Abstract
The near-nozzle characteristics of a transient fuel spray were investigated via the measurement of drop sizes and velocities, and microphotographs of the near-nozzle region for a range of gas-to-liquid density ratios. In addition, a steady-state single-phase hydrodynamic simulation of the internal nozzle flow was performed to observe the effects of needle position on the internal flow. Measurement of droplet size and velocity near the nozzle on the edge of the spray showed that the average droplet velocity peaked during needle opening and needle closing, and changed throughout the spray event. Drop sizes tended to be small on the spray edge. Microphotographs of the near-nozzle region showed that the spray was most widely dispersed immediately after injection begins, narrowing rapidly to a constant spray angle. The same behavior was observed even for injection into near-vacuum conditions. However, once the spray was established, aerodynamic interactions were necessary for near-nozzle atomization. The single-phase internal flow calculation showed that the magnitude of the turbulence intensity in the fluid was related to needle position. The position for cavitation, as indicated by regions within the nozzle tip with pressures less than the saturation pressure of the liquid, did not seem to be related to needle position, however.
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