Modified "Hot" Beta engine

[Tom Booth]

I've been a mechanic working on IC gasoline engines since High school, so learned all that theory in the video when I was 16. It doesn't take much of an increase in compression ratio to cause knocking in an IC engine because they are already maxed out with as high compression as possible without causing pre-ignition. A heavy carbon build up in the cylinder head reduces the available space in the combustion chamber for example.

Stirling engines don't have ignition of a fuel mixture so, what limits compression?

I think of the displacer chamber as being the "combustion chamber". It is the air pace above the piston (or below) at TDC that gets heated.

Most Stirling engines have small pistons with these enormous displacer/heating chambers, so compression ratio is hardly even a consideration. It's virtually non-existent, by IC standards.

I don't see the cold side of the Stirling engine as a place where you wasn't the heat to go. The "cold' should be a consequence of the conversion of heat into work. Cold does not cause conversion of heat into work, though it might sometimes look that way, and that has been the prevailing theory for 200 years.

I'm not "against" the Carnot theory or the second law. If it were true, I'd happily use it.

I don't see that there is any "trade-off" between efficiency and power either. Efficiency is how effectively heat is converted into "work". The more efficient the engine, the more powerful. These are not opposites. There is no trade-off.

So, if high compression, historically, is considered a good thing, theories about why that may be aside for the moment, how could high compression, like in the very successful IC engines be achieved with this humongous "combustion"/displacer chamber.

Well, some Beta type engines, as you pointed out, have: "negative dead space" refers to the volume in which the power piston infringes upon the space that the displacer acts on."

I did not know this, or I should say, I noticed it, as an observation, which gave rise to this discussion, but I was not aware that there was a name for it.

So, with this shared cylinder space or overlap, I saw a possibility for maximizing this "negative dead space" to increase the compression ratio, virtually, without limitations.

The "true" cold side or heat/energy "sink" is, or should not be the cold side of the displacer chamber. But the face of the piston. The surface of the piston is where the real energy exchange is taking place, converting heat into work.

This Beta arrangement, (not using any regenerator) has an additional, desirable consequence. There is no longer any redundant "cold side" of the displacer chamber. Instead, the only thing opposite the hot side of the displacer is the face of the piston!

Now, blah, blah, blah, theory, theory, theory, Carnot said you need cold as well as heat, the greater the temperature difference between the hot and cold "reservoirs" the more efficiency, 2nd law, efficiency limit, blah blah blah....

All complete nonsense.

[VincentG]

I'm all for raising compression as much as possible but it makes the heat input issues of ECE even more challenging.

[Tom Booth]

I'm all for raising compression as much as possible but it makes the heat input issues of ECE even more challenging.

As far as I can figure, a Stirling engine apparently sneaks heat in backwards, via a "heat pump" action.

If the temperature of the working fluid at TDC during compression equals or exceeds the temperature of the hot heat source how could heat be added that way ?

So.... What's going on? If this is true even with a "normal" low compression Stirling engine?

Apparently the heat is absorbed into the working fluid from the cold side at BDC.

Higher compression also means a higher expansion ratio, which means greater cooling at BDC when the temperature of the working fluid is actually BELOW the temperature of the ambient surroundings.

"Heat" is also taken in from atmospheric pressure between BDC and TDC disguised as acceleration of the piston.

At TDC the piston accelerating from BDC is decelerated and all that energy is converted back into heat.

When driven as a heat pump the working fluid of a Stirling engine rather quickly falls to the cryogenic range, but I think it quite likely this takes place during normal engine operation as well. In other words, the "cold" side is actually the primary heat source, just as it is for an ordinary heat pump.

However, because the working fluid quickly takes in heat and warms up to the temperature of the cold side this has gone unnoticed, besides never having been suspected, so never looked for and also because of the difficulty of monitoring the actual temperature of the working fluid.

So, what this would mean is heat is needed on the "cold" side, as much or moreso than on the "hot" side.

Which would help to explain what's going on here:


https://youtu.be/u-YfPEFBh70?si=xwGoOh3HdXFXMN5Z


It appears, and he seems to state, that the "cooling water" is being preheated to near boiling.

Resize_20240117_015646_6621.jpg (112.24 KiB) Viewed 9215 times

This makes no sense in terms of conventional heat engine theory, but makes perfect sense if the engine is acting as a heat pump, drawing the majority of its power from the "cooling water".

From what he says about the "flexing", the engine has a high compression ratio. Large bore piston, fairly long throw.

The higher the compression, the greater the potential cooling on expansion. The colder the working fluid at BDC the more rapid the heat intake between BDC and TDC while the piston is accelerating.

Aside from all of this being completely contrary to 200 years of thermodynamics theory, I think it makes perfect sense and explains the observable evidence.

Anyway, instead of making getting heat into the engine more difficult, if all this is true, then high compression/expansion makes "pumping" heat into the engine easier.

You may just need to preheat the cooling water.

