High-Speed Diagnostics in a Natural Gas-Air Rotating Detonation Engine

A natural-gas-fueled rotating detonation engine was operated at flow conditions typical of gas turbine engines. High-speed broadband chemiluminescence images, particle image velocimetry (PIV), and dynamic pressure measurements were used to characterize the combustion process. A parametric survey was performed with variations of reactant mass flux (50-500 kg/(m2.s), inlet air temperature (520-710 K), equivalence ratio (0.6-1.7), and degree of oxygen enrichment of the oxidizer stream (23.2-33.5% oxygen mass fraction). Robust detonative behavior was observed over a range of parameters with highest pressure fluctuation amplitudes (P '/Pc similar to 2-2.65) observed with oxygen enrichment of 26-32% and mass flux of300-400 kg/(m2.s). A detailed discussion of two representative cases is presented: one operating with a single rotating wave and another with two corotating waves. In both cases, a minor wave was also detected, which circumscribed the annulus in the reverse direction of the major wave(s). PIV was performed at 100 kHz immediately downstream of the combustor exit. These measurements indicate predominantly axial flow from the exit nozzle, with strong velocity fluctuations corresponding to the detonation precession. Singular spectrum analysis revealed that fluctuations in the axial and azimuthal velocity components remained in-phase, with frequency content that matches the chemiluminescence and pressure signals.