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Rotating detonation engines (RDEs) have been actively researched around the world for application to next-generation aerospace propulsion systems because detonation combustion has theoretically higher thermal efficiency than conventional combustion. Moreover, because cylindrical RDEs have simpler combustors, further miniaturization of conventional combustors is expected. Therefore, in this study, with the aim of applying RDEs to space propulsion systems, a cylindrical RDE with a converging–diverging nozzle was manufactured; the combustor length [Formula: see text] was changed to 0, 10, 30, 50, and 200 mm; and the thrust performance and combustion mode with the different combustor lengths were compared. As a result, four combustion modes were confirmed. Detonation combustion occurred with a combustor length of [Formula: see text]: that is, a converging rotating detonation engine. The thrust performance of this engine was 94 to 100% of the theoretical rocket thrust performance, which is equivalent to the thrust performance of conventional rocket combustion generated at [Formula: see text]. This study shows that detonation combustion can significantly reduce engine weight while maintaining thrust performance.

To create a new flyable detonation propulsion system, a detonation engine system (DES) that can be stowed in sounding rocket S-520-31 has been developed. This paper focused on the first flight demonstration in the space environment of a DES-integrated rotating detonation engine (RDE) using S-520-31. The flight result was compared with ground-test data to validate its performance. In the flight experiment, the stable combustion of the annulus RDE with a plug-shaped inner nozzle was observed by onboard digital and analog cameras. With a time-averaged mass flow of [Formula: see text] and an equivalence ratio of [Formula: see text], the RDE generated a time-averaged thrust of 518 N and a specific impulse of [Formula: see text], which is almost identical to the ideal value of constant pressure combustion. Due to the RDE combustion, the angular velocity increased by [Formula: see text] in total, and the time-averaged torque from the rotational component of the exhaust during 6 s of operation was [Formula: see text]. The high-frequency sampling data identified the detonation frequency during the recorded time as 20 kHz in the flight, which was confirmed by the DES ground test through high-frequency sampling data analysis and high-speed video imaging.

A detonation engine system is successfully demonstrated for the first time in space using sounding rocket S-520-31 of the Japan Aerospace Exploration Agency/Institute of Space Astronautical Science. Detailed flight results of an S-shaped pulse detonation engine (PDE) installed in the rocket are presented herein. The flight is conducted to confirm that the PDE and its system operate at scheduled sequences in space, confirm the reproducibility of the PDE cycle, and despin the rocket around its axis. It is confirmed that the PDE operated successfully for 14 cycles in space. The experimental plateau pressure of [Formula: see text] is [Formula: see text] of the calculated plateau pressure, which suggests that detonation occurred in 14 cycles. The pressure profiles of the cycles are similar, and the pressure integrals are [Formula: see text], confirming the excellent reproducibility of the PDE cycle. A probability statistical approach assuming a Gaussian distribution is applied to determine the average angular acceleration difference between processes of the PDE operation, mixture supply, and oxygen supply. The results suggested that the PDE despun the rocket via the thrust produced via detonation combustion, which is consistent with a quasi-steady-state model with an accuracy of [Formula: see text].

Carfilzomib is a medicine that was recently approved for the treatment of cancer of bone marrow (multiple myeloma) that comes back or does not respond to previous treatment (relapsed or refractory). Data gathered from the hospitals, where the medicine is commonly used, was used to generate evidence. We looked at how well carfilzomib works in Japanese participants and if it is safe. Overall, 63.5% of participants treated with carfilzomib had side effects and 37.7% had serious side effects. Death occurred in 3.1% of participants during the study. Decrease in bone marrow and blood cells, infections, heart and kidney disorder, liver failure or dysfunction, and high blood pressure occurred in 5% or more participants. In 46.5% of participants the tumors had disappeared or shrank. In Japanese participants, carfilzomib was found to be safe and effective treatment for cancer of bone marrow that comes back or does not respond to previous treatment.

