Dual-pump CARS thermometry and species concentration measurements in a supersonic combustor

The dual-pump coherent anti-Stokes Raman spectroscopy (CARS) method was used to measure temperature and the absolute mole fractions of N₂, O₂ and H₂ in a supersonic combustor. Experiments were conducted in NASA Langley Research Center's Direct Connect Supersonic Combustion Test Facility. In this facility, hydrogen and air burn to increase the enthalpy of the test gas; O₂ is then added to simulate air. 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 then injected at Mach 2 and at a 30° angle with respect to the freestream. One wall of the duct then expands at a 3° angle for over 1 meter. The ensuing combustion is monitored optically through ports in the side of the combustor. CARS measurements were performed at the nozzle exit and at four different planes downstream fuel injection. Maps were obtained of the mean temperature, as well as quantitative N₂ and O₂ and qualitative Ha mean mole fraction fields. Correlations between fluctuations of the different measured parameters are presented for one of the planes of data.