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

Abstract

Because of the high viscosity of fuel in low-temperature environments, jet fuel in a pressure-swirl (or simplex) atomizer undergoes a transitional stage in which an unstable mode of the jet is found. This transitional instability at low fuel temperature is 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 flow rate takes place. 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 flow-rate 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 which case turbulence begins to dominate. The objective of the current work is to measure the effect of liquid temperature and viscosity on the atomization behavior of a pressure-swirl nozzle. 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.