伊東山 登

One of the most important goals in aerospace engineering applications is the creation of new “flyable” systems. In a flight demonstration using the sounding rocket S-520-34, we show the first successful operation of a bipropellant cylindrical rotating detonation engine using liquid ethanol and liquid nitrous oxide, Detonation Engine System 2 (DES2), in a space environment. From the pressure and temperature histories, the combustion was finished before all propellants were consumed because nitrogen was supplied earlier than the ideal depletion time due to spin stabilization of the sounding rocket. Therefore, the combustion pressure decreased from the nitrogen-supply start time. The short-time Fourier transform result indicated that the deflagration mode, two-wave mode, and single-wave mode occurred in sequence. This was attributed to the locally lower liquid temperatures, wall temperature, and mixture ratio at ignition near the wall, where the rotating detonation wave propagated. A comparison of the filling mass and consumption indicated that the mass flow rate estimated using control surface theory reflects an actual phenomenon. As for the propulsive performance, the experimental characteristic exhaust velocity was almost the same as the ideal value. Moreover, a specific impulse efficiency of more than 90% was achieved throughout the rotating detonation engine operation.

A rotating detonation engine (RDE) featuring two fixed channel geometries, with angles [Formula: see text] (converging) and [Formula: see text] (diverging), was investigated experimentally. Optical observations, pressure measurements, and thrust measurements during gaseous [Formula: see text] combustion tests were conducted to investigate the effects of axial flow speed on detonation waves and the acceleration process of the internal flow. The results were compared with [Formula: see text] combustion data to assess how heating value affects the internal flow. An acrylic wall was used to capture the side view of the internal flow, and a stainless-steel wall equipped with eight or nine pressure ports in the axial direction measured pressure. Combustion tests were performed under both low-back-pressure and atmospheric conditions. Strong circumferentially propagating [Formula: see text] luminosity and a broadband chemiluminescence area were observed from the side of the RDE. A high-luminescence area propagating downstream of the main combustion region was inclined backward or forward relative to the direction of propagation, depending on the channel’s angle. The time-averaged pressure distribution suggested that the internal flow accelerated to critical speed in the middle of the engine within the diverging channel and near the exit in the converging channel, indicating distinct acceleration mechanisms depending on the channel angle.

This paper explores the innovative direction control of rotating detonation waves in rotating detonation engines (RDEs) by adjusting the ignition location and employing helical combustors with a sinusoidal cross section. In our experimental setup, we conducted 25 combustion tests using two distinct combustor geometries, each featuring different helical profile directions. The following conclusion drawn from the results: when the ignition was positioned 30.6–46.0 mm from the inlet, the detonation wave direction was invariably influenced by the helical direction. This correlation was statistically significant, with an occurrence probability (assuming a random direction probability of 0.5) being [Formula: see text], far exceeding the 0.05 significance level. Furthermore, the helical combustors generated a measurable torque due to the pressure differentials created by shock waves within the combustor. This torque, recorded between [Formula: see text] at a mass flow rate of 28.5–29.0 g/s, indicates the potential of power extraction from the combustor. Notably, the torque direction was also controllable via the helical direction. This study presents a significant advancement in propulsion technology, demonstrating a novel method to control detonation wave direction and torque generation in RDEs through helical combustor design, paving the way for more efficient and controllable propulsion systems.

Abstract In this study, we focus on the early stages of the Hartmann–Sprenger tube operation in the jet regurgitant mode to investigate three key relationships: (1) between the nozzle dynamic pressure and the start time of temperature rise at the resonance tube end, (2) between the nozzle dynamic pressure and the resonance tube end pressure, and (3) between the distance l from the resonance tube end to the contact surface and the rise in the end gas temperature of the resonance tube. The results showed that the condition for the rise in the resonance tube end gas temperature after the gas jet from the nozzle reached sonic flow was the stabilization of the average fluctuation pressure value at the resonance tube end in conjunction with the nozzle dynamic pressure. At the time of operation stabilization of the Hartmann–Sprenger tube, the average fluctuation pressure at the resonance tube end converged to a constant value almost equal to the nozzle dynamic pressure. This result means that the nozzle dynamic pressure is almost equivalent to the fluctuation pressure at the resonance tube end. Moreover, the distance l did not significantly increase with the resonance tube length L and remained nearly constant. The gas temperature at the resonance tube end obtained from the experimental results generally agreed with the temperature calculated from compression through an adiabatic and isentropic process from L to l.

