Starting envelope of the subdetonative ram accelerator

An experimental investigation has been undertaken to explore the effects of propellant composition, entrance Mach number, and projectile throat area v ariation on the subdetonative ram accelerator starting process. Upper and l ower limits on these parameters provide bounding conditions under which a s upersonic projectile ran successfully initiate and stabilize the combustion -supported shock system on the projectile necessary for acceleration. Relat ively energetic propellant combined with high entrance Mach number are obse rved to push the shock system ahead of the projectile, whereas low energy r elease together with low entrance Mach number are conducive to the shock sy stem falling behind. Decreasing entrance Mach number also causes the shock system to propagate ahead of the projectile under some circumstances, sugge sting that fundamentally different start failure mechanisms are responsible . Increasing the flow area at the throat lowers the Mach number for choking the diffuser, but causes difficulty in containing the combustion-supported shock system unless the Mach number is increased or the propellant energy release is decreased. Trends observed in this investigation and prior resea rch are used to develop a generalized starting envelope, illustrating where the success and failure boundaries lie in relation to one another on the p ropellant energy release vs Mach number plane.