Influence of the Injector Inlet Angle on the Flow and Spray Behavior of Shear-thinning Fluids in Impinging Jet Injectors

Abstract

Impinging jet injectors are often used in rocket propulsion systems, where storable liquid propellants shall be feeded. Also for gelled fuels and propellants this injector type is interesting due to its simplicity and relatively small contact areas between gel and injector housing compared to many other injector types. Gelled propellants are shear thinning fluids and show a significantly different rheological behaviour than Newtonian fluids. During storage and transport conditions with very low shear stress values their viscosity is very high and often combined with a distinct yield stress so that they are often described as semi-solid. During the feeding process through pipes and injectors, the structure of the gel is being destroyed, which leads to a decrease of viscosity up to its liquefaction inside the injector unit. Various experimental and theoretical investigations about the impinging jet injector processes with gelled propellants have been conducted in the past years and have shown that impinging jet injectors are interesting candidates for real engine applications. Up to now there are still gaps to be closed in the understanding of the working behaviour of impinging jet injectors with gelled fuels. The aim of the present publication is to present the results of an investigation concerning the influence of the interior injector inlet angle on the feeding process and spray behaviour of three different gelled fuels. For this task pressure loss measurements as well as shadowgraph images have been used to characterize the injection process.