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#51 2004-11-25 17:46:07

Dook
Banned
From: USA
Registered: 2004-01-09
Posts: 1,409

Re: Running on Compressed Air?

Carbon composite is lighter than titanium and would be strong enough.  The battery would freeze solid in the -100 F mars temperatures unless you had it encased in some type of heating device that would always be on. 

Forget the radio.  Pressure suits have radios built in plus it's not like you can talk anyway through the suit glass and there is little atmosphere to carry the sound to the mic.

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#52 2004-11-26 19:24:54

Timeslicer
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From: Arizona
Registered: 2004-06-19
Posts: 27

Re: Running on Compressed Air?

Probably quoted elsewhere here, but related to the discussion of liquid CO2 for propulsion - Zubrin's Grasshopper

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#53 2004-11-27 23:48:18

Austin Stanley
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From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
Website

Re: Running on Compressed Air?

I don't see any reason you couldn't build a air-powered 4-wheeler or something, but I guess the question then would be, how does an CA engine stack up against other options (particularly electrical, ICE, and fuel-cell).  What would be the typical power-weight ratio and fuel efficency of such a vehicle?  I've done a quick search but I haven't been able to find any data.


He who refuses to do arithmetic is doomed to talk nonsense.

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#54 2004-11-28 01:17:28

Austin Stanley
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From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
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Re: Running on Compressed Air?

Hmmm... after some more research I found some figures for a possible pneumatic engine.

The compressed air in the tank was expected to give some 25 Whr/kg or 90kJ/kg.  Which is not to impressive, chemical fuel sources generaly have >10MJ/kg.  So they are about 100 times more energy dense.  Even assuming 100% efficency for the pneumatic engine and say 25% for a chemical (perhaps combustion), you would come way ahead chemicaly.  Even conventional batteries have supperior energy densities, greater than 300kJ/kg.  And batteries have efficency (40-50%) on their side as well.

They do better on power-weight ratios however, with the figures I saw claiming 500W/kg.  This is on par with combustion engines, and better then batteries and fuel cells clock in at about 100W/kg.

As for the more etherial issues, I do not see an great advantage in compressed air over the other alternatives.  All pneumatic engine relies on the expansion of gases, so is probably going to have as many moving parts as any combustion engine would, giving it no advantage in reliability.  While refuling an air tank might be simpler than refuling a chemical vehicle, it is certianly less easily done than a battery powered vehicle.

OTOH, for a short range utility vehicle the power-weight ratio is much more important that fuel efficency/energy density.  Which is a point in favor for the pneumatic engine.

However for my money if you do not want to use chemical power for your short-range utility truck (because of complexity of refuling or whatever), then batteries are probably the way to go.  Their energy density is 10 times greater, and there power density is only 5 times less.  And they should be if anything easier to fuel and more reliable.


He who refuses to do arithmetic is doomed to talk nonsense.

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#55 2004-11-28 03:31:41

Euler
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From: Corvallis, OR
Registered: 2003-02-06
Posts: 922

Re: Running on Compressed Air?

Which is not to impressive, chemical fuel sources generaly have >10MJ/kg.

On Mars, you would also have to carry around the oxidizer for the chemical fuels, so their advantage in energy density would not be as large.

And batteries have efficiency (40-50%) on their side as well.

A lot of batteries can achieve 90% efficiency or higher.

Flywheels and capacitors would also come into consideration.  Both have had significant advances in recent years, with energy density approaching that of batteries, high efficiencies, and high power densities.

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#56 2004-11-28 19:09:25

Austin Stanley
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From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
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Re: Running on Compressed Air?

On Mars, you would also have to carry around the oxidizer for the chemical fuels, so their advantage in energy density would not be as large.

Already accounted for, most likely fuel-oxidiser combinations have energy densities ~10MJ/kg.

As for flywheels, there energy densities are on-par to supperior to batteries <400kJ/kg, and since all they need is transmition equipment there power-to-weight ratios are excelent.  But safety would be even more of a concurn than with compressed air.  If a rotor was to get loose at 20,000rpm, the effect would be disaterous.  Also, wouldn't a large rotating weight cause issue with manuverability.

