Inert material in APCP propellant

Discussion in 'Propulsion' started by boatgeek, Aug 13, 2019.

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  1. Aug 13, 2019 #1

    boatgeek

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    Preface: I don't want enough information that this needs to go into the Research subforum.

    In general, is there a value in having relatively inert material mixed into an APCP propellant? Obviously, titanium flakes/powder give you a sparky motor, at the cost of a lower specific impulse. Would you have the same reduced impulse with no sparks if you used a more inert material like silica? Is the reduction in performance roughly linear with percentage of inert material (20% inert material has 80% of thrust/impulse of standard)?

    Long ago, I had a notion of a service where one would receive people's/pet's cremated ashes, mix them into propellant, and launch them on a final flight. In theory at the right price point, you might be mixing so much that the limiting factor would be how many rockets you could launch since someone else was basically paying for the fuel. I shelved it as impractical pretty quickly, especially since I'm not really all that keen on research motors. After bringing it up again in the R rocket thread, I got to thinking about it again. Cremated ashes are largely calcium carbonate (aka limestone), so they might have enough oxygen bound in to be useful in propellant.

    Again, please keep this qualitative so we don't end up in the Research forum. And this is absolutely a crazy notion and likely not commercially feasible, though it may be a good way to send off a long time motor mixer.
     
  2. Aug 13, 2019 #2

    3stoogesrocketry

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    About 15 years ago , maybe more , Dennis Lappert from METRA help launch a final flight for somebody . While the ashes where not mixed into the fuel , the containment vessel that housed the ashes also had a larger( 1/4 pound ) bp scatter charge . The full M motor put a very large rocket to over a mile then the cloud that was formed had to be 1/4 mile wide .
     
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  3. Aug 13, 2019 #3

    prfesser

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    No. Just because something contains oxygen does not mean it provides oxygen for combustion. Ash is a product of whatever burns plus oxygen, and ash doesn't burn nor support combustion (unless you use stuff like fluorine, chlorine trifluoride, and other stuff that I want to be miles away from).

    FWIW it's not uncommon for pyrotechnicians to have their ashes placed into a shell, so they go out with a blaze of glory...

    Best -- Terry
     
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  4. Aug 13, 2019 #4

    tfish

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    I had to put my dog down back in March. He was about 63#. I took his ashes up to our Happy place back in June. The volume and weight of his ashes was about 2 quart zip locks and weighed about 4-5 pounds. You would need a P motor to hide that amount of ashes in. I've been involved with scatter my ashes at a launch flights. Just a big dust ball at apogee.

    Tony
     
  5. Aug 13, 2019 #5

    Steve Shannon

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    Rocket was such a good dog and he had a great owner!
     
  6. Aug 13, 2019 #6

    G_T

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    The combustion temp inside a rocket motor is quite high, and the atmosphere is pretty reactive in there. You get chemical combinations that are unstable at atmospheric temp and pressure. I wouldn't really consider anything inert in a rocket propellant.

    Gerald
     
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  7. Aug 13, 2019 #7

    tfish

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    Then again the "stuff" has already gone through 14-1800 degree cycle..mostly ash, bone and teeth pieces left.

    As a Firefighter going to fire calls at crematoriums was either problems with heat sensors setting or poor house keeping. They were always kind of funky to go to.

    Tony
     
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  8. Aug 13, 2019 #8

    boatgeek

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    To me, this indicates that like everything else in rocketry, ground testing would be required. There might be unpredicted effects during the burn.

    I've seen a couple of "last flights" as well, that's probably a more realistic final tribute than mixing ashes into a motor.
     
  9. Aug 13, 2019 #9

    Nytrunner

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    Are there any regulatory issues with ash disposal via rocket? I recall someone local mentioning that handling remains in such a way was frowned upon, but I forget his exact words.

    Is it acceptable as long as permission is received from the landowner?
     
  10. Aug 13, 2019 #10

    G_T

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    There's a bit of a difference between 1800 degrees and the 5000+ that can be encountered in a rocket motor. IIRC, my hottest test solid propellant burns at about 5600.

    Gerald
     
  11. Aug 13, 2019 #11

    boatgeek

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    I did look into that a few years ago. Scattering from the air is legal as long as you don't drop anything that will injure someone. What I've seen of ashes is that the particles are fine enough that as long as the apogee event is downrange of spectators, you aren't going to have any issues. It would be good form to ask a private landowner, and definitely don't scatter on a sod farm. Nobody wants to find bits of teeth and bone in their sod!
     
  12. Aug 13, 2019 #12

    Nytrunner

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    Good to know, thanks Boat!

    I'll just leave "1/4 pound payload scattering charges" lie....
     
