PLANAR 2 COLORS-LIF TECHNIQUE APPLIED TO TEMPERATURE MEASUREMENTS WITHIN HYDROCARBON DROPLETS

Fluorescence-based methods (Laser Induced Fluorescence, Planar-LIF, 2 Colours LIF...) represent attractive means for studying liquids (flows or droplets) in a non-intrusive way. For example, the dependency of fluorescence on temperature makes possible the visualization of the entire temperature field within a droplet or a flow. The utilization of ratiometric methods based on the ratio of the fluorescence measured at two different wavelengths (also called 2 colours LIF), allows one to disregard the variations of some experimental parameters, such as incident laser power, dye concentration, measurement volume. That is particularly relevant in the case of evaporating droplets where, for example, significant variations in the concentration of the dye and of the measurement volume can be expected. The present study focuses on the application of 2 colours LIF for temperature field measurements within ntetradecane droplet radiatively heated. To this aim, a fluorescent tracer miscible with hydrocarbons (BOD-Me) was characterized in terms of spectral bands of absorption and fluorescence, dependency of fluorescence signal with temperature prior to its use for temperature measurements within n-tetradecane droplets. In the experimental conditions applied, the temperature inside droplets appear quite homogenous. A dedicated experimentation was carried out to visualize the motion of the fluid inside the droplets. The formation of strong convective cells due to the heating was clearly observed. The high mixing rates, with a fluid velocity greater than 50 mm/s, may explain the absence of significant thermal gradient within the droplets, as observed by fluorescence measurements.