Development of an injector test rig for shear thinning gel propellants.

Abstract

This work describes the development of an injector test rig to characterise the behavior of shear-thinning gelled rocket propellants. The work falls under a broader program of research into gel propellants conducted by the Aerospace Systems Research Institute (ASRI). Gels represent a new class of propellant for rocket propulsion applications. They offer potential advantages over conventional liquid and solid propellants but their behaviour through injector orifices is poorly understood. Consequently, there is no standardised design procedure for gelled propellant injectors, although computational fluid dynamic (CFD) methods have shown potential. The aim of this research was to design, build and commission an injector test rig utilising single-element impinging injectors to generate experimental data on gel sprays such as breakup length, and droplet size. The rig is intended to inform gel injector design methodologies by providing experimental data against which CFD-generated simulations can be compared and refined. MATLAB® image processing tools were used to analyse spray sheet images and quantify the resulting fluid structures generated by the test rig. The study included the design and manufacture of the propellant/simulant feed system, injector insert, injector manifold, frame and propellant/simulant supply tank. Two adjustable converging injection orifices were used to form spray sheets at 45°, 60° and 90° impinging angles. For testing purposes, two water-based simulants were formulated using hydrocolloid xanthan and guar gum gelling agents at 0.5, 1.0 and 1.5 wt%. Rheological characterisation of the gels was performed to verify their shear-thinning behavior using a rotational rheometer. Spray sheets were then generated at injector pressure drops in the range of 140 kPa to 1400 kPa. A MATLAB® model of the system was developed to establish control parameters for the desired outputs and the rig was controlled via a LabVIEWTM application. The rig provides a platform for further research into the behavior of gelled rocket propellants, with an intended focus on hydroxylamine nitrate (HAN) and ammonium dinitramide (ADN).