    Last edited: Aug 13, 2019
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  13. Aug 13, 2019 #13

    ChuckH

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  14. Aug 13, 2019 #14

    shreadvector

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  15. Aug 14, 2019 #15

    rocket_troy

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    In a typical rocket motor combustion chamber, yes, most things will be decomposed to either elemental or very basic molecular species. Very stable metal oxides or fluorides might have enough strength in their bonds to withstand the onslaught of photons and molecular KE to stay attached, but for the sake of the point of inertness, this is mostly a peripheral point.

    Generally, for the context of this discussion, we broadly define inertness to mean the ability or likelihood of an ingredient/additive to *not*contribute energy to the reaction/combustion.

    For that to occur, the sum of the formation enthalpy of the products of the reaction of such species needs to be not lower than the sum of the formation enthalpy of the reactants. Not necessarily a simple thing to numerically analyse for isolated reactants, but in some instances, some basic rules of thumb can be applied.

    For eg. if our additive was a very stable metal oxide, we can generally assume it will be inert within the reaction if all the other reactants are either oxygen, nitrogen or hydrocarbon based. Generally, the exceptions will be if our propellant also contained a reactive metal with an electronegativity lower than the metallic cation of our additive or (in a much rarer instance) if it contained fluorides with a cation possessing a higher electronegativity than our additive’s metallic cation.

    Eg: if our additive was Al2O3

    It would be safe to assume it will be inert for:
    AP+R45+Curative propellant
    Or AP+R45+Organic cross linkers + organic plasticizers + organic bonding agents + surfactants + curatives
    Or even AP+R45+Curative+misc organics+Al propellant

    Where it typically might not be inert is where there could be pure magnesium added, or any pure group 1 or 2 elemental metal (exception Be)

    So, the point to remember is that even if there was enough energy within the chamber to completely decompose our Al2O3 molecule, the Al+ cation will preferentially recombine with *any* free oxygen within the chamber/exhaust to provide a no NETT release of energy unless one of the above mentioned exceptions is available.
     
    Last edited: Aug 14, 2019
  16. Aug 14, 2019 #16

    jsdemar

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    I like how you worked "decompose" into your reply. ;-)
     
  17. Aug 14, 2019 #17

    G_T

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    I'm thinking in terms of, for example, TiO2. TiO2 in propellant, Ti2O7 available during combustion (PEP analysis), and back to TiO2 in the exhaust plume. No net energy change, so it is "inert". However it does participate in chemical reactions in the chamber and alter the behavior of the propellant a bit. Going by memory for a quick example.

    Any true catalyst would be inert in a chemical reaction by some definitions of "inert". I don't find that definition of inert particularly useful in this context. But otherwise I agree with what you are writing.

    Gerald
     
  18. Aug 14, 2019 #18

    rocket_troy

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    Yup, good points. A catalyst by definition doesn't react but certainly can contribute significantly to the reaction and regression rate of the propellant. Probably more in the transition metal compounds domain, but certainly a worthy exception to include.
     
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  19. Aug 14, 2019 #19

    prfesser

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    Somewhere I've seen a paper published that said that one of the two forms of TiO2 made (anatase or rutile, I forget which) was a plateau-type catalyst for APCP.

    Actually, a catalyst often does react, but is regenerated in a later step. (been demonstrated with isotope-labeled substances.) Solid catalysts often provide a surface that facilitates the two (or more) reactants joining. Homogeneous catalysts---same phase as the reactants--- often react in one micro-step of the overall reaction, and are then regenerated in a later step. Example: iodide ions (I-) in solution catalyze decomposition of H2O2 by reacting with one H2O2 molecule to form hypoiodite ion, IO-. When the highly reactive IO- hits another H2O2, an O atom comes off and combines with the IO- to form oxygen gas, O2, and I- again.

    Chlorine atoms in the upper atmosphere catalyze decomposition of ozone by a multi-step reaction, where the Cl reacts and is then regenerated. It's been calculated that one Cl can destroy about 50,000 ozone molecules up there before it reacts with another Cl to form more-stable Cl2 molecules.

    Relevance to rocketry: This is part of what makes determination of the specific role of AP catalysts so difficult. Does the catalyst facilitate one or more reactions in the solid/liquid phase, or does vaporized catalyst do something in the combustion chamber proper? Or both? One paper I read listed about 20 or so different possible mechanisms of transition metal oxides in APCP...

    Quiz on Friday. Whaddaya mean, you didn't take notes?...;)

    Best -- Terry
     
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  20. Aug 14, 2019 #20

    G_T

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    Yep, some catalysts are essentially recycled in a chemical reaction, making it easier for a reaction to progress than would be the case if the catalyst was not present. Other catalysts provide a suitable surface helping to align molecules in a more ideal fashion to improve the rate of reaction. Examples of such catalysts (for various reactions) would be hot Platinum or Palladium sponge (catalytic converter) or hot Cerium Oxide in a ceramic matrix (also useful for Nitrous Oxide decomposition), etc.

