Performance evaluation of hybrid rocket using hydrogen peroxide with various solid fuel grain geometries

Abstract

Hybrid rockets are safer than solid motors, have high specific impulse performance, and are structurally simpler and less costly than liquid rockets, and have been used as propulsion engines for sounding rockets. However, due to the low regression rate of the fuel, the hybrid rocket has a higher length to diameter ratio than a solid motor or liquid rocket. This leads to flight instability, increased structural load, increased weight, and combustion instability. To alleviate the effects of low regression rate, a simple circular multi-port geometry was considered to improve the length to diameter ratio. As the propellant, 90 wt.% of hydrogen peroxide and high density polyethylene were used. A multi-port design was implemented to control the fuel length and the merging of the fuel ports at the same diameter while maintaining the rocket performance of single port fuel. For this purpose, the fuels with 1, 2, 3, and 14 ports were designed by predicting the final port diameter by the regression rate for the propellant combination. Compared to the single port fuel, the length was reduced to 60 percent for 3 ports, and 30 percent for 14 ports design. As the result of experiment at the same thruster shape and oxidizer flow rate, the regression rate of the fuel increased with the decrease of the length and the increase of number of ports, and the efficiency of characteristic velocity, the volume, specific impulse increased. The pressure instability increased slightly in 2 and 3 ports fuels compared to the single port and decreased in the fuel with 14 ports. The frequency characteristics showed low frequency of less than 50 Hz for all fuels and the similar tendency of pressure instability for over 50 Hz range. The application of the simple cylindrical multi-port improved the rocket performance and shortened the length to diameter ratio of the hybrid rocket.