Calculations on the compressed air to an engine cycle

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Remundo
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Re: Calculations on the compressed air cycle for a motorization




by Remundo » 07/06/20, 01:30

GuyGadebois wrote:I might say bullshit, but why not run the engine directly with nitrogen? : Cheesy:

not too often then, because with each cycle we lose energy,

not nitrogen, by its cryogenic liquid state is rather seen here as a method of temporary storage, as would be the water of a pumping and turbine station by its elevation.
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Eric DUPONT
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Re: Calculations on the compressed air cycle for a motorization




by Eric DUPONT » 07/06/20, 08:29

Remundo wrote:what Eric says here in somewhat approximate terms is correct, in fact he speaks of an isothermal compression of a perfect gas with an ideal machine, followed by expansion under the same conditions.

For slow machines with large heat exchangers, it is playable, but of course there are still losses.


the gas does not need to be perfect for it to be 100% reversible. the water diffused in the cylinders make very good exchangers.
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Re: Calculations on the compressed air cycle for a motorization




by Remundo » 07/06/20, 12:23

do not confuse the thermal agent and the heat transfer fluids ...

otherwise an "ideal gas" is a fluid in which there is no friction, in reality there is always some viscosity, in liquids too.
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Re: Calculations on the compressed air cycle for a motorization




by Eric DUPONT » 07/06/20, 12:39

the water in the cylinder absorbs the heat of compression heat.
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Re: Calculations on the compressed air cycle for a motorization




by Remundo » 07/06/20, 12:58

maybe but you are out of service here, we have already discussed this "idea" which leaves me perplexed, forming ice crystals in a compressor / piston regulator ... : roll:

Your coolants must be separated from the air to liquefy, even the residual moisture of this air must be removed before liquefaction.
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Re: Calculations on the compressed air cycle for a motorization




by Eric DUPONT » 07/06/20, 15:16

I'm talking about the compression of isothermal air with water rather than by one or more exchangers
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Re: Calculations on the compressed air cycle for a motorization




by Remundo » 07/06/20, 16:57

at compression it is annoying too; water becomes liquid, or is already liquid, as an incompressible fluid, you really have to be careful not to break the mechanics ...
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Re: Calculations on the compressed air cycle for a motorization




by obelix39 » 07/06/20, 23:38

Remundo wrote:
obelix39 wrote:I do not think I am mistaken in saying that all the losses which cause a drop in yield are thermal, whether mechanical friction, heating of electric cables by the passage of current, etc. ... During a production of potential mechanical energy, whether by raising a mass to take advantage of gravity, compressing air to take advantage of the pressing force, or rotating a mass at high speed to take advantage of its inertial energy, etc. ... If we recover all of the dissipated thermal energy, we obtain a yield of 100%, is that correct?

it depends on how you count the energy and what you want to do with it. Numerically yes, the energy is conserved, so if you are the losses + the mechanical work recovered, you will find everything that has been supplied to the machine


To stay on topic (Calculations on the cycle of compressed air for an engine), if we compress air in order to run a compressed air engine, we produce about 65% of mechanical force in the form of compressed air stored in a tank, and 35% of heat is produced, of which 94% can be recovered (this is what is done in industry) for heating, hot water production, hot air , etc ... Even if the energies produced are different, from the moment they are used, they are not losses but rather "useful" energy. We can therefore compress air using 97% of the starting energy. I find that pretty good! The fact of not recovering the heat during the compression makes the use of compressed air not very profitable, and this is the case I believe with Guy Nègre's car.

It remains to be seen the performance of the engine ...
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Re: Calculations on the compressed air cycle for a motorization




by Remundo » 08/06/20, 01:16

yes it is a form of cogeneration: heat losses are dissipated to heat a home. We can thus go up to high yields, up to 100%, but heating a house to 20 ° C is much less noble than mechanically operating a machine or producing electricity.

The "useful" energy has nuances, a nobility or not, and its counting in the form of "yield" (we also speak of efficiency which is a broad notion of yields) depends greatly on a certain subjectivity in the definition mathematical performance.
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Re: Calculations on the compressed air cycle for a motorization




by obelix39 » 08/06/20, 06:50

Remundo wrote:yes it is a form of cogeneration: heat losses are dissipated to heat a home. We can thus go up to high yields, up to 100%, but heating a house to 20 ° C is much less noble than mechanically operating a machine or producing electricity.

The "useful" energy has nuances, a nobility or not, and its counting in the form of "yield" (we also speak of efficiency which is a broad notion of yields) depends greatly on a certain subjectivity in the definition mathematical performance.


Of course, by introducing a notion of nobility it lowers the yield ... Unless it is for you only a way of expressing that you do not like compressed air?
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