Effects of Orifice Geometry on Gelled Propellants Sprayed from Impinging-Jet Injectors

Abstract

G ELLED propellants are liquid propellants with an addition of one or more gellants that impart non-Newtonian behavior [1]. To obtain high combustion efficiency, fine atomization is necessary for this type of propellant. However, the addition of gellants can cause an increase in gel viscosity, making it more difficult to atomize the propellant into fine drops and reach high combustion efficiency in rocket engines. Impinging-jet injectors have been widely used in liquid rocket engines. The shape of the liquid sheet, breakup length, and drop size formed by the impinging jets for Newtonian fluids have been studied extensively [2–5]; the effect of viscosity on sheet formation and breakup has also been studied at length [6–11]. However, the effects of jet-orifice geometry on spray characteristics have received much less attention. Some researchers [12–15] reported that orifice geometry (e.g., the distance between the two orifices, orifice shape, aspect ratio. and length-to-diameter ratio) strongly affects the breakup process of liquid sheet formed by the collision of two jets. The impinging-jet injector is also the most popular injector type used to atomize gelled propellants. The atomization characteristics of gels in impinging-jet injectors have been studied bymany researchers [16–23]. However, all the impinging-jet injectors used in the aforementioned works had exit orifices with a circular section. Although there are some works that examined the flow and breakup characteristics of elliptical liquid jets [24,25] and rectangular jets [26], the spray characteristics of impinging-jet injectors with orifices of different shapes for gelled propellants have not been reported. This Note reports the experimental observations of flow structure and breakup characteristics of a gelled propellant simulant from impinging-jet injectors. The effect of injector orifice section shape and geometry on the breakup characteristics of the liquid sheet is principally discussed.