FURTHER DEVELOPMENT OF A VARIABLE FUEL FLOW AUTOMATIC MIXING VALVE FOR PRESCRIBED INJECTION RATIO

The production of an emulsion by emulsification plant without the addition of chemical additives always requires an injection device of the dispersed phase (water or ethanol) into the continuous phase (fuel oil). In this way a preliminary mixture of immiscible liquids is produced at the right volume ratio. Such a mixture is processed downstream to have an emulsion with the dispersed phase drop mean diameters less than 4 μm. Since Gas Turbines have a variable fuel flow related to the delivered power, there is the necessity of maintaining a prescribed dispersed phase to continuous phase volumetric ratio when the fuel flow varies. This paper deals with an automatic device that is capable of producing the prescribed injection ratio of the dispersed phase into the fuel oil when the fuel oil flow rate changes. Such a device is developed to be coupled with an emulsification system that provides to break an immiscible part of fluid in a very small drops. The system is for feeding fuel into engines (S.I. Gasoline, Diesel, Gas Turbine combustors) operating at variable loadings i.e variable liquid fuel flow. The mixer (PMD, Pre-Mixer Device) has been presented at ASME Turbo Expo (Montreal 2007) for diesel #2 operating at 25°C with the viscosity being assumed as constant because of its variation is in a reduced range. In this paper, different fuels having different viscosities (diesel oil of different numbers, rapeseed oil, sunflower oil, etc) have been tested. The major modeling aspect concerns with the behavior of the annular orifice that produces a membrane displacement. A bibliographic analysis has been performed and the main results are reported in this paper. Since the architecture of the orifice, its geometry and the flow conditions were not reported in the bibliography, systematic experiments have been performed. Such experiments where carried on for various liquids having various viscosities for different geometric arrangements and force acting on the membrane. The analysis of results led to formulate models to describe both the flow discharge and effective force coefficients. The paper gives a complete outlook of the experiments and of the above models. The viscosity dependent models have been introduced in to the PMD simulation code. Such models that take the influence of viscosity into account have been developed and some scale-up rules have been established. An amply description of the sizing and scale-up models are presented together with modification to improve the prototype behavior operated with fluids having different viscosities. Experimental results concerning the influence of viscosity of the continuous phase are presented and widely discussed taking the model as reference.