Stirling engine efficiency

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asit_tripathy87
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Stirling engine efficiency

Post by asit_tripathy87 »

can u tell me please what factors determines the efficiency of a
Stirling engine & will it be going to affect it"s efficiency if we
install valves.
stan.hornbaker
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Response to Stirling engine efficiency

Post by stan.hornbaker »

A Stirling Engine is an External Combustion Engine, completely different from ICE's. The Stirling does NOT have valves which are not applicable. Any attempt to install valves would make it a Non-Stirling.

Maximum possible efficiency is the ratio of the difference of the absolute temperatures divided by the the higher absolute temperature.

Other factors such as materials of construction, specific designs, etc. will affect the overall power output.
stepan___1718
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Response to Stirling engine efficiency

Post by stepan___1718 »

The theoretical efficiency of the Stirling engine is same as Carnot efficiency of heat engine, (Th-Tc)/Th, where Th and Tc are the absolute temperatures. The practical efficiency of Stirling engine is the ratio of the mechanical energy output from engine to the heat energy input. This ratio is dependent on the construction of the engine and most importantly the working gas used.
Installing valves to Stirling engine will not increase the efficiency but will reduce the reliability.
bptdude___2569
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Response to Stirling engine efficiency

Post by bptdude___2569 »


The known simple Stirling engines have low power, and any mechanical addition is likely to just make it stop working, unless it add a whole lot more power than it consumes. The known Stirling engines with significant power are engineered and manufactured to extreme tolerances and thus make themselves not cost effective.

Whatever the very high known theoretical efficiency of a Stirling, people just have not cracked that nut yet, as far as engineering level design.

While so many have ideas about what is or isn't a Stirling, and Internet debates rage, it basically is a heat engine that contains a sealed gas, that is heated on one end, and cooled on the other, using the expansion and contraction of the gas to extract the power. The gas is always sealed, never vented and refilled. Trivial hydrogen leak through the metal that is replaced is an acceptable exception.

For example, a steam engine is not a Stirling, because it vents steam that is replaced, as part of the power cycle.

The engine is always considered to be externally heated, as in the burning fuel or heat source is outside, and then transferred inside. The same goes with the cooling.

Valves? Tricky question. Almost everybody on this site will yell at me to even suggest you might have valves and still call it a Stirling. But, it depends on how you use the valves.

Dispite the fact I can not get even crappy little toy models to work, personally, I have worked out some theory designs I hope one day in my retirement to begin to build.

While not giving the farm away on my ideas, the basics are that heating the outside casing continuosly for heat input is silly. You need to heat the gas inside, not make the container glow red.

There is also a major power advantage to gain by timing the heat to a specific moment in the cycle, and at that point, as quickly as possible.

These two concepts will introduce complexity that should more than pay for themselves in power, if done as I dream. The power obtained will be closer to an internal combustion. The major downfall of Stirling theory and practical engines is at these points.

While you do not want to use valves to bring in new gas or fuel, or vent out gas or exhaust, there may be a place for valves in a way people do not usually think of.

When this is conquered, the regenerator can be thrown out, another Stirling heretic concept. It substitutes speed of heating/cooling and volume required for gas expansion and compression, for a horrible loss of power effeciency. Even though I will sure get beat up for it, if you think about it, if you can flash heat the gas in the hot end, at the right moment, it should be obvious the regenerator is pointless and just acts as cement swimming flippers.

If we had the full set of working notes from Rev Stirling and his brother, you might find they came up with the regenerator because they were willing to give up some power in exchange for not having to burn half the forest of wood with bellows to get enough heat to make the thing work at all.

But we can do better, now, right ?

ceo___1402
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Response to Stirling engine efficiency

Post by ceo___1402 »

I partially agree with what you posted. Introducing heat where the cycle starts instead of at the middle of the end of the power cycle could put power to the cycle sooner making the engine produce more power. Using helium instead of air can help allot too since it expands allot more that air does when heated and it weighs less so it creates less drag on the motor. On the regenerator...even if you could flash heat like you want to, which may be possible but expensive with little or no benefit the heat is still in the engine regardless so there is no point wasting it. Why not reuse it
bptdude___2569
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Response to Stirling engine efficiency

Post by bptdude___2569 »



yes, we all know about helium. but something more fundamental needs to change before we max out the design with such things. air would work fine for now for small models and test engines.

flashing the heat { or cold, *wink* } is a huge factor, not yet really done in Stirlings. the placement of timing is not THAT different from internal combustion engines. the concept is to gain a similar power output. you would start the flash just before TDC { Top Dead Center }, is my guess. "may be possible" HA HA HA.. do not talk like a New York lawyer ! :) of course it is possible, the question is practical, and you should not assume expensive. that is just part of the engineering that backs up the theory. there are several ways, which may have little overhead, especially if that is the only way to make the engine have high power output.

the regenerator is NOT reusing heat like you and so many people think. it is merely playing a trick, that allows lower delta between the hot and cold side, and still have the engine run, but with reduced power, not more. it also does other things interacting with the pressure equation, but I don't think you are ready for that one.

for short, the regenerator, while seems to be needed by so many, is actually doing the opposite of flashing the heat. that is all I will say for now.

but, thank you for your interest, and I look forward to more of your posts.

- Joe


justin2929
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Response to Stirling engine efficiency

Post by justin2929 »

Joe, would you mind elaborating on the idea of "flashing" the heat? I canÂ’t seem to conceptualize that one.
bptdude___2569
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Response to Stirling engine efficiency

Post by bptdude___2569 »


Well, since you asked so nicely!
:)

The pressure equations are written such that there is a sorta smooth transition in an evenly flowing manner, much like a pair of waves.

