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The inner flow containing the ignition process of a throatless and diverging (constant diverging angle α = 5 deg) rotating detonation engine (RDE) was experimentally investigated by both optical observation and pressure measurement. An RDE that had an acrylic engine wall with a length of 70 mm and an inlet diameter of 20 mm was tested under a low back pressure condition using gaseous C 2 H 4 − O 2 as the propellants. A high-speed camera captured the ignition process, of which there were two types: deflagration-to-detonation transition and direct initiation. In addition to the visualizations of the inner flow, the pressure values in an RDE with an acrylic wall were compared with those of an RDE having a stainless steel wall with 8 pressure ports in the axial direction. The comparison revealed that the RDE exhaust flow was supersonic. A strong self-luminescence and CH* luminosity area near the injector surface during combustion suggested that the short completion of detonation combustion enabled the thermal choking of the subsonic propellant gases even when the channel was diverging. Moreover, the axial position of the erosion in the acrylic wall indicated that the heat release region was near the injector surface. Finally, a theoretical flow model for the RDE was compared to the experimental data, and the results suggested that the inner flow in the RDE can be reasonably described as a quasi-one-dimensional steady flow. [ABSTRACT FROM AUTHOR]

To analyze non-ideal phenomena, such as burned gas backflow and non-detonation combustion, which affect the rotating detonation wave Mach number, simultaneous self-luminous visualization, time-averaged static pressure, fluctuating pressure, and thrust measurements with gaseous ethylene and oxygen were performed. Consequently, by doubling the number density of the fuel injectors, the hydrodynamic blockage ratio at the oxidizer inlet increased approximately 1.7-fold under the same oxidizer inlet area conditions. This may be attributed to the increase in the detonation propagation Mach number owing to the enhanced mixing of fuel and oxidizer. The relationship between the parasitic combustion fraction in front of the rotating detonation wave and the Mach number was also investigated by using a distributed heat release model. Consequently, it was suggested that experimental Mach number decreased from approximately 4.1 to 2.8 with increase in a mixture mass flux, and the theoretical detonation wave propagation Mach number was 7.3. • Mach number of rotating detonation wave was experimentally estimated. • Hydrodynamic blockage ratio increased with number density of fuel injectors. • Propagation speed of detonation wave increased with mixture mass flux. • Fluctuating pressure ratio decreased with increase in mixture mass flux. • The Mach number decreased from 4.1 to 2.8 with increase in mixture mass flux. [ABSTRACT FROM AUTHOR]

In this study, the critical conditions of diffracted detonation waves expressed in terms of reflection point distances in Kawasaki and Kasahara (2020) were investigated for a wider range of fuel-oxidizer mixtures. In H 2 /O 2 , C 2 H 2 /O 2 , C 2 H 4 /O 2 , C 2 H 6 /O 2 , C 3 H 6 /O 2 , C 2 H 6 /N 2 O, and C 3 H 6 /N 2 O mixtures, these mixtures are used to measure the reflection point distance through the modification of the initial pressure and equivalence ratio of the mixture at room temperature. Moreover, the critical ideal reflection point distance divided by the channel width, which this dimensionless parameter was identified in the critical condition region of detonation diffraction. The results revealed that this region was in the range of 3.8 ± 0.8 for all investigated mixtures even though the equivalence ratio varied. The parameter l r,i p 0 is the product of the ideal reflection point distance and the initial pressure, which is proportional to the energy (work) per unit area required for re-initiation. The larger the product of the reflection point distance and the initial pressure, the more difficult the mixture is to re-initiate, and the inverse of this parameter represents the ease of re-initiation, which can be considered an index of detonability. Detonability, which is the objective of clarification in this study, was found to have the order C 2 H 2 /O 2 > C 2 H 4 /O 2 > C 3 H 6 /O 2 > C 2 H 6 /O 2 > H 2 /O 2 in the vicinity of the stoichiometric ratio, which is similar to the case using Matsui and Lee's critical initiation energy. [ABSTRACT FROM AUTHOR]

HAN-based liquid monopropellant has been studied for its possible substitution of hydrazine toxic component. The onset temperature of decomposition was provided by DTA-TG thermal analysis. Moreover, the effect of 5 M HNO 3 and 5 M NH 2 OH addition on catalytic decomposition was also examined. The major products measured by mass spectrometer were N 2 , NO, N 2 O, NO 2 , H 2 O and NH 3 . Otherwise, the burning rates of HAN-based monopropellants were measured from the strand burner videos taken by high speed camera. The effect of methanol addition; as fuel; on the burning rates was demonstrated. On the other hand, HAN-based liquid monopropellant was tested and decomposed in 20 N thruster and different catalysts were compared. Honeycomb catalysts were tested instead Shell 405 catalysts, the obtained data demonstrate the improvement of burning reactions and pressure slopes after HAN-based decomposition. [ABSTRACT FROM AUTHOR]

Liquid propellants are commonly used in rocket engines due to their high energy density. In this study, we focused on the use of liquid ethanol and liquid nitrous oxide as propellants in a cylindrical rotating detonation engine (RDE) for practical applications, and examined the effects of various conditions on the bipropellant RDE performance. We varied the vapor quality of nitrous oxide in a mixture of liquid and gaseous nitrous oxide due to the flash boiling. In addition, we varied the liquid ethanol temperature, the injector stiffness, and momentum angle of the propellant. We then analyzed the effects of these changes on the propagation mode of the RDE under atmospheric pressure conditions. The results showed that a rotating detonation wave was observed under the combination of high vapor quality of nitrous oxide, high injector stiffness, high liquid ethanol temperature, and high momentum angle. The propagation velocity was obtained as 73∼83 % of the Chapman-Jouguet velocity. Long-duration combustion tests were also conducted, and the internal combustion structure was confirmed from the erosion of the carbon-carbon (C/C) composite material. The detonation wave was considered to propagate near the bottom of the RDE with liquid propellants from the erosion heights of the C/C composite. The erosion height was confirmed to be consistent with the fill height calculated using the sound speed of the nitrous oxide. In addition, characteristic exhaust velocity efficiencies of more than 85 % were achieved in all combustion tests. [ABSTRACT FROM AUTHOR]

A reflective shuttling detention combustor (RSDC) is a two-dimensional combustor with two reflection walls. Unlike a rotating detonation combustor (RDC), an RSDC can visualize the entire area of the combustor via an optical technique. In addition, the RSDC can reproduce the counter-rotating detonation mode in RDC. In present study, CH* luminescence and schlieren image were observed to investigate the dynamics of the RSDC. The reflective wall distance was set to 45 mm (Type L) and 25 mm (Type S). As the results, the wave speed of 1226 ± 64 m / s in the single wave mode in Type S was 76% of that in Type L. It was found that the detonation propagation speed decreased with a reduction in the reflection wall distance. Superimposing the luminescence images on the schlieren images revealed that the mixture was mainly burned by deflagration behind shock wave. In addition, the experimental mixture fill height was in good agreement with model in which the mixture filling process was temporarily stopped by detonation and refilled at a constant speed. Using the maximum fill height obtained by the model, it was found that the detonation mode was in the region of 3 ± 0.6 of the dimensionless quantity (the reflection wall distance divided by the wave number and maximum value of the mixture fill height). [ABSTRACT FROM AUTHOR]