Fuel Regression Characteristics of Axial-Injection End-Burning Hybrid Rockets Using LOX

Axial-injection end-burning hybrid rocket (AIEB-HR) is a nonconventional hybrid rocket, employing multiport fuel consumed along the axial direction by a diffusion flame established at the end of each port. The research aims to study the fuel axial regression rate using liquid oxygen at different pressures. A total of 21 firing tests performed in a pressure-controlled chamber with two different multiport grain geometries are discussed. Three different modes—regression mode, flame spread mode, and transition mode—were observed. As compared to the properties of GOX combustion, the flame spread is inhibited by the latent heat of LOX. An experimental correlation of the regression rate with the pressure, mass flow rate, and port diameter is obtained. The results show that the regression rate strongly depends on the pressure and is mostly insensitive to the other parameters, similar to solid propellants. The [Formula: see text] ratio obtained in this study was much higher than the optimal ratio. The optimal oxidizer-to-fuel-mass ratio ([Formula: see text]) requires a chamber pressure of approximately 5.7 MPa, oxidizer port velocities of 1.0 m/s, and a high filling rate of around 0.985.