Study on the influence of operating conditions and tangential inlet diameter on the spray characteristics of gas-centered swirl coaxial injectors

This work seeks to experimentally investigate the spray characteristics of gas-centered swirl coaxial (GCSC) injectors used in LOx/kerosene rocket engines. High-speed photography, phase-Doppler anemometer and adaptive flow flux measurement system were used to capture the spray characteristics under different flow rates, tangential inlet diameter (d_t) and ambient pressure (p_a), and standardized methodologies were established for characterizing the spray angle, breakup length, droplet size, flow flux and self-pulsation frequency. First, the results showed that the spray angle increases with increasing liquid flow rate at constant gas-to-liquid mass flow rate ratio (GLR). When GLR increases while keeping the liquid flow rate constant, the breakup length decreases, the Sauter Mean Diameter (SMD) decreases faster as approaching the centerline and the droplet distribution downstream becomes more uniform. Self-pulsation was observed under specific condition, with frequencies in the range of 300–400 Hz revealed by Fast Fourier transform and Proper orthogonal decomposition analyses. Then, it is found that increasing the tangential inlet diameter (d_t) enlarges the coefficient of discharges and reduces spray angle. While, reducing the tangential inlet diameter (d_t) from 0.90 mm to 0.40 mm can suppress self-pulsation. Finally, this study investigates the influence of ambient pressure on atomization characteristics by two distinct control-variable methodologies. As p_a rises from 0.1 to 1.0 MPa, while maintaining a constant flow rate, the spray angle increases, and self-pulsation vanishes. While maintaining a constant gas-to-liquid momentum flux ratio (J) and liquid flow rate, p_a shows negligible impact on the spray angle, which fluctuated around 59° and are consistent with the normalized empirical correlation formula.