Thermal lag engines might be more easily understood after studying a jam jar pulse jet engine.
https://m.youtube.com/watch?v=ZRV3f2sj5yM
They should scale up or down, at least a little bit. Since they rely on tuning, size will change their operational rate.
Ted Warbrooke's Stirling 1: Question
Re: Ted Warbrooke's Stirling 1: Question
The ratio between freezing and boiling changes, when comparing Celsius to Fahrenheit.Nobody wrote: ↑Thu Feb 10, 2022 5:37 am It is very clear now to me why Tom won't ever understand the simple concept of the Carnot limit.
Clearly the function of SA/V ratio is not constant. It is a function of Side Length. And therefore his subterfuge is nothing more than a straw man argument, at best.
Changing units does change ratios. The ratio between freezing and boiling changes, when comparing Celsius to Fahrenheit. Tom brought that up and didn't even notice.
Thank you very much Alphax.
It is very clear that as engines get smaller the hot side gets closer to the cold side, the straight across wasted heat loss will be more and more difficult to prevent, higher. Smaller engines will have lower efficiency. For the same design, size being the only only change.
And breaking up a rock with a hammer into small bits creates more surface area, that is why a small engine cannot be made larger because the large engine, like the large rock would have less surface area.
I think Alphax and Nobody must be one and the same as It just doesn't seem possible that any two different people could actually share such flawless logic.
The point is, with different measuring scales it APPEARS that the "ratio" changes. But that does not change the ACTUAL property of water.
The weather outside doesn't change by using a different thermometer. You can't thaw out your pipes in winter by switching from Fahrenheit to Celsius to change the melting point of water.
An individual small bit of gravel does not have more surface area than a bolder, just because there is collectively, more surface area in a bag of gravel than the bolder that was crushed to make the gravel.
And yes, Carnot efficiency is a similar bit of silliness.
I suppose MY problem may be, I haven't received enough education to have my logical faculties completely emulsified in order to see that indeed, a small marble has more surface area than a bowling ball and reading from the C° or F° graduation on a thermometer determines if it will rain or snow.
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
@ Nobody:
I wondered if someone might suggest these - they are fascinating in their own right! I love them....
And they have a some similarities to Thermal Lag engines because:-
(a) heat (and heat transfer) appears to drive the pulsing, rhythmic, oscillating, resonant behaviour (or is it the other way round....??)
(b) work it clearly being done,
However, there are some differences too:-
(1) a Thermal Lag (and indeed all Stirlings) are EXTERNALLY heated, the jam jar pulse engine is INTERNALLY heated (ECE ct ICE),
(2) The jam jar pulse engine is oxidising fuel INTERNALLY and using up oxygen and producing carbon dioxide
(3) It follows from (2) that if the engine is to run any length of time it must (i) intake fresh air and (ii) exhale CO2 through the lid hole.
(4) It follows from (3) that the jam jar pulse engine is an OPEN system, all Stirlings are CLOSED systems
(5) and following on from 5, their thermodynamic cycles are different.
Having said all that, I agree that the two DO have some remarkable behavoural characteristics. The most striking of which is that rhythmic, resonant cyclic, oscillating pulse action which is self-sustaining and self regulating.
In some ways the jam jar pulse engine is even more impressive that the Thermal Lag Stirling because it the only true internal combustion engine that runs with NO MOVING PARTS and is able to regulate its own import of oxygen into the cylinder and export oxidation products without valves (assuming you could keep one running for a few minutes).
I can't help but mention their relative work outputs (or output power) - the jam jar pulse engine is far more powerful than a comparable Thermal Lag engine because it is able to suck in fresh oxygen and blow out combustion products. If you use the same amount of fuel to power the hot cap of a comparable Thermal Lag engine you will not get anywhere near as much power out from the piston (for a number of reasons).
This highlights one of the persistent myths of Stirling engines in general - it is believed by many that they have some sort of ultimate potential for high efficiency that can one day be made to outperform internal combustion engines, if only we were smart enough to make them work "properly". And that is, sadly, wrong. In round terms, no Stirling engines have reached the overall efficiency of a modern Diesel engine, and it seems highly improbable that one ever will.
But I do agree whole heartedly - there is something to be learned from the jam jar pulse engine that directly impinges on Thermal Lag engine design.
What could it be?
Thermal lag engines might be more easily understood after studying a jam jar pulse jet engine.
I wondered if someone might suggest these - they are fascinating in their own right! I love them....
And they have a some similarities to Thermal Lag engines because:-
(a) heat (and heat transfer) appears to drive the pulsing, rhythmic, oscillating, resonant behaviour (or is it the other way round....??)
