Propagation mode of detonation waves in a narrow gap has been studied experimentally. The gap was formed by a pair of metal plates of 1500 mm in length which were inserted in a detonation tube. Two metal spacers were interposed at both side edges of the plates to arrange a gap size of 2.0 mm. The plates are supported by 15 combination probes which were composed of pressure and ion probes. Using the combination probe it is possible to detect a shock and a reaction front individually at one measurement point. A test gas was hydrogen-oxygen mixture diluted with argon or nitrogen and an initial pressure was 39 kPa. Velocity profiles and smoked foil records reveal five propagation modes in the gap: stable, quasi-stable, galloping, single head, and failure mode. In the quasi-stable mode, the propagation velocity is almost constant, while cell size on smoked foil records has larger variation as compared to the stable mode. The galloping mode shows large velocity fluctuation more than ±500 m/s and wide variety of the cell size along the propagation direction. In the single head mode one triple point travels downstream reflecting at the sidewall. The velocity deficit normalized by the propagation velocity at the gap entrance is dependent on the gap size normalized by the cell size, although the velocity deficit has little dependency for lean hydrogen-oxygen mixtures.
Control technique of the oscillatory combustion in a swirl-type combustor was investigated to suppress the pressure perturbation and the combustion noise. In this study, development of an active combustion control (ACC) on oscillatory flame was carried out with feedback system using loudspeaker and microphone as an actuator and a sensor, respectively. Modern H2 control algorithm based on experimental modal analysis for system identification was applied to control the oscillatory flame. Furthermore, for the future development of closed loop feedback system using the secondary injection method, optimization of the injection method was carried out. To examine the exothermic fluctuation, LIF measurement was carried out. OH radical distribution near the region of flame holder was visualized. As the results, two types of oscillatory flames were observed in this investigation. One of them was characterized by low-frequency mode. On the other hand, oscillatory flame with high-frequency mode was produced with a remarkable frequency near the resonance of the combustor. As for the performance of the developed ACC system, pressure fluctuation was suppressed with an efficiency of about 30% decrease. Furthermore, as for the secondary injection, it was found that jet interaction near the flame holder was an effective way to control the oscillatory flame.