Anything can be rocket fuel, if you try hard enough?

[Dman979]

I was joking originally, but I wonder if what I said in this post is true: can anything be rocket fuel, if you try hard enough?

I think that LOX makes things burn, but is it possible to launch a rocket with, say, leftover mashed potatoes and LOX?

Or to use apples to go suborbital?

A few caveats: "fuels" shouldn't be chemically changed before ignition. So you can't ferment apples, take the alcohol, and burn it. You must burn the apples.

[UmbralRaptor]

If it has lots of sugars, alcohols, long hydrocarbon chains, etc, it'll burn. Stable combustion may be difficult in some cases, though.

[Vaporo]

I think the answer is simple. Can you burn water (excluding nuclear fusion)? No. Not "anything" can be rocket fuel. Even if you limit yourself to flammable materials, like dried apples, I'm still pretty sure that they would not contain enough energy density to lift anything off the ground. Someone who has finished a chemistry course should probably weigh in, though.

EDIT: However, you can literally use anything with mass as a propellant. Not fuel, though.

[Luckless]

A big part of the issue is whether or not you can get the fuel shaped into a useable form such that you can achieve rapid enough combustion. Doing some form of a hybrid solid-liquid engine may achieve 'usable' results from a surprising number of fuels.

I used packed flour for a test rocket for a hybrid engine back in high school. (Forget what we were using for an oxidizer, I wasn't the one dealing with the chemistry for our experiments.) We achieved 'okay' thrust levels, but nothing exceptionally impressive as far as I remember.

But combustion is an interesting thing. Part of our rocket escapades ended up in setting fire to a gravel pit... Fuel mixture looked good on paper from the energy release point of view... We just hadn't really accounted for 'minor' things, like whether or not the engine would melt before achieving lift. But it did lead to a few interesting experiments on the ground.

[Budgie]

The joke at my university rocket group, when anyone asks about fuel, is that you can indeed make a rocket out of anything (sausages and snakes are always cited), but you won't necessarily get the required thrust levels, as stated above me, to fly anything worth flying

[NuclearNut]

I wonder, would lemons get enough thrust? Imagine, a rocket powered by flammable lemons.

I feel that what we need is someone with way too much time and free access to both LOX and lemons to test the flammable lemons rocket theory.

[ChrisSpace]

Almost any gas can be used as propellant in a nuclear thermal rocket, although hydrogen is obviously the most efficient.

[RainDreamer]

Almost anything with mass would work with a mass driver... but that wouldn't be called fuel.

[Streetwind]

Relevant XKCD: https://what-if.xkcd.com/21/

[p1t1o]

I wonder, would lemons get enough thrust? Imagine, a rocket powered by flammable lemons.

I feel that what we need is someone with way too much time and free access to both LOX and lemons to test the flammable lemons rocket theory.

I can't believe you've set this up for me so well...

Lemon oil, being around 99% Limonene, actually makes a very good rocket fuel.

And yes, it does apparently leave the launch pad smelling deliciously of lemons!

I was reading a history of rocket fuel research (normally such a document would be pretty dry, but this is rocket fuel, so you can imagine there are plenty of erm..."energetic" anecdotes of note) and came across it in there. Its a good read, linked below, also goes into plenty of detail about why certain things make good fuels and other things dont, and various factors affecting the design of liquid fuelled rockets.

A must-read for Kerbals!

http://web.gccaz.edu/~wkehowsk/ignition.pdf

[KerikBalm]

I think the answer is simple. Can you burn water (excluding nuclear fusion)? No.

It should react with flourine.

2H2O +4F -> 4HF + O2

No?

[p1t1o]

It should react with flourine.

2H2O +4F -> 4HF + O2

No?

(It would be F2 just fyi)

I didn't think so, water is pretty stable - by removing an O2 from water, the reaction is essentially "un-burning" hydrogen.

But on checking, apparently water spontaneously ignites under a stream of fluorine!

I would imagine that it would make a pretty poor rocket fuel though, the stability of water ought to make the energetics of the reaction quite un-favorable. You can see from the picture in the link below, that the water burns (!) but its not exactly a blazing inferno.

Source:

https://books.google.co.uk/books?id=1t8DAAAAMBAJ&pg=PA106&redir_esc=y#v=onepage&q&f=false

[Rath]

Touch it with flourine and it will probably burn, no matter what it is.

[KerikBalm]

(It would be F2 just fyi)

No, it wouldn't

I didn't think so, water is pretty stable - by removing an O2 from water, the reaction is essentially "un-burning" hydrogen.

No, it wouldn't... it would be "burning hydrogen just a little more".

Oxygen is very electronegative... but Flourine is even more electronegative. Flourine will outcompete Oxygen for the electron of Hydrogen.

And if you had HF, you might be able to react it with Cesium or Francium, which is even more electropositive than Hydrogen, and will give up its electron to Flourine more readily than hydrogen.

but Fr-F.... I don't think you can burn that... I'm not aware of any more electropositive element than Francium (in theory, and even heavier element could be.. but then the half life is on the order of what.. femtoseconds?), and there's certainly nothing more electronegative than Flourine.

Although if you use matter-antimatter propulsion, then any matter can be part of the fuel.

