Injection of cryogenic propellants under low pressure conditions

In this paper, we conduct an experimental investigation to explore the cryogenic propellants’ (LO_x, LCH₄ and LN₂) behavior under vacuum conditions. Due to the sudden depressurization the flashing phenomena occur, and the spray injection is visualized with the high-speed Schlieren technique. Based on the nucleation theory, a non-dimensional parameter ζ is proposed for such phenomena indication. The test results show that the superheat exerts ζ significant effect on the cryogenic spray behavior, and the parameter ζ works well for the flashing phenomena indication under a wide range of operation conditions. From the mechanical atomization regime to the fully flashing regime, the corresponding ζ decreases from much larger than 1 to smaller than 1, and such parameter is around 1 in the fully flashing onset regime. During the test, the solid nitrogen and solid methane were observed, which may cause several issues to the start-up of the upper stage rocket engine.