TEMPERATURE MEASUREMENTS OF ACETONE FLASHING JET BY LASER INDUCED FLUORESCENCE M. R. Vetrano (1) , A. Simonini (1) , T. Regert (1) and J. Steelant (2) (1) von Karman Institute for Fluid Dynamics, 72 Chaussée de Waterloo,1640 Rhode-St.-Genèse, Belgium, vetrano@vki.ac.be, Simonini@vki.ac.be , regert@vki.ac.be (2) ESTEC-ESA, Keplerlaan 1, 2200AG Noordwijk, The Netherlands johan.steelant@esa.int ABSTRACT Flash atomization occurs when a liquid jet is injected in an environment where the pressure is much lower than the liquid saturation pressure. As a consequence an enhanced atomization is observed. The modelling as well as the prediction of flashing is of an extreme importance in various industrial and scientific fields. The scope of this paper is to present the thermal characterization of a flashing jet by means of the PLIF (Planar Laser Induced Fluorescence) technique. A simplified 1D model is used to compare with the experimental data. 1. INTRODUCTION Flash atomization occurs when a liquid jet is injected in an environment where the pressure is much lower than the liquid saturation pressure; in this case, the liquid is defined as superheated. A liquid jet undergoing flash atomization is in an unstable thermodynamic state and a rapid phase transition occurs giving rise to nucleation and bubble growth. Flashing can have some potential benefits in propulsion systems as the enhanced atomization helps in the generation of a fine spray. Moreover an increase in effective spray angle and a decrease in spray penetration is also observed, resulting into an improved fuel-oxidant mixing and hence a better combustion efficiency. For upper-stage of launchers operating in vacuum, the flashing of the propellant also occurs during the start-up [1]. During flash atomization, phenomena like nucleation, bubble growth & breakup and droplet evaporation occur. Up to know the prediction of such phenomena is extremely difficult due to the lack of validated theoretical models for each of these phenomena. It is then obvious that the scientific community needs a reliable and accurate experimental database to verify the accuracy of model predictions and their range of validity. The experimental characterization of flashing jets is a difficult task due to the metastable thermodynamic state of the fluid. Several authors have used non-intrusive measurement techniques such as High Speed Video imaging, phase Doppler interferometry and Particle Image Velocimetry ([1],[3]). It has been reported that the use of intrusive technique, such as a thermocouples determining the liquid temperature, have as consequence the inception of flashing leading to misinterpretation of the phenomena downstream of the thermocouple. The scope of this paper is to show the first preliminary results using a non-intrusive measurement technique, namely the Planar Laser Induced Fluorescence, to thermally characterize the liquid phase of an acetone flashing atomization. The paper is organized as follows. After a brief introduction, the flashing phenomenon is described and the most relevant non-dimensional numbers used to characterize such kind of atomization are introduced. Then the experimental technique is introduced and the experimental set-up is described. The paper continues showing examples of the experimental results; finally the liquid temperature on the axis of the atomization is compared with the one numerically obtained using the model of Abramzon and Sirignano [4]. 2. THE FLASHING PHENOMENON As already mentioned, the flashing phenomenon takes place when a fluid is injected in an atmosphere, having a pressure much lower than the liquid saturation pressure at the injection temperature. Figure 1 shows the consequences of this injection. Assuming to have a fluid element at the pressure and temperature condition P inj and T inj in the liquid state. If we abruptly decrease its pressure up to a value P inf , keeping the same temperature T inj , the fluid element will be in an unstable thermodynamic condition since it will still be in liquid phase but will possess a pressure/temperature condition of the vapour phase. As consequence the fluid element will release the excess of heat in order to approach the saturation thermodynamic condition. Of course the example shown is valid for a single fluid element and changes in the vapour concentration around the fluid element is not considered. In this situation, the superheat degree of the transition is defined as the T SH = T inj - T inf .