Its been a week i have seen so many videos and animations but i still don't get it how it runs , what happens to the air inside
I only get to the part , Hot cylinder is heated and the air inside is expanded and it pushes the piston forward and in that time the cold piston is in the middle , How it keeps running then?
Can someone give me detailed explanation.. I will be very thankful to you
Please Someone help me , How Alpha Stirling engine works?
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notfairchild
- Posts: 1
- Joined: Fri Mar 20, 2020 9:15 pm
Re: Please Someone help me , How Alpha Stirling engine works?
Momentum. That is why a fly-wheel is part of every Stirling design.
Re: Please Someone help me , How Alpha Stirling engine works?
Hi notfairchild. I too remember that the Alpha type engine was hard to understand. I wish I had known to do this: Look at a Gamma type animation until understanding. Then apply that understanding to a Beta type animation. Once you have that, imagine the displacer being stationary and imagine the hot chamber end is the hot piston in an Alpha. Hope that helps.
Bumpkin
Bumpkin
Re: Please Someone help me , How Alpha Stirling engine works?
"Hot cylinder is heated and the air inside is expanded and it pushes the piston forward..."
"Momentum. That is why a fly-wheel is part of every Stirling design."
I've concluded, after studying the operation of many Stirling engines over the years, that that is not all there is to it.
For example, "free piston" and various other Stirling engines can operate without any flywheel. The piston, nevertheless, after being pushed out by the heated expanding gas, reverses direction, although any momentum of the piston would seem to dictate that the piston should continue to move out.
My conclusion is that while the heated gas expands, pushing the piston, the heat energy is exhausted or rather converted to another form of energy i.e. "work". so that the result is: the heated expanding gas becomes nearly instantly cold and contracts back in upon itself.
There are numerous examples on YouTube of people removing the connecting rod from the flywheel of their Stirling engine, regardless, the engines run, and run quite well with no flywheel at all.
Here's one example to start with:
https://youtu.be/DyPxNNJQo9M
So yes "Hot cylinder is heated and the air inside is expanded and it pushes the piston forward..." This uses up the heat/energy resulting in the gas temperature dropping so that the cooled gas contracts and the direction of travel of the piston reverses.
"Momentum. That is why a fly-wheel is part of every Stirling design."
I've concluded, after studying the operation of many Stirling engines over the years, that that is not all there is to it.
For example, "free piston" and various other Stirling engines can operate without any flywheel. The piston, nevertheless, after being pushed out by the heated expanding gas, reverses direction, although any momentum of the piston would seem to dictate that the piston should continue to move out.
My conclusion is that while the heated gas expands, pushing the piston, the heat energy is exhausted or rather converted to another form of energy i.e. "work". so that the result is: the heated expanding gas becomes nearly instantly cold and contracts back in upon itself.
There are numerous examples on YouTube of people removing the connecting rod from the flywheel of their Stirling engine, regardless, the engines run, and run quite well with no flywheel at all.
Here's one example to start with:
https://youtu.be/DyPxNNJQo9M
So yes "Hot cylinder is heated and the air inside is expanded and it pushes the piston forward..." This uses up the heat/energy resulting in the gas temperature dropping so that the cooled gas contracts and the direction of travel of the piston reverses.
Re: Please Someone help me , How Alpha Stirling engine works?
How this is possible, I think (could be very wrong), has to do with "elastic collision" of gas molecules or atoms.
https://en.m.wikipedia.org/wiki/Elastic_collision
The energy (heat) introduced into the engine invigorates the molecules so they bounce around faster or harder (with more force) but the energy is not lost with all this bouncing around, until there is some actual TRANSFER of force, or transfer of energy OUT OF THE SYSTEM such as when the particles collide with an object that has some "give". That is, when the particles hits the piston and the kinetic energy is transfered causing the piston to move.
When a gas molecule hits the side of the engine chamber, that does not give or move, the molecule just "bounces" off and it's energy is retained. (Not 100% perhaps, but much more than when hitting the piston where the majority of energy transfer takes place).
Every time an individual gas molecule hits the piston, and the piston moves the motion/kinetic energy (heat) of that individual molecule is lost. Other fast moving molecules take over, continuing to hit and move the piston until all the added energy introduced to the engine is lost.
But, now the piston actually has momentum and continues to move. In doing so it strikes gas molecules in the air outside the engine on the other side of the piston transferring energy.
