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

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