A Numerical Investigation Of Cavitation Flow Characteristics In A Common Rail Injector’s Nozzle

With the increasing demand for power and emission performance of diesel engine, the pressure of electronic controlled fuel injection system raised quickly. The cavitation phenomenon in the high-pressure diesel nozzle is more and more widely concerned, and the existing experiments have proved that the pressure is not stable in the injection duration, the presence of nozzle cavitation and pressure fluctuations can significantly affect the fuel spray and evaporation, resulting in a significant impact on combustion and emissions performance of diesel engine. Hence, deep study should be do on the phenomenon of cavitation flow and unstable cavitation process caused by pressure fluctuations.At first, this study esf(?)ablish a numerical simulation model of multiphase flow inside the injector nozzle using mixture model, and consider the cavitation phenomenon by combine oit with the single bubble dynamics equation (Rayleigh Plesset). Do a detailed analysis for the important model parameters of the initial bubble number density and the critical cavitation pressure and gives the method for determining them. Then, use the experimental data of cavitation flow on a foreign science paper published by Winklhofer to validation the numerical simulation model, the results show that the model can exact predict the cavitation flow in the injector nozzle.After the establisher of the numerical simulation model, the study using the model investigated the influence of the injection pressure difference, the nozzle entrance circle radius to nozzle diameter ratio (r/D), the nozzle K-factor, nozzle length to nozzle diameter ratio (L/D), the nozzle wall roughness height to nozzle diameter ratio (Ks/D) on the nozzle internal flow characteristics, summarized and analyzed to get the influence law of the parameters, and given the optimal selection of the value.Secondly, this paper use the quasi-steady-state method investigated the transient cavitation flow characteristic in the injector nozzle, and got the transient evolution process of the pressure field and velocity field and cavitation inside the nozzle duration injection, also include the out flow characteristic of the nozzle.Finally, we analysis the reason of the pressure fluctuation and unsteady cavitation inside the nozzle duration the fuel injection, and discussed the frequency and amplitude range of the pressure fluctuation. Then investigated the influence of pressure fluctuation’s frequency and amplitude on the nozzle’s out flow characteristic and the cavitation process inside the nozzle on the condition of simple pressure fluctuation, and summarized the influence law and its reason. After that we also use the real pressure wave which measured from the nozzle volume investigated the nozzle flow characteristic and cavitation process inside the nozzle. The study showed that the pressure fluctuation and unsteady cavitation process inside the nozzle generated the unsteady turbulent kinetic energy, velocity, mass flow rate of the diesel flow on the outlet of the nozzle, and the unsteady flow parameters will formation the unsteady fuel injection and atomization, it will have a significant impact on the combustion and emission performance of diesel engine.