Influence of Nozzle Orifice Geometry and Fuel Properties on Flow and Cavitation Characteristics of a Diesel Injector

Cavitation refers to the formation of bubbles in a liquid flow leading to a two-phase mixture of liquid and vapor/gas, when the local pressure drops below the vapor pressure of the fluid. Fundamentally, the liquid to vapor transition can occur by heating the fluid at a constant pressure, known as boiling, or by decreasing the pressure at a constant temperature, which is known as cavitation. Since vapor density is at least two orders of magnitude smaller than that of liquid, the phase transition is assumed to be an isothermal process. Modern diesel engines are designed to operate at elevated injection pressures corresponding to high injection velocities. The rapid acceleration of fluid in spray nozzles often leads to flow separation and pockets of low static pressure, prompting cavitation. Therefore, in a diesel injector nozzle, high pressure gradients and shear stresses can lead to cavitation, or the formation of bubbles.