Instantaneous mole-fraction PLIF imaging of mixing layers behind hypermixing injectors

A theoretical model is presented for the determination of the optimum excitation frequency for the production of a fluorescence signal which is proportional to the mole-fraction of the target species while having minimal sensitivity to pressure and temperature variations. The results of the model are applied to the mixing region behind a range of scramjet fuel injectors in a shock tunnel with the aim of obtaining measurements of fuel mole-fraction. Experimental images are presented of fluorescence in streamwise and cross-planes. Analysis of the flowfields produced by a castellated and a plane-base injector shows that the castellated injector has a slight advantage over the plane-base injector, particularly in the near field.

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