Studies on rotary atomization

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PhD; 2021; Interdisciplinary centre for energy research

In rotary fuel injection systems, the fuel is atomized with the help of centrifugal force provided by the rotation of the injector. The rotational power can be directly provided by the shaft of a gas turbine, which can go up to the rotational speed of 100000 RPM. Therefore, there is no need for extra systems such as a fuel pump or a pressure chamber. This makes the rotary injection system very compact and suitable for small gas turbines. Also, the injection orifice diameter in these systems is large enough to be used for high viscosity and slurry fuels, as small diameters can cause clogging. There is a strong need to study and understand the spray characteristics of these types of injectors to adapt combustors for challenging fuels such as high energetic fuels containing boron nanoparticles. Also, there is a need to develop correlations for improved prediction of spray characteristics. The present work is motivated by the demand for high-energy-density fuels, such as fuel slurries. In the first part of the study, the spray characteristics of rotary atomization were investigated experimentally. A high-speed rotating facility has been developed in which a 1.5-kW electric motor was used with a maximum operating speed of 40000-RPM. The spray characteristics of pure water, water-ethanol blend, and water-glycerol blend were investigated to understand the variation of liquid physical properties such as viscosity and surface tension on spray characteristics. It is shown that at lower rotational speeds, the effect of viscosity and surface tension are evident, but at higher speeds, the inertial effects dominate. To understand the spray characteristics from slurry fuels, aqueous colloidal silica nanoparticle suspension with different nanoparticle loading is used. Results showed that even with the particle loading, the variation in SMD is the function of liquid physical properties and does not have a unique dependency on particle loading. The jet visualization and spray characteristics such as breakup length and droplet size were measured using the shadowgraphy technique. For droplet size measurements, a long-distance microscope (LDM) attached to a CCD camera with laser-induced fluorescent backlight is used. The Spray patternation has been studied with water by passing a laser sheet to the spray and capturing scattering images. The images of the liquid flow inside the orifice were captured using a transparent atomizer made of acrylic. The second part of the study comprises of analyzing the liquid flow physics. A novel non-dimensional number has been derived to account for the Coriolis force induced inside the orifice. From the images of liquid flow inside the orifice, it has been shown that the flow physics can be explained using this non-dimensional number. There are eight different parameters affecting the spray characteristics, viz. viscosity, density, surface tension, liquid feed rate, atomizer rotational speed, atomizer diameter, orifice diameter, and orifice length. A new empirical correlation has been established to account for the variation in all these parameters, and this correlation is shown to be very effective over a wide range of parametric space. The last part of the study involves the design proposal of a novel orifice structure, which comprises of two stages; also, the feasibility of the design was investigated.