Converging–diverging nozzles are common in rocket engine systems to increase the exhaust velocity and improve thrust performance. In this study, we focused on the acceleration of subsonic burned gas without a structural throat via detonation to realize a simple and compact engine. We developed and tested a rotating detonation engine (RDE) without a throat and with a diverging channel (constant diverging angle α=5 deg). Gaseous C2H4 and O2 were used as the propellants, and the mass flow rate ranged from 62 to 134 g/s in the combustion tests under low back-pressure conditions. We measured pressure and thrust, as well as high-speed imaging of self-luminescence of the combustion and imaging of the exhaust plume. The pressure at the exit was less than one-fifth of the maximum pressure in the RDE, significantly below the value for a sonic flow. The results suggested that the exhaust flow was supersonic, with values up to Mach 1.7, without the need of a converging section within the engine. In addition to the estimated Mach number from the measured pressure, the exhaust plume images coherently indicated the existence of supersonic exhaust.

A cylindrical rotating detonation engine (24 mm diameter) with multiple injector holes on the combustor side wall for both propellant injection and cooling by injector gas flow was designed and te...

A rotating detonation engine (RDE) generates a continuous thrust with one or more rotating detonation waves. Because of the velocity on the order of kilometers/second, the reaction zone is relatively small. Therefore, the RDE realizes a short combustion chamber length. However, the detonation waves induce an azimuthal motion of propellant, resulting in torque around the thrust axis. Because the motion does not contribute to the thrust, the torque is important in terms of performance loss. Herein, we conducted combustion tests with a six-axis force sensor to simultaneously measure 0.149±0.009 Nm torque and 48.1±0.9 N thrust. A comparison of detonation waves captured by high-speed camera revealed that the torque followed the direction and was offset when the waves existed in both of two directions simultaneously, which indicates the possibility of controlling the torque. Under a mass flow rate at 87±9 g/s and an equivalence ratio at 1.43±0.28, when the azimuthal component of shear force was 8.8±0.6% of the thrust, 0.77±0.10% of the total kinetic energy of the exit flow was distributed to the azimuthal component of velocity and did not contribute to the thrust. We therefore concluded that the effect of the azimuthal motion on the RDE’s performance was small.

Linking peace to tourism has led to key questions in the academic literature. Is tourism a generator of peace or simply its beneficiary? Can tourism be a social force or is it merely an industry? W...

For rotating detonation engines, the high-pressure region behind the detonation causes backflow into the plenum, making it difficult to properly design injectors to achieve the target pressure balance due to blockage of a part of the injector area during engine operation. In this paper, we present the pressure and thrust measurement of a rotating detonation engine with two different triplet injectors (fuel injector diameters of 0.8 mm and 1.0 mm) using gaseous methane, gaseous ethylene, and gaseous oxygen. The detonation wave propagation velocity with the fuel injector diameter of 0.8 mm was approximately 200 m/s higher than that with the fuel injector diameter of 1.0 mm. Combustor pressures and specific impulses were almost identical for both fuel injector diameters in this study. For our evaluation of the extent to which the available injector area can be utilized during engine operation, the effective injector area ratio was defined as the ratio of the plenum pressure during burn time to the pre-ignition value. Regardless of fuel species and fuel injector orifice diameter, the effective injector area ratio decreased proportionally with the ratio of combustor pressure to pre-ignition plenum pressure. This result implies that the pressure balance between the upstream plenum pressure and the combustor pressure can be roughly determined taking the effect of backflow into consideration.

