Modelling of cavitation in diesel injector nozzles

Abstract

This is the unspecified version of the paper.This version of the publication may differ from the final published version. A computational fluid dynamics cavitation model based on the Eulerian-Lagrangian approach and suitable for hole-type diesel injector nozzles is presented and discussed. Permanent repository link Modelling of cavitation in diesel injector nozzles E. G I A N N A D A K I S, M. G A V A I S E S A N D C. A R C O U M A N I SThe model accounts for a number of primary physical processes pertinent to cavitation bubbles, which are integrated into the stochastic framework of the model. Its predictive capability has been assessed through comparison of the calculated onset and development of cavitation inside diesel nozzle holes against experimental data obtained in real-size and enlarged models of single-and multi-hole nozzles. For the real-size nozzle geometry, high-speed cavitation images obtained under realistic injection pressures are compared against model predictions, whereas for the largescale nozzle, validation data include images from a charge-coupled device (CCD) camera, computed tomography (CT) measurements of the liquid volume fraction and laser Doppler velocimetry (LDV) measurements of the liquid mean and root mean square (r.m.s.) velocities at different cavitation numbers (CN) and two needle lifts, corresponding to different cavitation regimes inside the injection hole. Overall, and on the basis of this validation exercise, it can be argued that cavitation modelling has reached a stage of maturity, where it can usefully identify many of the cavitation structures present in internal nozzle flows and their dependence on nozzle design and flow conditions.

Simulation of Heating Effects Caused by Extreme Fuel Pressurisation in Cavitating Flows through Diesel Fuel Injectors

“…The cavitation model used in the present study treats fuel vapor as discrete bubbles whose trajectory is calculated on a Lagrangian frame of reference. Detailed mathematical documentation of the model and extensive validation with experimental data can be found in [29]; nevertheless, the basic aspects of the physical sub-models and their numerical implementation are highlighted here, in order to help the reader to better understand the model fundamentals. Moreover, the extension of the current model to account for variable fuel viscosity and density is presented.…”

“…The effect of bubble coalescence and bubble-to-bubble interaction on the momentum exchange and during bubble growth/collapse is also considered. More details and a thorough validation of the model can be found in [28,34]. The time step used for the simulation of the nozzle volume flow has been varied between 10 -6 s, which is short enough to capture the transient development of the vortices formed inside the nozzle.…”

“…However, the model has been thoroughly validated against experimental data obtained at lower injection pressures in real-size transparent Diesel injectors as well as in enlarged transparent nozzle replicas; more details can be found in [28,36].…”

VOF Simulation of The Cavitating Flow in High Pressure GDI Injectors

“…To simulate fuel injection, the continuous liquid core in the near-nozzle region is modeled by discrete parcels which typically are assumed to have the same characteristic size as the nozzle exit diameter and phenomenological models are used to account for breakup [8], as well as collision and coalescence of liquid droplets [9]. The above mentioned method requires a precursor nozzle flow simulation of the Eulerian liquid phase to predict the flow conditions at the nozzle exit [10]. The coupling between the internal and the external nozzle simulation is inherently weak, due to potential inconsistencies of the two-phase models in the two separate simulations [10].…”

“…The above mentioned method requires a precursor nozzle flow simulation of the Eulerian liquid phase to predict the flow conditions at the nozzle exit [10]. The coupling between the internal and the external nozzle simulation is inherently weak, due to potential inconsistencies of the two-phase models in the two separate simulations [10]. On the other hand, engine sprays, and sprays in general, could be better described using a continuum for both the liquid and the gas phases, where conservation laws are solved under Eulerian flow assumptions and grid is refined until its resolution allows for solving droplets or bubbles without introducing any conceptual particles.…”