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Aerospace Isopropyl rocket engine

  1. Jan 7, 2016 #1
    Y'know, just because. Will it be possible to create a rocket engine using isopropyl alcohol as fuel? Why or why not?

    (will be used just for show and not really for sending ships to space. I'd rather have an entire school intact than it being blown to bits if I used hydrogen)
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  3. Jan 7, 2016 #2
    The challenge with liquid fuels in amateur rocketry is the oxidizer.

    With solid fuels, there are a number of oxidizers that are solids and not too hard to mix in using amateur techniques. Some common choices are ammonium nitrate and potassium nitrate. It is also possible to make amateur rockets with solid fuels and gaseous oxidizers. These are known as hybrid rocket motors, the controlling the flow rate of the gaseous oxidizer controls the burn rate of the fuel. Often, O2 gas is simply used as the oxidizer in amateur rockets, but some professional designs use hydrogen peroxide.
  4. Jan 7, 2016 #3
    So is that a yes, or a no? I'm taking it as a yes.
  5. Jan 7, 2016 #4
    If you can't figure out what your oxidizer will be, it's a no.
  6. Jan 7, 2016 #5
    So if I take O2 as an oxidizer, it's a yes?
  7. Jan 7, 2016 #6
    If you can figure out a practical and achievable design to mix the fuel and oxidizer in the combustion chamber with available resources, it might be a yes.

    It is theoretically possible. It will be practically difficult for amateurs.

    How will the isopropanol and O2 be stored in the rocket? How will their flow into the combustion chamber be controlled at the proper rates to ensure proper thrust and a near stoichiometric mixture?

    The amount of $ and expertise and weight needed to address these issues makes alternate designs (different fuels) much more practical.

    Doing it to say you did is irrelevant if it costs and weighs 10 times more than more practical designs.
  8. Jan 7, 2016 #7


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    You also have to be careful of the source of your rocket fuel. Most of the isopropanol which is commercially available has been diluted in water to varying degrees.

    The stuff from the drug store can be 50%, 70%, or 90% isopropanol. Sometimes, you have to look hard to find the 90% kind.
  9. Jan 7, 2016 #8
    This is a good point. We use 90% isopropanol as our most common cleaning solvent in the lab. We pick it up at Walgreens and they seem to always have it.

    For rocket fuel, I would probably use ethanol instead. 95% ethanol is available in liquor stores as Everclear. It's more expensive due to the tax, but cutting the water in half would improve the qualities as a fuel, and odds are a single bottle will go a long way in amateur rocketry. Just don't drink the stuff.

    Ethanol and isopropanol are our favorite lab solvents, because they are safe for skin contact. Even though we usually wear gloves, contact is hard to avoid and other common solvents tend to be dangerous (except water).
  10. Jan 7, 2016 #9


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    That's what I use it for. Sometimes, though, the stock may be limited at a particular store.
    This presents a couple of possible problems.

    The OP seems to indicate that he is a student of some sort. I wouldn't advocate that any possibly underage students go cruising to the local liquor store for alcohol, lest they get themselves or the store in trouble for selling alcohol to minors.

    Carrying potable alcohol on school grounds could violate a number of school regulations and/or local laws. I would rather the OP get a chance to shoot his rocket, rather than face suspension from school or a trip to jail.

    It would be wise for the OP to obtain permission/clearance from school officials before bringing these materials to school.
  11. Jan 7, 2016 #10
    Yeah, I'm not the best artist (I'm struggling with 2 art projects and failing them miserable right now) but I'll try to show the supposed design.

    I'm trying to do something new. If this doesn't work, then that's a new thing to learn today!
    Isopropanol Engine.jpg
    The oxidizer and isopropyl alco might as well as get mixed in the pump.
  12. Jan 7, 2016 #11
    Mixing a liquid and a gas in a controlled and defined ratio in most pumps is tricky business.
  13. Jan 8, 2016 #12
    What if, pipes with different diameter so different amounts will flow?
  14. Jan 8, 2016 #13

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    Whoa! Slow down!

    If you are talking oxygen in the vapor stage, every gram of alcohol is going to need 19 grams of oxygen. That's 13 liters.

    If you want to get the volume down by pressurizing the oxygen, what experience do you have with high pressure systems? If you want to get the volume down by liquifying the oxygen, what experience do you have with cryogenics?
  15. Jan 8, 2016 #14
    I actually don't need this to be flying. Yes, I'm planning to use gaseous oxygen. Volume is not very much a problem.
  16. Jan 8, 2016 #15


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    The pump probably will be an issue though. Pressure fed will likely be much simpler and easier to make functional. There's a lot of potential for danger here as well - rockets (by their very nature) have a lot of energy, and can sometimes violently release that energy in unexpected ways. I'm not convinced you know what you're doing well enough to end up with much more than just a pipe bomb here.
  17. Jan 8, 2016 #16
    I will note that I saw 91% isopropanol in the pharmacy section of Sam's Club while waiting for my flu shot today.
  18. Jan 10, 2016 #17

    Vanadium 50

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    I'm not sure this makes me feel better. A rocket that doesn't fly is pretty much just a flamethrower.
  19. Jan 10, 2016 #18


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    I wouldn't necessarily agree with that - you can learn a lot from static firing a rocket, and the supersonic exhaust and large amounts of thrust produced by a rocket make it fairly different from a flamethrower. If all you are interested in is the pyrotechnics, there are significantly cheaper and better ways to make large amounts of fire.
  20. Jan 10, 2016 #19


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    In that case, I have a great bargain for you. A tank suitable for your gaseous O2 oxidizer sits unused and abandoned in Green Cove Springs, Florida. It was built for the NASA space shuttle. Make them a reasonable offer. :wink:

  21. Jan 10, 2016 #20
    We've done a lot of static firing to measure thrust curves and quantify impulse and specific impulse and the effects of various factors. Sure, it can be useful to tweak a design and diagnose issues.

    But if the whole design has insurmountable technical barriers to actually flying (too heavy, etc.), what's the point?
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