Efficient atomization of gel propellants using an impinging-jet injector with self-excited oscillation chambers

Efficient atomization of gel propellants is crucial for enhancing the performance of propulsion systems in missiles and spacecraft. Given the limitations of conventional injectors for gel atomization, novel injector designs and comprehensive experimental measurements are urgently required. In this study, the atomization characteristics of four gel propellant simulants with different gelling agent concentrations were experimentally investigated using a novel impinging-jet injector equipped with self-excited oscillation (SEO) chambers. To evaluate atomization performance, the spray pattern, droplet size distribution, and injection pressure drop were measured under various conditions. Furthermore, the proper orthogonal decomposition (POD) and power spectral density (PSD) methods were employed to analyze the role of self-excited oscillations in improving atomization. Results show that the SEO injector introduces dominant high-frequency perturbations that amplify surface instabilities and accelerate the breakup of the impinging sheet. Compared with conventional injectors, the SEO injector achieves a fully developed spray at lower flow rates and produces smaller, more uniform droplets, with the Sauter mean diameter (SMD) reduced to less than half that of conventional designs. In addition, the atomization quality of the SEO injector shows low sensitivity to gel viscoelasticity, demonstrating better adaptability across propellant formulations. However, achieving enhanced atomization requires a higher pressure drop due to the conversion of pressure potential energy into surface energy. This study reveals the underlying mechanism of SEO-enhanced atomization and confirms the superior performance of the SEO injector, providing a valuable reference for improving the efficiency and applicability of gel propellant injection systems.