A combustor was developed to operate with natural gas and air as the primary propellants at elevated chamber pressures and air preheat temperatures representative of land-based power generation gas turbine engines. Detonation dynamics were studied to characterize the operability of rotating detonation-based pressure gain combustion systems for this application. Measurements of chamber wave dynamics were performed using high-frequency pressure transducers and high-speed imaging of broadband combustion chemiluminescence. The rotating detonation engine was tested with two injector configurations across a broad range of mass flux (200-500kg/m2/s), equivalence ratio (0.85-1.2), and oxygen mass fraction (23.2-35%) conditions to determine the effect of operating parameters on the propagation of detonation waves in the combustor. Wave propagation speeds of up to 70% of the mixture Chapman-Jouguet detonation velocity and chamber pressure fluctuations greater than 4 times the mean chamber pressure were observed. Supplementing the air with additional oxygen, varying the equivalence ratio, and enriching the fuel with hydrogen revealed that combustor operability is sensitive to the chemical kinetics of the propellant mixture. Comparing the operational trends of the two injector configurations suggests that one design mixes the incoming propellants more effectively. Although most test conditions exhibited counter-rotating detonation waves within the chamber, the injector design with superior mixing characteristics was able to support single-wave propagation.

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.