Experimental study on the effect of electrode insertion depth on the breakup behavior of ADN-based propellant droplets under microwave irradiation

In this study, we report a novel phenomenon of vibration, internal nucleation, and breakup of ammonium dinitramide (ADN)-based liquid propellant droplets under microwave irradiation and electrode intrusion. Experiments were conducted on a self-developed microwave test platform based on a rectangular resonant cavity. Electrodes were vertically positioned at the location of maximum electric field strength within the cavity, and the droplets were suspended on quartz fibers, with the electrode tips inserted to varying depths from the bottom of the droplet. The influence of electrode insertion depth on the breakup behavior of ADN-based liquid propellant droplets was investigated by varying the depth. To quantitatively characterize the skirt structure formed during droplet breakup, four parameters were proposed: bottom diameter of the liquid skirt ( d s 1 ), top diameter of the skirt ( d s 2 ), skirt height ( h s ), and skirt angle ( θ s). Finally, the conditions and modes of droplet breakup were analyzed based on the observed phenomena. The results showed that the electrode insertion depth had a significant effect on the droplet breakup morphology. As the nondimensionalized insertion depth( L ∗ ) decreased from 0.387 to 0.179, the duration of nucleation was reduced from 0.8 ms to 0.1 ms, a decrease of 87.5%. • Reveals electrode-assisted microwave-induced vibration, internal nucleation, and breakup in ADN-based propellant droplets. • Electrode depth critically dictates three distinct droplet behavior modes. • Quantifies breakup morphology via novel dimensionless ”liquid skirt” parameters. • Nucleation duration drastically shortened by 87.5% with decreased electrode depth. • Introduces a novel, controllable droplet fragmentation method for propellant application.