I still tend to think that batteries would be the way to go, if you decided to exclude chemical options.


He who refuses to do arithmetic is doomed to talk nonsense.

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#57 2004-11-28 19:28:24

BWhite
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From: Chicago, Illinois
Registered: 2004-06-16
Posts: 2,635

Re: Running on Compressed Air?

But it does mean we can't replace the engine in a Silverado and fire it to Mars. Nuts.  :laugh:

I envision a pressurized "Silverado" built from composites (at least crew compartment - - perhaps you want steel & aluminium for the chassis for durability) and with only "door" being along the centerline in the rear. The current drivers and passenger doors are eliminated in favor of a cabin wall made from plastics, in layers. Multiple layered glass windows with transparent polymer sheets between the glass.

Allow the rear airlock to work by itself or dock with a trailer.

4x4 with high ground clearance and the ability to adjust tire inflation from inside the cabin. Its internal combustion so you have plenty of power for driving where "off road" is the only choice.

With a trailer and additional fuel bottles, range could be quite substantial.

= = =

Mass? One Delta IVH can throw it easily enough as a stand alone supply drop. If you are doing a $30 billion Mars mission why cut corners by shaving off a stand alone Delta IVH launch?

Besides, make Ford, Dodge, Chevy, GMC, Mercedes, Land Rover etc. . . all compete for the privilege of donating three or four rovers (complete with hood ornaments) and let the winner pay for the Delta IVH shot. Think of the TV ads.

Would it be worth $500 million for a truck company to be awarded the Mars rover "contract" - - contract in quotes because NASA never pays them a single dime!!



Edited By BWhite on 1101691972


Give someone a sufficient why and they can endure just about any how

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#58 2004-11-29 07:11:53

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 14,035

Re: Running on Compressed Air?

I like the contest item on the big auto manufactures but would they go for it on presteg alone...

As for the first Mars buggy, I think it will be more in line with the lunar buggy concepts but on steriods. More general purposes than for the long haul concepts of mileage.

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#59 2004-11-29 08:47:02

Cobra Commander
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From: The outskirts of Detroit.
Registered: 2002-04-09
Posts: 3,039

Re: Running on Compressed Air?

I like the contest item on the big auto manufactures but would they go for it on presteg alone...

No, but it's a hell of an ad campaign.  :;):


Build a man a fire and he's warm for a day. Set a man on fire and he's warm for the rest of his life.

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#60 2004-11-29 09:25:04

BWhite
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From: Chicago, Illinois
Registered: 2004-06-16
Posts: 2,635

Re: Running on Compressed Air?

I like the contest item on the big auto manufactures but would they go for it on presteg alone...

As for the first Mars buggy, I think it will be more in line with the lunar buggy concepts but on steriods. More general purposes than for the long haul concepts of mileage.

I have a full length article in process. But here are a few tidbits.

Chrysler spent $50 million last year to sponsor ONE season of Trump's "The Apprentice" - - one season! Ford budgeted $100 million of September of 2003 for the new F150 pick-up truck.

A Delta IVH launch costs about $250 million. (A slightly smaller rover that could be lifted by Proton and thrown to Mars would only need $75 million for launch costs.) Both rovers (Delta IVH sized or Proton sized) would be bigger than the 1.4 mt used by Robert Zubrin in the Case for Mars baseline.

The winning rover "wins" the right to PAY Boeing $250 million or pay the Russians $75 million for a Proton launch. Then every time video feed comes in from Mars that Ford logo or Land Rover logo will be on camera, showing their product climbing a Marsian hill.

This could be a 5 year or 10 year advertising campaign, including themed ads running before the final selection is made. Require all entrants to accept a few dozen unpaid student interns during the development phase for further public outreach.

NASA gets a rover, landed on Mars, for free. Robert Zubrin's Mars Direct gets 1.4 MT added to its mass budget, more if food and gear are stashed in the rover before launch

Edited By BWhite on 1101741944


Give someone a sufficient why and they can endure just about any how

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#61 2004-11-30 13:52:33

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Running on Compressed Air?