To analyze a rotating detonation cycle (RDC) with burned gas backflow, simultaneous self-luminous visualization, pressure, and thrust measurements with gaseous ethylene and oxygen were performed. Three different geometric blockage ratios (bottom-wall-surface area to cross-sectional area of combustor) were set at 89.2 , 70.2 , and 51.7 % . The fuel and oxidizer mass flow rates and equivalence ratio were constant at 20.6 g / s , 41.2 g / s , and 1.7, respectively. During the combustion test, the single detonation wave rotated at 1557, 1459, and 1353 m/s, and the propagation speed increased proportionally for the geometric blockage ratio. The estimated fuel–oxidizer–based specific impulse was in the range of 148 ± 8 s , and the impact of the geometric blockage ratio and propagation speeds on this specific impulse was not confirmed. The hydrodynamic blockage ratio of the oxidizer injector due to the detonation wave was estimated using the oxidizer plenum pressure. It was found that the hydrodynamic blockage ratio linearly decreased with an increase in the geometric blockage ratio. This important trend suggests that the RDC operation is limited in the region of the lower geometric blockage ratio. It is also predicted that a reduction in the hydrodynamic blockage ratio while maintaining the geometric blockage ratio is required for stable RDC operation and achievement of pressure gain combustion. Moreover, the whole RDC structure including the burned gas back flow successfully visualized at the frame rate of 0.5 and 1 µs. The validity of estimated hydrodynamic blockage ratio was demonstrated by comparison with the visualization experiment. It was concluded that the hydrodynamic blockage ratio was primarily determined mainly by the time scale of the burned gas backflow.

The internal flow structures of detonation wave were experimentally analyzed in an optically accessible hollow rotating detonation combustor with multiple chamber lengths. The cylindrical RDC has a glass chamber wall, 20 mm in diameter, which allowed us to capture the combustion self-luminescence. A chamber 70 mm in length was first tested using C2H4single bondO2 and H2–O2 as propellants. Images with a strong self-luminescence region near the bottom were obtained, confirming the small extent of the region where most of the heat release occurs as found in our previous research. Based on the visualization experiments, we tested RDCs with shorter chamber walls of 40 and 20 mm. The detonation wave was also observed in the shorter chambers, and its velocity was not affected by the difference in chamber length. Thrust performance was also maintained compared to the longer chamber, and the short cylindrical RDC had the same specific impulse tendency as the cylindrical (hollow) or annular 70-mm chamber RDC. Finally, we calculated the pressure distributions of various chamber lengths, and found they were also consistent with the measured pressure at the bottom and exit. We concluded that the short-chamber cylindrical RDC with equal length and diameter maintained thrust performance similar to the longer annular RDC, further expanding the potential of compact RDCs., Available online 17 August 2020

Detonation combustors are considered promising alternatives to conventional combustors because they offer high thermal efficiency and fast combustion. However, especially for the rotating detonation combustor, the theoretical propulsive performance has not been confirmed in experimental studies because the highly unsteady flow field hinders the measurements process. To understand the involved phenomena in more detail, a reflective shuttling detonation combustor (RSDC) with a rectangular combustion chamber was developed. The interior of the chamber can easily be visualized owing to its two-dimensional quality. Utilizing the RSDC, several combustion tests with gaseous ethylene and oxygen were conducted for different values of mass flow rates and equivalence ratios. Combustion modes from the tests were classified into four types based on the fast Fourier transform (FFT) analysis of the luminous intensity of the CH* self-luminescence images captured by a high-speed camera and a band pass filter. Simultaneously, the theoretical total pressure of a conventional isobaric combustor was compared to the static pressure measured at the bottom of the RSDC chamber. For the detonation modes, the ratio between experimentally measured static pressure and the theoretical pressure varied depending on the location in the chamber owing to the distribution of the time-averaged static pressure. Furthermore, the pressure ratio of the detonation modes was up to 18% lower than that of the deflagration mode potentially owing to the flow velocity induced by the detonation waves.

