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Brown Iron Oxide Doped Propellant

and End (Port) Burning Rocket Motors

In my quest for a propellant to make end burning motors, I tried brown iron oxide doped KNO3-sucrose propellant because Richard Nacha reported unusually higher burn rates with it.  He thought it was an anomaly but finally decided his results were valid.  He only tested 1% BrIO and it was in KNO3-Dextrose propellant.  His final results discussion was that further testing with actual motors was warranted but apparently he never did do that and went on to other projects.  So I decided to try other percentages and tested 1% to 5% and found that 3.5% was the optimal burn rate at atmospheric pressure.  Like Richard, I have left off still needing to do more testing which I plan to do when I have a pressure test setup.  I ended up with 38 separate burn tests at atmospheric pressure. Actually there were more than that but some either burned down one side faster than the other or was obscured by the smoke and I wasn't able to get accurate times.  The spread of the data was a little disappointing.  I was hoping to have more consistent tests.  That is why I kept running more and more tests.  Nevertheless, a curve emerged that I think is useful in determining what ratio of doping oxide is probably optimal.  some of the tests used 1/4" diameter, 3" test strands with no OD inhibitor and others used a .8" diameter, 1.38" long grains with an OD inhibitor (a standard grain cast in a 3/4" nominal pvc pipe).  I used a digital video recorder to determine the burn time.

If you look at Richards graph, fig 3 on http://www.nakka-rocketry.net/oxidex.html, you can see how much faster the burn rate is.  You can also see that there wasn't much difference at atmospheric pressure so without the elevated pressure tests, there is no way to know how the different percentages of BrIO would actually perform in a motor.  

Here are the test results plotted.

I made three test motors and tested them.  They were tested with 1% BrIO before I decided to test what percentage would be best.  I didn't get to further motor tests with the higher percentage because another motor I tested after these cato'd, damaged my test fixture and I didn't get it repaired before I left off testing.  (Got a new job and didn't have much time anymore).  They were single grain (obviously) and used three different throat diameters.  Here is the data on them.

Here is the successful motor before it was fired.  This one used circumferential holes to retain the nozzle and header. Here, although it is hard to see with the glare, you can see how small the throat is in relation to the motor diameter.     Here you can see the washer that was used in the nozzle (lower half) to hold the throat diameter.  Because of the relatively long burn time, the Rockite nozzle material was eroded on the exhaust side of the washer to a larger diameter.  There were no leaks in this test. Note that the inhibitor sleeve burned through in places.  It should have been a little thicker but even so, it just discolored the inside motor wall but didn't actually melt or burn it.     This is one of the failed nozzles.  You can see how the exhaust gases eroded a path on the outside of the nozzle.  The pressure probably expanded the motor tube enough for a leak to start and once it started, it eroded in a split second at that pressure.  Note that this motor used an internal ring to retain the nozzle.  That is why the left hand side of the nozzle is a smaller diameter.  That is the part that went through the center of the retainer ring.

        Video clip of successful end burner motor firing.  .mpg format, 3 megs

        Video clip of a typical grain test.  .mpg format, 2.4 megs

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