Recently, pressure gain combustion (PGC) has been a subject of intense study because of its potential to increase the thermodynamic efficiency of power generating gas turbines by several percentage points. The rotating detonation combustion/combustor (RDC) can provide large pressure gain within a small volume through rapid heat release by detonation wave(s) that propagate continuously in the circumferential direction. The RDC has been investigated mainly for propulsion applications using hydrogen fuel. In contrast, we present experimental results from an RDC operated on methane and oxygen-enriched air mixtures to represent the reactants in advanced power generating gas turbines. The propagation of detonation and oblique shock waves in the RDC is investigated through High Speed Video (HSV) imaging and Ion Probe (IP) data.

HSV imaging requires optical access to the RDC, which can be difficult especially when the RDC is integrated with the gas turbine inlet hardware. Additionally, HSV systems are quite expensive. In contrast, IPs are inexpensive and have the advantages of small size and flexibility in the placement location and can be flush mounted causing minimal interference with the propagating wave. In this study, the detonation wave is tracked by high-resolution HSV imaging at framing rate of 200 kHz. At the same time, IPs are used to detect the rotating oblique shock wave inside the RDC, and different analysis techniques are explored to quantify the wave speed. IP voltage data are analyzed by differentiation, correlation and fast-Fourier transform methods to compute the wave speed (or rotation frequency), and the results are compared with those from the HSV image analysis. The uncertainty of different methods is discussed, and finally, the analysis techniques are applied to investigate the wave characteristics during an experiment.

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