Experimental analysis of low-frequency oscillation instability in two-phase rotating detonation waves within a cylindrical combustor

Experiments were conducted in a cylindrical air-breathing rotating detonation engine (RDE) fueled by liquid kerosene to examine the interaction between fuel-jet evolution and detonation modes. The tests covered inflow total temperatures from 650–1250 K and various equivalence ratios (ERs), with axial high-speed imaging and high-frequency pressure measurements used to characterize fuel-jet behavior and rotating detonation wave (RDW) dynamics. The RDW operated in a single-wave mode in all detonation cases. Wave continuity, RSD V , and FFT analysis identified three regimes: stable detonation, deflagration/quenching, and unstable detonation with low-frequency oscillation. Stable detonation was defined by RSD V < 7.5% and a single dominant RDW frequency, whereas unstable detonation showed additional low-frequency components and higher RSD V . The operability map showed that the stable ER range narrowed from 0.30–1.20 at 1250 K to approximately 0.30–0.44 at 650K. RDW velocity deficit and peak normalized visible fuel-jet height increased with increasing ER and decreasing inflow total temperature. Under unstable conditions, relative luminosity and fuel-jet-height fluctuations reached approximately 150% and Rpv ≈ 0.85 at higher momentum ratios. The low-frequency modulation showed an axial phase lag, and its peaks did not coincide with either the estimated Helmholtz-mode or longitudinal acoustic-mode range. The oscillation is therefore more likely associated with coupled pressure feedback, fuel redistribution, and kerosene evaporation/mixing delay. These results provided experimental evidence for the coupled evolution of optically observed kerosene jet structures and RDW dynamics in liquid-fueled air-breathing RDEs.