Characterization of Regression Rate and Combustion Process in a High-Pressure 2D Hybrid Rocket Engine with Optical Access

A new slab combustion chamber employing hydrogen peroxide (H2O2) and hydroxyl-terminated polybutadiene (HTPB) was designed and commissioned by the German Aerospace Center (DLR), Institute for Aerodynamics and Flow Technology in Braunschweig at the DLR site Trauen. The combustion chamber has four helium-cooled quartz glass windows, which provide an insight into the combustion process above the fuel slab and enable its characterization with optical measurement techniques. The experiment allows studying the combustion process at pressures of up to 25 bars and oxidizer mass flows of up to 200 g/s. A H2O2 catalyst chamber, which delivers a mixture of hot water steam and oxygen, enables self-ignition without an additional igniter system. The regression rate during the test runs is measured with two ultrasonic probes and other methods. During the experiments a highspeed camera, a two-color pyrometer and infrared temperature measurements were also used. Three different fuel formulations based on HTPB with HDPE and PA6 polymeric particles at various chamber pressures and oxidizer mass flows have been examined. The preliminary results of the measured ignition times indicate a strong pressure dependency. Patterns on the fuel slab surfaces and images of the combustion process suggest a highly turbulent boundary layer flow. The regression rate seems to mainly depend on the oxidizer mass flow through the chamber with similar mass flow inclines for the HTPB and PA6 fuel formulations. In contrast the results for the HDPE formulation indicate a stronger incline at pressures of 15 bars, which might be caused by pre-test heat-up procedures