Single-Cycle Impulse from Detonation Tubes with Nozzles

Abstract

Experiments measuring the single-cycle impulse from detonation tubes with nozzles were conducted by hanging the tubes in a ballistic pendulum arrangement within a large tank. The detonation-tube nozzle and surrounding tank were initially filled with air between 1.4 and 100 kPa in pressure simulating high-altitude conditions. A stoichiometric ethylene–oxygen mixture at an initial pressure of 80 kPa filled the constant-diameter portion of the tube. Four diverging nozzles and six converging–diverging nozzles were tested. Two regimes of nozzle operation were identified, depending on the environmental pressure. Near sea-level conditions, unsteady gas-dynamic effects associated with the mass of air contained in the nozzle increase the impulse as much as 72% for the largest nozzle tested over the baseline case of a plain tube. Near vacuum conditions, the nozzles quasi-steadily expand the flow, increasing the impulse as much as 43% for the largest nozzle tested over the baseline case of a plain tube. Competition between the unsteady and quasi-steady-flow processes in the nozzle determine the measured impulse as the environmental pressure varies.