Atomization characteristics of gas–liquid internal mixing of non-Newtonian fluids

Non-Newtonian fluids play a significant role in aerospace propulsion, yet the atomization strongly depends on nozzle structure, influencing combustion efficiency. However, existing studies have offered limited comparisons of how nozzle structure affects the atomization behavior. This study provides a comprehensive structural comparison of non-Newtonian spray nozzles and identifies their distinct atomization characteristics, aiming to provide new insights for optimizing non-Newtonian atomization systems. Nine nozzle configurations were designed, including external mixing straight/helical groove and internal mixing straight/helical groove nozzles with different sleeve outlet diameters (0.3, 0.4, and 0.5 mm) and Y-jet nozzles. Three representative fluids (glycerol–water solution, xanthan gum, and polyethylene oxide solutions) were tested. The results show that internal mixing nozzles generally achieve superior atomization, while external mixing designs are limited by pressure constraints. The Y-jet nozzle is characterized by a bimodal droplet size distribution, containing both extremely small and extremely large droplets. Moreover, in internal mixing nozzles, helical groove nozzles widen the spray angle by nearly 50% and reduce the Sauter mean diameter of shear-thinning fluids by about 40% compared with straight groove designs. For Newtonian fluids, reducing the sleeve outlet diameter promotes jet instability, whereas viscoelastic fluids require larger outlets to mitigate clogging. Furthermore, viscoelasticity suppresses jet breakup, necessitating higher gas pressures to disrupt molecular chains.