(b) work it clearly being done,
However, there are some differences too:-
(1) a Thermal Lag (and indeed all Stirlings) are EXTERNALLY heated, the jam jar pulse engine is INTERNALLY heated (ECE ct ICE),
(2) The jam jar pulse engine is oxidising fuel INTERNALLY and using up oxygen and producing carbon dioxide
(3) It follows from (2) that if the engine is to run any length of time it must (i) intake fresh air and (ii) exhale CO2 through the lid hole.
(4) It follows from (3) that the jam jar pulse engine is an OPEN system, all Stirlings are CLOSED systems
(5) and following on from 5, their thermodynamic cycles are different.
Having said all that, I agree that the two DO have some remarkable behavoural characteristics. The most striking of which is that rhythmic, resonant cyclic, oscillating pulse action which is self-sustaining and self regulating.
In some ways the jam jar pulse engine is even more impressive that the Thermal Lag Stirling because it the only true internal combustion engine that runs with NO MOVING PARTS and is able to regulate its own import of oxygen into the cylinder and export oxidation products without valves (assuming you could keep one running for a few minutes).
I can't help but mention their relative work outputs (or output power) - the jam jar pulse engine is far more powerful than a comparable Thermal Lag engine because it is able to suck in fresh oxygen and blow out combustion products. If you use the same amount of fuel to power the hot cap of a comparable Thermal Lag engine you will not get anywhere near as much power out from the piston (for a number of reasons).
This highlights one of the persistent myths of Stirling engines in general - it is believed by many that they have some sort of ultimate potential for high efficiency that can one day be made to outperform internal combustion engines, if only we were smart enough to make them work "properly". And that is, sadly, wrong. In round terms, no Stirling engines have reached the overall efficiency of a modern Diesel engine, and it seems highly improbable that one ever will.
But I do agree whole heartedly - there is something to be learned from the jam jar pulse engine that directly impinges on Thermal Lag engine design.
What could it be?
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
A clue: self regulation constant frequency (or oscillating frequency, if you prefer).
It turns out that frequency (RPM if you fit a flywheel) is one of the determinants in power output.
You will have seen (above) that I am suggesting that the unlikely tactic of changing the wire wool regenerator grade (fine/coarse etc) and packing density have a direct effect on altering that frequency, without changing the mass and volume of the regenerator material.
Since that frequency determines output power, you can't avoid the idea that the regenerator wire grade (surface area to volume) and packing density control (to some extent unknown) the engine's power output given constant heat input.
It turns out that frequency (RPM if you fit a flywheel) is one of the determinants in power output.
You will have seen (above) that I am suggesting that the unlikely tactic of changing the wire wool regenerator grade (fine/coarse etc) and packing density have a direct effect on altering that frequency, without changing the mass and volume of the regenerator material.
Since that frequency determines output power, you can't avoid the idea that the regenerator wire grade (surface area to volume) and packing density control (to some extent unknown) the engine's power output given constant heat input.
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
Just so I'm not accused of cheating in the way I present my argument, I need to point out two things:-
(1) that neither Tailer's original Thermal Lag engine nor the heavily instrumented Calcoen and Vandermeersch Thermal Lag engine actually use wire wool as regenerators (as far as I am aware this is true).
(2) all other, more recent (and Ted Warbrook's original 'Stirling-1') do have wire wool regenerators (at least all the ones that I have seen do).
The interesting aspect of the plethora of little home made Thermal Lag engines (on Youtube and other places) is not only that they all work, and work surprisingly vigorously, but that they can be made to work extremely easily using wooden or plastic pistons in the cold end and a low thermal conductivity ceramic (pyrex) as the tube which nicely limits thermal leakage and shorting.
But there is a little trick that helps "get them going" and that is to include a slight restriction (often called a pulse tube) between piston and hot end. This restriction is sometimes present as no more than a thermal break where two lengths of glass tubes are joined by a metal joiner piece. It appears to be important that there is a pulse tube, but its actual proportions aren't critical to some sort of happy outcome (i.e. that the engine can self-regulate and maintain steady state oscillation without a moving displace piston). This, of course, is the whole point of the 'Lag' in the name 'Thermal Lag' - the engine itself drives the lag rather than giving up energy to drag a displacer around to move the working fluid with "brute force'. Just like a jam jar pulse engine does (by slightly different means).
For best results it seems the pulse tube/restriction should be in almost intimate contact with the returning piston face.
Even more interesting is that the restrictor/pulse tube also lies at the heart of two different scientific interpretations of how Thermal Lag engines actually work (the two camps being Tailer and West Versus Calcoen and Vandermeersch).