Mass? One Delta IVH can throw it easily enough as a stand alone supply drop. If you are doing a $30 billion Mars mission why cut corners by shaving off a stand alone Delta IVH launch?

Because you can't send the rover on a seperate vehicle to the landing site accuratly enough. "Plus or minus a few hundred kilometers" isn't good enough. The initial manned lander must be equipped with the long-range rover in the event of a missed landing or the MAV/ERV vehicle.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#62 2004-11-30 14:15:16

John Creighton
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From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
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Re: Running on Compressed Air?

Because you can't send the rover on a seperate vehicle to the landing site accuratly enough. "Plus or minus a few hundred kilometers" isn't good enough. The initial manned lander must be equipped with the long-range rover in the event of a missed landing or the MAV/ERV vehicle.

The accuracy in landing will depend entirely on how much fuel have to land. It is like a missile. Traditional missiles can only turn so fast because of their fins so if you aim bad your guidance system has no hope of reaching target. Cruse missiles are like a plane and can be guided to the target much more precisely. Similarly on mars if you budget enough fuel for the landing you can land as precisely as you want. This could be worth while if the crew lender is much lighter then the cargo Lander. As far as a suitable distance that depends entirely on the terrain the rover must cross. You can travel a few hundred kilometers in a few hours on good terrain.

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#63 2004-11-30 15:16:04

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 14,035

Re: Running on Compressed Air?

Parachute steering is one of the items that have been given some thought and actual contracts are already in the works.
As for other alternatives I gave some in the Earth Re-entry, Moon or Mars Lander and return vehicle. One do all, part of CEV? can one ship do all for how to combine the shapes and features to get a more accurate and a much more robust load to planet surface lander for the mass cargo that we will need.

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#64 2004-11-30 16:35:47

BWhite
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From: Chicago, Illinois
Registered: 2004-06-16
Posts: 2,635

Re: Running on Compressed Air?

Mass? One Delta IVH can throw it easily enough as a stand alone supply drop. If you are doing a $30 billion Mars mission why cut corners by shaving off a stand alone Delta IVH launch?

Because you can't send the rover on a seperate vehicle to the landing site accuratly enough. "Plus or minus a few hundred kilometers" isn't good enough. The initial manned lander must be equipped with the long-range rover in the event of a missed landing or the MAV/ERV vehicle.

First, the BIG rover lands with (near) the ERV & nuclear reactor 26 months before the crew arrives. Successful landing and operation of the ERV and rover is a [GO] [NO GO] junction for the launch of Mars One.

Second, at the time the MarsOne crew lands, a 2nd rover and a 2nd ERV/nuke is spaceborne coming in behind the crew to support the 2nd landing scheduled for 26 months after MarsOne.

MarsOne misses the ERV & rover landing zone? Drop the back-up ERV & rover near Mars One. Robert Zubrin has mapped out landing circles for maximum support amongst missions.

Third, you can always include a bare-bones rover capable of carrying two people just in case both big rovers break down and cannot be driven robotically to where the crew has landed. Use it to go collect and repair the big rover.

Methane/LOX fuel comes from either of the 2 ERV/nuke units by processing the atmnosphere combined with seed hydrogen.

Still worried? If the rovers can be carried via Proton, send as many as you think you need - - at $75 million per launch the costs are miniscule compared with the project as a whole. If not used by the crew, those extra rovers engage in robotic exploration.

Frankly, having a rover (or two) driving around Mars and refueling by remote operation avoids the danger that a landing mishap (crumpled landing strut, for example) damages your on board rover. MarsOne lands but topples into a small crater. Pressure integrity is saved for the crew but the rover is smashed. Then what?

= = =

Besides, if MarsOne lands too far from the nuke/ERV how do you fuel the on board rover anyway?

edited By BWhite on 1101854363


Give someone a sufficient why and they can endure just about any how

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#65 2004-11-30 17:53:26

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,701
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Re: Running on Compressed Air?