This additional motion of the piston causes expansion and cooling of the gas inside the engine. In other words, the momentum of the piston causing an expansion of the gas in the engine results in a refrigerating effect.
The hot expanding gas in the engine becomes rather suddenly, or almost instantly cold. Now the relatively hot atmospheric air outside the engine (individual molecules again) pushes the piston back down the cylinder.
If this is all understood, it can, perhaps, be seen why a flywheel is unnecessary and why, perhaps, even a heat sink is not really needed, so long as heat is not introduced in excess of what the gas can transfer to the piston at any given moment (or cycle).
This is, at the moment, unproven speculation on my part, but, it is the conclusion I've come to in trying to understand how these engines work. In particular, how it's possible that they can run without a flywheel.
IMO, heat does not have time to be conducted away to a heat sink in a fast running engine. Think how long it takes to preheat a Stirling before it will run at all. Often several minutes. That is the speed, or rather the slowness of heat conduction through metal. Yet, the gas in such an engine gains and looses it's heat many times per second if running at, say 300 to 500 RPM.
- Translational_motion.gif (398 KiB) Viewed 10463 times
The energy (heat) introduced into the engine invigorates the molecules so they bounce around faster or harder (with more force) but the energy is not lost with all this bouncing around, until there is some actual TRANSFER of force, or transfer of energy OUT OF THE SYSTEM such as when the particles collide with an object that has some "give". That is, when the particles hits the piston and the kinetic energy is transfered causing the piston to move.
When a gas molecule hits the side of the engine chamber, that does not give or move, the molecule just "bounces" off and it's energy is retained. (Not 100% perhaps, but much more than when hitting the piston where the majority of energy transfer takes place).
Every time an individual gas molecule hits the piston, and the piston moves the motion/kinetic energy (heat) of that individual molecule is lost. Other fast moving molecules take over, continuing to hit and move the piston until all the added energy introduced to the engine is lost.
But, now the piston actually has momentum and continues to move. In doing so it strikes gas molecules in the air outside the engine on the other side of the piston transferring energy.
This additional motion of the piston causes expansion and cooling of the gas inside the engine. In other words, the momentum of the piston causing an expansion of the gas in the engine results in a refrigerating effect.
The hot expanding gas in the engine becomes rather suddenly, or almost instantly cold. Now the relatively hot atmospheric air outside the engine (individual molecules again) pushes the piston back down the cylinder.
If this is all understood, it can, perhaps, be seen why a flywheel is unnecessary and why, perhaps, even a heat sink is not really needed, so long as heat is not introduced in excess of what the gas can transfer to the piston at any given moment (or cycle).
This is, at the moment, unproven speculation on my part, but, it is the conclusion I've come to in trying to understand how these engines work. In particular, how it's possible that they can run without a flywheel.
IMO, heat does not have time to be conducted away to a heat sink in a fast running engine. Think how long it takes to preheat a Stirling before it will run at all. Often several minutes. That is the speed, or rather the slowness of heat conduction through metal. Yet, the gas in such an engine gains and looses it's heat many times per second if running at, say 300 to 500 RPM.
Re: Please Someone help me , How Alpha Stirling engine works?
Consider also, a chamber full of air without any piston.
Take a pop/soda drink plastic bottle with the cap on, sitting in the sun. The air inside, heated by the sun will GRADUALLY expand, causing the bottle to swell from the pressure.
But take the bottle out of the sun, place it in a cool spot. It will again, GRADUALLY cool down and loose pressure, taking, perhaps, just as long to cool down and decompress as it took to heat up.
Why doesn't a Stirling engine take just as long to cool down so as to draw the piston back, as it took to heat up to get it started? How can a piston be drawn back with no momentum from a flywheel to push it back?
Now on the other hand, suppose the bottle heats up inside enough to build up so much pressure the cap blows off. What happens?
All that built up energy goes, mostly towards blasting the cap off into the air. Not only that, but all the gas in the bottle goes rushing toward the opening, building up velocity and a kind of momentum of it's own, and if it could be measured somehow, quickly enough, I think it would be found that the sudden explosive release of gas from the bottle would result in the partial evacuation of gas from the bottle, leaving behind a vacuum inside the bottle.
In essence, I think this is how a Stirling engine operates, except, instead of a bottle cap we have a piston and instead of just blowing off into the air, the piston "blows off" down a long cylinder, and the vacuum it leaves behind draws it back again.
