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The effects of the exit convergent ratio on the propagation behavior (i.e., initiation processes and propagation characteristics) of rotating detonations utilizing liquid kerosene have been experimentally investigated by varying the exit convergent ratio from 1 to 10 (i.e., CR = 1, 1.25, 1.67, 2.5, 5 and 10) and the mass flow rate of oxidizer. Oxygen-enriched air with an oxygen volume fraction of 40% and kerosene have been used as oxidizer and fuel, respectively, which are supplied into the combustion chamber through an atomizer-slit configuration. Experimental results indicate that rotating detonation waves can be initiated and propagate with different propagation modes under different exit convergent ratios. Three different propagation modes have been obtained, i.e., a deflagration mode, an ignition failure mode and a stable detonation mode. Moreover, the results show that the convergent ratio significantly influences the propagation modes, and when the combustion chamber outlet with a smaller convergent ratio is employed, stable rotating detonation waves can be obtained easily. In addition, it is observed that the time of establishment of the detonation wave increases with the convergent ratio. • Effects of the exit convergent ratio on the propagation characteristics have been studied. • Three fundamental operating modes have been observed at different conditions. • Stable rotating detonations can be obtained easily with a smaller convergent ratio. • The influence of the exit convergent ratio on the initiation time has been investigated. [ABSTRACT FROM AUTHOR]

To reduce hardware complexity and increase operating frequency, a simplified double-frequency scheme has been developed to obtain high-frequency detonations for pulse detonation rocket engines based on the valved and valveless schemes. This study focuses on characteristics of this simplified scheme. The critical points where detonations transit to deflagrations are considered at different operating conditions to clarify the lower boundaries of stable operations. Experimental results indicate that an ideal buffer zone may not be formed similar to the traditional valved schemes. Comparisons with the valveless scheme without the purge process show that the upper limits of oxidizer percentages are consistent to ensure stable operations, which implies that the present scheme operates potentially as the valveless mode. Detailed studies on the employed solenoid valves and impacts of retonations on the upstream passages demonstrate that solenoid valves are not able to realize intermittent supply control effectively. It is concluded that practical operations utilizing solenoid and rotary valves to control periodic supplies may also operate under a valveless scheme actually with a different upper limit of oxygen percentage in oxidizer. [ABSTRACT FROM AUTHOR]