Transitional instability of a pressure-swirl atomizer due to air-core eruption at low temperature

Because of the high viscosity of fuel in low temperature environments, a pressure swirl (or simplex), jet fuel undergoes a transitional stage in which an unstable mode of the jet is found. These types of instabilities are observed not only at an external location, where the pulsation of a hollow cone is visualized, but also inside the atomizer, where measurement of the flow's inlet pressure and flowrate occurs. The breakdown of an air-core (formed due to high centrifugal acceleration inside the swirling atomizer), may explain the instability. When the jet is stable at high temperature, a hollow cone is formed and the mass flowrate distribution forms a hump at the spray collection plate, at the downward location. When the fuel temperature is decreased, the hollow cone spray becomes a solid cone spray, due to the disappearance of the air core inside the atomizer. In this case, turbulence begins to dominate and droplet characteristics (i.e., Sauter mean diameter) become dependent on the Kolmogrov length scale. In the experiment, kerosene-based aviation fuels (referred to as Fuel-A and Fuel-B) are the working fluids. The inner diameter of the orifice at the fluid exiting location is 1 mm. The ranges for the operating pressure and fuel temperature are 0.2 MPa < P < 1.0 MPa and 253 K < T < 313 K, respectively.