Combustion Water Bottle Rockets

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mark.f
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Tue Apr 19, 2011 6:22 pm

This isn't a theory thread... it works. :D

Took me all of a few minutes to build and $0. Best part is, it's portable, and no air pump/compressor required at all. All you need is water and plastic bottles.

Ignition is accomplished with an Aim n' Flame piezo, with the wires run through a scrader valve with core removed press fit into the top of the 1/2" pipe with a little electrical tape to seal the wires and improve fit.

To be honest, I didn't even know if this was going to work, as static friction held my little pneumatic's bottle chamber on without set screws at up to 50 PSI, although that was with an o-ring.

Another thing is that this design doesn't require o-rings or any other way to seal the bottle onto the pipe, other than the close fit, since the internals are at atmospheric pressure before launching.

Anyway, enough talking, on to the pictures and video.

Here lies a dead YouTube video :(
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Spark gap.
Spark gap.
Portable!
Portable!
Last edited by mark.f on Sun Apr 05, 2020 7:39 pm, edited 1 time in total.
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Lockednloaded
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Tue Apr 19, 2011 7:17 pm

Very cool! Have you done test w/ and w/out water? You should also add some stabilizing fins
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warhead052
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Tue Apr 19, 2011 7:29 pm

Can we get a how to?
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mark.f
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Tue Apr 19, 2011 7:35 pm

Lockednloaded wrote:Very cool! Have you done test w/ and w/out water? You should also add some stabilizing fins
I know I should add some fins. Guess it's not really a "rocket" so much as a "runaway engine". :) Done a few tests just using the combustion gases as the reaction mass, with varying "nozzle" sizes (see my avatar), with predictably dismal results of no more than several feet. You really need something with more mass coming out of the "nozzle" for significant thrust.
warhead052 wrote:Can we get a how to?
It's a piece of 1/2" PVC pipe with an end plugged off with two electrodes. Really not much to explain...

EDIT: forgot to mention when it gets dark I might see if I can get some night videos to record the combustion flash. Should be a neat blue streak on camera...
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saefroch
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Tue Apr 19, 2011 7:37 pm

Without water it would be quite silly, because the extra mass being propelled out the nozzle increases thrust tremendously (conservation of momentum, I think).

Have you considered trying to do this with a smaller nozzle, or making this into a 2X hybrid design? It could have some serious potential then...
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Tue Apr 19, 2011 7:45 pm

Mark, I admit that kinda was a stupid question, but how do you get it to spark underwater?
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Tue Apr 19, 2011 8:01 pm

warhead052 wrote:Mark, I admit that kinda was a stupid question, but how do you get it to spark underwater?
He doesn't. The electrodes clear the water and ignite the flammable gas mixture above the water.

Mark, what's performance like compared to a normal rocket (~70-100 psi)? I might give this a go...all lathe turned of course ;)
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saefroch
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Tue Apr 19, 2011 8:30 pm

My physics teacher had us launch off bottle rockets at 140psi, some we let go to 160psi. One ruptured, but that does show you can take most of them that high. Those that didn't exceed 140psi survived two launches.

1.5X hybrid? :wink: Please?
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Tue Apr 19, 2011 8:44 pm

Want to know of a way to make that air tight? Stick your pvc about 1 inch off the bottom of the bottle, mark it, then heat it up and push it together to make a little bulb. It works perfectly and holds up to 140, (thats what I have been able to test it at...)
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Tue Apr 19, 2011 8:48 pm

inonickname wrote:Mark, what's performance like compared to a normal rocket (~70-100 psi)? I might give this a go...all lathe turned of course ;)
Go for it. :D Although I can't really attest to the performance. I've only tried a few traditional rockets with auto coupling nozzles that had similar performance. I need to pick up some 2L bottles to test with as well.
saefroch wrote:1.5X hybrid? :wink: Please?
Ha! Maybe at some future date. That would require much more attention to detail than I'm willing to put out at this point. :roll:

My video camera didn't capture the night shots so well, I've included just a GIF below. I might try long exposure at some point, which may be interesting...

EDIT:
warhead052 wrote:Want to know of a way to make that air tight? Stick your pvc about 1 inch off the bottom of the bottle, mark it, then heat it up and push it together to make a little bulb. It works perfectly and holds up to 140, (thats what I have been able to test it at...)
I've heard of that done before, but never tried it. Would probably work, but I'd like to keep the "launch tube" flexible, so it can launch more than one size of bottle, and I can experiment with different spark placements. When the pipe is inserted, water doesn't leak through the neck at all. For some of the video I took tonight, I fueled up the bottle, inserted the tube, and left it sitting for some time while I set up the camera.
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Animation. Pretty sad quality, but much more impressive in real life.
Animation. Pretty sad quality, but much more impressive in real life.
warhead052
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Tue Apr 19, 2011 9:10 pm

It can launch more than one size bottle, but you have to make sure theres enough room. Use 1/2" pvc, and it works perfectly.
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mark.f
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Tue Apr 19, 2011 9:45 pm

What I mean is that, if I were to place the "bulb" at the neck of the 20 oz. bottle to where the spark gap was at the very top of the rocket, if I switched to a 2L bottle, the spark would be lower. I'd also like to see if there's any difference between a centrally located spark and a spark at either extreme end of the "combustion chamber".
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jackssmirkingrevenge
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Wed Apr 20, 2011 12:30 am

Just after firing, are you shaking your hand dry or did it hurt you?

Interesting concept, I would have thought the water would have absorbed enough heat from the combustion to make it weak compared to a pneumatic water rocket. On the other hand, you could be generating steam which helps with propulsion ;)
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inonickname
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Wed Apr 20, 2011 1:22 am

jackssmirkingrevenge wrote:Just after firing, are you shaking your hand dry or did it hurt you?

Interesting concept, I would have thought the water would have absorbed enough heat from the combustion to make it weak compared to a pneumatic water rocket. On the other hand, you could be generating steam which helps with propulsion ;)
There probably isn't enough time for sufficient heat loss to happen, given the relatively small powered flight time of a water rocket.
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Zeus
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Wed Apr 20, 2011 1:58 am

I've been playing around with a few crude combustions (ignition circuit testing) and I'm rather suprised with the power.

A 500mL chamber was blown out of my hand at one point when I had a barrel jam, turns out one can put too much in a barrel.

At another point the chamber was blown quite a few meters when I had another jam, and it had to break free of the wires for the ignition. I can see this working quite well.

Edit, n00by missing of keys. Also, another w00t, favourite calibre amount of posts. 303 of course
/sarcasm, /hyperbole
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