COMPARISON OF NO AND OH PLANAR FLUORESCENCE TEMPERATURE-MEASUREMENTS IN SCRAMJET MODEL FLOWFIELDS

The use of nitric oxide (NO) and the hydroxyl radical (OH) as temperat ure tracers, in a two-line planar laser-induced fluorescence technique , is examined in the context of a supersonic mixing and combustion flo wfield. The temperature measurements were based on the sequential exci tation of two transitions, either in the A <-- X (0,0) band of NO near 226 nm or the A <-- X (1,0) band of OH near 283 nm. The measurements were obtained for each species through the use of two lasers and two c ameras, with each camera integrating signal induced from only one of t he lasers. Both temporally resolved and frame-averaged temperature mea surements of each species are presented. Additional results include si multaneous NO and OH visualizations, in which seeded NO marks the fuel jet fluid and nascent OH marks the reaction zones and convected combu stion gases. A detailed temperature comparison shows good agreement in the common measurement regions and indicates that shot noise is the l argest source of uncertainty. The comparison also illustrates the impo rtance of a careful interpretation of the measurements, since, dependi ng on the origin of the tracer and the degree of mixing, the measureme nts may be biased toward the fuel, freestream, or reaction zone temper atures.