I am not sure any of our existing boosters could put a pressurized rover on Mars anyway. Mars Direct put 27 tonnes out of 140 on Mars (19%). The biggest Delta can launch 25 tonnes to low Earth orbit. if it could land 19% on Mars (which is probably optimistic) that's 4.75 tonnes, which is rather close to the mass of these rovers, AND the 4.75 tonnes has to include landing gear and such. I'm not sure automated cargo landers would be worth using unless the could put at least 10 tonnes on Mars. That requires a bigger launch vehicle.

       -- RobS

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#66 2004-11-30 19:46:26

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Running on Compressed Air?

"The accuracy in landing will depend entirely on how much fuel have to land"

The amount of rocket fuel needed to hover helecopter like over long ranges would be extreme, and you can't adjust your trajectory much during reentry since you must keep the heat shield oriented just so.

No no Bill, see unless you can get the landing accuracy down to only a few tens of kilometers, forget about it, it doesn't matter if you throw a dozen spare rovers at the landing site.  It must be within walking distance of a stand-alone space suit.

Doubling the number of landers also doubles the risk that one will fail, and if the manned lander can't make it down as it is supposed to, then we have bigger things to worry about. As far as driving it on remote, I don't like that idea either, which precludes the safety of having two working LSS systems (HAB and rover) when you get down to the surface. There is the risk the big rover will just drive into a ravine or somthing during the time lag between mission control Mars too, and no dinky light rover will be able to tow it out.

As far as the fuel, the rover will obviously reach Mars with tanks loaded.

One option hited at in a NASA DRM document is to use dynamic RTGs for power, which would give unlimited range and auxillary power in any condition with reliability.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#67 2004-11-30 23:10:11

Austin Stanley
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From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
Website

Re: Running on Compressed Air?

I'm not crazy about the remote driving solution, but it may be one of the best ones that exists.  If the trip is taken slowly enough, there should be little risk that the rover will fail due to some terrain problems.  Given the duration of the crews stay on mars, taking the time to be safe should not be an issue.  Additionaly, the crew on mars should be able to opperate the vehicle remotely, eliminating the issue of time lag.  Communication bettwen the two might be an issue however, I'm not sure if the long-distance radios would be able to handle the necessary bandwith, necessitating a satilite-uplink.

More serious issue to me are the fact that the rover might simply break down on it journy, or the two sites might be simply inacessible to one another.  Mars contains some extream geography, and it is not inconceivable that you just might not be able to get there from where you are (within you range limitations especialy).

The two factors are concurns no matter how the launch is configured.  Having the rover at the base camp does not prevent the ERV from being landed in an inacessible location or the rover from breaking down on its way bettwen the sites.  Indeed, if the Hab and ERV are widely seperated the crew are in some distress even if everything goes well.  The ERV represents a signifigant portion of there equipment and safety margin, and if the crew are not able to get there easily in the advent of an accident, it may well spell disaster.

My solution to these issues is two-fold.
#1.  There should be two pressurised rovers at the base, and only one should sortie at any one time.  This ensures the base as a fall-back shelter in case of some sort of disaster, and it provides a method for rescuing the crew of the other rover should the have  some sort of accident.

#2.  The first mission will always be the most dangerous.  But follow up missions can be relived of some of this danger by being targeted at the first base.


He who refuses to do arithmetic is doomed to talk nonsense.

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#68 2004-12-01 06:42:51

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 14,035

Re: Running on Compressed Air?

The planet wide exploration would mean that we would not be landing at the same site and would mean several missions before we would.
Pressurized rover is a nice thing but not a necessity on the first few missions, having a backup and parts for repair might mean sending the rovers on a seperate rocket. Maybe shipping Segways for each astronaut would fit the bill. They are light weight, battery powered, take up little space and weight not very much.
Or design a modified tricycle with high ground rock clearance, sort of a battery powered ATV.

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#69 2008-03-11 20:43:37

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 14,035

Re: Running on Compressed Air?