    Except for hybrids we generally don't deal with that second form of catalyst in rocket motors. At least I don't THINK so!

    The first form, does get to be a big question mark. Liquid state in the melt zone? Gaseous state? Both? Depends on the catalyst.

    For TiO2, IIRC it is the rutile form, that being the most stable. But the exact results depend on which of the three manufacturers tested (at the time of the paper I read) provided the source. Trace contents (dopants) made a difference. To me that implies some of the action was likely in the solid or melt phase rather than all being gaseous. But I'm just guessing. And going by memory. That's a bad combination!

    I'll stop here as we are probably getting a little close to research.

    Gerald

    PS - Yep, always have folded sheet of paper in pocket, and pen. Takes notes... But then the folded papers accumulate so I throw them out. So what notes??? :)
     
  21. Aug 14, 2019 #21

    boatgeek

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    Can we at least go open book? :)

    Seriously, this has been really interesting. If I'm reading this right, as the motor is burning at 5000 or so degrees, pretty much all of the component chemicals are gasified (either melted/evaporated or sublimated) and possibly broken down into component ions before being spat out the nozzle. Is that a fair reading? Is all of this equally true of a Q-Jet A motor and a Research Q motor? If that's the case, then inert [in the sense of not contributing fuel] material mixed into the motor would just suck up some of the energy created by the regular fuel as it was gasified and accelerated out the nozzle.

    Which brings up another question: how do sparky motors work? I assumed that the titanium never melted, but 5000 degrees is well over the melting point of Ti. I would think that if the titanium chips/flakes melt, the Ti would spread out enough that you wouldn't see individual sparks. Do they hold out against melting just long enough to get out the nozzle?
     
  22. Aug 14, 2019 #22

    Nytrunner

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    That's my understanding of why skidmarks and such are inefficient (low total impulse). A significant fraction of "propellant" mass is just being spat out of the nozzle

    Similar smoke motors that are rich in binder and put all that gunky soot that folks like.
     
  23. Aug 14, 2019 #23

    G_T

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    There are solids which are stable at those temperatures. In the combustion chamber formed by the burning fuel of a solid rocket motor (APCP) you typically have a solid particulate and liquid fog present along with the gasses. This is actually pretty important, as that smog provides accoustic dampening. Otherwise solid motors would be as loud as liquid motors. Some special case motors which lack this smog are that loud.

    Yes, to some extent, "inert" ingredients do suck up energy. They start cold and exit pretty hot. So they don't tend to help ISP. But, they serve other purposes.

    Titanium for sparkies melts and at least somewhat burns in the motor. The pieces for a sparkie are made large enough that they do not burn fully in the combustion chamber. Mostly they melt and a little burns. Hot melted Ti burns quite nicely in the atmosphere when thrown out the nozzle... The pieces may not be fully melted to start with, depending on size of particle and size of motor. Titanium is a fuel, just not one of the best ones. Also such motors are designed to have much less than ideal oxidizer content, to minimize the burning of the Ti where you can't see it in the motor. They are basically fireworks in an APCP formulation. Or a nozzle sandblaster, depending on your point of view.

    Gerald
     
  24. Aug 14, 2019 #24

    heada

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    20-100 Ti sponge. ~$24/pound

    Sparky motors really are just giant fireworks
     
  25. Aug 15, 2019 #25

    Binder Design

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    Google "Orange Sunset Formula". Replace calcium carbonate with cremation ashes and scale the motor to the amount of ashes you have to meet the correct percents. Win.
     
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  26. Aug 16, 2019 #26

    base890

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    Why put all the cremains into on motor, I’d think 100 flights better than any one.

    Except for the 1/4 mile cloud - that’s pretty cool.
     
  27. Aug 16, 2019 #27

    djs

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    So what would you call this one... "Last Sunset"?
     
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  28. Aug 16, 2019 #28

    MClark

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    Cremated remains can be pretty chunky and porous, not a good thing in a propellant.
    For best chance of it working it would need to be ground, A task not for me.

    It's always best to test a new propellant before launching. What is going to be used in the static test? Old Uncle George nobody really liked?

    M
     
  29. Aug 16, 2019 #29

    jsdemar

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    The laws get more complicated when offering a commercial service to dispose of cremated remains. BLM, for example, requires going through a permit process if charging for the service. But, an individual can spread ashes as "casual use" of BLM land... away from trail areas and bodies of water.
     
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  30. Aug 16, 2019 #30

    numbo

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    This has been done for pyro techs by putting ashes in a firework shell. Often, the shell is premade and not all the ashes are used. The rest can be scattered in another spot that is memorable to the person, or placed in an urn. I could easily see some folks satisfied to be scattered by hand or by rocket at multiple launch sites and a lake they fished at, or the like.
     

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