Ram accelerator operation in the superdetonative velocity regime

Abstract

Preliminary experiments on superdetonative propulsive cycles at a ram accelerator facility using projectiles fabricated from aluminum and titanium alloys have demonstrated that acceleration is possible at velocities greater than the Chapman-Jouguet (CJ) detonation speed of a gaseous propellant mixture. Projectile materials were found to play a significant role in these experiments. Theoretical modeling was successful in predicting projectile drag in nonreactive gas mixtures at hypersonic velocities. When this drag was subtracted from the ideal thrust of a supersonic combustion ram accelerator, the net thrust closely matched that measured in the experiments. The dependence of the maximum operating Mach number on both the projectile diameter and propellant heat release was examined. The peak velocity capability of the experimental projectile geometry is predicted to be about 1.5 times the CJ speed of the propellant mixture. It was found that the drag resulting from an increase in projectile diameter was more than offset by the corresponding enhancement in thrust, and that velocities of nearly twice the CJ speed are possible. (Author)