With all the trouble I am having with an internal combustion engine I am wondering how one running on compressed air would fair.

Here are some links to share:
Compressed Air Cars to hit the Indian Roads in 2008

aircar.jpg

The air car can reach a top speed of 69 mph and can travel about 120 miles on a single fill of compressed air. It takes about 4 hours to fill the tank with compressed air at home or just 2 minutes using an industrial air compressor at the pump. The cost to refill the tank is expected to be approximately $2 for the full tank.

Car runs on compressed air, but will it sell?

The MiniCATS three-seater compact, a commercial version of a prototype showcased at the 2002 Paris Motor Show, will be priced at $9,850. The CitiCATS six-seater sedan will retail for $16,000.




A car that runs on air, in India soon

21mlook1.jpg

MDI explains that 90m3 of compressed air is stored in fibre tanks. The engine is powered by compressed air, stored in a carbon-fiber tank at 30 MPa (4500 psi). The tank is made of carbon-fiber in order to reduce its weight. The engine has injection similar to normal engines, but uses special crankshafts and pistons, which remain at top dead center for about 70 degrees of the crankshaft's cycle; this allows more power to be developed in the engine.


World's First Air-Powered Car: Zero Emissions by Next Summer

air-car-0607.jpg


Here is what the engines look like....

air-car-engine-0607.jpg

Not really any danger for the tanks to explode at pressure as these are a composite unit that has an inner metal bottle.

This would be a good use for any insitu left over gasses from the processing for methane and oxygen from the Sabatier and RWGS reactions as it is already at a good starting pressure of greater than 75 PSI in order to liquify the CO2 for the start of the processing.

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#70 2008-03-12 19:25:53

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Running on Compressed Air?

You don't really want to push your rover with liquid CO2 though, the stuff would not boil efficiently enough to push your rover.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#71 2008-03-12 20:08:39

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,445
Website

Re: Running on Compressed Air?

liquid N2?


-Josh

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#72 2008-03-12 20:38:53

GCNRevenger
Member
From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Running on Compressed Air?

You don't want cryogenic anything. The reason is the energy that actually pushes the rover comes from the kinetic energy of the gas in the tank. And where is a condensed cryogen get this energy? On Earth, the air is warm and thick, so you could get some energy that way, but on Mars the air is cold and thin and thus provides little energy.

Or to put it another way, compressed gases store energy, like a coiled spring, while a cryogen is an energy sink (or more accurately a heat sink), which is sort of the opposite of what you want.

Furthermore, with a cryogen heated by the Martian atmosphere, you would have trouble with CO2 condensing as dry ice on the radiator/heat exchanger.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#73 2008-03-17 02:52:52

Michael Bloxham
Member
From: Auckland, New Zealand
Registered: 2002-03-31
Posts: 426

Re: Running on Compressed Air?

I'm disappointed that the idea of mars cars powered by compressed CO2 is so quickly dismissed. Powering cars with a compressed version of the local atmosphere would be a simple and elegant method of propulsion; if it could be made to work. Is there anyone here that could look into the physics a little further?


- Mike,  Member of the Clean Slate Society

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#74 2008-03-17 06:33:13

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 14,035

Re: Running on Compressed Air?

The part that many may be missing is that in order to make methane from insitu CO2 the first steps are to compress the gas to 5 earth atmospheres pressure in order to liquify it for the sabatier process.

Waste pressures are higher from the process.

Have been without a car as engine needs rebuilding. The compression of some cylinders are poor so will need to replace the rings. This cars spec for the cylinder chamber pressure on compression is in the 100 to 180 PSI so it would just need volume of gas at that pressure to achieve motion nit necessarily one that reaches 5000.

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#75 2008-03-17 22:46:41

Michael Bloxham
Member
From: Auckland, New Zealand
Registered: 2002-03-31
Posts: 426

Re: Running on Compressed Air?

I imagine average combustion pressures would be much higher though.

Has steam power been discussed here before?


- Mike,  Member of the Clean Slate Society

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