Characterizing primary atomization of cryogenic LOX/Nitrogen and LOX/Helium sprays by visualizations coupled to Phase Doppler Interferometry

TL;DR

This study provides experimental data on cryogenic LOX/Nitrogen and LOX/Helium spray atomization using optical diagnostics and phase Doppler interferometry, aiding the validation of droplet formation models in rocket engine simulations.

Contribution

It introduces a new experimental setup with optical diagnostics for primary atomization of cryogenic jets, focusing on fiber-type regimes and droplet size/velocity measurements near the nozzle.

Findings

Radial evolution of droplet size shows smaller droplets at the edges.

Axial velocity increases with helium or nitrogen as atomizing gases.

Drop size distribution remains larger near the LOX jet core.

Abstract

There is a need for experimental data in conditions representative injection in rocket engines to validate or initiate droplet formation models used in numerical simulations. A new cryogenic vessel was built upon the MASCOTTE test bench to study the atomization of a single oxygen liquid jet, under non-reactive conditions, with simultaneous optical diagnostics. A test plan was built to explore the fiber-type regime occurring in liquid rocket injection systems, with a fixed Reynolds number and a large range of Weber number and momentum flux ratio, compared to existing studies. High-speed images are used to describe qualitatively the fiber-type regime and to visualize were droplets are present, in order to prepare the drop-size measurements. A Phase Doppler Interferometer is used to measure the size and velocity of droplets produced by atomization of a liquid oxygen jet by a co-flowing gas. Droplet size and velocity measurements were performed with a PDI close to the nozzle exit in order to provide data on droplets produced by the primary atomization process, which can be useful for numerical simulations initialisation. The radial evolutions of the axial velocity and of the drop size distribution show similar trends as observed in the literature. The axial velocity is investigated for different operating conditions with helium or nitrogen as atomizing gas, showing an increase on the side of the spray. The radial evolution of the droplet size shows a translation of the drop size distribution on the edge of the spray towards the smaller sizes, indicating that the biggest liquid elements stay close to the LOX jet.