[p1t1o]

No, it wouldn't

Umm...yes it would.

http://www.chemspider.com/Chemical-Structure.22932.html?rid=882cd613-337d-44dd-a079-50d05352f2db&page_num=0

No, it wouldn't... it would be "burning hydrogen just a little more".

Well semantically, that would be if the end product was H2OF, which is probably impossible. The reaction literally removes oxygen from the hydrogen, a direct reversal of hydrogen combustion.

I know what you are getting at though. The energy released on burning water in fluorine ought to be proportional to the difference in energy released between burning straight hydrogen in oxygen, and straight hydrogen in fluorine.

Burning hydrogen in fluorine liberates more energy, so by "un-burning" the water, and "re-burning" the hydrogen in fluorine you do get a net release of energy, hence the reaction occurs.

Given that hydrogen burning in fluorine is an extremely vigorous reaction, its makes sense that burning water in fluorine is significantly less so , as a deal of energy goes into removing the oxygen, thus the "un-burning".

[cypher_00]

A team from the University of Delft is trying to break the European height record. Their goal is getting to 50Km.

They use the following interesting combination:

"This engine, the DARE developed DHX-200 Aurora, runs on nitrous oxide as oxidizer and a mixture of sorbitol (coffee sweetener), paraffin (candle wax) and aluminium powder as fuel."

Read more here: http://dare.tudelft.nl/stratos-ii/

[KerikBalm]

Umm...yes it would.

Ah, I misunderstood then.

Yes, Flourine would be diatmoic like Oxygen/Clorine gas/Bromine/ and so on, before the reaction

I though you were suggesting that the reaction would be something stupid like:

H2O +2F -> H2 + F2O .... since you were talking about un-burning hydrogen/removing oxygen from the hydrogen.

My mistake, I misinterpreted what you said.

Well semantically, that would be if the end product was H2OF, which is probably impossible. The reaction literally removes oxygen from the hydrogen, a direct reversal of hydrogen combustion.

Well, yea, I guess it depends on what you mean by burning. If burning is simply combining with oxygen... then sure.

But there is little difference between a chemical reaction with oyxgen gas, and a chemical reaction with Flourine gas.

If you put a piece of wood+ some heat in F2 instead of O2... I would still call the resulting reaction "burning"

"Combustion /kəmˈbʌs.tʃən/ or burning[1] is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products,"

"In chemistry, oxidizing agent has two meanings. In one sense, an oxidizing agent is a chemical species that removes an electron from another species. It is one component in an oxidation-reduction (redox) reaction. In the second sense, an oxidizing agent or an oxidizer is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combustion, many explosives, and organic redox reactions involve atom-transfer reactions."

Flourine is an oxidant... a better oxidant than Oxygen... ironically enough.

By those above definitions, the reaction is still burning. The redox potential is even greater.

Hydrogen is even further oxidized, which is why I said its "burning hydrogen just a little more" ... quite the opposite from " 'un-burning' hydrogen"

At least as far as the net effect. Hydrogen gets oxidized a bit more, so it is burned a bit more than before.

[p1t1o]

Yes, net effect is "more burnt", but the reaction is not very vigorous (compared to other fluorinations) which can be explained due to the loss of energy used to break H-O bonds, a direct reversal of an oxygenation.

[KerikBalm]

Yea, of course the reaction is not very vigorous... Oxygen is alreayd pretty electronegative.

The energy used to break H-O bonds would be the activation energy, there are plenty of vigorous reactions that have high activation energies.

It just comes down to a relatively small difference in bond energy between H-O and H-F bonds.

Likewise, You should be able to burn H2S with O2, or HCl with F2... but the energy difference will be quite low, and its not very vigorous either.

I doubt it would even be enough for one to see a flame.

The resulting Isp from these reactions would be terrible... terrible rocket fuel

[p1t1o]

Its not strictly an activation energy as energy is not required for the reaction to progress, the reaction is spontaneous, and further, the energy used to break the H-O bonds is not returned to the system.

My metaphor holds dammit!

[KerikBalm]

The energy released is released as heat... just like burning wood in O2 requires heat... is that not activation energy?

Would F2 burn H2O at 10 kelvin? 1 kelvin? At what temperature does the reaction start? (I don't know, but I assume at low enough concentrations/temperature, the reaction won't be spontaneous)

[p1t1o]

No, the heat energy comes from the extra energy provided by the greater oxidation potential of the fluorine, the energy used to break the H-O bonds is (after several short lived intermediate steps) contained within the O=O bonds that are formed. You can then release this energy by using the O2 to oxidise something else, where it will be released as heat.

Technically the H2O reaction does have an activation energy, but that is not what is causing the H2O+F2 reaction to be less vigorous than H2+F2.

The H2O+F2 activation energy is provided by the ambient heat, spontaneous at room temperature.

Wood burning has a higher activation energy, but this energy is returned to the system as part of the heat released.

[KerikBalm]

anyway... we digress... it is possible to burn water... the Isp is terrible though, so its not going to be a rocket that gets you to orbit....

Plus... your rocet will be super heavy if you're going to be storing flourine.

[p1t1o]

Word. Peace/Out man.

[Dman979]

So from what I just read, anything can be rocket fuel? Awesome!

*Grabs leftover mashed poatoes, toothpaste, water, and F1 Engine)