Performance Measurements of Multicycle Pulse-Detonation-Engine Exhaust Nozzles

Abstract

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 fillfractions 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. NomenclatureAR = area ratio of nozzle (D 2 nozz /D 2 comb ) D comb = PDE combustion chamber diameter D nozz = exhaust nozzle-exit diameter ff = fill-fraction Isp = fuel-based specific impulse Isp ref = reference fuel-based specific impulse L comb = PDE combustion chamber length L nozz = length of nozzle M exit = exit Mach number T = thrust T ref = reference thrust t = time t cycle = PDE cycle time β = nozzle length ratio (L nozz /L comb )

Investigation of Thrust Augmentation and Acoustic Performance by Ejectors on PDE

“…Another parameter of importance is the axial position of the ejector inlet relative to the PDE tube exit. Downstream ejector placement between one and two PDE diameters provides optimum levels of thrust augmentation [16][17][18]. In addition to ejector geometry and axial position of the ejector, there are still other operating parameters that have been shown to affect the performance of a PDE, such as fill fraction that represents the proportion filled with detonable mixture relative to the PDE tube volume.…”

“…In addition to ejector geometry and axial position of the ejector, there are still other operating parameters that have been shown to affect the performance of a PDE, such as fill fraction that represents the proportion filled with detonable mixture relative to the PDE tube volume. Although the PDE thrust has been shown to decrease with a reduction in fill fraction, better specific thrust performance is obtained at lower operating fill fraction [11,14,18]. However, the acoustic signature, as another important influence on PDE performance, receives much less attention.…”

Single-Cycle Impulse from Detonation Tubes with Nozzles

“…As demonstrated by a number of experimental [7,12] and numerical [1,[13][14][15] studies, the filling and purging portions of a cycle can significantly affect the nozzle flow processes. In our tests, the environmental gas contained within the nozzle is initially at rest at the environmental gas pressure.…”

“…or experiments conducted at atmospheric environmental pressures [7][8][9][10]. Additional studies on nozzles are reviewed by Morris [5], Kailasanth [11], and Allgood et al [7].…”

“…Additional studies on nozzles are reviewed by Morris [5], Kailasanth [11], and Allgood et al [7]. The goal of this work was to characterize nozzle performance on single-cycle detonation tubes for a variety of nozzle pressure ratios expected at realistic operating conditions.…”