Experimental Investigation of Throttleable H₂O₂ and Polypropylene Hybrid Rocket Motor

This study experimentally investigated the propulsion performance of a swirling-type throttleable hybrid rocket motor using hydrogen peroxide and polypropylene. An in-house throttle valve consisted of a servomotor, and an industrial ball valve was integrated to instantaneously control the oxidizer mass flow rate. Several ground static hot-fire tests with fixed oxidizer mass flow rates of 425 g∕s (100%) and 350 g∕s (82%) and many step-varying oxidizer mass flow rates were performed to examine its propulsion performance. The hybrid rocket motor achieved an impressive sea-level I_sp of 240 s, an engine I_sp efficiency of more than 97%, and a thrust uncertainty of less than 5% when the oxidizer flow rate was fixed as 425 g∕s. For the multiple-step hot-fire test results, the thrusts and chamber pressures were both found nearly proportional to the oxidizer mass flow rates with different proportionalities. The overall O∕F ratio of the tests is 5.61, which is hardly shifted, unlike most hybrid rocket data reported previously. In summary, the total impulse and thrust are both linear to total oxidizer mass consumption in the range of 50–100% of 425 g∕s. This major finding would indeed broaden the application of hybrid rocket motors to future space technology.