Abstract: Fuel atomization and penetration are known to significantly affect the combustion and emission processes in diesel engines. High-pressure common rail system can supply better diesel spray to enhance combustion efficiency and reduce emission. With the fuel pressure increasing, spray process becomes more and more complex which makes the study on atomization mechanism more challenging. Under the super high pressure, the internal turbulent flow and cavitaing flow of the nozzle are important to fuel spray characteristics, especially the cavitaion has been the key to relating the internal flow of nozzle and atomization behavior. So it is necessary to simulate fuel spray coupling with internal cavitaing flow of the nozzle. The internal geometry of injector nozzle is measured with the X-ray phase contrast imaging. The more exact CFD model of nozzle is established using geometry parameters from the measurement, which is used for the three-dimensional numerical simulation of the cavitating flow in nozzle. Moreover, analysis of the influence of cavitaing flow in the nozzle hole on spray is made and a coupling spray simulation is carried out with the output data of cavitaing flow in nozzles using FIRE v2010. The results of this work show that the characteristics of cavitating flow in orifice have an effect on both macroscopic properties and microscopic properties. Compared with simulation result, a spray experiment under high pressure is tested on a high-pressure common rail injection system, which has verified the spray model. On base of the verified spray model coupled with the cavitating flow in nozzle, multi-schemes of cavitating flow in nozzle and subsequent spray are simulated with various geometry parameters of nozzle. These simulation results supply a theoretical basis for the optimization design of the high-pressure common rail injection system.

Key words: cavitaiong flow in nozzle, coupling model, diesel, spray