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I finally got the big version of the hybrid motor ready to test. We did a static test that was meant just to test ignition and coming up to pressure. It used just enough peroxide to flow for three seconds. The motor did not ignite in that time, although it seems like it came close. In the video below you see a few bits of burning plastic come out of the nozzle, but then the peroxide runs out and the remainder of the flow is nitrogen from the oxidizer tank blowing down.
Video of hybrid test
I was pretty conservative on how much catalyst paint I used. There were just two stripes down the length of the grain. At the beginning of the firing there is a stream of liquid peroxide coming out of the nozzle. The fuel grain is a flower petal geometry with six lobes, and I wonder if the peroxide was running in a rivulet down one of the lobes where there was no catalyst. There is a small catalyst pack in the injector that is meant to atomize the peroxide and spray it around. The same method seemed to work just fine in the small engine, but it doesn't seem like it's getting a good spray in this engine. Another possible issue is that the grain is three times the diameter and three times the length of the small engine to have nine times the surface area to match nine times the throat area. But this gives twenty seven times the chamber volume so I may need more catalyst paint to get enough reaction for it to come up to pressure. My plan is to paint the entire inside surface of the grain and try the same test again. If that doesn't work I'll have to redesign.