An experimental study was performed to investigate the characteristics of two different combustion instability modes in a swirl-stabilized combustor. The first is the eigenfrequency corresponding to the half-wave of the combustion chamber section, and the second is the quarter-wave eigenmode of the inlet mixing section. The purpose of this study is to understand the effects of the swirl number on each combustion instability mode and analyze their generalized characteristics. Premixed gases composed of hydrocarbon fuels (C2H4 and CH4) and air were burned by independently varying the experimental conditions. Three dynamic pressure transducers and a photomultiplier tube were installed to detect pressure oscillations and heat release fluctuations in the inlet and combustion chamber sections, respectively. A high-speed camera was used to capture the instantaneous flame structures. In the swirl-stabilized combustor, the bands of the dominant frequencies were strongly dependent on the swirl number of the swirler vane. When the swirl number was low, the entire combustion system was often coupled with the quarter-wave eigenmode of the inlet mixing section. However, as the swirl number increased, the combustion instability mode was almost independent of the mixing section acoustics. Analysis of the phase difference and flame structure clearly demonstrated the differences between each eigenmode. The results provide new insights into the effect of the resonance mode in the inlet mixing section on combustion instability, depending on the swirl number in the swirl-stabilized combustor.

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A 3D printing shear/swirl coaxial injector was made to apply a 1-ton methane engine. The shear coaxial type was manufactured with a kind of recess length of 5.5 mm, and the swirl coaxial type was produced with four types of recess lengths of 0, 2, 4, and 5.5 mm. Results of cold-flow test conducted using water and air as simulated propellants at room temperature and pressure. Differences in spray patterns appeared depending on the internal structure of the injector and the recess length. Further, in the swirl coaxial injector, a spray vibration phenomenon accompanied by high-frequency noise arose, and to investigate this, dynamic pressure measurement was performed. Dynamic pressure data was analysed through FFT(Fast Fourier Transform), and it was determined whether or not self-pulsation occurred from the PSD(Power Spectral Density) consequence. As a result, it can be confirmed that the swirl coaxial injector's recess length is an essential parameter for self-pulsation. Furthermore, based on the perturbation results, self-pulsation occurs through the two propellants' interaction and propagates from the gas side to the liquid side.

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