Also much of the kinetic energy of the gas has been transfered to the piston, or to an external load. So, in addition to the partial vacuum created by the gas rushing into the cylinder behind the piston, there is also a sudden cooling of the gas due to the transfer of it's energy to the piston. As a result, the piston is drawn back. IMO it is not drawn back due to dissipation of heat to any kind of heat sink. That would take too long to explain how an engine could run at 500 RPM without any flywheel. It would be like the bottle cooling down in the shade, without the cap having popped off, If it had to rely on heat being conducted away to a heat sink, the engine might do, at best, I would think, about 1 RPM.
Take a pop/soda drink plastic bottle with the cap on, sitting in the sun. The air inside, heated by the sun will GRADUALLY expand, causing the bottle to swell from the pressure.
But take the bottle out of the sun, place it in a cool spot. It will again, GRADUALLY cool down and loose pressure, taking, perhaps, just as long to cool down and decompress as it took to heat up.
Why doesn't a Stirling engine take just as long to cool down so as to draw the piston back, as it took to heat up to get it started? How can a piston be drawn back with no momentum from a flywheel to push it back?
Now on the other hand, suppose the bottle heats up inside enough to build up so much pressure the cap blows off. What happens?
All that built up energy goes, mostly towards blasting the cap off into the air. Not only that, but all the gas in the bottle goes rushing toward the opening, building up velocity and a kind of momentum of it's own, and if it could be measured somehow, quickly enough, I think it would be found that the sudden explosive release of gas from the bottle would result in the partial evacuation of gas from the bottle, leaving behind a vacuum inside the bottle.
In essence, I think this is how a Stirling engine operates, except, instead of a bottle cap we have a piston and instead of just blowing off into the air, the piston "blows off" down a long cylinder, and the vacuum it leaves behind draws it back again.
Also much of the kinetic energy of the gas has been transfered to the piston, or to an external load. So, in addition to the partial vacuum created by the gas rushing into the cylinder behind the piston, there is also a sudden cooling of the gas due to the transfer of it's energy to the piston. As a result, the piston is drawn back. IMO it is not drawn back due to dissipation of heat to any kind of heat sink. That would take too long to explain how an engine could run at 500 RPM without any flywheel. It would be like the bottle cooling down in the shade, without the cap having popped off, If it had to rely on heat being conducted away to a heat sink, the engine might do, at best, I would think, about 1 RPM.
Re: Please Someone help me , How Alpha Stirling engine works?
In another thread in this forum, about ten years ago, I suggested:
"If more heat is extracted as work than what actually reaches the heat sink, then theoretically, insulating the cold end of the displacer chamber against the external ambient temperatures would improve engine efficiency."
viewtopic.php?f=1&t=478
I think some familiar with general Stirling engine operation in here at the time found this idea rather hilarious. But, if in actuality, a Stirling engine is able to convert heat into energy very efficiently, then at the moment when the piston is at its furthest throw, and there is an actual vacuum behind it, and the outside atmosphere has more "pressure" (molecular kinetic energy) than the internal gas inside the engine, for the piston to be able to return without a flywheel, I think, logically, the outside ambient air temperature must be, momentarily, "hotter" than the internal temperature of the "working fluid".
If that is true, then when the piston is at its furthest throw down the cylinder, the temperature of the outside atmosphere may be greater than the gas inside the cylinder. Allowing ambient heat to infiltrate this "cold end" of the engine, would, I think, only reduce the temperature differential and rob the engine of some power. Admittedly, that is something of a wild and seemingly, completely absurd speculation, but I still think it could actually be true. It might be worth experimenting with anyway.
In an alpha type engine, the idea might be to pack the cold cylinder with ice and wrap that with insulation to prevent ambient heat from getting to the ice and melting it.
"If more heat is extracted as work than what actually reaches the heat sink, then theoretically, insulating the cold end of the displacer chamber against the external ambient temperatures would improve engine efficiency."
viewtopic.php?f=1&t=478
I think some familiar with general Stirling engine operation in here at the time found this idea rather hilarious. But, if in actuality, a Stirling engine is able to convert heat into energy very efficiently, then at the moment when the piston is at its furthest throw, and there is an actual vacuum behind it, and the outside atmosphere has more "pressure" (molecular kinetic energy) than the internal gas inside the engine, for the piston to be able to return without a flywheel, I think, logically, the outside ambient air temperature must be, momentarily, "hotter" than the internal temperature of the "working fluid".
