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As rocket Science and Space Exploration is becoming more and more popular, I'm currently running some numbers, whether it would be possible to build a rocket engine for showing at schools or universities, without the need to be fit for flight.

The idea is to have a "normal" chemical combustion engine, but as performance is not a optimization criterion, but safety and availability for amateurs is I still search for a good fuel: The different oxidizers used in rocket motors are either cryogenic(LOX) or highly corrosive (Hydratzine and other Hypergolic Propellants), toxic and cancerous - nothing one would like to handle and which is cheap and easy to buy...

Is there any option for an oxidizer to combine with gasoline or ethanol as fuel, or a different combination of fuel and oxidizer? They should both be liquid (as pumps for liquids are available) and react strongly enough to build up the pressure in the chamber, but be individually safe enough to be handled without needing to consult a doctor if you accidentally spill a bit of it. I know that for an oxidizer this is a bit contradicting requirements, but maybe there is a good candidate.

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    $\begingroup$ Do you require a liquid fuel engine, or would a hybrid do? Also, I guess gasoline is safe, compared to other things, but it's not the first thing I think of when I want a combustible liquid that's safe to handle. $\endgroup$ – Wayne Conrad Mar 3 '17 at 16:42
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    $\begingroup$ Could you expand a bit on your safety standards for this? $\endgroup$ – Schlusstein Mar 3 '17 at 16:58
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    $\begingroup$ You might want to consider just what they will let you demonstrate in a school environment. Even RCS thruster sized pressure fed engines are tested more or less in either a bunker or widely cleared area in the desert, and those are the ones built by professionals... $\endgroup$ – Tristan Mar 3 '17 at 17:02
  • $\begingroup$ A cold gas thruster would be a good choice for demonstration at schools and universities. No toxic fuel, no cryogenic oxidizer, no fire or explosiom risk. May be operated with cheap compressed nitrogen or air. $\endgroup$ – Uwe Nov 29 '17 at 19:19
  • $\begingroup$ I personally am curious about a gaseous-fuel engine, which would basically be a welding torch with a converging-diverging nozzle. $\endgroup$ – ikrase Jan 22 at 7:33
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Nitrous oxide can be used as monopropellant, producing oxygen and nitrogen in ratios not too distant from atmospheric air (about 36%), and by itself is pretty harmless and easy to obtain as cartridges for whipped cream maker. The small, inexpensive, safe, self-contained cartridges are very nice for short "demonstration runs".

Adding another fuel, be it liquid or solid, or even gaseous will improve specific impulse (and visual entertainment value), but is optional - and with nitrous oxide deflagrating without fuel, it can be prettty much anything - rubber in a hybrid motor, or kerosene for liquid fuel motor, or you could use propane-butane lighter gas as a cryofuel... perfect for a "demonstrator" device if you can showcase different fuels.

You can also use atmospheric air (out of a compressor) as oxidizer, to provide a performance comparison.

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Concentrated hydrogen peroxide and ethanol could be a workable combination if you want two liquids.

This has a very nice advantage that you can add water to either solution to reduce performance.

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A few oxidizer options worth looking at:

  • compressed air. Easy to come by, inefficient as it contains so much nitrogen, but that might be an advantage.

  • compressed gaseous oxygen. Is used in welding, filling a 9 kg cylinder costs around $25. But if you get a good oxygen/gasoline fire going, I suspect your flame temperature will be high enough to melt metals. Having to cool the combustion chamber complicates your design. The less efficient combustion you get from compressed air will be easier on the combustion chamber.

  • nitrous oxide is used e.g. in the car tuning world, would fall somewhere between air and oxygen.

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  • $\begingroup$ Compressed gaseous oxygen is not as safe as compressed air or compressed nitrogen. $\endgroup$ – Uwe Mar 5 '17 at 9:19

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