Effects of orifice geometry on spray characteristics of impinging jet injectors for gelled propellants

This paper presents the results of an experimental study on breakup characteristics of gelled propellant liquid sheets formed by impinging jet injectors with different geometries of injector orifice (round, elliptic, and rectangular shape). Spray formation of gelled propellant from impinging jet injectors was described by carrying out experiments in a spray test facility. Considering the safety, a water based gel simulant was used instead of the gelled propellant in the experiments. The rheological characteristics of the gel simulant were tested. A high speed camera was used to grab the detailed information of the liquid sheet breakup process and spray development. The experiments were performed with injectors of different shape of injector orifice to test the geometrical effect of injector orifice on the spray characteristics. The experimental results showed that under the condition of identical sectional area, the shapes of liquid sheet formed by the impinging jet injectors with different shape of orifices were different. One special phenomenon is the thick liquid stream in the center of liquid sheet when the aspect ratio of rectangular orifice is great. The reason of this phenomenon is the axis-switching feature of the non-circular jets. The mass flow rates of square and elliptical orifices are larger than that of circular orifice. The flow rate of rectangular orifice becomes greater as the aspect ratio gets larger. The breakup length for injector with square orifice is shorter than that for injector with circular orifice. Although the elliptical jet behaves greater instability than circular jet, the liquid sheet breakup length of injector with elliptical orifice is not always shorter than that of injector with circular orifice. Generally, the breakup length of rectangular jet impinging injector increases with aspect ratio.