Obturator and detonation experiments in the subdetonative ram accelerator

An experimental investigation has been undertaken to improve understanding of the role of the obturator and detonations in the subdetonative ram accel erator starting process. Ram accelerator start experiments were conducted w ith various obturator geometries to determine the obturator dynamics and as sess its effect on the outcome of a start attempt. The obturator rapidly de celerates upon entrance and then moves backwards. Reversal of direction occ urs more rapidly after propellant ignition, for less massive obturators, an d solid geometries. Perforated geometries and decreasing obturator mass are less conducive to igniting a given propellant, as evidenced by the flowfie ld and start attempt outcome data presented. Wave unstarts were observed to occur with and without detonations, indicating more than one mechanism res ponsible for this type of start failure. Piston-initiated detonation experi ments were conducted by firing the obturators without the ram accelerator p rojectile. The piston experiments identified the detonation limits for a wi de range of propellants, but were found to not always be indicative of the upper Mach number at which a ram accelerator can be successfully started. I n some instances a successful start or wave fall-off would occur at Mach nu mbers above which a piston alone detonated the propellant. Thus, the projec tile can play a mitigating role in detonation initiation and use of piston detonation limits to quantitatively define a detonation wave unstart limit was not realized.