HTPE/PLA KMnO4 Class I Engine
There were five test in September (four succeeded & one failed). I varied the length of the PLA/KMnO4 fuel core as follows: 16.5 cm, 15.0 cm, 13.5 cm, and 12.0 cm. All other parameters were the same. I used a blend of 55 ml of ~ 87% HTP and 2.1 ml of denatured ethanol (O/F = 26.2) as the oxidizer. The propellant tank was pressurized to 130 psig using CO2 gas as the pressurant. I used a 1/4" stainless steel mist nozzle with a 1.0 mm orifice as the injector and a graphite phenolic nozzle with an initial throat diameter of 5 mm. The objective was to determine what effect the length of the fuel core had on the operation of the engine and to select the best length to continue. The ignition oxidizer flux of ~14 gm/cm2-sec, the run-time oxidizer flux of ~6 gm/cm2-sec, the fuel core regression rate of ~0.4 mm/sec, and the characteristic velocity of ~1390 m/sec were consistent on three out of the four successful test. The deciding factor was the oxidizer to fuel ratio, the thrust, and the burn time. For the 15 cm fuel core the O/F ratio was 2.3, close to theoretical. Ignition occurred in one second and lasted for ~7 sec. There was a net positive thrust of greater than 16.2 N at ignition and lasted throughout the burn. Based on these results, I've selected the 15 cm fuel core for the class I flight system.