The dynamic atomization characteristics of a gas-liquid pintle injector under backpressure: A numerical study

Pintle injectors have been widely used in variable-thrust engines. The inflow pulsation has significant impacts on the pintle injector performance, yet it has not been fully addressed, especially under a certain backpressure. We investigate the dynamic atomization characteristics of a gas-liquid pintle injector under varying backpressure conditions numerically. The Volume of Fluid to Discrete Particle Method (VOF-to-DPM) coupling approach is applied for interface and droplet tracking. We emphasize the effects of backpressure (0.5-2 MPa) and low-frequency inlet excitation (50-150 Hz) on the atomization of water/nitrogen. Our results show that increasing backpressure reduces the atomization field velocity, delays liquid film breakup, and enlarges the spray cone angle. The Sauter mean diameter (SMD) also increases with backpressure, which is attributed to droplet aggregation in high-pressure environments. In addition, we find that the inlet excitation induces a periodic wave structure in the atomization field, analogous to the klystron effect. The spacing of the wave peak is inversely proportional to the excitation frequency. Meanwhile, the global SMD decreases as the frequency increases, while localized periodic oscillations intensify. Moreover, the oscillation amplitude of the spray cone angle grows with frequency, and the phase-frequency delay remains minimal (<10%), suggesting a damped response of the pintle injector to dynamic perturbations. These results would help understand the dynamic atomization characteristics of pintle injectors under backpressure in variable-thrust engines.