Experimental Investigation of a LOX Spray under Hot Fire Conditions

Cryogenic propellant combustion systems have now been applied successfully for many years in rocket engines. However, a good modelling of the combustion needs a better understanding of the elementary mechanisms, in particular atomization and vaporization processes. To contribute answers to those questions a cryogenic test bench called MASCOTTE was built and a test program was conducted under a consortium of laboratories and manufacturers associating ONERA, CNRS, CNES and SEP. The main objective was to provide a good description of atomization and vaporization processes under hot fire conditions and, by this way, to get a better understanding of this kind of combustion. This article describes a first experiment performed during a combustion test program mainly focused on the LOX droplets size analysis. First, with the goal to provide preliminary information on the fluid dynamics of the LOX core breaking process, a visualization technique using a stroboscopic laser sheet associated with a high speed camera (2000 frames/s) was used. After those initial visualizations, the main objective of this work consisted in measuring LOX droplets size and velocity on the axial flow in order to get a good mapping of the spray characteristics around the LOX core. A PDPA system with one component of velocity was used for those measurements. The two experimental investigations give a good qualitative (by visualization) and quantitative (by Phase Doppler technique) description of the LOX spray in terms of atomization and vaporization processes in hot fire conditions. Three different zones have been detected: near the post tip, a first atomization zone; downstream, a relative long ligaments zone; and, finally, a well-defined droplets spray.