Inverse heat transfer method applied to capacitively cooled rocket thrust chambers

Measurements of the heat loads in experimental lab-scale rocket combustors are essential in order to obtain information about the mixing and energy release of the propellants, the injector/injector interaction as well as the injector/wall interaction. Usually the hardware used for single-element rocket thrust chambers is capacitively cooled in order to reduce the complexity of the system. The present work demonstrates an efficient method for estimating the time- and spatially resolved heat flux distribution at the hot gas wall of such engines using the information provided by temperature measurements in the material. The method is implemented in the code Roq̇FITT (Rocket q̇ Flux Inverse Thermal Tool) and is applied for the evaluation of test data of CH₄/O₂ and H₂/O₂ experiments. Three separate capacitive combustors are investigated, which are operated at the Chair of Turbomachinery and Flight Propulsion (LTF) of the Technical University of Munich (TUM): a single-element cylindrical, a single-element rectangular and a multi-element rectangular chamber. The use of the 3D inverse method for different load points gives significant information about the effect of the different propellant combinations, the choice of mixture ratio and pressure level, the spanwise heat flux distribution and hence injector/injector interaction as well as the transient effects during the igniter operation.