Look at the pressure equation for an internal combustion engine, and the mean of timing is critical to extracting and converting energy.

So, while my concept of a "Stirling" may be twisted, it still basically is a sealed heat engine, without even fluid state trasition.

The obejct for me then becomes to devise a basic alteration to the standard cyle. The Stirling brothers became famous for the use of the regenerator. Perhaps the modern equivalent is the add-on to the Stirling that converts its intended heat source of constant unusual source, and without too much system cost, pusles it nicely to the timing of the engine cycle.

The less the pressure of the cylinder when the piston is moving { or being moved } into place, and then suddenly on the other side of the top, gets a blast of highest practical pressure, the more the engine will produce power.

The Stirling is unusual in the, if your engine was built to it, could also push as well as pull the power piston. ICE { Internal Combustion Engines } can not do this. The Stirling, given real or delivered wide enough delta of hot and cold could be pushing and pulling at the same time. This is not the curent stat of the Stirling.

The Stirling is like flight, where it was almost a century after the theory of flight was well worked out in theory, before a couple of bicycle repairmen who liked kites worked out practical matters of flight controls and materials.

As to your question? Oh yeah.

One simple "flash system" would be used with a solar heat source. My own design { or maybe first done by others, I don't care } is to use existing trough base, but use fresnal technology instead of transfer to oil in pipe. Duct the super hot solar heat to one end of a commercial Stirling for electrical to hydrogen plant.

As the cylinder goes back and forth, it is tied to a simple apperature open and close, through which the solar blaze may enter, just at the proper timing of the cycle.

Hey, even that is not perfect, and would have many questions, like what magic material will be the side of the engine that passes solar blaze but otherwise is fine.

The idea is that the energy is pulsed.

The flashing could be done by a engine that has the end quick heated or quick cooled by having numerous spikes suddenly thrust into that end, coming from the external means of heating or cooling. Overhead, yes, but leave that to the cleverest engineer. Give him the theory that it would indeed work, if he could make one.

Again, keep at the high level of concept, and pusle the heat delta, will have its own equation of engine power increase for same heat delta.

:)

Does that answer your question?

Regards,
Joe
bptdude___2569
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Response to Stirling engine efficiency

Post by bptdude___2569 »


Well, since you asked so nicely!
:)

The pressure equations are written such that there is a sorta smooth transition in an evenly flowing manner, much like a pair of waves.

Look at the pressure equation for an internal combustion engine, and the mean of timing is critical to extracting and converting energy.

So, while my concept of a "Stirling" may be twisted, it still basically is a sealed heat engine, without even fluid state trasition.

The obejct for me then becomes to devise a basic alteration to the standard cyle. The Stirling brothers became famous for the use of the regenerator. Perhaps the modern equivalent is the add-on to the Stirling that converts its intended heat source of constant unusual source, and without too much system cost, pusles it nicely to the timing of the engine cycle.

The less the pressure of the cylinder when the piston is moving { or being moved } into place, and then suddenly on the other side of the top, gets a blast of highest practical pressure, the more the engine will produce power.

The Stirling is unusual in the, if your engine was built to it, could also push as well as pull the power piston. ICE { Internal Combustion Engines } can not do this. The Stirling, given real or delivered wide enough delta of hot and cold could be pushing and pulling at the same time. This is not the curent stat of the Stirling.

The Stirling is like flight, where it was almost a century after the theory of flight was well worked out in theory, before a couple of bicycle repairmen who liked kites worked out practical matters of flight controls and materials.

As to your question? Oh yeah.

One simple "flash system" would be used with a solar heat source. My own design { or maybe first done by others, I don't care } is to use existing trough base, but use fresnal technology instead of transfer to oil in pipe. Duct the super hot solar heat to one end of a commercial Stirling for electrical to hydrogen plant.

As the cylinder goes back and forth, it is tied to a simple apperature open and close, through which the solar blaze may enter, just at the proper timing of the cycle.

Hey, even that is not perfect, and would have many questions, like what magic material will be the side of the engine that passes solar blaze but otherwise is fine.

The idea is that the energy is pulsed.

The flashing could be done by a engine that has the end quick heated or quick cooled by having numerous spikes suddenly thrust into that end, coming from the external means of heating or cooling. Overhead, yes, but leave that to the cleverest engineer. Give him the theory that it would indeed work, if he could make one.

Again, keep at the high level of concept, and pusle the heat delta, will have its own equation of engine power increase for same heat delta.

:)

Does that answer your question?

- Joe
justin2929
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Response to Stirling engine efficiency

Post by justin2929 »

I think I understand Joe! You should check this out. http://www.proepowersystems.com/Stirlin ... arison.pdf
Look at page 14. I think that this, being an open cycle, would be considered a Brayton
Cycle, while an Ericsson cycle is a closed system that nonetheless works the same way. My beef with this engine is that it creates the illusion that since its an open cycle, you need not be concerned with that one weak link in the practicality of the Stirling engine (In my opinion J), the cold sinc heat rejection rate. I think that in practice this engine would suffer form the same problems at a Stirling, with the added drawback that the gas choice must be air and therefore forgoing the seven fold greater conductivity of HE. If im hearing you right Joe, would you install a valve between the compression cylinder and the expansion cylinder, and when the compression Cylinder is at TDC, (and the exp cylinder would be at TDC as well) release the compressed gas at that instant, thereby allowing for more time for heat rejection in the cold sync as well as reducing system pressure experienced by the hot piston because of its isolation form the compression pressure?
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