Mach Number Effects on Baffled-Tube Ram Accelerators

The ram accelerator was developed at the University of Washington in the late 20th century as a mass driver system for the purpose of accelerating projectiles to orbital velocities. The baffled tube ram accelerator (BTRA) system was to accommodate more energetic propellant mixtures and widen the operating velocity range of the ram accelerator system. This is accomplished using a series of large-chambered baffles and alignment rails in place of the original smooth bore tube. The work presented here includes experimental results which offer greater insight into the effects of in-tube pressure variation, propellant heat release, and propellant dilution. Projectile net thrust was found to scale with in-tube fill pressure as predicted by theory. Thrust was found to increase with heat release, although the effect was diminished as propellant chemistry approached the ideal stoichiometric fuel/oxidizer ratio. Finally, alterations in diluent gases in the propellant mixture were found to allow for higher overall propellant heat release during stable operation, while Mach number effects from different diluent gases showing lesser impact than expected.