Experimental research of regression rate of N₂O and metalized HTPB hybrid rocket motor

Regression rate behavior of metalized fuel was investigated through motor experiments using the propellant of N₂O and HTPB fuel containing Al, Mg and carbon ingredients. Results of regression rate, combustion chamber pressure and combustion efficiency were obtained with three kinds of grains and multi-oxidizer mass flow rates. To analyze the effect of radiation heat flux on regression rate, equations were deduced to correlate and separate regression rate into two parts: one was convective evaluated by total mass flux and the other was radiative evaluated by radiative heat flux of condensed phase products. The radiation regression rate is about 30%~60% of total regression rate in all oxidizer to fuel mass ratio range except oxide-rich. The trends of radiation regression rate variation and its ratio to convective regression rate are analogous to condensed mass fraction of combustion products versus oxidizer to fuel mass ratio. And the regression rate generally increases with oxidizer mass flux. It also indicates that combustion efficiencies mostly between 80% and 97% are analogous to the normalized square value of theoretical combustion temperature in ranges around stoichiometric ratio and oxide-rich.