ID 89

Primary Atomization of a Cryogenic LOX/N2 and LOX/He jet in a Coaxial Rocket Injector

 

Abstract:

In liquid propellant rocket engines, combustion efficiency and stability depend greatly on the atomization of the cryogenic liquid oxygen (LOX) by the surrounding hydrogen gas. The drop size distribution of the spray is a key parameter to describe physical processes in such a turbulent flame. There is a need of experimental data in injection conditions representative of rocket engines to validate and initiate droplet formation models used in numerical simulations. The chosen operating conditions are here non-reactive to build a comprehensive parametric study of the influence on primary atomization of three main parameters of the spray: the atomizing gas flow vorticity thickness, the Weber number and the fluid density ratio, between LOX and two atomizing gases: helium or nitrogen. A new cryogenic vessel was built upon the MASCOTTE test bench at ONERA, to study the atomization of a single LOX jet by an inert gas with simultaneous optical diagnostics. High-speed shadowgraphy is used to visualize the whole spray while a Phase Doppler Interferometer is used to measure the size and velocity of LOX droplets. The test vessel can be pressurized up to 30 bar and is used to reach fibre-type injection conditions, i.e. high Weber number (>1000), high Reynolds number (>10000) and a momentum flux ratio J > 1, representative of a liquid rocket engine injection device. Several aspects of the experimental results are discussed: the mathematical form of the measured droplet size distributions and the influence of the injection parameters on the mean droplet size and velocity.