Contribution à la combustion des émulsions de l'eau dans le fioul lourd

Maître de thèse : Jérôme BellettreHeavy Fuel-oil, used engine oil or animal fat are dense, viscous combustibles that can be used within boilers. To burn these combustibles as a water-in-oil emulsion is known to decrease both the flame length and the carbonaceous residue, in comparison with raw combustible. Indeed, the microexplosion phenomenon, which means the rapid (<0.1 ms.) vaporization of inside water droplets, breaks the emulsion droplet into many smaller droplets. The first step of this work is to demonstrate an unsteady modelisation of the emulsion droplet enabling, thanks to an adequate criterion (vaporization of the liquid-metastable water droplets) to establish a numerical prediction of its microexplosion delay. This prediction is faced with experimental measurements available in the literature, along with different combustion parameters and emulsification variables, totalizing 27 different situations. Secondly, this model of individual emulsion droplet is included in a spray combustion model, taking into account the microexplosion phénomenon : The results enable a comparison between the flames (~150 kW) obtained with raw and emulsified combustible. This comparison of flame lengths and temperature fields is in qualitative accordance with trends described in experimental works from the literature. Finally, an experimental campaign on an industrial middle-scale (~200 kW) boiler enables to record a reproducible decrease (from 30 to 35%) in carbonaceous residue using a water-in-oil emulsified heavy fuel-oil, in comparison with pure heavy fuel-oil. The measured distribution of cenosphere diameters at the exhaust of the boiler gives an indication for microexplosion.Les fiouls lourds, les huiles usagées ou les graisses animales constituent des combustibles denses et visqueux qu'il est possible de valoriser. Brûler ces combustibles en émulsion avec l'eau diminue la longueur de flamme et surtout la formation de résidus carbonés solides (particules) par rapport au combustible pur. Car le phénomène de micro explosion, qui consiste en la vaporisation rapide (