The Effect of Transient Nozzle Flow on Detonation Tube Impulse

Impulse generation with gaseous detonation requires conversion of chemical energy into mechanical energy. Because of the poor performance of straight detonation tubes compared to conventional propulsion systems and the success of using nozzles on rocket engines, the effect of nozzles on detonation tubes is being investigated. The first experimental investigation measuring impulse by gaseous detonation in tubes with nozzles operating in varying environment pressures using the ballistic pendulum technique is presented. Converging, diverging, and converging-diverging nozzles were tested to determine the effect of divergence angle, nozzle length, and volumetric fill fraction on impulse. The largest increases in specific impulse, 72% at an environment pressure of 100 kPa and 43% at an environment pressure of 1.4 kPa, were measured with the largest diverging nozzle tested that had a 12◦ half angle and a length of 0.6 m. There are two regimes of nozzle operation depending on the environment pressure that is observed from these data. The experimental data are compared to calculations of the impulse obtained by steady flow expansion through the nozzle with finite rate kinetics.