Investigation of end-burning type hybrid rocket motor doped with high entropy alloy

Abstract

Hybrid rocket motors (HRMs) have become an attractive propulsion system due to their advantages over solid and liquid rockets, such as safety, environmental friendliness, low cost, and typically not containing toxic additives. However, low regression rate and poor combustion efficiency are critical weaknesses that affects the performance. To address this issue, extensive investigations have been conducted on the end-burning hybrid rocket (EBHR) doped with high entropy alloys (HEAs) to improve the regression rate and increase combustion efficiency. Static firings were conducted to obtain the thrust, regression rate and specific impulse. Simulations were also performed using NASA CEA software to assess HEAs’ performance in HRMs. The characteristic velocity, specific impulse, and adiabatic flame temperature were the propulsive parameters analyzed. The present investigation focuses on a single port EBHR utilizing paraffin wax doped with HEAs as the fuel. Experimental results showed that the inclusion of 5% HEAs contributed to a 45.4% increase in the regression rate, 28.03% increase in thrust, and 25.89% increase in specific impulse compared to pure paraffin wax. The EBHR demonstrated an overall lower performance compared to the conventional HRM due to unstable combustion throughout the firings. According to the simulations, the higher the HEAs’ concentration, the better it performs at an oxidiser-to-fuel ratio (O/F) of 1.0-1.3. Gaseous oxygen (GOX) as the oxidiser provides the best performance overall but hydrogen peroxide (H2O2) performs better at O/F greater than 4. The experiments and simulations demonstrate the potential of HEAs to enhance the regression rate, thrust, and specific impulse of HRMs. End-burning has also shown no fluctuations of O/F and chamber pressure during steady-state, which might be helpful in some applications. The findings also highlight the influence of initial fuel mass, mass flux, and HEAs’ concentration on the hybrid rocket’s performance. These improvements can expand the range of applications for hybrid rockets and contribute to the growth of commercial space activities, scientific research, and space exploration efforts.