Laser-Based Measurements of OH, Temperature, and Water Vapor Concentration in a Hydrocarbon-Fueled Scramjet

Abstract

‡‡ In this investigation, two laser-based measurement techniques are implemented in a direct-connect hydrocarbon-fueled scramjet combustor. Planar laser-induced fluorescence (PLIF) of the OH radical is used to examine the flame structure within the combustor. Tunable diode laser-based absorption spectroscopy (TDLAS) is used to measure water vapor concentration and static temperature near the combustor exit. Combined with conventional measurements and Reynolds-averaged CFD simulations, these optical diagnostic techniques significantly enhance the information that is obtained from the scramjet combustor. In this study, wall pressure data show the combustor to be operating in dual-mode with two regions of elevated pressure corresponding to the primary and secondary flameholding zones. The OH radical is well-distributed across the combustor with high OH concentrations occurring along the body, side, and cowl walls. TDLAS measurements indicate non-uniform body-to- cowl profiles in both temperature and water concentration. Near-wall regions are found to be the hottest while the core region is cooler. Similarly, the highest concentrations of water vapor are found near the walls. In general, CFD results compare well with the experimental data, although there are dissimilarities that are probably related to turbulence and chemistry sub-models within the CFD code.