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• On-orbit non-intrusive perturbation measurement of Hall effect thrusters. • 10 kHz to 100 kHz analysis better than full frequency domain. • Perturbation signal amplified by scatter numbers in the far-zero region. • The physical core represented by the scatter numbers is the dwell time. • Dwell time is mainly related to breathing oscillations. The failure of Hall effect thruster (HET) is usually the result of the accumulation of several tiny abnormal disturbances during operation. Timely and accurate early warning of perturbations is an important guarantee for the normal operation of thrusters. In this study, when the perturbation rate of HET signal (anode voltage or anode flow rate) is −4% to 4%, the time scale signal of breathing oscillation (BO) in the frequency range of 10 kHz to 100 kHz is statistically analyzed. Experiments show that when the signal is perturbed, the balance between ionization and acceleration of plasma in the discharge channel is destroyed, resulting in the dwell time of the wave peaks and valleys of BO in the far-zero region with the perturbation law, which visually shows that the number of scattered points at the corresponding current value changes regularly. According to the above statistical characteristics, this paper proposes a new condition monitoring index, namely the number of scattered points in the wave peaks side of the far-zero point area, and designs a perturbation indicator for the operating condition of the HET. Compared with direct monitoring of discharge current in engineering, this indicator can amplify the influence of the perturbation signal on BO, and has better identification and accuracy. Meanwhile, the indicator does not use invasive measurement and complex equipment, and is promising to be applied to the monitoring and diagnosis of the perturbation operation state of the on-orbit thruster. [ABSTRACT FROM AUTHOR]

Round combustors as a very desirable kind of supersonic combustor, face the difficulty of combustion organization. The typical cone-strut structure can accomplish some combustion organization, but it has a very high congestion ratio and is hence inefficient. To solve this problem, a method of combining cone-strut configuration and plasma/oxygen addition is proposed in this paper, and its scheme, experiment and combustion mechanism are studied. In the scheme of combustion organization, the fuel injection scheme and plasma arrangement scheme of the approach are projected, accomplished with the advantages of reducing congestion ratio from 20%-26%–13%. In the experiments of combustion organization, the effect of realizing combustion organization of such approach is proved, and three typical combustion organization states, which may be due to low congestion ratio, are displayed one by one, and its transformation speeds between three typical combustion organization states are investigated. In the speculations of mechanism, a set of simplified equations are provided for the first time, and these equations indicate that why the approach is effective and why the three kinds of combustion organization states display one by one. This research has theoretical and technical implications for the development of cone-strut configuration in round combustors. • Provide a combustion organization method of cone-strut/plasma torch with oxygen feedstock for round supersonic combustor. • Experiments confirm feasibility of this method and point out the key stage that affect combustion organization. • The wakeflow equations including combustion reaction is used to explain the feasibility and particularity of the method. [ABSTRACT FROM AUTHOR]

A new method of dual-frequency excited plasma (DFEP) is proposed to enhance ignition for supersonic combustion chamber. It is demonstrated experimentally that this method successfully achieves the acceleration of flame establishment and achieves the purpose of intensified ignition for supersonic flame in a real axisymmetric supersonic combustion chamber. The differences between the DFEP method and the traditional DC excited plasma (DCEP) method in the stage of local-flame establishment, the state of local-flame holding, the state of global-flame backpropagation, and the state of global-flame downstream transport are compared. It is found that the DFEP method can not only shorten the time of the state of the local-flame holding from 292.2 ms to 49.3 ms, but also prevent the suspension of the global-flame when the global-flame is in backpropagation, but this method cannot increase the local-flame propagation velocity and the global-flame backpropagation velocity. Detailed analysis and speculate together indicate that the effect of DFEP on flame comes from its ability to reduce the suspension time of the flame. The reason why DFEP has such a ability is discussed, and a new view never projected before is speculated: ➀ The flame (and shockwave) itself is in an unstable equilibrium between the positive feedback of backpropagation, the negative feedback of flow and the constraint of the expanding section, and the suspension time of flame (as well as shockwave) is positively related to the probability of the shockwave leaving the expanding section by self-excited oscillation. ➁ The extra active O radicals generated by the DFEP can increase the combustion heat release rate and the shockwave intensity, thereby providing a new path to help heat accumulation and making the flame easier to escape from the expanding section under the action of self-excited oscillation. [ABSTRACT FROM AUTHOR]

Facing the requirement of flameholding in a supersonic combustion chamber, a flameholding experiment under dual frequency excited plasma (DF excited plasma) was carried out in an axisymmetric supersonic combustion chamber. The flame establishment process was observed by using a high-speed-camera, and the flameholding characteristics with or without DF excited plasma were analyzed under different equivalence ratio(ER). The experimental results show that the flame will be enhanced by using dual-frequency excitation plasma in the supersonic combustion chamber: the flameholding mode was transformed from a global flame to a local flame, as well as the pressure of the combustion chamber was decreased significantly, when the DF excited plasma is switched off. In the ER range of 0.51 (0.18+0.33)∼0.60 (0.18+0.42), the DF excited plasma could induce a transformation from a local to a global flame, while if the ER is too high (ER>0.69 (0.18+0.51)) or too low (ER<0.18), the action of the DF excited plasma always couldn't. A basic feedback mechanism of the flameholding was proposed, with the consideration of the experimental results. The O radicals generated by the DF excited plasma was one important factors for flame reverse propagation, and the existence of the global flame was another necessary factor. Under the combined action of the O radicals of DF excited plasma and the global flame, the positive feedback process in the combustion chamber will be intensified, and the flame will propagate reversely. [ABSTRACT FROM AUTHOR]