Hot-Fire Characterization of a LOX/CH4 Swirl Coaxial Injector Element up to Combustion Pressures of 100 bar in an Optically Accessible Chamber

Kurzfassung

This study presents the results of a hot-fire characterization campaign featuring a single liquid-centered swirl coaxial injector element, designed for high thrust LOX/natural gas main stage engines. The experiments are conducted in a research combustion chamber with full-length optical access windows. Objectives of this characterization campaign are the evaluation of the injector element’s performance under varying operating conditions, as well as the visualization of the atomization and combustion processes. The test campaign is conducted at the European Research and Technology Test Bench P8.1 of the German Aerospace Center’s (DLR) Institute of Space Propulsion in Lampoldshausen, Germany. Accordingly, the steady-state chamber pressure during the hot-fire tests ranges from 35 to 105 bar while the oxidizer-to-fuel mixture ratio is varied between 2.5 and 3.5. The corresponding mass flow rates for the element reach up to 0.458 kg/s and 0.133 kg/s for liquid oxygen and natural gas, respectively. For different load points the methane injection temperature is also modified in the range from 180 to 240 K. The key parameters of the investigation include the injector’s discharge coefficents for both liquid oxygen and methane, liquid oxygen core breakup length and opening angle, flame shape, expansion and anchoring characteristics. The results presented in this study show a load point dependence of the fuel injector’s discharge coefficients, where a strong relationship between discharge coefficient and Reynold’s number is observed. The liquid oxygen core atomization is found to be dependent on the propellant momentum flux ratio, where higher numbers yield improved atomization and a reduction of the core expansion angle. In the frame of this study full-length CH* flame emission images for different load points are also presented and compared to each other in respect to flame morphology and relative near injector intensity. Higher momentum ratios at the injector element are shown to both moving the flame intensity center closer to the injection plane as well as promoting flame anchoring. The findings contribute to a deeper understanding of the tested injector element, and injectors of a similar type, in representative environments.