Dual-pump coherent anti-Stokes Raman scattering measurements in a supersonic combustor

The dual-pump coherent anti-Stokes Raman scattering (CARS) method was used to measure temperature and the mole fractions of N₂ and O₂ in a supersonic combustor. Experiments were conducted in NASA Langley Research Center's Direct-Connect Supersonic Combustion Test Facility. In this facility, H₂- and oxygen-enriched air burn to increase the enthalpy of the simulated air test gas. This gas is expanded through a Mach 2 nozzle and into a combustor model consisting of a short constant-area section followed by a small rearward-facing step and another constant-area section. At the end of this straight section, H₂ fuel is injected at Mach 2 and at a 30-deg angle with respect to the freestream. One wall of the duct then expands at a 3-deg angle for over 1 m. The ensuing combustion is probed optically through ports in the side of the combustor. Dual-pump CARS measurements were performed at the facility nozzle exit and at four planes downstream of fuel injection. Maps are presented of the mean temperature, as well as N₂ and O₂ mean mole-fraction fields. Correlations between fluctuations of the different measured parameters are also presented.