Abstract

In general, a recess in shear coaxial/swirl coaxial injectors positively affects the stable combustion and combustion efficiency. However, a recess in a liquid-centered gas-liquid swirl coaxial injector may cause spray oscillations, known as self-pulsation. In this study, the effects of the recess length on the spray dynamic characteristics and their mechanisms were investigated. Four liquid-centered liquid-gas swirl coaxial injectors with different recess lengths were manufactured by metal additive manufacturing. Cold-flow tests were performed in a broad range of liquid and gas Reynolds numbers through the injectors. Pressure fluctuations in the gas and liquid injector manifolds were measured using dynamic pressure sensors, and high-speed instantaneous spray images were captured using a high-speed camera. The data obtained from the two measurement methods were analyzed using the fast Fourier transform technique. The recess length affects the frequency and intensity of the self-pulsation and stability map. In all injectors, the self-pulsation frequency increases with the liquid Reynolds number, but the effect of the gas Reynolds number differs with the recess number. Thus, the characteristics of self-pulsation change depending on whether the recess number <1 or ≥1. The present experimental results were utilized in proposing self-pulsation mechanisms based on the recess number.

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