Characterization of Liquid Impinging Jet Injector Sprays for Bi-Propellant Space Propulsion: Comparison of PDI and High-Magnification Shadowgraphy

Abstract

[EN] Impinging jet sprays are investigated in the reference case of like-doublet injector, for application to bi-propellant combustion. Green propellants are considered, namely ethanol as a fuel and hydrogen peroxide as an oxidizer, that is well represented by water. This study reports original comparisons between standard spray characterization (PDI) and high-magnification shadowgraphy of the spray (2.5 x 3.2 mm, 2.5 µm per pixel) based on short laser backlight illumination (5 ns). Shadowgraphy images describe accurately the inner spray structure and provide the size and velocity of droplets. This diagnostic is used to analyse the influence of jet momentum (driven by injection pressure) on impinging jet atomization, as well as the evolution of spray topology, drop size distribution and average diameter along the spray centreline. The application of shadowgraphy to the dense region of water and ethanol sprays shows the different atomization behaviour of these two fluids with respect to their surface tension. Elliptical droplets are characterized inside the spray, which confirms the interest of a direct visualization of droplets in such dense sprays.