Design considerations for single-stage and two-stage pneumatic pellet injectors

Performance of single-stage pneumatic pellet injectors is compared with several models for one-dimensional, compressible fluid flow. Agreement is quite good for models that reflect actual breech chamber geometry and incorporate nonideal effects such as gas friction. Several methods of improving the performance of single-stage pneumatic pellet injectors to muzzle velocities ranging from 2 to 2.25 km/s in the near term are outlined. Two-stage pneumatic injectors have the potential for much higher muzzle velocities (4--6 km/s) because of the higher gas pressures and temperatures achievable with the second-stage compression. The design and performance of two-stage pneumatic pellet injectors are discussed, and initial data from the two-stage pneumatic pellet injector test facility at Oak Ridge National Laboratory are presented. Finally, a concept for a repeating two-stage pneumatic pellet injector is described