if the engine is attached to loads such
as centrifugal water pumps or generators, but loads such
as saws and milling machines have the capability to stall
the engine if their load is applied too quickly. If the
engine is stalled, it can be restarted immediately by
unloading it and turning the flywheel again.

6. Once the engine is up to full power and doing its work,
the operator needs only to keep the fuel hopper full and
maintain a load. If the load is removed for any reason,
the engine will speed up, but not to a harmful degree; it
will quickly reach a speed at which its power output drops
to zero, and it will continue to run.

http://www.cd3wd.com/cd3wd_40/VITA/STIR ... IRLING.HTM

This does not explain the WHY, but it is clearly stated that by gradually increasing the load the engine "grows stronger". (i.e. increases in torque) If the load is removed, the engine speeds up and looses torque.

The load must be applied gradually to give the engine time to adjust rather than causing it to stall.

Generally, people tend to run a model Stirling engine without a load, without doing any work, and as you have described previously, it does not seem possible to have such an engine do any additional work other than keeping itself going because it lacks torque.

But the reason it lacks torque is because it has been allowed to run in a no-load condition. As explained in this paper, under such no-load circumstances, the engine speeds up and its potential for power output (torque) "drops to zero".

If a load is applied gradually, then the engine will "grow stronger".

The reason that this happens is that the excess heat which was reducing the temperature differential in the no-load condition is now being diverted to power the load. As a consequence of the heat now being converted into work, less heat reaches the heat sink and the temperature differential increases. As the load is gradually increased so the temperature differential increases and so the torque increases.

Habitually running Stirling Engines without a load has created the illusions that these engines have no torque and therefore have no capacity for doing any kind of work.

This is false.

If a Stirling Engine is given some work to do, it will compensate: i.e. "grow stronger".

If you don't do the "experiment" you will never make such an observation.