If that is true, then when the piston is at its furthest throw down the cylinder, the temperature of the outside atmosphere may be greater than the gas inside the cylinder. Allowing ambient heat to infiltrate this "cold end" of the engine, would, I think, only reduce the temperature differential and rob the engine of some power. Admittedly, that is something of a wild and seemingly, completely absurd speculation, but I still think it could actually be true. It might be worth experimenting with anyway.
In an alpha type engine, the idea might be to pack the cold cylinder with ice and wrap that with insulation to prevent ambient heat from getting to the ice and melting it.
Re: Please Someone help me , How Alpha Stirling engine works?
This is an extreme example, but gas under pressure, escaping from a container gets cold.
This is, I think, kind of what happens during the power stroke of a Stirling engine.
The gas, under pressure, "escapes" into the cylinder, following the piston as it travels outward.
What happens when gas under pressure escapes confinement and drops in pressure?
It gets cold.
So, insulate the cold end of a Stirling?
Consider what happens when the gas escaping from a CO2 fire extinguisher is "insulated" from the ambient heat. In this case the insulation is accomplished with a cloth pillowcase:
https://youtu.be/tLNHDxd6nDc
There are several other YouTube videos on how to make dry ice with any CO2 canister or cartridge, such as used with a pellet gun.
Just catch the escaping CO2 gas in some kind of cloth bag. This keeps the gas from warming by ambient heat, causing it to get so cold as it escapes that it freezes into solid dry ice.
https://youtu.be/VqlBWqNgIE0
This is, I think, kind of what happens during the power stroke of a Stirling engine.
The gas, under pressure, "escapes" into the cylinder, following the piston as it travels outward.
What happens when gas under pressure escapes confinement and drops in pressure?
It gets cold.
So, insulate the cold end of a Stirling?
Consider what happens when the gas escaping from a CO2 fire extinguisher is "insulated" from the ambient heat. In this case the insulation is accomplished with a cloth pillowcase:
https://youtu.be/tLNHDxd6nDc
There are several other YouTube videos on how to make dry ice with any CO2 canister or cartridge, such as used with a pellet gun.
Just catch the escaping CO2 gas in some kind of cloth bag. This keeps the gas from warming by ambient heat, causing it to get so cold as it escapes that it freezes into solid dry ice.
https://youtu.be/VqlBWqNgIE0
Re: Please Someone help me , How Alpha Stirling engine works?
Here is an animation from Wikipedia:
I believe the "power stroke" or phase is when hot expanding air is "escaping" and expanding through the channel and into the cold cylinder. As it does so it is doing work and simultaneously cooling. (Similar to how CO2 escaping a fire extinguisher gets cold. In theory, if the CO2 escaping the fire extinguisher also performed work, it would loose even more heat and become even colder than it normally does).
In thermodynamic theory, heat and work are equivalent. So for the amount of work performed pushing out the (cold side) piston, an equivalent amount of heat is lost from the expanding/escaping gas. Though, unlike a fire extinguisher, in a Stirling engine, the gas is not escaping into the open air, but just from one cylinder to another. In the process of expanding and doing work, the gas gets cold and subsequently contracts drawing the piston(s) in again.
According to the standard idea of how a Stirling engine works, though, this is all pure rubbish I suppose.
Heat engine theory generally claims that heat goes THROUGH a heat engine like water through a turbine. I think that that is not actually true, except perhaps for excess heat.
- Alpha_Stirling.gif (116.04 KiB) Viewed 10454 times
In thermodynamic theory, heat and work are equivalent. So for the amount of work performed pushing out the (cold side) piston, an equivalent amount of heat is lost from the expanding/escaping gas. Though, unlike a fire extinguisher, in a Stirling engine, the gas is not escaping into the open air, but just from one cylinder to another. In the process of expanding and doing work, the gas gets cold and subsequently contracts drawing the piston(s) in again.
According to the standard idea of how a Stirling engine works, though, this is all pure rubbish I suppose.
Heat engine theory generally claims that heat goes THROUGH a heat engine like water through a turbine. I think that that is not actually true, except perhaps for excess heat.
Re: Please Someone help me , How Alpha Stirling engine works?
I tried to modify the gif from Wikipedia, because it does not really show any actual indication of heat flow, or the expansion heating and cooling of the gas.
