Cryogenic Flow from a Coaxial Injector Under low-Pressure In-Space Conditions

Abstract

The effect of near -vacuum operating pressure on the evolutionary behavior of cryogenic fluid injected from a single -element coaxial injector has been examined experimentally . The investigated injector simulate s one element of the injector array of cryogenic rocket engine s under realistic operating c onditions. Actual rocket -engine propellants, liquid oxygen and gaseous hydrogen , are simulated by chemically inert and safe to operate liquid nitrogen and helium. This work focuses specifically on the transient evolution of liquid nitrogen jet under in -spa ce conditions. The diagnostic technique s utilized here are high -speed Mie -scattering and Schlieren imaging. The results showed that the behavior of liquid nitrogen jet wa s significant ly affected by the low -pressure conditions as well as the strong heat shi elding effect of coaxial helium jet . The cryogenic jet undergoes extraordinary jet expansion at sub -atmospheric pressures . Initial freezing of liquid nitrogen droplets and ligaments was observed close to the injector exit . The heat transfer from the warm surroundings to cold liquid nitrogen jet wa s reduced significantly in the presence of coaxial gaseous jet, which confined the cold liquid nitrogen jet and prevented its expansion to some extent .