A Lagrangian approach was proposed to analyze induction and reaction times in the cellular gaseous detonation. Two-dimensional simulations in an argon-diluted and non-diluted hydrogen-based mixtures were performed with detailed chemistry, along particle trajectories. The distribution of the induction and reaction times inside the cell was significantly different between the Eulerian and the Lagrangian perspectives, the latter showing non-monotonic behavior. Preferential thermodynamic paths laid along the Rankine–Hugoniot curve and behind transverse waves (TW). All particles were ignited within half and one cell cycle for the diluted and non-diluted mixture, respectively. The ignition mechanisms were not only one-dimensional, but also multi-dimensional, with ignition behind the TW being the most important, and collision of TW and triple points being secondary. A new topology inside the cell could be drawn, from the intersection of the ignition front with TW. TW appeared as phase waves in the (x,t) diagram. Comparison of H2O mass fraction between local and equilibrium values indicated that a local chemical disequilibrium remained (superequilibrium), due to TW. Equating the mean sonic plane with thermochemical equilibrium in the non-diluted case is not completely accurate. Furthermore, the characteristic time scales for chemical and hydrodynamic phenomena were compared. The diffusive phenomenon did not make any contribution in the mixtures tested. In comparison with the Zel'dovich–von Neumann–Döring model, a shorter average induction time was found in the non-diluted mixture, which is not in line with the results from previous Favre approaches. The average reaction time was also shorter in both mixtures.

There are few experimental studies on rotating detonation engines (RDEs) with liquid propellants. This study reveals the static thrust performance of a cylindrical RDE with ethanol and liquid nitrous oxide as propellants under atmospheric pressure. This RDE had an inner diameter of 40 mm, a maximum combustor length of 230 mm, a nozzle contraction ratio of 1.7, and a nozzle expansion ratio of 9.1. Nineteen experiments were conducted at total mass flow rates of [Formula: see text], mixture ratios of 3.6–5.9, and combustion pressures of 0.35–0.46 MPa, resulting in a maximum detonation velocity of [Formula: see text] (approximately 80% of the theoretical detonation velocity, [Formula: see text]), maximum thrust at sea level of 294 N, and maximum specific impulse at sea level of 148 s. In addition, the maximum characteristic exhaust velocity, [Formula: see text], was [Formula: see text], which was 99% of the theoretical value. The characteristic length of the combustion chamber at this time was 0.15 m. Since conventional rocket combustion requires 1.57 m to achieve the same [Formula: see text] efficiency, this study shows that detonation combustion can reduce the combustor size by 88%.

A coupled cylindrical rotating detonation engine (RDE) with two cylindrical RDEs (both combustors had a combustor inner diameter of 23 mm and an axial length of 30 mm) placed next to each other was tested for rocket clustering application. The objective of the experiment was to achieve two-engine synchronized initiation with a single igniter. Experiments were conducted on the inner wall of the combustors with different connecting-hole diameters and wall heights to evaluate the ignition delay time, combustion mode, and propulsion performance. The propellants were gaseous ethylene and oxygen, and experiments were conducted under constant conditions of mass flow rate ([Formula: see text]), equivalence ratio ([Formula: see text]), and backpressure (approximately 10 kPa). When the two combustion chambers were completely separated by a wall, ignition occurred with a time delay of 260 ms in the chamber without an igniter. However, when a large hole ([Formula: see text] diameter) was placed in the wall separating the two combustion chambers, synchronous initiation was successful. Synchronous initiation was also successful when the wall height was lowered (7-mm height). Under both conditions, the same level of specific impulse was achieved as for RDEs operating at the same mass flux.

Two-dimensional numerical simulations with the particle tracking method were conducted to analyse the dispersion behind the detonation front and its mean structure. The mixtures were 2H$_2$–O$_2$–7Ar and 2H$_2$–O$_2$ of increased irregularity in ambient conditions. The detonation could be described as a two-scale phenomenon, especially for the unstable case. The first scale is related to the main heat release zone, and the second where some classical laws of turbulence remain relevant. The dispersion of the particles was promoted by the fluctuations of the leading shock and its curvature, the presence of the reaction front, and to a lesser extent transverse waves, jets and vortex motion. Indeed, the dispersion and the relative dispersion could be scaled using the reduced activation energy and the $\chi$ parameter, respectively, suggesting that the main mechanism driving the dispersion came from the one-dimensional leading shock fluctuations and heat release. The dispersion within the induction time scale was closely related to the cellular structure, particles accumulating along the trajectory of the triple points. Then, after a transient where the fading transverse waves and the vortical motions coming from jets and slip lines were present, the relative dispersion relaxed towards a Richardson–Obukhov regime, especially for the unstable case. Two new Lagrangian Favre average procedures for the gaseous detonation in the instantaneous shock frame were proposed and the mean profiles were compared with those from Eulerian procedure. The characteristic lengths for the detonation were similar, meaning that the Eulerian procedure gave the mean structure with a reasonable accuracy.