Robert Stützer

Hot-fire tests were performed with a single-injector research combustor featuring a large optical access (255 × 38 mm) for flame imaging. These tests were conducted with the propellant combination of liquid oxygen and compressed natural gas (LOX/CNG) at conditions relevant for main- and upper-stage engines. The large optical access enabled synchronized flame imaging using OH* and CH* radiation wavelengths covering an area of the combustion chamber from the injection plane to shortly before the contraction section of the nozzle for two sets of operating conditions. Combined with temperature, pressure and unsteady pressure measurements, these data provide a high-quality basis for validation of numerical modeling. Flame width and opening angle were extracted from the imaging in order to determine the flame topology. A two dimensional Rayleigh Index was calculated for an acoustically unexcited and excited interval. These Rayleigh Indices are in good agreement with the thermoacoustic state of the chamber.

A Q-switched laser system was applied to a research rocket combustor in order to ignite cryogenic propellants by inducing several plasma breakdown events. The optical emission was analyzed using LIBS and other techniques.

Experiments at the European Research and Technology Test Bench P8, located at the DLR Institute of Space Propulsion, were carried out to validate the feasibility of laser ignition on the research rocket combustor “BKA”. Propellant injection in BKA was carried out via 15 coaxial injectors with liquid oxygen as oxidizer and gaseous hydrogen or gaseous methane as fuel. Crucial parameters such as the equivalence ratio between oxidizer and fuel (ROF), plasma temperature, ignition time, and breakdown thresholds can be determined using appropriated methods for plasma analyses. Two settings for LIBS measurements have been used for the comparison between cryogenic rocket combustion (ignition) and experiments on gaseous compositions. The research rocket combustion chamber “Brennkammer A” (BKA) was laserignited with the opportunity to evaluate the ignition spark, and on the other hand, well-defined gas mixtures inside a laboratory-scale cavity were analyzed using plasma spectroscopy. Moreover, taking the molar masses of the constituents into account, the local ROF inside the ignition spark is derived.