Shear coaxial injector lox droplet measurements as a function of hydrogen injection temperature

A hydrogen gas chiller was designed and fabricated in order to simulate the hydrogen temperature ramping test for liquid rocket engines in a single-element gaseous hydrogen/liquid oxygen combustion chamber. Hot fire PDPA measurements of droplet sizes and velocities as a function of the gaseous hydrogen temperature for a fixed mass flow and shear coaxial injector configuration were obtained as the hydrogen temperature was varied from 130 to 290 K, resulting in a doubling of the hydrogen/oxygen velocity and momentum flux ratios. Measured droplet Sauter and arithmetic mean diameters decreased as the hydrogen temperature increased. However, even though the hydrogen temperature change resulted in a doubling of the velocity and momentum flux ratios, the droplet Sauter mean diameter only decreased by 12.5%. These results indicate that the increase in droplet size as the injected hydrogen temperature is decreased may not be a significant contributor to the resulting combustion instability for liquid rocket engines operating at the conditions examined in this study.