Monday, September 24, 2012

Hybrid rocket engine with acrylic and gaseous oxygen

I built a small rocket engine for demonstration purposes. The engine is built from a 2" diameter acrylic rod through which I drilled a 0.5" hole. The oxygen at 80 psi or less is passed through the hole and then is forced through a convergent-divergent nozzle at the tail end. The nozzle's throat is about 0.25" and expands to 0.625". I lit the engine by inserting a burning cotton swab (with wooden stick) while a small amount of oxygen was flowing. The acrylic catches fire very easily in a pure oxygen environment. The engine can be throttled and shut off completely, which is a major benefit to hybrid engine designs. Solid-fuel rockets cannot be throttled or shut off, which makes them difficult to control.



9 comments:

Anonymous said...

hum, any chance the oxygen feeding tube would start burning from the inside, when the pressure is lowered but not completely shut ?

Kenneth Finnegan said...

Convergent/divergent nozzles are because a convergent nozzle can only accelerate a flow to sonic speed (which makes sense, if you consider that back pressure can't propagate forward faster than the speed of sound). Weirdly, once a flow becomes sonic, to speed it up more, you use a divergent nozzle.

Anonymous said...

Just wanted to say that you make really great videos! I can't believe I didn't notice your Youtube-channel before.

Do you have any plans of making a rocket and launch it?

Erin said...

Echoing Kenneth. That deserves a correction.

Very small nitpicks aside, this is a very neat educational tool and absolutely deserves the attention it's getting (I've already seen it on Universe Today). Maybe you should see if you can get some Schlieren photography of the interior burn dynamics :)

Norman Yarvin said...

Are you actually getting choked flow there? I don't see any Mach diamonds.

Armadillo had a good video, a while back, of what the transition to choked flow looks like (and sounds like):

http://media.armadilloaerospace.com/2004_09_05/GOX-GH2test.mpg

Jamie Frost said...

Saw your video on dump.com -- awesome stuff!

Very cool tidbit I took from a nasa video, they channel liquid oxygen along the inside of the nozzle to use evaporative cooling to prevent the nozzle from liquifying at several thousand degrees. Perhaps some sort of liquid cooling on your tailstock aluminum nozzle mount (run liquid o2 through the alum to make it gaseous for reinjection at the top = cool the aluminum and get high pressure from low volume liquid o2.

Again, very cool stuff!

@anonymous first comment; oxygen doesn't burn. unless you ignite the metal oxygen feed tube, there is no fuel in that hose to burn, only oxygen, and oxygen doesn't oxidize itself :P

thinkingscifi said...

that is awesome...

Norman Yarvin said...

Looking at the video more closely, I think I can see a few brief bursts of choked flow, where the exhaust narrows down and the noise increases.

Anonymous said...

Very nice! Ever thought of doing fusion. If you are interested, try fusor.net. Keep up the good work.

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