The nature of sawtooth wave and its distinction from continuous rotating detonation wave

Abstract

To pinpoint the nature of the sawtooth wave, extensive experiments of methane-air continuous rotating detonation (CRD) are conducted in a hollow chamber around the boundary of the operating range. The time occupancy ratio and the increasing ratio of pressure rise (Δti/ΔTi and ΔPi/Δti) derived from high-frequency pressure data, and the integral of chemiluminescence intensity (ICI) based on self-luminescence images are proposed as quantitative parameters to distinguish the detonation wave and the sawtooth wave. The results show that the sawtooth wave is a critical unstable mode between conventional isobaric combustion and CRD, propagating with high Δti/ΔTi and low ΔPi/Δti. Meanwhile, the reaction zone of sawtooth wave is verified to be stabilized in the center of combustor through the self-luminescence observation. Especially, the multiple transition processes from the sawtooth wave to the CRD wave are accurately captured, and simultaneously represented as the change from single-peak waveform to double-peak waveform on ICI, the rise of ΔPi/Δti, and the reduction of Δti/ΔTi. The significant distinction of the sawtooth wave and the CRD wave in the coupling characteristics is confirmed through Short-Time Fourier Transform processes on ICI and high-frequency pressure. For the CRD wave, the propagation frequency of the reaction zone matches that of the pressure wave, whereas not for the sawtooth wave. It is ascertained that the reaction zone is decoupled with the pressure wave for the sawtooth wave, and the nature of the sawtooth wave is deflagration combined with a weak pressure wave.