Optical Diagnostics of Cavity-Stabilized Combustion in an Axisymmetric Dual-mode Supersonic Combustion Flow path

Cavity-stabilized combustion is performed in a generic axisymmetric dual-mode reactive flow path with varying fueling locations and equivalence ratios at a total enthalpy matching that of Mach 7 flight. Quantitative pressure measurements are performed simultaneously with qualitative broadband and OH-PLIF optical diagnostics. For low equivalence ratios or pre-isolator fueling, autoignition is not observed within this flow path. Higher equivalence ratios (ϕ = 0.75 and ϕ = 1) at pre-cavity fueling locations exhibit cavity-stabilized combustion but produce two visually different modes within the diverging-area combustor region of the engine. Pressure traces in the same region do not show any significant difference. For initially non-lighting conditions, a modified aero throttling scheme is utilized to encourage ignition, then disabled for the remainder of the run before steady-state measurements are taken. A high-pressure plume of ethylene is injected downstream of the cavity flame holder to increase backpressure and temporarily provide conditions favorable for ignition. With this scheme, most unassisted non-lighting cases are capable of igniting and remaining stable for the remainder of the run, even once the aerothrottle injection is disabled.