Design and Testing of Injectors for a 1N C/C-SiC Thrust Chamber

Abstract

This thesis deals with the development and testing of five different injectors for the application with existing C/C - SiC thrust chambers at the German Aerospace Center (DLR). The thrusters have the thrust class 1 N and are cooled through radiation. The injector designs include two showerhead injectors, a doublet, a 2-on-1 and a coaxial injector. These variants are developed for liquid feeding operation under the propellant combination of nitrous oxide and ethane in terms of a self-pressurized propulsion system. The objective of the injectors is to ensure thermal steady state operation of the propulsion system without hot spot formation on the combustion chamber wall and high efficiency. The two-phase injection is considered through specific models in the design of the injector flow pattern to achieve high performance. The choice of liquid feeding for the operation is justified by a developed simulation. In the simulation the thermodynamic state of the two-phase propellant tanks, the flow through the injector and the combustion chamber state are implemented and their properties in the evolution of time during a blowdown can be determined. The spray behavior of the injector variants is analyzed in cold flow tests resulting in major manufacturing deviations of exit orifice diameters and exit angles, which impacts the overall injector performance. This performance of the injectors is investigated during hot gas tests at the test bench M11.3 at DLR Lampoldshausen. The 2-on-1 injector shows hot spots on the thruster chamber wall. The showerhead injectors show poor ignition behavior and provides poor thermal behavior of the thrust chamber wall. The doublet injector shows moderate performance. The coaxial injector is determined as the most promising solution. It shows the highest combustion efficiency and reliability while simultaneously providing a uniform heat distribution in perimeter direction of the thrust chamber without any hot spot formation. The latter aspect is qualified during long duration tests of 5 min, where thermal steady state is reached.