I think that this is where the jam jar pulse engine can give some insight to how (some) Thermal Lag engines actually do work - they seem (to me) to require a thermal break or a pulse tube/restriction in between piston and hot end.
(1) that neither Tailer's original Thermal Lag engine nor the heavily instrumented Calcoen and Vandermeersch Thermal Lag engine actually use wire wool as regenerators (as far as I am aware this is true).
(2) all other, more recent (and Ted Warbrook's original 'Stirling-1') do have wire wool regenerators (at least all the ones that I have seen do).
The interesting aspect of the plethora of little home made Thermal Lag engines (on Youtube and other places) is not only that they all work, and work surprisingly vigorously, but that they can be made to work extremely easily using wooden or plastic pistons in the cold end and a low thermal conductivity ceramic (pyrex) as the tube which nicely limits thermal leakage and shorting.
But there is a little trick that helps "get them going" and that is to include a slight restriction (often called a pulse tube) between piston and hot end. This restriction is sometimes present as no more than a thermal break where two lengths of glass tubes are joined by a metal joiner piece. It appears to be important that there is a pulse tube, but its actual proportions aren't critical to some sort of happy outcome (i.e. that the engine can self-regulate and maintain steady state oscillation without a moving displace piston). This, of course, is the whole point of the 'Lag' in the name 'Thermal Lag' - the engine itself drives the lag rather than giving up energy to drag a displacer around to move the working fluid with "brute force'. Just like a jam jar pulse engine does (by slightly different means).
For best results it seems the pulse tube/restriction should be in almost intimate contact with the returning piston face.
Even more interesting is that the restrictor/pulse tube also lies at the heart of two different scientific interpretations of how Thermal Lag engines actually work (the two camps being Tailer and West Versus Calcoen and Vandermeersch).
I think that this is where the jam jar pulse engine can give some insight to how (some) Thermal Lag engines actually do work - they seem (to me) to require a thermal break or a pulse tube/restriction in between piston and hot end.
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
The jam jar pulse engine pulses (rather dramatically!) because as soon as you light it, it starts to run out of oxygen to burn the fuel. So it immediately begins to cool and in doing so the gas volume contracts and in doing so sucks in fresh air through the hole. This charge of fresh air refreshes the flames (which have subsided but not gone out) which gratefully spring back into life, only to rapidly use all that nice fresh oxygen and cool down once more. An so the cycle repeats, rapidly alternating between "suck" and "blow" to breath in fresh O2 and breath out stale CO2 at a steady oscillating frequency (well, for as long as the fuel lasts...)
A Thermal Lag engine is - to me - more impressive in the way it is able to manage a similar steady state oscillation by itself. What I keep asking here, though, is what others think that a scaled up version might do...... better?......worse?...... and (hardest of all).....why?
A Thermal Lag engine is - to me - more impressive in the way it is able to manage a similar steady state oscillation by itself. What I keep asking here, though, is what others think that a scaled up version might do...... better?......worse?...... and (hardest of all).....why?
Last edited by Alphax on Thu Feb 10, 2022 8:36 am, edited 1 time in total.
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
Also... for Tom's benefit.... try watching the video of the jam jar pulse engine with the sound turned up.
The engine is doing a significant amount of work by making sound as it sucks and blows.
The engine is doing a significant amount of work by making sound as it sucks and blows.
Re: Ted Warbrooke's Stirling 1: Question
I made my own intake and exhaust manifold set for my pickup a few years ago, and prior to cutting metal I tried to absorb what lore I could on the subject. My project was mildly successful, but certainly not worth the hassle, except that I get stubborn. Thing is, I suppose some of the same dynamics relates to these engines, but the main point I took away from said study is that even in that more established arena of performance tuning; there still seems to be a bit of black art with no consensus amongst the practitioners, particularly with low-budget folks limited to back-yard obtainium. So — I doubt there’s ever been or will be a definitive study of Thermal Lag engines, because we all hang our hats on different compromise points.
Scaling up — I think the original Tailer design worked without doctoring the flow dynamics, so I don’t see why not. I seem to remember looking at some very paltry performance numbers though, and for my own part, I believe managing the flow to get the best timing is very important if you expect much power. It does seem like the most impressive engines are small, and the same flow management schemes may not scale up. I suspect that the magic of perfect proportioning and design is more important for Thermal Lag engines than it is for Stirling engines, because the charge has to pass through an exchanger on its own inertia, after having been delayed in some way.
