Abstract
Gelled propellants are of interest for rocket and ramjet propulsion systems because of their safety and performance benefits. During spray tests with doublets, such as on impinging jet injectors, it was observed that the breakup of the fluid sheet of several gels did not lead to the formation of droplets; instead, threadlike structures were formed. Such structures may cause a reduction in combustion efficiency and the accumulation of unburned material in the combustion chamber. The goal of the work presented here is to determine which physical properties influence thread formation. Spray tests were conducted with Boger fluids under atmospheric conditions concerning pressure and temperature with a like-on-like impinging jet injector. The range of injection velocities from 5 to over 70 m/s was studied. Images of the sprays were obtained with a shadowgraph technique. In order to obtain quantitative results from shadowgraph images, a code was implemented to determine a characteristic dimension of the threads. A clear correlation between the relaxation time, which is an indicator of the intensity of elastic effects, and the dimension of the obtained threads was observed. These results suggest that thread formation is caused by nonlinear elastic effects, while shear viscosity and surface tension do not seem to influence the formation of these structures.
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