Characterizing Droplet Dynamics in Cryogenic Jet Flames for Rocket Propulsion

Recent research has focused on the atomization processes in cryogenic jet flames, particularly in rocket-type combustors. The study, titled "Droplet size and velocity measurements in a cryogenic jet flame of a rocket-type combustor using high speed imaging," authored by Nicolas Fdida, Lucien Vingert, Arnaud Ristori, and Yves Le Sant, aims to characterize the behavior of liquid oxygen (LOX) sprays in gaseous hydrogen (GH2) under reacting conditions.

The research highlights that atomization is a critical factor influencing flame behavior when propellants are injected in subcritical conditions. Traditional laser-based drop size measurement techniques often face challenges due to low validation data rates in the breakup region, where liquid particles are not spherical. To address this, the authors employed high-speed shadowgraph imaging to capture the sizes and velocities of the LOX droplets atomized by a GH2 co-flow.

The experiments were conducted in a controlled environment at the Mascotte test bench at Onera, where the reacting case was compared to a cold flow test using gaseous helium instead of GH2. The study utilized two different imaging methods to obtain velocity measurements of the dispersed phase in reacting conditions, applying both Particle Tracking Velocimetry (PTV) and Particle Image Velocimetry (PIV) algorithms to the same shadowgraphs.

Results indicated that droplet sizes measured through image processing in the atomization zone were consistent with Sauter mean diameters from existing literature. Furthermore, the correlation between droplet size and velocity demonstrated the influence of the flame on droplet size evolution, which could have implications for improving combustion efficiency in rocket engines.

This research contributes to the understanding of cryogenic combustion dynamics and may inform future advancements in rocket propulsion technologies. The full paper can be accessed at arXiv:2408.17132.