Investigation of Supersonic Combustion with Angled Injection in a Cavity-Based Combustor

Abstract

Self-ignited supersonic combustion experiments have been performed using a cavity-based injector in the T3 free-piston shock tunnel, using various combustor inlet and fuel-flow conditions. Planar laser-induced fluorescence on the hydroxyl radical and fast-acting pressure transducers are used to investigate the flow characteristics. Four hydrogen injectors are located upstream of an open cavity. The separated shear layer reattaches, generating an oblique shock at the cavity's trailing edge and establishing the major flow structure. The normalized pressure rise due to combustion increases as the equivalence ratio increases and the freestream stagnation enthalpy decreases, over the range of conditions' tested. Angled injection upstream of the cavity allows the cavity to act as a flame holder. High injection pressure helps to ignite immediately upstream of the injector and forms two flame layers over the cavity. The fluorescence peak signal shows periodic maxima near the cavity, and the interval between peaks decreases as the equivalence ratio is increased. Low-total-enthalpy conditions also exhibit longer ignition-delay distances. Comparison of fluorescence images and static pressure measurements indicates that, at these conditions, the heat release is mostly initiated by the shock wave from the cavity's trailing face and the ignition above the cavity does not have a strong influence on the downstream combustion.