Numerical and experimental investigation on the effects of aft mixing chamber diaphragm in hybrid rocket motor

This paper focuses on the investigation of an aft mixing chamber diaphragm in a hybrid rocket motor. Both numerical and experimental researches are carried out to study its effects on the motor performances. The hybrid rocket motor with star fuel grain is utilized. The 90% hydrogen peroxide (HP) oxidizer and hydroxyl terminated polybutadiene (HTPB) based fuel are adopted as propellants. The diaphragm configuration settled in the aft mixing chamber includes four circular-holes with a uniform circumferential distribution. For both motors with and without the diaphragm, three-dimensional numerical simulations with gaseous combustions considered are carried out to study the flow field characteristics and motor performances. The comparison results show that the diaphragm can improve the mixing of the oxidizer and fuel. It has evident effect on increasing the motor efficiencies. Two firing experiments are conducted with full scale motors to investigate the effects of the diaphragm. The diaphragm used in the test is composed of a central steel framework and a closed thermal insulation layer. With the diaphragm employed, the combustion efficiency increases from 93.9% to 97.34% and the specific impulse efficiency increases from 80.77% to 87.28%, which verifies the positive effect of the diaphragm. Both numerical and experimental studies indicate that the scheme of the aft mixing chamber diaphragm proposed in the paper can improve the efficiencies of the hybrid rocket motor obviously.