Theoretical study on leakage characteristics of an oil-injected single screw CO2 compressor

• The mathematical model of the SSCC working process has been established. • A two-phase leakage model for oil and gas, incorporating oil-CO 2 miscibility, is coupled with the mathematical model. • The direct and indirect leakage of CO 2 are analyzed under different clearance. • The performance parameters of the SSCC are analyzed under various conditions. Single Screw CO 2 Compressor (SSCC) is an essential component for utilizing CO 2 as working fluid. The miscibility of lubricating oil and CO 2 makes it more complicated to determine leaks in compressors. To investigate the leakage characteristics of the SSCC, a mathematical model for its operating process is developed. This model integrates an oil and gas two-phase leakage model, which considers the solubility of oil and CO 2 . The study examined SSCC leakage and performance across varying clearances, speeds, and suction/discharge pressures. Results show that, under constant operating conditions, only indirect leakage of CO 2 dissolved in the oil occurs at smaller clearances. However, as the clearance increases, direct leakage of CO 2 is observed. An increase in clearance results in greater leakage and a decrease in volume and adiabatic efficiency. In addition, the effect of the fitting clearance on leakage is significantly more pronounced than meshing clearance. At the same speed, an increase in the suction pressure or a decrease in the discharge pressure increases the compressor’s volumetric efficiency. As the suction or discharge pressure increases, the adiabatic efficiency first increases and subsequently decreases. The optimum suction and discharge pressures for achieving maximum adiabatic efficiency at varied rotational speeds differ.