MCS 7 Chia Laguna, Cagliari, Sardinia, Italy, September 11-15, 2011 STUDY OF THE MICRO-EXPLOSION TEMPERATURE OF WATER IN OIL EMULSION DROPLETS DURING THE LEIDENFROST EFFECT E. Mura*, P. Massoli**, C.Josset**, K.Loubar* J.Bellettre*** Ernesto.mura@emn.fr * GEPEA, UMR 6144 CNRS, EMN, 4, rue Kastler, 44307 Nantes, Fr **Istituto Motori CNR, Via Marconi 8, 80125 Napoli, It *** LTN, UMR 6607 CNRS, Univ-Nantes, rue Pauc, 44306 Nantes, Fr Abstract To burn water in oil emulsions (W/O) is considered as an effective alternative to bring out waste oil because of a significant reduction in carbon monoxide, nitrogen oxides and particulates in the exhaust. These advantages have different origins, an important contribution is provided by the phenomenon of micro-explosion. In this work, the influence of the size of the dispersed water droplets (D 32 ), for three iso-water emulsion, in the micro explosion phenomenon is studied by the hot plate technique. The temperature of the emulsion droplet and the visual evolution of the samples are evaluated using a synchronized thermocouple/CCD system. The results show that the size distribution of the dispersed water droplets plays an important role in the phenomenon of micro explosion. Moreover, some internal phenomenon as the separation process between water and oil seems to be discriminate. Introduction Today, stocks of fats and oily waste from animals and plants are subject to grow up because of the increasing production of food industries. These residues have a very important energy potential not too different from conventional fuels such as diesel [1]. However, these products have a fatty acid content of up to 70% by mass [2] and it is impossible to burn them because of the production of a large amount of pollutants. To burn water in oil emulsions (W/O) is considered as an effective alternative to bring out waste oil [3,4]. Several authors have worked on the use of emulsified products in boilers or internal combustion engines. The results show a significant reduction in carbon monoxide, nitrogen oxides and particulates in the exhaust [1,5,6]. These improvements are correlated with the presence of water during the combustion process. These advantages have different origins, an important contribution is provided by the phenomenon of micro-explosion. When a W/O emulsion droplet is heated in a flame, in function of several variables (differences in boiling point, water content, pressure) [7], its temperature could exceed the water boiling point maintaining it in liquid phase. This condition is called metastable state and not any change in phase appends until the limit of stability is reached:            The isothermal compressibility diverges and the change in phase occurs. In a macroscopic system this limit is strongly affected from small perturbations as spontaneous molecular fluctuations [7]. The metastable state is broken by nucleation of small embryos of the new phase by homogeneous or heterogeneous process [8,9]. At this point, the nucleation rate strongly increasing for a minimum rise in temperature leading to a vigorous expansion of the