Mechanistic Assessment of Swirl Coaxial Injection by Quantitative X-Ray Radiography

Abstract

Detailed x-ray radiographic experiments were conducted to evaluate the time-averaged spray characteristics of a liquid rocket swirl injector. Sprays issued from a single liquid-centered swirl coaxial element—with and without coannular gas flow—were exposed to focused, monochromatic x rays produced by a synchrotron light source. Two-dimensional attenuation data are presented at various axial stations and reveal both projected mass distribution of liquid in the injector near field and mass-weighted axial velocity integrated over time. Measurements describing spray morphology are also inferred from the x-ray data and compared with those measured through objective image processing of visible light imagery. The gas flow is observed to reduce spray cone angle up to 50% and increase liquid film thickness up to 20% in the near field. Measurements compare well with those extracted from imagery of the pressure-swirl spray; however, the x-ray technique is more robust in resolving liquid film thickness for the optically dense swirl coaxial spray.