That Derwood engine is plenty big and even if it happened to represent some upper limit, you could always add cylinders. It seemed fussy, but he may have got that worked out. It seemed powerful but I don’t know if he ever did an actual brake test on it. The thing I didn’t like is that it seemed to need a LOT of temperature difference. He may have worked that out but I don’t know. And a lot of respect to his work, BUT —
I wouldn’t want a high-temp hot air engine. This always gets me in trouble with the fanatics and their theoretical theorizing, but I have mentioned here several times before that other than for experimenting or modeling, running hot air engines on any fuel that could be used in a more efficient internal combustion engine is a waste. And photovoltaics are so cheap now that it’s silly to think of concentrated solar. So the only hot air engines I see as useful are in the mid temperature range of non processed or crudely processed fuels. Which leads to needing a large surface area for any meaningful heat transfer. Which leads to pancakes. Which scale favorably if the thickness stays the same. Which was sorta the point of a previous post. Which is likely irrelevant anyway since I have no idea how to make a pancake Thermal Lag engine. But I’m just saying it might be worth considering for some of you smart folks.
Bumpkin
Scaling up — I think the original Tailer design worked without doctoring the flow dynamics, so I don’t see why not. I seem to remember looking at some very paltry performance numbers though, and for my own part, I believe managing the flow to get the best timing is very important if you expect much power. It does seem like the most impressive engines are small, and the same flow management schemes may not scale up. I suspect that the magic of perfect proportioning and design is more important for Thermal Lag engines than it is for Stirling engines, because the charge has to pass through an exchanger on its own inertia, after having been delayed in some way.
That Derwood engine is plenty big and even if it happened to represent some upper limit, you could always add cylinders. It seemed fussy, but he may have got that worked out. It seemed powerful but I don’t know if he ever did an actual brake test on it. The thing I didn’t like is that it seemed to need a LOT of temperature difference. He may have worked that out but I don’t know. And a lot of respect to his work, BUT —
I wouldn’t want a high-temp hot air engine. This always gets me in trouble with the fanatics and their theoretical theorizing, but I have mentioned here several times before that other than for experimenting or modeling, running hot air engines on any fuel that could be used in a more efficient internal combustion engine is a waste. And photovoltaics are so cheap now that it’s silly to think of concentrated solar. So the only hot air engines I see as useful are in the mid temperature range of non processed or crudely processed fuels. Which leads to needing a large surface area for any meaningful heat transfer. Which leads to pancakes. Which scale favorably if the thickness stays the same. Which was sorta the point of a previous post. Which is likely irrelevant anyway since I have no idea how to make a pancake Thermal Lag engine. But I’m just saying it might be worth considering for some of you smart folks.
Bumpkin
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
Bumpkin,
I see where you are going with the idea. And, I have to say....... I do like the idea of a "Thermal Lag Pancake" engine. It had not occurred to me, and I will give it some thought now that you have suggested it. It won't be quick, though. I'm a slow thinker........Which leads to pancakes
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
Bumpkin,
I suspect the reason that some folk get upset when you say that is because it touches a raw nerve.
It is true - Stirling engines (at least the experimental ones and desk top ones that we make and have access to) will never be able to compete with an internal combustion engine that could use the same fuel. And they never will, although a precision engineered Stirling engine can theoretically approach the same overall power-output per unit fuel used as a Diesel engine. But even that has never been done and there is evidence that it may never be achieved! Not everyone wants to be reminded of that......
This always gets me in trouble with the fanatics and their theoretical theorizing, but I have mentioned here several times before that other than for experimenting or modeling, running hot air engines on any fuel that could be used in a more efficient internal combustion engine is a waste.
I suspect the reason that some folk get upset when you say that is because it touches a raw nerve.
It is true - Stirling engines (at least the experimental ones and desk top ones that we make and have access to) will never be able to compete with an internal combustion engine that could use the same fuel. And they never will, although a precision engineered Stirling engine can theoretically approach the same overall power-output per unit fuel used as a Diesel engine. But even that has never been done and there is evidence that it may never be achieved! Not everyone wants to be reminded of that......
Re: Ted Warbrooke's Stirling 1: Question
Talking of scaling things up, the various SS canisters and bottles have been trickling in. No sign of those really big Stainless steel fire extinguishers yet, though.
Size comparison with a "toy" Stirling:
For what it's worth, IMO a perfectly scaled up engine would run just the same as the model, assuming the heat source was also scaled up.
If a smallish engine could be built that could be set down with the nose in a campfire, and generate enough power to charge a battery, it might be nice to take along on a camping trip.
I don't know if this qualifies as a Stirling 1 type engine. Probably not. It has a displacer, but not an ordinary piston, instead it has a thin metal diaphragm.
