injector Configuration and Development of a Methodology to Scale Between Cold-Flow and Hot-Fire Evaluations

The Air Force Research Laboratory (AFRL) is undertaking a program to improve the development of a gas-centered swirl coaxial liquid injector. The injector in a liquid rocket engine atomizes and mixes the fuel with the oxidizer to produce efficient and stable combustion that will improve stability performance and provide the required thrust for the rocket engine without endangering hardware durability. The rocket injector has been experimentally investigated by using a combination of methodologies called cold-flow and hot-fire testing which have been scaled by other laboratory facilities. The AFRL identified few condition parameters for hot-firing testing that could be simulated through cold-flow conditions that include pressure settings and adjustments of the mass flow rate liquid. These conditions were designed to match the momentum flux ratio, density, and velocity between gas and liquid flows. The data was then used to determine which configuration has the best spread and mixing trade-off. The cold-flow and hot-fire testing results were then evaluated in order to identify spray instabilities occurring in both sets of methodologies and to understand how an injector produces a stable spray. Based on this approach, the spray characteristics and mixing efficiency of the propellants in the rocket injector demonstrate similar performance efficiency in wide range of mixture ratios and pressure conditions to those in hot firing testing compare to those in cold flow testing. Thus, the liquid rocket injector appears to be viable candidate, from a performance point of view, for consideration in future missions