Mixing and entrainment of liquid fuel in a cavity-based scramjet model combustor

• Innovative application of IR-based diagnostics for liquids in high enthalpy flow environments. • Quantitative evaluation of novel liquid injection strategies in cavity-based scramjet systems. • Measurement result interpretation based on fundamental flow physics. • Addressal of primary injector design considerations, like penetration and deposition height effects. • Coupling fundamental processes of mixing and stabilization by supporting combustion experiments. This work quantitatively investigates liquid fuel mixing and entrainment in a cavity-based scramjet model combustor, focusing on potential and limitations of using an infrared imaging-based measurement technique. The proposed approach produces time-averaged path density maps that enable characterization of fuel distribution in a high-enthalpy supersonic crossflow. Using this method, a total of seven strut-assisted fueling strategies is systematically evaluated at a constant fuel mass flowrate. The discussion of measurement results addresses both the observed distribution maps and profiles, and their interpretation based on known physical processes of supersonic jet breakup, plume evolution, and crossflow interaction. The gained insights reveal key factors to fueling strategy design, such as jet penetration depth and orifice placement along the strut and injector location relative to the cavity. A series of combustion experiments were conducted to evaluate the flame holding characteristics of the injection strategies, allowing the mixing results, expressed in path-integrated fuel density, to be contextualized in terms of stabilization performance of the combustor. While path density is less intuitive, its proportionality between cases enables positioning within the stabilization envelope. In addition, the path density is a useful quantity for direct comparison to numerical modeling efforts. Together, these findings highlight the utility of infrared imaging to study mixing trends for guiding the design of advanced liquid fueling schemes in supersonic combustors.