It's not perfect, but it gives a better idea of what I personally THINK goes on in an Alpha type Stirling engine, but of course, it is just my guess or opinion and could be completely wrong.
IMO, the heated expanding gas from the hot side is what does the work of pushing the cold side piston and driving the engine.
Also, as I've illustrated, the heat does not ever really reach the sink or cooling fins. I believe that could be accomplished with a careful balancing of heat input to match the load on the engine so that there would be little if any excess heat to be removed. In reality, it is questionable if that ever really happens in any real engine, but from my observations, I think it sometimes does, otherwise I cannot fathom how some Stirling engines could continue to run without a flywheel. Also, with a regenerator (not shown in the gif) even LESS heat would be getting through the channel to the cold side.
It's not perfect, but it gives a better idea of what I personally THINK goes on in an Alpha type Stirling engine, but of course, it is just my guess or opinion and could be completely wrong.
- alphastirling.gif (60.05 KiB) Viewed 10451 times
Also, as I've illustrated, the heat does not ever really reach the sink or cooling fins. I believe that could be accomplished with a careful balancing of heat input to match the load on the engine so that there would be little if any excess heat to be removed. In reality, it is questionable if that ever really happens in any real engine, but from my observations, I think it sometimes does, otherwise I cannot fathom how some Stirling engines could continue to run without a flywheel. Also, with a regenerator (not shown in the gif) even LESS heat would be getting through the channel to the cold side.
Re: Please Someone help me , How Alpha Stirling engine works?
I do think constant volume or a trapezoidal working curve for the displacer is something that has been done with some Stirling engines and may have been Stirlings original intent. I'm not so sure about the piston. I'm skeptical that Robert Stirling ever intended any trapezoidal motion for the piston.Sadi wrote: ↑Sat Jun 20, 2020 8:11 am Dear Tom,
When someone says "STIRLING ENGINE", one should always think about whether he is referring to the historic Heat engine built by Robert Stirling or he instead, is referring to the "Modern Heat Engine" operating in the thermodynamic "Stirling cycle".?!
You have noticed very well that the ubiquitous animation by which Wikipedia allegedly demonstrates the work of the Stirling engine does not actually show either! This animation only shows what happens when two cylinders with the corresponding pistons are connected to the working shaft with a displacement of 90°. But that mechanism is not a Stirling engine, nor does it properly demonstrate the operation of a Heat Engine operating in the Stirling cycle!
This "animation" is the main reason (culprit) that most people "just think they know" what a Stirling engine is and that most designers misuse the name Stirling engine for their "heat engines". That's why it's a futile effort to fix that animation!
Robert Stirling's ingenious idea was to bring the working medium from its state after hot expansion (Tmax, Vmax) or cold compression (Tmin, Vmin) to its initial "working" state at "CONSTANT VOLUME" (Vmin, Vmax)! This idea has not been realized to this day because all "constructors" just improvise!
The Stirling engine (Stirling cycle) requires a "trapezoidal working curve" of the working elements of the machine, while a direct connection of the working elements of the machine to the working axis gives a "sinusoidal working curve". Therefore, it is necessary to construct a kind of "DRIVE" between the "thermodynamic part of the machine" (working medium) and the "mechanical part of the machine" (flywheel and working shaft), which would turn the sinusoidal motion of the reciprocating mechanism into a trapezoidal motion of the Stirling engine!
But who is working on it? Is no one?
I would think that this would be accomplished in regard to the displacer by having the displacer drop and lift (or move side to side, end to end, whatever) very quickly while the piston is at, or near TDC and BDC. Constant volume would be maintained while the crank is rounding the curve and the piston is "paused" at the end of its stroke and about to change direction, movement of the displacer during that phase does not change the total volume.
This tiny little LTD engine, I think, closely approximates this by using a magnet to lift the displacer, which results in a sudden rise and then a sudden drop of the displacer, and the regenerator is built right into the displacer, so you do have that simultaneous regeneration during constant volume you mentioned before.
https://www.youtube.com/watch?v=czVQVCIi7CU
If you have some reference indicating Stirling intended a trapezoidal curve for both displacer and piston I would find that interesting, though I'm not at all sure it would be possible in practice, or of any benefit.
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Sockmonkey
- Posts: 50
- Joined: Wed Jul 31, 2019 5:32 pm
Re: Please Someone help me , How Alpha Stirling engine works?