Hot water is great for heat transmission. Much better than air which is more an insulator.

[Tom Booth]

Of course, we don't want to draw any hasty conclusions based solely on speculation about one engine. I can think of other more conventional explanations.

The guy has his cans pressed together. Perhaps there could be an air leak that seals itself when the metal swells at the higher temperature.

However, after years and years of making observations and doing experiments, as well as doing the math over and over and over and over, time after time after time, the conventional theory and conventional math does not even come within miles of actual experimental results.

Engines that shouldn't run at all, run better, "waste heat" that should be present in abundance can't be measured, etc.

Conventional theory leads to unresolvable paradoxes, like how can heat be absorbed or rejected across a non-existent, or "up hill" temperature gradient?

So, overall, these are not "wild speculations" but rather a fairly, IMO anyway, coherent theory that is consistent with all the facts. Experimental observations, known and well established scientific principles, anecdotal accounts, casual observations, common sense mathematical derivations, etc.

[Fool]

You seem to leave out the following fact/data:

I don't doubt your calculations, but the energy lost, if the thermocouple is reversed then becomes the energy gained by the top plate, which you say was just 876 joules over the course of 11 minutes or 1.32 joules/second.

That one point of data seems to refute your entire theory that Stirling Engines operate by "cooling" the cold plate. "Energy gained" equals heating, not cooling.

1.32 watts rejected to the cold plate would seem to indicate that, for an efficiency of 5%, only about 1.389 watts of heat were entering the engine's hot plate. That leaves a maximum of 0.069 watts of power to output, probably way less. For the record that test engine was not providing any useable power, for a measured power output of zero, indicating zero efficiency.

200 years of Thermodynamics seems to more closely describe that power and heat rejection.

To provide needed data, power out must be measured. A dyno can be made at home very cheaply that would benefit stated experiment. Just use an rpm meter, a kitchen scale, a ruler, and a hinge.

Ps, That quote comes from a source even you can trust.

It's from this thread, a little further than halfway down:

viewtopic.php?f=1&t=5547&start=105

2023 July 10 at 7:14 pm

[Tom Booth]

You seem to leave out the following fact/data:

I don't doubt your calculations, but the energy lost, if the thermocouple is reversed then becomes the energy gained by the top plate, which you say was just 876 joules over the course of 11 minutes or 1.32 joules/second.

That one point of data seems to refute your entire theory that Stirling Engines operate by "cooling" the cold plate. "Energy gained" equals heating, not cooling.

1.32 watts rejected to the cold plate would seem to indicate that, for an efficiency of 5%, only about 1.389 watts of heat were entering the engine's hot plate. That leaves a maximum of 0.069 watts of power to output, probably way less. For the record that test engine was not providing any useable power, for a measured power output of zero, indicating zero efficiency.

200 years of Thermodynamics seems to more closely describe that power and heat rejection.

To provide needed data, power out must be measured. A dyno can be made at home very cheaply that would benefit stated experiment. Just use an rpm meter, a kitchen scale, a ruler, and a hinge.

Ps, That quote comes from a source even you can trust.

It's from this thread, a little further than halfway down:

viewtopic.php?f=1&t=5547&start=105

2023 July 10 at 7:14 pm

Do you happen to recall the context of that experiment?

The engine was running on top of an 85 watt steam generator that boils a small amount of water continuously.

The steam was enclosed within a short wide length of PVC pipe under the engine so that the steam condensing on the bottom of the engine could drip back down into the boiler.

You do realize steam, condensing on a metal plate releases the heat in the steam. I'm pretty sure you must also be aware of what happens when a pot of boiling water is covered with a lid. The lid will lift off the pot to let out the steam due to the build up of pressure. (Unless of course the steam is rapidly cooled and condensed to remove the heat rapidly, such as in a double boiler).

Resize_20240119_115717_7225.jpg (86.63 KiB) Viewed 9109 times

Given it can be assumed about 80 Joules of heat per second were being delivered to the bottom metal plate of the engine, that no steam was escaping and there was no pressure build up inside the length of PVC pipe, is it reasonable to assume that only 1.389 joules per second are crossing the 60 thousandth of an inch thick metal plate to reach the air inside the engine? Air being rapidly fanned across the plate by the displacer?

Your rationale is the equivalent of putting an 800 watt space heater in the ice box of a refrigerator and claiming the refrigerator does not work because the temperature in the ice box went up by a whopping 10 joules.

To me that looks more like 790 watts of cooling power from the refrigerator, in spite of the slight rise in the air temperature inside the refrigerator.

If it wasn't working as a refrigerator, with an 800 watt space heater inside, the temperature should have gone up much more than 10 joules.

[Tom Booth]

For the record that test engine was not providing any useable power, for a measured power output of zero, indicating zero efficiency.

"For the record", There is quite valid thermodynamics "work" involved just driving the piston, rotating the flywheel, overcoming friction etc.

