Mole-Fraction-Sensitive Imaging of Hypermixing Shear Layers

Abstract

A theoretical model that determines the optimum excitation frequency for obtaining a fluorescence signal with a strong dependence on fuel mole fraction is presented for supersonic fuel-air compressible mixing studies. The challenge associated with this is to maintain a high sensitivity to fuel mole fraction with minimal sensitivity to temperature and pressure in a flow with large temperature variations and pressure gradients. The results of the model are applied to the mixing region behind various scramjet fuel injectors in a shock tunnel to measure fuel mole fraction. Hydrogen fuel at a Mach number of 1.7 is injected into a mostly N2 freestream at Mach 4.8. Experimental fluorescence images are presented in streamwise and spanwise planes.