A novel anti‐freezing methane propellant subcooling approach and its performance analysis

Using subcooled propellant could improve the overall performance of spacecraft. In cryogenic propellant subcooling process, liquid nitrogen is the most common cold source. For methane propellant, ice blockage may occur in the propellant subcooling operation since the saturation temperature of liquid nitrogen is lower than the freezing temperature of liquid methane. In this paper, a novel anti‐freezing subcooling approach for methane propellant is proposed. By mixing light alkane such as ethane or propane into methane, a methane mixture propellant with lower freezing temperature could be prepared. To guide the propellant preparation, the working principle of the subcooling scheme is introduced, and the thermodynamic performance of the mixed propellant is analyzed. The results show that for the methane–ethane system, the lowest freezing temperature is 72.9 K when the methane mole fraction is about 0.71. Icing‐free subcooling can be achieved in a liquid nitrogen heat exchanger subcooled approach when the methane fraction is controlled within 0.54 to 0.80. For the methane–propane system, the minimum freezing temperature of 72.0 K occurs at the methane fraction of 0.68, and the non‐icing range is about 0.42–0.79. For the methane–ethane–propane ternary system, the lowest solidification temperature even reaches 63.1 K. Moreover, apparent propellant densification could be yielded by the proposed subcooling scheme. In general, the present subcooling scheme can effectively avoid the freezing risk in the methane subcooling process and also prepare a densified methane propellant, and the new scheme is beneficial for fully exploiting the potential performance of the subcooled methane propellant.