Ketone dopant-induced dynamic quenching of liquid fuel fluorescence for two-phase flow visualization

Dynamic quenching of fuel fluorescence by ketone dopants in liquid phase is investigated to suggest an optical method for two-phase flow visualization in a liquid-fueled combustor. The fuel fluorescence is triggered by high peak-power 266 nm laser pulses. It is found that ketones can serve as quenchers absorbing the fluorescence of a widely used liquid fuel, exo-THDCPD (exo-tetrahydrodicyclopentadiene). The impact of the dynamic quenching on the fuel fluorescence is validated under various ambient temperature conditions to simulate two-phase fuel flows in preheated ambient air. The signal intensity ratio with and without the dopants (quenching ratio) is below 0.4 % near 290 nm when the ketone concentration in the mixture is 5 %, while the quenching effect is insignificant in the spectral range above 325 nm. As a result, the proposed technique is successfully demonstrated in a model supersonic combustor, delineating vapor-dominant regions in the two-phase supersonic flows.