[Fool]

I don't doubt that there is thermodynamic work being produce, probably around 10 milliwatts. Just enough to overcome friction. An indicator diagram would be an excellent addition to the stated experiment for verification.

I would like to see the diagram show an amount of 10 watts or more.

10 watts plus 1.32 watts still doesn't come close to the 85 watts you are using. Maybe you should try running it on a 10 watt light bulb, or a five watt power resistor? Did the steam generator run dry? If it did it would mean the water carried away a good share of the heat as vapour. Did the PVC walls of the chamber get warm? Hot? Or just the engine's bottom plate?

[Tom Booth]

I don't doubt that there is thermodynamic work being produce, probably around 10 milliwatts. Just enough to overcome friction. An indicator diagram would be an excellent addition to the stated experiment for verification.

I would like to see the diagram show an amount of 10 watts or more.

10 watts plus 1.32 watts still doesn't come close to the 85 watts you are using. Maybe you should try running it on a 10 watt light bulb, or a five watt power resistor? Did the steam generator run dry? If it did it would mean the water carried away a good share of the heat as vapour. Did the PVC walls of the chamber get warm? Hot? Or just the engine's bottom plate?

About 8 minutes into the video I lifted the engine to take a look.

Resize_20240119_200323_3751.jpg (56.77 KiB) Viewed 9064 times

It had not run dry at that point, and if I recall, did not through to the end.

Let's just say, I'm all for additional, independent experiments with more/better measurements and controls. There is plenty to criticize and I don't claim any one experiment in isolation proves anything, but your low ball efficiency guesses etc. are low even by Carnot efficiency limit standards and don't prove anything either.

Pretty obviously IMO, there was much more heat being pushed to the little engine than it could easily utilize. Yes, the top plate of the engine did heat up, quite a bit, over the course of 10 minutes running on top of water at a full, constant boil.

PVC is a very poor conductor of heat, compared with the metal plate on the engine. Air outside the PVC was not being vigorously agitated. Still, there might have been better insulation around the PVC to prevent heat loss, more temperature readings at more points and so forth.

All, in all though, I've done similar experiments with more controlled heat input, experiments insulating the entire engine etc. etc.

I NEVER see the kind of MASSIVE heat "rejection" predicted by the Carnot formula.

It is, IMO rather silly to argue as you and so many others on the Science forums do, that the engines supposed very low efficiency is why the heat rejection is so infinitesimal.

The Carnot formula predicts the lower the efficiency the GREATER must be the heat rejected!

[Fool]

Yes. But to verify it, one needs either useable work out, or an indicator diagram, plus temperature verses time. You've provided temperature verses time for the cold plate already. It's rejecting 1.32 Watts.

Calling my guess low balling is not going to help anymore than calling yours high balling. Accurate data is what is needed. Please.

[Tom Booth]

Yes. But to verify it, one needs either useable work out, or an indicator diagram, plus temperature verses time. You've provided temperature verses time for the cold plate already. It's rejecting 1.32 Watts.

Calling my guess low balling is not going to help anymore than calling yours high balling. Accurate data is what is needed. Please.

Great, you can be sure I'll keep doing experiments as time and finances allow.

All I'm saying, if you think the engine is 5% efficiency, on an 85 watt heat source there should be about 80 watts of that arriving at the "sink" (according to the Carnot formula) If that had been a test question for a thermo exam': "If Qh is 85 Joules and Qc is 1.32 Joules what is the efficiency of the engine" what would the correct answer be?

A. 5%
B. 98.5%

[VincentG]

Watching the linked video had me going back to this thread. Skip to 6:30 to see the damage from overheating. The glass displacer melted before the hot cap! I suppose there could be an alternative explanation but at first glance it looks like the gas inside was hotter than the torch, as you suggested above.

https://youtu.be/dtuvNYMS84I?si=pVpfvvUAnc2MOAp3

[Tom Booth]

Imagine a fire piston.

If you heated up a glass fire piston from the outside with a torch, how much would that alone heat the air inside? Then compress the plunger, the heated air is going to then get very much hotter.

The timing advance in a Stirling engine is such that the air inside is suddenly heated just before, and also AS the plunger (piston) is on the way down so the heating and compression is almost or partially simultaneous.

[VincentG]

Thats the idea Tom, I'm just surprised it seemed to be actually happening in a small scale engine. Of course there could be another explanation but its just one more unknown with these things.

[Tom Booth]

Thats the idea Tom, I'm just surprised it seemed to be actually happening in a small scale engine. Of course there could be another explanation but its just one more unknown with these things.

Of course the glass the inner displacer is made of could be different (lower melting point) than the outer displacer cylinder.

In a small engine with a lot of dead air space and very low compression the effect is probably negligible, but IMO compression could not fail to increase the temperature of the gas to one degree or another. "Heat of compression" is an established fact and depends on the compression ratio. The higher the compression ratio the more "heat of compression".