Recently, Kawasaki and Kasahara (2019) reported that reflection point distance, which is a detonation characteristic length relevant to the diffraction process, is a useful measure; i.e., the critical condition for detonation diffraction can be universally expressed in terms of the diffraction point distance, independent of mixture stability. However, their findings were limited to their experimental conditions only. In this study, we performed high-speed visualization of processes of cylindrical (line-symmetric) detonation diffraction around a 90-degree corner for two series of experiments to obtained reflection point distances, lr, as a novel characteristic length, and examined critical conditions of reinitiation expressed in terms of the reflection point distance. In the first experimental series, stoichiometric C2H2/O2 mixtures with 50% Ar dilution were employed, and the channel width lc was varied to 5, 10, 15, and 20 mm to investigate the influences of the boundary condition of the flow field. In the second experimental series, H2/O2, C2H2/O2, or C2H4/O2 mixtures with different equivalence ratios were employed to investigate influences of the reaction systems. Our results confirmed that the channel width does not affect the reflection point distance or the critical condition. The critical condition was also independent of fuel species and equivalence ratio, and can be uniquely expressed as lr / lc = 4.0 ± 0.6 in terms of the reflection point distance.

This study evaluated the propulsion performance of a nozzleless, cylindrical rotating detonation engine (RDE). Using a C2H4–O2 mixture, the RDE was tested in a low-back-pressure environment at propellant mass flow rates of 8–45 g/s. In high-speed imaging of the self-luminescence within the combustor, rotating luminous regions were observed at mass flow rates above 22 g/s. Measured pressure distributions suggest that burned gas reached sonic velocity at the combustion chamber outlet. This paper proposes the structure of internal flow in the RDE and confirms that calculated pressure distribution based on the structure was close to the experimental distribution. This study also estimated the RDE’s thrust by pressure and momentum exchange and confirmed it by experimental measurement. Moreover, the theoretical thrust calculated under the assumption that exhaust is a sonic flow agreed with the load cell thrusts, suggesting that RDE combustion is perfectly completed inside the chamber. Specific impulses are 80–90% of specific impulses for ideal correct expanded flow for all mass flow rates, and its value was close to that of an annular RDE. In addition, RDE performance will increase by about 20% if the RDE is equipped with a divergent nozzle and the gas is correctly expanded to back pressure.

Fluorescent molecules based on a fluorinated isoxazole scaffold were synthesized and investigated for their photochemical properties. The introduction of a fluorine substituent into 3,5-diarylisoxazoles led to an increase of fluorescence intensity and exhibited a redshift in the emission intensity. α-Fluorinated boron ketoiminates (F-BKIs) were also synthesized via a ring-opening reaction of 4-fluoroisoxazoles and exhibited highly fluorescent luminescence and aggregation-induced emission (AIE), showing promise as a new fluorophore.

The multiple-ion-probe measurement method is a method to measure a propagating flame using ion probes installed on the wall surface of a combustion chamber. The dynamic behavior of the propagating flame along the wall surface can be regenerated from the dataset of flame signals from individual ion probes. Although this method only captures flames near the wall surface, the flame propagation behavior can be indirectly visualized. Because this method can attain very high temporal resolution, it can provide precise measurements of high-speed phenomena such as knocking in spark-ignition engines and detonation in detonation combustors. This study aimed to investigate the ability of a developed 64-channel multiple-ion-probe measurement system to characterize a propagating flame. To this end, three flames with substantially different propagation velocities were measured using the proposed multiple-ion-probe measurement system. During the experiments, methane–oxygen stoichiometric mixtures diluted with different amounts of nitrogen were used. The flame propagation velocity varied within the range of several m/s for a turbulent flame to 2.4 km/s for detonation by varying the dilution ratio of nitrogen. In the case where a mixture with a nitrogen mole fraction of 0.71 was used, a phenomenon of repeating stagnation and reacceleration of the propagating flame was observed. Furthermore, the phenomenon considered to be flame quenching was also observed near the wall. In the case of no dilution (nitrogen mole fraction = 0.00), multiple-ion probes with an installation interval of 1.5 mm indicated that the velocity fluctuated within the range of −500 m/s to +2000 m/s with respect to the Chapman–Jouguet detonation velocity of 2390 m/s. Experiments involving soot foil recording conducted in parallel confirmed that this velocity fluctuation was derived from the detonation cell structure and that micro-explosions in the detonation front could be captured using the multiple-ion-probe method.

