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In this study, we tested a rotating detonation engine (RDE) fueled by liquid kerosene. A scheme of circumferential array atomization with an injection throat upstream of the annular combustor was used to realize the kerosene-fueled rotating detonation. The propagation characteristics of rotating detonation waves (RDWs) were analyzed by varying the distance between the pressure-swirl atomizers and the injection throat. The dynamic pressure signals and the visualized high-speed images were captured in the combustor. When the fuel atomizers were close to the injection throat, an unstable detonation mode appeared during the operation of the combustor. There was a periodical extinction and reinitiation of detonation waves in the combustor because the wave formed in the combustor could not propagate self-sustainably. In the fuel-lean tests, the rotating detonation degenerated to the combustion mode intermittently. Subsequently, unstable detonation was detected during the recovery stage from combustion to detonation mode. As the equivalence ratio increased, the rotating detonation process exhibited better continuity, but the duration of unstable detonation also increased. The continuity and stability of the rotating detonation process could be significantly improved by lengthening a certain distance between the atomizers and the injection throat. The experimental results indicated an optimal location of the fuel atomizers for stable operation, which could serve as a reference for the design of the injection structure of liquid-fueled RDEs. [ABSTRACT FROM AUTHOR]

• A novel acoustic atomizer has been designed to facilitate the liquid-fueled detonations. • The atomization characteristics and the flow pattern of the atomizer were analysed. • The maximum operating frequency of PDE reached 25 Hz. • The atomizer could effectively work under high-pressure condition in the detonation tube. The principle of a Hartmann-type acoustic nozzle is to generate ultrasonics to atomize the liquid fuel. Due to its outstanding performance on the atomization, the acoustic atomizer has been applied to internal combustion engine. Thus it possesses the potential to facilitate the liquid-fueled detonation initiations. In this paper, an acoustic atomizer was designed and established for a pulse detonation engine (PDE). The atomization characteristics and the flow pattern of the nozzle were analysed by a laser diffraction analyser and a high-speed camera. Multi-cycle detonation initiations experiments were conducted with the acoustic atomizer. The experimental results indicate that the performance of the nozzle was influenced by the air supply pressure, air-to-liquid fuel mass ratio and geometric parameters of the nozzle. The minimum Sauter mean diameter (SMD) measured was about 16 μm. The feasibility of the acoustic atomization scheme on cyclic detonation initiations was verified when the maximum operating frequency of the PDE reached 25 Hz. It suggests that the atomizer can effectively work under high-pressure condition in the detonation tube. [ABSTRACT FROM AUTHOR]

The propagation modes of rotating detonation waves supplied with liquid kerosene and oxygen-enriched air were experimentally investigated. Experiments were conducted while maintaining the equivalence ratio at approximately 0.7 and varying the mass flow rate of the oxidizer from 585.3 to 1493.8 g/s. Three propagation modes were obtained, and the propagation characteristics of rotating detonation waves in each mode were extensively analyzed. The results reveal that for the test model with an equivalence ratio of 0.7, the rotating detonation waves exhibit three types of modes in sequence as the mass flow rate of the oxidizer increases, namely, single-wave mode, single/dual-wave hybrid mode, and dual-wave mode. The propagation modes of rotating detonation waves vary randomly in the single/dual-wave hybrid mode, and the mode transition processes are more likely to be accompanied by transient detonation wave extinction due to the lower activity of liquid kerosene. For the single/dual-wave hybrid mode, the pressure feedback of rotating detonation waves to oxidizer plenum in the single-wave mode is greater than that in the dual-wave mode, which is related to the higher pressure peaks of rotating detonation waves in the single-wave mode. Moreover, the relative standard deviation of the propagation frequency is calculated to evaluate the propagation stability of the rotating detonation wave. It was found that the rotating detonation waves possess higher propagation stability in the dual-wave mode than in the single-wave mode. • Propagation modes of rotating detonation waves fueled by liquid kerosene were investigated. • The RDWs showed single-wave mode, single/dual-wave hybrid mode, and dual-wave mode. • RDW numbers varied randomly many times in the single/dual-wave hybrid mode. • The mode transition process was generally accompanied by RDW extinction. [ABSTRACT FROM AUTHOR]

• Experiments of Rotating Detonation Engine fueled by liquid kerosene in room temperature. • Clear modal change process of liquid RDE. • The modal transformation law was reproduced through numerical simulation method. • Quantitative analysis of combustion efficiency under different modes by statistical method. In a liquid kerosene rotating detonation engine (RDE), detonation waves often exhibit different propagation modes. The propagation characteristics with different modes are worthy of further study. To further investigate the propagation characteristics, a series of experiments was conducted, and the flow field characteristics under different modes were comparatively studied using high-speed photography and pressure sensors. The modal features and mode change trends obtained in the experiments were simulated using numerical methods. Based on this, the combustion efficiencies of the different modes were quantitatively characterized. The results showed that with increasing propellant mass flux, the detonation wave gradually changes from the two-counter wave mode to the single-wave mode, and the interim mode is a hybrid mode. Compared with the two-counter wave mode, the velocity deficit of a single wave is smaller, and the reaction zone is more compact. Numerical simulations show that a higher proportion of fuel is consumed by more violent chemical reactions in the single-wave mode; that is, the combustion efficiency in the single-wave mode is higher than that in the two-wave mode. The results provide a reference for further understanding the liquid fuel detonation phenomenon and improving fuel combustion efficiency. [ABSTRACT FROM AUTHOR]

• Experiments of Rotating Detonation Engine fueled by liquid kerosene in room temperature. • A new method for analyzing frequency characteristics in two-counter wave mode. • Analysis and verification of the mechanism of quenching and re-initiation in liquid-fueled Rotating Detonation Engine. • Stable propagation and smaller velocity deficit of liquid-fueled Rotating Detonation Engine in room temperature. In a rotating detonation engine (RDE), specifically a low-activity liquid fuel RDE, ensuring the continuous and stable propagation of detonation waves is important. In the RDE experiment with oxygen-enriched air as the oxidant and liquid kerosene as the fuel at room temperature, the stability of the rotating detonation wave (RDW) is found to be extremely inadequate. This inadequacy is manifested by more than 10 times of quenching and re-initiation within 500 ms. This frequent quenching and re-initiation phenomena considerably differ from those of the gaseous fuel RDE. Consequently, the velocity deficit of the detonation wave increased and the propulsion performance of the RDE was affected. In a further study using pressure sensors and high-speed cameras, the quenching phenomenon was found to be related to the supply state of the propellant, and the re-initiation phenomenon was related to the chemical reaction zone in the combustion chamber. To verify the foregoing, a special control test was performed. After improving the supply state of the corresponding propellant, the unstable characteristic of liquid fuel was effectively suppressed and a stable RDW with a velocity of 1321 m/s was obtained. The results of this study reveal the mechanism of liquid fuel quenching and re-initiation. This mechanism significantly restrains the instability of liquid fuel detonation waves. [ABSTRACT FROM AUTHOR]