Interpretation of Core Length in Shear Coaxial Rocket Injectors from X-ray Radiography Measurements
Technical paper, Jun-Jul 2014
AIR FORCE RESEARCH LAB EDWARDS AFB CA ROCKET PROPULSION DIV
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Shear coaxial injectors are so named because they rely on the shear between an outer lower-density high velocity annulus and a higher-density low-velocity inner jet to atomize and mix a liquid and a gas. These injectors have an intact core, and the high amount of scatter its corrugated surface produces creates large optical densities. These high optical densities, in turn, make interrogation of the spray field in the region of the core difficult. In combustion applications, such as rockets, this region is also the area of flame holding, so is of primary importance in predicting combustion behavior. To overcome the problems of multiple scattering, the near-injector region was studied using X-ray radiography at Argonne National Laboratorys Advanced Photon Source. These results clearly show regions of differing behavior throughout the downstream distance examined. These regions correspond to changes in atomization behavior and can be used to quantify core length and understand more clearly what this term means. Three methods are explored to measure core length from X-ray radiography data and are compared to two-phase core length measurements from the literature. The core length non-dimensionalized by the inner jet diameter was found to scale with the momentum flux to the -0.66 power.
- Rocket Engines