One thing I really like about that one is that it has a proper firebox around the hot cylinder. Every display model I've seen just has it hanging over an open flame. That really drives me nuts as a good insulated firebox would not only heat it up working temperature faster, it would also cut down on the fuel consumption a lot. Fuel efficiency is half the reason for Stirlings in the first place!
Re: Please Someone help me , How Alpha Stirling engine works?
For all the comments above, I read and think, why not, add another comment, here goes:
Any heat engine involves drawing heat from a higher temperature source, extracting some mechanical work, ( or power) and then dumping the remaining energy to a colder reservoir.
In the stirling alpha 2 piston engine, the otto cycle gas engine, the jet turbine, all involve compression , with the gas being colder, and then expansion to create more work out , of a hotter gas. In the stirling the gas is traded back and forth, you can see in the 2 piston stirling that the compression is always when the gas is colder, and then the cold, slightly hotter gas is transferred to the bigger piston, where the hotter gas has more energy, ( enthalpy) and pushed down the larger area power piston with more work done, then then smaller cold piston using some of the system mechanical work to compress the gas while it is still relatively cold. The key, is the back work is squashing cold air, raising the pressure, and always taking less energy to do that , than the work output, when the gas is heated and more energy, ( enthalpy) used to push the output side piston downward. The efficiency of the stirling is related to the volumes, pressures, ( piston sizes) and temperature differences when the gas is compressed cold, and when the gas is expanded hot. The displacer variants are clever ways to use the displacer to produce a cooled volume of air when the back work compression is done, and producing a heated volume when the forward ( output) work is accomplished with the hot expanding gas. The net engine work is always the difference between the back work, ( input, typically stored by the flywheel, or momentum temporarily) and the forward, or output work. The reasons stirling engines suck for compact power is the fairly small differences between the hot gas and cold gas, that's why you need giant volumes of pistons and strokes to make very much net power. Steam engines have almost no back work, you're just pumping liquid water into a high pressure boiler, and huge amounts of output work.
Any heat engine involves drawing heat from a higher temperature source, extracting some mechanical work, ( or power) and then dumping the remaining energy to a colder reservoir.
In the stirling alpha 2 piston engine, the otto cycle gas engine, the jet turbine, all involve compression , with the gas being colder, and then expansion to create more work out , of a hotter gas. In the stirling the gas is traded back and forth, you can see in the 2 piston stirling that the compression is always when the gas is colder, and then the cold, slightly hotter gas is transferred to the bigger piston, where the hotter gas has more energy, ( enthalpy) and pushed down the larger area power piston with more work done, then then smaller cold piston using some of the system mechanical work to compress the gas while it is still relatively cold. The key, is the back work is squashing cold air, raising the pressure, and always taking less energy to do that , than the work output, when the gas is heated and more energy, ( enthalpy) used to push the output side piston downward. The efficiency of the stirling is related to the volumes, pressures, ( piston sizes) and temperature differences when the gas is compressed cold, and when the gas is expanded hot. The displacer variants are clever ways to use the displacer to produce a cooled volume of air when the back work compression is done, and producing a heated volume when the forward ( output) work is accomplished with the hot expanding gas. The net engine work is always the difference between the back work, ( input, typically stored by the flywheel, or momentum temporarily) and the forward, or output work. The reasons stirling engines suck for compact power is the fairly small differences between the hot gas and cold gas, that's why you need giant volumes of pistons and strokes to make very much net power. Steam engines have almost no back work, you're just pumping liquid water into a high pressure boiler, and huge amounts of output work.
Re: Please Someone help me , How Alpha Stirling engine works?
some more comments. Stirling engines are used in reverse for high reliability cooling, very high efficiency, etc. I find them facinating, and potentially useful. The "suck" comment is the pound for pound efficiency of the stirling. of course there's not N2 problems with Stirlings either, because they are an external combustion engine. but for raw power per pound, you might find gas IC engines putting out 1 or 2 HP per pound, cars with 350 HP engines, motocycles with 200 HP, just phenomenol. For the otto cycle, IC combustion temps of a few thousand degrees and perhaps net temps into the 100's and 100's of degrees C, the Th-Tc/ ( Th+Tc) thermal efficiency of the IC is quite good. The stirling tries to save the energy with the regenerator, but it is typically modest. Unless I am wrong, maybe someone can give me a link to a 350 HP stirling engine?