Stirling or Steam Engines for power Generation on Mars?

[Redsand11j]

Hi, everyone. I found your forum when trying to find the specifics of Sterling versus Steam power for use in an early Mars colony. On Earth, steam turbines predominate in power generation facilities. However, the economy in an early Mars colony will be much different than that of a fully industrialized country. I am provisionally using a population range of 500-10,000 people for this stage of the colony's development.

The colony will be, to whatever extent is possible, built with materials available on Mars. There is Iron available, as well as some polymers, and there will have to be some sort of lubricant available, to grease wheels etc. if necessary. Whichever heat engine is used, it will probably be made primarily of Carbon Steel, possibly composited with Basalt fibers, which can increase tensile strength.

The heat source will be the sun, because I think that concentrated solar power is the most viable source of electrical energy for Mars.

Because the Martian economy will not be very technologically advanced, Steam Turbines are essentially out of the question. That means that Sterling and Steam are on fairly equal footing in terms of efficiency, with both Starling and non-turbine steam maxing out at about 50% of the Carnot efficiency at any given temperature. As many of you probably know, the Carnot efficiency is the maximum possible efficiency for a heat engine at a given temperature, and is equal to 1-Tc/Th. My Hot side temperature is 220 C (493 K, 428 F), though if possible the heat engine should be able to operate at much lower temperatures due to the sun setting. The cold side is at 0 C (273 K, 32 F), and if it could work down to hot side temperatures of 30-35 C (303-308 K, 86-95 F), that would be great, though less is acceptable. Running a steam engine at lower pressure should make this workable.

The working fluid for a Stirling engine would probably be Nitrogen gas.

So, based primarily on the factors of simplicity, reliability, and efficiency (as well as anything else that you think may be important), which do you all think is more suited to use in a Mars colony's power generation facility?

The thread where I am investigating this can be found on the Newmars forums, the forums for the Mars Society. The thread is here, if anyone is interested. I thank you all very much for your help in this.

[Longboy]

........Stirling does not work in a Martian atmosphere.

[jimlarsen]

NASA gets Stirlings to work on satellites, so I am guessing Mars would be easy.

[Redsand11j]

Longboy:

I am not talking about a hot air engine, but a bona fide Stirling engine, with the working fluid contained inside. I'm thinking argon would be best, since it's fairly common in the Martian atmosphere.

[jimlarsen]

You want the lightest (least dense) gas available. Lighter gasses expand and contract more with temperature changes. Heavier gasses do not work as well. That is why we put helium or hydrogen in our motors. If you find water and electricity on Mars you will be able to make hydrogen.

[Redsand11j]

Well, Hydrogen would be good, except the engine will probably be made of Iron or steel. These are subject to Hydrogen Embrittlement, which makes Hydrogen extremely undesirable as a working fluid.

[jimlarsen]

Then you don't want to use iron or steel. If you want high efficiency you want to use copper.

[Longboy]

........Stirling does not work in a Martian atmosphere.

Longboy,

Excuse me?

Why not?

RS

...........That would be because Stirling doesn't work in a vaccuum. If you know Stirling principle, you will know how atmospheric pressure on Earth allows Stirling engines to run.

[Longboy]

Longboy:

I am not talking about a hot air engine, but a bona fide Stirling engine, with the working fluid contained inside. I'm thinking argon would be best, since it's fairly common in the Martian atmosphere.

.......you "are" talking about a hot air engine if you mention Stirlings. Using argon or ordinary breathable Earth air, exactly what in the vaccuum of space is going to push the power piston back up the bore?

[Longboy]

NASA gets Stirlings to work on satellites, so I am guessing Mars would be easy.

......can you post a reference Jim, I'd like to see how they did it!

[jimlarsen]

I have not researched it personally, but it has been the topic of conversation in the Hot Air Engine Society in Yahoo Groups. You might find some references to it if you search through their archives. It might also just be a legend! :)

http://tech.groups.yahoo.com/group/HotA ... ISO-8859-1

[speedless]

Hi
Finally some sence!
Thanks theropod2 for staighten this out.
Nice to see some one who actually examens issues before commentating.

I was a bit confused,not by the POLL question but from some of the replyes.

Any type of stirling (alfa,beta,gamma) will work as long as there is outside pressure for reference-point.
And as theropod2 wrote,if needed make a closed system.
links;
http://search.nasa.gov/search/search.js ... e=stirling
http://www.kockums.se/en/products-servi ... oject-a26/

Back to the POLL
As a pioner i dont think i would like to rely on a design that needs hard to get materials or is complex to maintain.
It should be simple and imported "as is".(with plenty off spareparts)
Guess a coloni at first would have to rely on suplies from earth on a regular base.(every forth year?)
It will take some time before the coloni is capabel to use the natural sources.
The only choise i can come up with,is (Oh No) nuclear power,so sorry but neigther stirlings or steam are addequit, considering the need for powering a habital on mars.
On a long time base it will be COST vs. POLITICS,access to materials,knowlegde (in that order),that will deside the powersource.

I dont think stirling or steam engines is really a choise here,my vote is blank!

Jan

[Longboy]

Longboy,

The atmosphere of Mars is well below that of earth, but it is not a vacuum. The average Martian mean surface pressure is 600 pascals (0.087 psi), compared to Earth's sea level average of 101.3 kilopascals (14.69 psi) source WIKI.

Methods exist to run a Stirling in an isolated chamber and transfer the rotation energy via magnetic couplers to the external environment, whether that be a vacuum or not. This chamber could be pressurized with whatever gas the designer so chooses, and as long as the sealing is adequate the engine would still work.

I see no reason the think a properly design Stirling, and associated support systems, could not work quite well on the surface of Mars. RS.

.........Essentually for you and I and for Stirling the Martian atmosphere is a vacuum. As long as you qualify a Martian Stirling within a "isolation chamber" (not presented in your original posting) that replicates Earth conditions , then I would agree that Stirling can run on Mars.

[Andrzej]

Stirling engine - VERY GOOD can work on Mars!!!
Better than on Earth!
Because - You has very good cooling from one side, that is big problem on Earth / cooling/!
Andrew

[xtetra]

Likewise the moon no? Understanding of course that it was a pressurized and sealed unit. If oriented towards the sun on the lunar surface it seems that one side would be very very warm and the other very cold, giving you the temperature differential needed to increase output.