Visualization Experiment And Numerical Simulation Of Cavitating Flow Characteristics In Diesel Injection Nozzles

In the working process of the Diesel engines,good atomization effects which are the most direct factors on affecting the combustion process have an important influence on economy,power and emission characteristics.As the terminal of injection system,the injection nozzle has a decisive effect on the fuel atomization.Therefore,the influence of cavitating flow in the nozzle must be considered in the study of spray.Extensive research suggests that the influence of cavitating flow in the nozzle is much larger than the interaction between the spray and the ambient air.Hence,the research of the cavitating flow has a great significance on revealing the spray mechanism.The generation of the cavitating flow in the nozzle is not only affected by the external factors(geometric dimension,dynamic factors),but also by the internal factors(fuel properties).According to the internal and external present researches,a visual experimental system is conducted to study the cavitating flow in the nozzle,based on the experimental system and the 5 times proportion-amplified transparent nozzle,the different injection pressure,fuels,fuel temperature and the needle lift on the cavitating flow in the nozzle hole and the spray construction near the orifice are thoroughly studied.Based on the experimental investigations,the numerical simulation confirms the accurate threedimensional numerical model,and then analysis the larger scope of different injection pressure,fuels,fuel temperature and the needle lift on the cavitating flow in the nozzle under the real model.Researches suggest that the moment and the intensity of the cavitating flow are changed with the different test conditions.The fuel which has low viscosity and high saturated vapor pressure appears cavitation easier,the pressure of the initial cavitation and super cavitation are relatively small,and the cavitation intensity is stronger.With the increase of the fuel temperature,the saturated vapor pressure increases sharply,the initial cavitation pressure decreases,under the same cavitation number,the cavitation intensity is stronger.With the decrease of the needle lift,the volume flow rate decreases gradually,the flow coefficient increases,the initial cavitation appears earlier and the cavitation intensity is stronger.Besides,the cavitating flow in the nozzle which is observed in the experiment is asymmetrical,the cavitation distribution in the nozzle below is more than above.When the super cavitation flow appears,with the increase of the cavitation number,the cavitating flow in the nozzle varies little,the spray cone angle increases obviously because of the collapse of the bubbles.Compared with the cavitation number,the reynolds number has little relationship to the cavitating flow in the nozzle.Finally,the changes of the gas volume fraction,the liquid fuel rate,and the pressure distribution in the real model under different conditions are analysed through the numerical simulation,which sets up a foundation for the further study on the cavitating flow.