Characterization of Supersonic Turbulent Combustion in a Mach-10 Scramjet Combustor

Turbulent combustion remains an unsolved problem, and the simulation models that have been developed, although accurate for subsonic turbulent combustion, have limited accuracy when applied to supersonic combustion. An experiment has been developed to characterize supersonic turbulent combustion in a geometrically simple flowpath that is capable of accurately reproducing the complex and highly nonuniform flow structures present in flight-candidate scramjet engines. An inlet-fueled scramjet engine was designed with a symmetrical intake to reproduce the correct flow structures. This was tested with an inflow condition of Mach 7, using a Mach-10 flow enthalpy of 4.6MJ/kg to reproduce the combustion conditions in a flight vehicle operating at Mach 10. The turbulent flame was directly observed in the flow using planar laser-induced fluorescence of OH radicals. These results have been complemented by large-eddy simulations of the experimental conditions, showing that the combustion process in scramjets is multimode, where neither premixed nor non-premixed combustion dominates, and both substantially contribute to heat release. These modes are present simultaneously inside the engine. For both modes, combustion is confirmed to happen over multiple combustion regimes. This work provides new insight into the supersonic turbulent combustion process and enhances our understanding of combustion in scramjet engines.