Investigation of fuel regression rate in a lab-scale HTPB/n20 hybrid rocket motor

The investigation aimed to acquire fuel regression rate and evaluate the regression behavior. The tests were conducted on lab-scale hybrid rocket motors with propellant combinations of liquid N20 and HTPB based fuels. Two types of metalized fuels, with A1 and Mg powders additives and certain amount of AP, were casted into tubes of grains. They were burnt under chamber pressures around 4MPa. in a typical configuration hybrid motor with multi- orifice axial injection. A method based on fuel properties was developed to evaluate the regression rates of HTPB based fuels. The fuel regression rates from tests were calculated from test data and thoroughly examined. A modified method based end-point average method was developed to reasonably eliminate the fuel consumed during burnout periods. The classical exponential law between regression rate and oxidizer mass flux was obtained. The relations were compared with predicted ones and matched for certain extent. The primary results of the experiments showed that the power exponent value was obviously lower than the theoretical 0.8 from literature. Pressure effect was examined. Investigation of the axial distribution of fuel regression rate was observ ed through splitting the grains after burning. The port profile showed apparently sharp descending from the inlet to the location where the flow boundary layer edge supposed to merge and the trend became indistinctively till to the outlet.