In response to the demand of commercial rocket companies for liquid methane subcooling

methane filling systems were designed with liquid nitrogen used as the cold source. Corresponding theoretical calculations under different methane filling flow rates and different liquid nitrogen pressures were also carried out. Referring to the existing liquid oxygen and kerosene filling system

two different control strategies for methane subcooling and filling system were proposed to prevent liquid methane from condensing due to liquid nitrogen. Comparisons between the two systems were made. Six different processes realized by the two systems were introduced and analyzed. Resut showed that

the filling system based on back pressure control was more reliable than that based on liquid level control. At the same time

the former could realize online real-time filling process

because it could ensure that the liquid nitrogen temperature was always higher than the methane freezing point by controlling the liquid nitrogen pressure in the heat exchanger. The heat exchange area of the methane subcooler was proportional to the methane flow rate and the nitrogen pressure. In the specific engineer implementation

the appropriate flow rate and liquid nitrogen pressure should be selected in order to reduce the subcooler size and equipment manufacturing costs.