The thermal expansion behaviors of few-layered graphene (FLG)/Al composites fabricated via spark plasma sintering and hot extrusion were evaluated. We demonstrated the first example of efficiently reducing the coefficients of thermal expansion (CTEs) of Al composites by incorporating FLG. The CTE of the Al matrix decreased from 26.72 × 10−6 K−1 to 25.53 × 10−6 K−1 with incorporating of merely 0.4 vol% of FLG. Due to the detachment of FLG-Al interface at elevated temperatures, the CTEs of the composites were slightly higher than those estimated by theoretical prediction. This result was further confirmed by the presence of hysteresis phenomenon of the cyclic expansion behavior of the FLG/Al composite. Moreover, the FLG exhibited a high constraining efficiency of ∼13, being more effective at lowering the CTEs of Al composites as compared to other traditional fillers. This work could be significant for guiding the design of high-performance graphene/Al composites for thermal management applications.

A high operating frequency of a pulse detonation engine is required to increase the thrust-to-engine weight ratio or thrust density. The semi-valveless pulse detonation cycle (PDC) proposed by Matsuoka et al. (2017) can achieve a high operating frequency exceeding several kilohertz. For achieving a higher operating frequency close to the upper limit of gas dynamics, it is necessary to minimize the process in which the buffer layer is applied to avoid self-ignition of the detonable mixture. Experiments were conducted, and a one-dimensional numerical model was developed to investigate the minimum thickness of the buffer layer and the required duration for the stable PDC operation. Ethylene was used as a fuel and pure oxygen as an oxidizer. The total length of two combustors with an inner diameter of 10 mm was 40 and 80 mm. Therefore, the thickness of the buffer layer of approximately 20 mm was suggested for the stable PDC operation. This result indicated that 10% of the duration of one PDC was required to prevent self-ignition (SI). In the failed PDC, the early and late SI were confirmed. Interestingly, high-frequency PDC operation with a short combustor can suppress late SI and results in a higher success rate with the same thickness of the buffer layer. Furthermore, a stable PDC operation of a 1916 Hz with a combustor with a total length of 40 mm was demonstrated.

Fabricating high-strength Al matrix composites without sacrificing their electrical conductivity is a critical issue in the design of Al-based conductors. Here, we demonstrate for the first time, an example of improving the interfacial load transfer and strength of few-layer graphene (FLG)/Al composites by an appropriate interfacial reaction. Monocrystalline Al4C3 nanorods that tightly conjoined the FLG platelets with the Al matrix were produced by manipulating the sintering temperature. As revealed by transmission electron microscopy and by a shear lag model that provides a quantitative estimate of the strengthening, the Al4C3 nanorods ensured an efficient load transfer at the FLG-Al interface, thereby giving rise to a considerable enhancement of strength in the composite. Moreover, the electrical conductivity is almost as high as that of pure Al, which could be a significant step toward the preparation of high-performance Al-based conductors.

Although filled skutterudites are very promising thermoelectric (TE) materials at intermediate temperature, most of the high-performance skutterudites reported are multiple-filled materials that tend to have poor stability and machinability. Here, we successfully fabricate single-filled skutterudite based composites with uniformly dispersed β-SiC nanoparticles via cryogenic grinding and spark plasma sintering. The nanocomposites show not only increased Seebeck coefficient owing to a possible energy filtering effect, but also reduced lattice thermal conductivity through enhanced phonon scattering. A maximum ZT value of 1.42 at 850 K with greatly improved mechanical properties is achieved, which is very attractive for the application in TE devices.

Metallic or ceramic micro/nanoporous materials have attracted particular attention due to some interesting structural and functional properties. There exist a variety of methods for producing porou...