Instantaneous two-line PLIF temperature imaging of nitric oxide in supersonic mixing and combustion flowfields

Instantaneous planar laser-induced fluorescence (PLIF) imaging diagnostics were developed and applied to study the mixing and combustion of a transverse jet in supersonic crossflow. Freestreams with and without 21% oxygen were studied, and two geometries were investigated including injection from a flush wall and from downstream of a rearward facing step. Jet-to-crossflow momentum ratios of 1.49 and 1.94 were examined, which are representative of a realistic SCRAMJET combustor.; NO seeded in the jet or the jet and crossflow was used as the fluorescence tracer, following excitation of A{dollar}sp2Sigmasp+ gets{dollar} X{dollar}sp2Pi{dollar} (0,0) band transitions near 226 nm. Fluorescence visualizations were used to investigate the turbulent jet structure and mean flowfield characteristics, and two-line temperature imaging was used to examine the mixing and heat release, using both instantaneous and frame-averaged measurements. The temperature measurements were based on the fluorescence ratio determined from excitation of two rovibronic transitions, using two sequentially pulsed dye lasers and two intensified cameras.; The general methodology for designing two-line temperature experiments is presented, and a number of application considerations are discussed, including transition selection, temperature sensitivity, dynamic range limitations, measurement resolution, photon statistical noise, and shot-to-shot laser fluctuations. The results indicate that NO is a useful temperature tracer of fuel and unburned gas in supersonic combustion flows, with the temperature uncertainty typically dominated by shot-noise. Shot-to-shot laser fluctuations are a less significant source of temperature uncertainty, especially for cases where in situ calibration is possible.; The instantaneous images show that large, vortical structures are present in the mixing layer throughout the imaged region ({dollar}sim{dollar}18 jet diameters). The penetration of the fuel is found to increase with increasing jet-to-crossflow momentum ratios for each geometry, with the step geometry showing deeper penetration for a given momentum ratio. The instantaneous temperature images show that pockets of relatively unmixed fuel persist within the plume for several jet diameters, with the plume reaching a relatively uniform temperature in 12-15 jet diameters. The measured temperature fields (frame-averaged) within the plume core indicate higher mixing rates for the lower momentum ratio in a given geometry, and higher mixing rates for the step geometry at a given momentum ratio.