Ground based experiment and numerical calculation on thermodynamic vent system in propellant tank for future cryogenic propulsion system

Abstract

In planned planetary explorations, cryogenic liquids such as liquid hydrogen (LH2), liquid oxygen (LOX), and liquefied natural gases (LNG) are used as fuel and oxidants in the propulsion systems of spacecraft. Such explorations require long-term storage of those cryogens, as well as heat insulation technology to protect the heat from the outside and pressure control technology to suppress rises in pressure due to gas evaporation in the propellant tank. However, current vent systems that discharge the evaporated gas to the outside of the spacecraft are suboptimal because the propellant’s uncertain position in the tank when the spacecraft operates in microgravity environments causes a significant loss of propellant during venting. In response, we examined a method using a mixing jet in a thermodynamic vent system (TVS) that adjusts the tank pressure by cooling the inside of the tank and reducing boil-off gas.In this study, a verification experiment on the TVS performed by jet mixing using simulated liquid (LN2) was carried out. Subcooled mixing jets were supplied under vent-free conditions, and it was possible to reduce the temperature and pressure in the test tank. On the other hand, it was found that depending on the liquid level and supply flow rate of the mixing jet, the tip of the mixing jet could not reach the free surface, and reduction of tank pressure could not be realized.