Numerical simulation of the effects of nozzle geometry on the in-nozzle flow-characteristics of flash boiling sprays
This paper investigated the influence of nozzle geometry on the in-nozzle flow and phase-change process of flash boiling sprays in the direct-injection gasoline-engine cars.A one-dimensional two-phase-flow model was developed based on the thermal non-equilibrium assumption to analyze the in-nozzle flow characteristics of the flash boing spray with different nozzle lengths,different diameters,different rounding angles at the inlet,and different taper angles.The model's results were verified through the accuracy comparison with the previous experimental results by the authors'team.The results show that the longer the nozzle channel length,the smaller orifice diameter,and the more intense of the phase transition in nozzles,while the round corners at the nozzle entrance reduces the vapor generated inside nozzles.The convergent nozzle has a smaller pressure drop and the generation of vapor phase inside the nozzle is reduced accordingly,while the divergent nozzle increases the vapor generation rate.The different nozzle geometries change the pressure distribution and the velocity distribution in the nozzle.The pressure distribution governs the bubble growth rate,while the velocity distribution affects the bubble growth time,both of which ultimately affect the phase change characteristics within the nozzle.
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