Jet fuel for carbon dioxide atmosphere

[MBobrik]

What would be the most practical fuel to power a jet engine in a CO2 atmosphere ?

I know there are very reactive chemicals that react rapidly with CO2, I know that for example magnesium burns in CO2, but magnesium is solid, and I think it would be very hard to design a jet engine that runs on solid fuels.

There are also strong oxidizers like dioxygen difluoride which burn with almost everything, but those are usually too instable to be practical.

There is also the reverse water shift reaction, H2 + CO2 => CO + H2O, but it is endothermic.

Tried to google it directly, but all what I found were articles about global warming.

I have found that the H2S + CO2 reaction would be exothermic, but found no information about whether it could proceed fast enough to be useful.

.

So, has someone a better idea ? What fuel could be used to power a jet plane in a carbon dioxide atmosphere ?

[shynung]

I'm thinking of a monopropellant-based engine. Swap the combustion chamber in a regular jet engine with a reaction chamber with catalyst inside.

That, or a thermal jet engine running off a nuclear reactor.

Edited April 9, 2014 by shynung

[Ralathon]

Why bother with a jet engine? Just use an electric propeller instead.

[christok]

Monosilane has been seriously considered for Mars + Venus.

[MBobrik]

Monosilane has been seriously considered for Mars + Venus.

Monosilane. Cool. I knew someone here will find something.

[YourEverydayWaffle]

If they figure out how to stabilize H202 more, I'm pretty sure that H202 pumped into an atomizer toward a silver screen or a screen of magnesium dioxide with binder as a catalyst would work. NASA's doing work with those engines, and they're pretty powerful. Only problem is that H2O2 is very unstable when purified, so if anything got into that engine, it would likely hurt itself badly. Also, they're environmentally friendly, although that doesn't really matter when you're on another planet.

[Armchair Rocket Scientist]

There are probably some fluorine compounds that will oxidize CO2. The problem is, they will also oxidize pretty much everything else that you could make a fuel tank or engine out of.

If you're talking about the atmosphere of Venus, fill a balloon up with nitrogen (actually a decent amount of the stuff in the Venusian atmosphere) and use either a propeller or thermal jet for propulsion. If you're talking about the atmosphere of Mars, electric propellers will still work, but the air is so thin you'd need a massive wingspan.

[shynung]

If they figure out how to stabilize H202 more, I'm pretty sure that H202 pumped into an atomizer toward a silver screen or a screen of magnesium dioxide with binder as a catalyst would work. NASA's doing work with those engines, and they're pretty powerful. Only problem is that H2O2 is very unstable when purified, so if anything got into that engine, it would likely hurt itself badly. Also, they're environmentally friendly, although that doesn't really matter when you're on another planet.

That's practically monopropellant, isn't it? In that case, swap the peroxide with hydrazine for a performance boost.

[KASASpace]

Magnesium salt-water?

You separate the magnesium into a fine powder just before burning it.

I'm kind of thinking ramjet here.

[Idobox]

Solid fuel ramjets are a thing. They are basically ramjets with a coating of solid fuel in the combustion chamber, and I'm pretty sure they're a common type of missile engine.

[victory143]

Just make an engine that takes in CO2, cools it to a liquid (never heard of liquid CO2 before though), then heats it up rapidly using a radioactive substance. The CO2 would expand explosively and then could be pointed out a nozzle to generate thrust.

[Nemrav]

well, I guess turbo fans are jet engines, I think you might go turbo-fan/pusle jet (back to the 1950's), you simply compress a ton of the air (or in this case co2) and shoot it out.... maybe you could mix the compressed gas with rocket fuel and see if it is all thrusted out at high velocity when lit ?

I'm not really good at science am I.....

[jwenting]

yes Nemrav, but the problem is compressing it. For that you need to have a compressor, which you need to drive, for which you need a powersource.

In a turbofan engine basically there's a turbojet at the core that generates the power to drive the fan blades that drive the compressor that compresses the air.

In an oxygen rich atmosphere, that power comes from burning fuel with atmospheric oxygen. In a CO2 atmosphere you can't do that and have to carry your oxidiser along with you.

Which is not very efficient, as it adds a lot of mass and volume to your design.

[Mecha Pants]

There has been some work on a Rocket System that uses CO2 as an oxidizer. Though my limited digging hasn't turned up much beyond this US government grant award from 2001 and a very interesting project summary.

Edited April 12, 2014 by Mecha Pants

[Hyratel]

you could use an "Air Turborocket" - it replaces the compressor jet segment with a gas-generator cycle rocket engine, and is basically a turbopump for air thrust

[OgreMagi]

mars direct idea I read about in science fiction analogue in the 1990's suggested several ideas for mars propulsion.

one is a simple wing filled with hydrogen, it wont easily combust in a co2 atmosphere and it can generate lift with the combination of wing/hydrogen ballest. their suggestion was to land device that could make methane from the air with a h2 in storage and a small nuclear reactor slowly over 18 months.

the same nuclear plant could be used as a thermal rocket compressing the atmosphere initially for a boost, like a ramjet.

[vetrox]

Kethane...duh

[qeveren]

There's always that old standby when you need to burn something nominally non-flammable: chlorine trifluoride.

[KASASpace]

Just make an engine that takes in CO2, cools it to a liquid (never heard of liquid CO2 before though), then heats it up rapidly using a radioactive substance. The CO2 would expand explosively and then could be pointed out a nozzle to generate thrust.

That would probably cost too much heat energy, unless you brought a reactor.

But, you said to cool it.

On Mars, little cooling would be needed, if any.

[NERVAfan]

There are also strong oxidizers like dioxygen difluoride which burn with almost everything, but those are usually too instable to be practical.

Aw, I want to see the dioxygen difluoride engine!

Just make an engine that takes in CO2, cools it to a liquid (never heard of liquid CO2 before though)

That's because at standard pressure CO2 goes straight from gas to solid or solid to gas; the liquid phase only exists at higher pressures (Wikipedia says only at 5.1 atmospheres and up).

[victory143]

More power is need for the CO2 rocket then. MOAR POWER *runs to Garage*

[FREEFALL1984]

Why bother with a jet engine? Just use an electric propeller instead.

a fair proposal but due to the thinner atmosphere (equivalent to atmospheric pressure on earth at 35km) a fixed wing aircraft would need to be moving at extremely high speeds to generate enough lift to get off the ground, which on a nice flat runway might be feasible but on the rocky surface of mars would be far too risky. A giant quad rotor might be a more suitable solution but the thin atmosphere would mean the rotor blades would need to travel at extreme speeds, meaning it would need a huge amount of power to generate enough lift to leave the surface, the only way to produce such a large amount of power would be to have a thermonuclear generator or a conventional chemical engine generator, both options would be ineffective since they would add so much weight to the craft (in the form of an oxidizer for the liquid fueled engine) it would need to be ludicrously big to lift off. which would prevent it from being effectively launched.

My suggestion is to use a lighter than air aircraft filled with the natural atmosphere and using a thermally absorbent material for the balloon to provide almost free lift during daylight hours, then using a conventional electric propeller for propulsion, which could be powered by banks of solar panels. The only obvious issue with this design is requirement of perfect weather conditions which would be difficult to predict due to the foreign nature of the martian weather systems.

[11of10]

I remember reading about a German WW2 enterprise in building a coal powered jet engine... seems it's this: http://en.wikipedia.org/wiki/Lippisch_P.13a .. maybe something similar with magnesium?