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.

通常，剪切同轴/涡流同轴喷射器中的凹槽对稳定燃烧和燃烧效率有积极影响。然而，液心气液旋流同轴喷射器中的凹槽可能会导致喷雾振荡，称为自脉动。在这项研究中，研究了凹槽长度对喷雾动态特性的影响及其机制。通过金属增材制造制造了四个具有不同凹槽长度的液心液气旋流同轴喷射器。冷流测试通过喷射器在广泛的液体和气体雷诺数范围内进行。使用动态压力传感器测量气体和液体喷射器歧管中的压力波动，并使用高速相机捕获高速瞬时喷雾图像。使用快速傅里叶变换技术分析从两种测量方法获得的数据。凹槽长度影响自脉动和稳定性图的频率和强度。在所有喷射器中，自脉动频率随着液体雷诺数的增加而增加，但气体雷诺数的影响随着凹槽数的不同而不同。因此，自脉动的特性取决于凹槽数 <1 或 ≥1。目前的实验结果被用于提出基于凹槽数的自脉动机制。但气体雷诺数的影响与凹槽数不同。因此，自脉动的特性取决于凹槽数 <1 或 ≥1。目前的实验结果被用于提出基于凹槽数的自脉动机制。但气体雷诺数的影响与凹槽数不同。因此，自脉动的特性取决于凹槽数 <1 或 ≥1。目前的实验结果被用于提出基于凹槽数的自脉动机制。