(Lisbon Symposia会议论文)两色激光诱导荧光测温的新进展

The present paper deals with a new optical diagnostic that aims to measure the droplet temperature measurements in sprays based on the two-color laser-induced fluorescence (LIF). The principle of the twocolor LIF technique is to induce the fluorescence of a tracer previously seeded in the liquid of interest. More precisely, it was highlighted that a non-linear effect of the droplet size on the fluorescence ratio remains.Typically, the fluorescence ratio increases widely when the droplets diameter D decreases whereas the temperature is assumed constant. More, it has been shown that increasing the tracer concentration C leads to decrease the size effect. Then, a correction function was introduced in the two-color LIF model to take into account the size effect. A third spectral band of detection can be use to determine this correction. The present paper aims to investigate more thoroughly the non linear effect and its coupling with other phenomena, such as multiple scattering of the laser light that induces off-field fluorescence. Indeed, the depth of field of the collection optics used for collection is larger than the excitation volume. Thus, the collected fluorescence signal is the addition of the contributions of the fluorescence induced in the presumed volume and the florescence induced outside this volume in the depth of field of the collection optics. This unwanted fluorescence could induce a new bias in the fluorescence ratio. Therefore, a long distance microscope, with a lower depth of field, is used and tested. In order to understand this phenomenon, combined LIF and PDA measurements have been developed. This technique allows achieving fluorescence ratio per droplet size class. First results obtained with combined LIF/PDA device show clearly that the microscope reduces widely the depth of field effect. More, it seems that increasing again the dye concentration can reduce this new effect.