Tabletop Hybrid Demo Rocket Engine

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I was browsing through YouTube one day when I came across a video of a hybrid rocket engine that was such a new concept to me, I wasn't sure how it could have possibly worked. The crazy thing about this engine was that you were able to actually view the inside of the rocket engine, right into the combustion chamber, and watch the fuel burning away. I watched the video several times and researched this type of engine as much as I could, eventually I found out that the combustion chamber was made out of cast acrylic, which is a very strong clear plastic (basically Plexiglass). The acrylic also acted as the fuel, so what you are actually viewing is the slow erosion of the actual combustion chamber, so then engine cannot be ran too long, or it will eventually erode through the entire acrylic rod, or rupture if the walls become too thin. I then wet out to built one. At the time I did not have a milling machine, so I just rough cut the aluminum pieces with a hacksaw, drilled some holes in them and made a cheap graphite nozzle that would fit in the one hole. Then I made the piece that would allow the oxygen gas enter, and added two nitrile O-Rings, and the assembly simply pressure fits together with the addition of some long bolts and nuts.

As you can see above, the assembly is quite simple, and it is a very basic engine, but non-the-less, the engine is throttleable, and quite easy to control, while still creating considerable amounts of thrust for such a small demonstration unit. The first 4 firings went quite well, but then the engine began to collect small amounts of lampblack in the nozzle, from the imperfect combustion of the fuel. After those firings, I simply cleaned the nozzle out, and began machining a stainless chamber that would fit in place of the acrylic demonstration fuel grain. The reason for building the stainless combustion chamber is that is can hold much more pressure that acrylic, therefore creating much more thrust (duh!). Also with this new combustion chamber, i could test which fuels, or fuel combinations would produce the most thrust, as well as which were the most clean burning. Eventually, I found that a paper grain, saturated in parrafin wax was by far the most powerful and clean burning fuel I had used in the engine. Some of the other fuels I tested included plain paper grains (burnt quite well, but not very powerful), paper grains saturated with various alcohols (very considerable initial thrust, died out very quickly though), a solid parrafin wax grain (melted mess), and some various casted resins (polyester & epoxy). Below is a picture of the engine with the acrylic demonstration chamber in place (post fired)

Below is a video of one of the firings where debris built up in the nozzle.

Below are pictures of the front and rear of the engine. You can see that I put in one heavy duty check valve to ensure no flashback will get to my oxygen tank.

I will update this page with some pictures of the new chamber and some videos of the new tests as soon as I get a chance. (8/22/09)

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