Determination of the Rheological Model of Gel Propellant and Flow Characterization of Gel in a Pressure Swirl Injector

Gel propellants have the advantages of both liquid and solid propellants and present a promising future for the aerospace industry. Many gel propellants have shear-thinning behavior, which complicates their behavior in propulsion systems, especially the atomization process. On the other hand, the toxicity of many gel propellants makes the study of their dynamic behavior difficult. In the present work, non-toxic gel simulants were first prepared using a variety of gelling agents. Next, a gel simulant with a behavior similar to UDMH's basic gel fuel was selected from the prepared simulants. The dynamic behavior of the selected simulant gel was studied by different shear-thinning fluid models, and the most suitable rheological model was chosen. Eventually, the simulant gel dynamic behavior was simulated in a pressure swirl injector using the selected rheological model, and the results were compared to the experimental data. The results indicated that the simulant gel made from 0.85 wt.% of HPMC gelling agent is very similar to the basic UDMH gel in terms of dynamic behavior and power law index. Furthermore, among the rheological models, the Carreau-Yasuda model was able to predict the selected gel simulant behavior in a wide range of shear rates. A comparison of the experimental tests and numerical simulation of the gel simulant flow inside the swirl injector revealed that using the calculated constants of the Carreau-Yasuda model can predict the simulant gel dynamic behavior and the functional characteristics such as mass flow rate, discharge coefficient, and spray cone angle with less than 6% error.