Saturated laser-induced fluorescence in liquid kerosene seeded with a dye: influence of temperature and excitation intensity

Abstract

Fluorescence-based techniques are commonly implemented to characterize droplet sprays in flows at temperature above 293 K. Nevertheless, in the case of gas turbine altitude relight, aeroengines are exposed to critical operating conditions where the liquid fuel temperature can reach values as low as − 40 °C. As a result, it is necessary to address the influence of this parameter on fluorescence intensity for temperatures below room values. In this paper, an innovative saturated laser-induced fluorescence (SLIF) excitation scheme is proposed to overcome the strong temperature dependence of fluorescence in liquid kerosene seeded with a dye. The findings of this work are based on gated sequential images recorded with an intensified camera during and after the laser pulse duration so as to sample the temporal evolution of the fluorescence emission. The results show that, for low laser excitation intensity, the fluorescence intensity remains proportional to the laser power. However, a non-linear response is observed in the case of high excitation intensity. This difference can be used to limit the fluorescence dependence on temperature by carefully selecting the temporal window where fluorescence is detected. Finally, although the method presented in this paper is applied to cold liquid kerosene, its range of application can be extended to other liquids and other temperature ranges.