Anyway, I like this engine. there doesn't seem to be much dead air space in this thing, the displacer apparently takes up nearly the entire interior of the engine and only oscillates maybe a millimeter. He says 1/2 millimeter.
A strobe light helps to show the motion.
https://youtu.be/Sdf2fiSGOKo
There are half a dozen more videos, showing construction of the engine. This is one or the more interesting, showing how the huge close fitting displacer takes up nearly the whole interior of the engine.
https://youtu.be/QcppEhp2RfA
He uses a beryllium copper diaphragm instead of a piston, but perhaps silicone would work. Anyway, sheets of beryllium copper, I just now found on eBay are very inexpensive. The shipping adds to the price of course.
That is an engine I would like to build, or something very much like it.
I wonder if what he interprets as efficient air cooling due to the vibration is not actually due to very high efficiency.
He says it can run for hours and hours and never gets hot enough to require cooling.
Size comparison with a "toy" Stirling:
- Resize_20220211_052632_2504.jpg (337 KiB) Viewed 4754 times
If a smallish engine could be built that could be set down with the nose in a campfire, and generate enough power to charge a battery, it might be nice to take along on a camping trip.
I don't know if this qualifies as a Stirling 1 type engine. Probably not. It has a displacer, but not an ordinary piston, instead it has a thin metal diaphragm.
Anyway, I like this engine. there doesn't seem to be much dead air space in this thing, the displacer apparently takes up nearly the entire interior of the engine and only oscillates maybe a millimeter. He says 1/2 millimeter.
A strobe light helps to show the motion.
https://youtu.be/Sdf2fiSGOKo
There are half a dozen more videos, showing construction of the engine. This is one or the more interesting, showing how the huge close fitting displacer takes up nearly the whole interior of the engine.
https://youtu.be/QcppEhp2RfA
He uses a beryllium copper diaphragm instead of a piston, but perhaps silicone would work. Anyway, sheets of beryllium copper, I just now found on eBay are very inexpensive. The shipping adds to the price of course.
- Resize_20220211_063414_4949.jpg (165.31 KiB) Viewed 4754 times
That is an engine I would like to build, or something very much like it.
I wonder if what he interprets as efficient air cooling due to the vibration is not actually due to very high efficiency.
He says it can run for hours and hours and never gets hot enough to require cooling.
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
Tom
I wasn't aware of this engine, and I watched the video with fascination. I have to say I'm impressed and will watch the whole series. So thank you for pointing it out.
So far, I'd agree .... I think (without having seen the other videos yet) that this, or something along similar lines, would make a nice engine to build.
Like you, I've been tempted to stock up on steel thermos flasks, mugs and containers, but haven't got as far as you......
There are half a dozen more videos, showing construction of the engine. This is one or the more interesting, showing how the huge close fitting displacer takes up nearly the whole interior of the engine.
I wasn't aware of this engine, and I watched the video with fascination. I have to say I'm impressed and will watch the whole series. So thank you for pointing it out.
So far, I'd agree .... I think (without having seen the other videos yet) that this, or something along similar lines, would make a nice engine to build.
Like you, I've been tempted to stock up on steel thermos flasks, mugs and containers, but haven't got as far as you......
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
Ah..... having watched a few of barumman's excellent videos (thanks again for pointing them out) I see now how it works because he explains it so well.
This is the video in which he does that, even showing the internal workings of the original HARWELL TMG device which he has used as his working principle:-
https://www.youtube.com/watch?v=QCOn-UcvnBM
Very, very nice work indeed.
This is the video in which he does that, even showing the internal workings of the original HARWELL TMG device which he has used as his working principle:-
https://www.youtube.com/watch?v=QCOn-UcvnBM
Very, very nice work indeed.
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Alphax
Re: Ted Warbrooke's Stirling 1: Question
One thing about the Harwell TMG and barumman's excellent version of it is the beryllium copper diaphragm.
It is, of course, very ingenious. And I'm not criticising it at all, I think it is very clever. But it is acting precisely like a loudspeaker diaphragm and is the source of the significant hum that you can hear in the videos. That is to say it is converting some of the linear oscillatory motion into acoustic power outputs as well as electrical power outputs via the coils and magnet.
The interesting question is what is the magnitude of the acoustic power output (which is presently lost/dissipated) compared to the electrical power output?
It is, of course, very ingenious. And I'm not criticising it at all, I think it is very clever. But it is acting precisely like a loudspeaker diaphragm and is the source of the significant hum that you can hear in the videos. That is to say it is converting some of the linear oscillatory motion into acoustic power outputs as well as electrical power outputs via the coils and magnet.
The interesting question is what is the magnitude of the acoustic power output (which is presently lost/dissipated) compared to the electrical power output?