Effects of aluminum and aluminum hydride additives on the performance of hybrid rocket motors based on 95% hydrogen peroxide

This paper aims to study experimentally and numerically the effects of aluminum (Al) and aluminum hydride (AlH₃) additives on the performance of HRMs. A steady-state numerical model of HRM is established, which adopts the 95% hydrogen peroxide (HP) as the oxidizer. A firing test is completed for the certification of the numerical simulation model, the results illustrate that the regression rate of addition of 38% AlH₃ and 20% Al increases by 55.6% compared with pure hydroxyl-terminated polybutadiene (HTPB). A good agreement exists between the simulation regression rate and the experimental data. The deviations of thrust and pressure are less than 3.3% and 3.7%, respectively. Specifically, the error of the regression rate is only 0.3%, indicating that the accuracy of adopting numerical simulation method to predict the characteristics of the HRM is acceptable. Several steady-state simulations based on the different content of AlH₃ and Al are performed to investigate the effects on regression rate and combustion performance of the HRM. Due to the addition of H₂, the thermal conductivity increases with the decrease of the mass fraction of AlH₃, which leads to the increase of the regression rate. The regression rate of the fuel with 8% AlH₃ and 50% Al increases by 35.5% than the fuel with 58% AlH₃, demonstrating that the effect of Al on the regression rate enhancement is more than that of AlH₃. The theoretical specific impulse increases with the mass fraction of AlH₃. However, it is owing that the part of H₂ does not participate in the reaction with O₂ and the oxidizer to fuel ratio (O/F) is far from the optimal O/F, the specific impulse is lower than the theoretical specific impulse.