Performance measurements of multicycle pulse-detonation-engine exhaust nozzles

Performance measurements of multicycle pulse-detonation-engine (PDE) exhaust nozzles were obtained using a damped thrust stand. A pulse detonation engine of 1.88 m length was operated on a cycle frequency of 30 Hz at stoichiometric conditions. Both converging and diverging bell-shaped exhaust nozzles were tested for PDE fill-fractions ranging from 0.4 to 1.1. The area ratios of the nozzles were varied from 0.25 converging to 4.00 diverging. The nozzle length was negligible compared to the overall length of the PDE. The feasibility of normalizing the PDE nozzle thrust data was investigated by testing two different PDE combustion chamber diameters (2.54 and 5.08 cm) with the same nozzle area ratios. The optimum nozzle area ratio was found to be a function of the PDE fill-fraction. For fill-fractions at or below 0.5, the optimum configuration was a PDE without an exhaust nozzle. However, as the operating fill-fraction was increased to values close to or above one, thrust enhancement was obtained with a converging nozzle. The diverging nozzles also showed a relative increase in their performance with increased fill-fraction. Unlike the converging nozzles, the diverging nozzles and baseline configuration were observed to be sensitive to the ignition delay.