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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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