After the successful tests of 16th to 18th of August, it was decided to fire the PTDs (Pressure test devices) just once more, to gather more data points. This was done on Thursday, September 1st. We assembled two core-burning PTDs, with nozzles of 4.1 mm and 5 mm respectively, to obtain Klemmung values of 325 and 220. Both PTDs ignited well, but unfortunately, the safety valve of the first test was activated, due to the high pressure inside the combustion chamber. Next to that, the voltage gain of the data logger was set to a too high value, so that it clipped. Therefore, we only have some data regarding ignition and burn time from this test.
The second test, however, was more successful. After a good ignition, it burned in a steady manner until all 90 grams of propellant were consumed. Post-test analysis of the nozzle showed that it did not suffer from erosion or clogging, and hence had a constant throat area. This makes the pressure data of this test, which were successfully recorded this time (See Figure 1), very suitable to calculate the Characteristic Exhaust Velocity (or C*), an important performance factor of the propellant. It turns out that we reached a C* of 1452 m/s, where 1504 m/s is the theoretical maximum. This means we reached a combustion efficiency of 97%, which is quite good!

Figure 1: Chamber pressure in time

Again, some nice video footage was recorded as well. This will be published at our YouTube channel as soon as possible.
What remains now is the analysis of the data, of which we now have plenty. The preliminary results are looking good: we have a nice Pressure-Regression rate curve from 1 to 80 bars, which very nearly resembles a power function, as was expected. The graph is displayed in Figure 2.

Figure 2: Pressure regression rate

After we found from the analysis that the performance of this propellant is what we expected, we will continue with building a small rocket motor with it, to obtain more experience with materials and constructions that can be used with this propellant.