Large-Eddy Simulation (LES) of Spray Transients: Start and End of Injection Phenomena

Abstract

-This work reports investigations on Diesel spray transients, accounting for internal nozzle flow and needle motion, and demonstrates how seamless calculations of internal flow and external jet can be accomplished in a Large-Eddy Simulation (LES) framework using an Eulerian mixture model. Sub-grid stresses are modeled with the Dynamic Structure (DS) model, a non-viscosity based oneequation LES model. Two problems are studied with high level of spatial and temporal resolution. The first one concerns an End-Of-Injection (EOI) case where gas ingestion, cavitation, and dribble formation are resolved. The second case is a Start-Of-Injection (SOI) simulation that aims at analyzing the effect of residual gas trapped inside the injector sac on spray penetration and rate of fuel injection. Simulation results are compared against experiments carried out at Argonne National Laboratory (ANL) using synchrotron X-ray. A mesh sensitivity analysis is conducted to assess the quality of the LES approach by evaluating the resolved turbulent kinetic energy budget and comparing the outcomes with a length-scale resolution index. LES of both EOI and SOI processes have been carried out on a single hole Diesel injector, providing insights in to the physics of the processes, with internal and external flow details, and linking the phenomena at the end of an injection event to those at the start of a new injection. Concerning the EOI, the model predicts ligament formation and gas ingestion, as observed experimentally, and the amount of residual gas in the nozzle sac matches with the available data. The fast dynamics of the process is described in detail. The simulation provides unique insights into the physics at the EOI. Similarly, the SOI simulation shows how gas is ejected first, and liquid fuel starts being injected with a delay. The simulation starts from a very low needle lift and is able to predict the actual Rate-Of-Injection (ROI) and jet penetration, based only on the prescribed needle motion. Finally, guidelines and future improvements of the model are discussed concerning the simulation of the transient injection phases.Résumé -Simulations aux grandes échelles (Large-Eddy Simulation, LES) de transitoires de jets liquides : phénomènes de début et fin d'injection -Le présent article rend compte d'études sur les transitoires de jets Diesel, prenant en compte l'écoulement interne de l'injecteur et le mouvement de l'aiguille, et démontre comment des calculs d'écoulement interne et de jet peuvent être réalisés dans le cadre d'une approche de type simulation aux grandes échelles (Large-Eddy Simulation, LES) en utilisant un modèle eulérien de mélange. Les contraintes sous-mailles sont modélisées avec un modèle de Structure Dynamique (Dynamic Structure, DS), un modèle LES à une équation non basé sur une viscosité turbulente. Deux problèmes sont étudiés avec un niveau élevé de résolution spatiale et temporelle. Le premier concerne un cas de fin d'injection (End-Of-Injection, EOI), où l'ingestion de gaz, la cavitation, et la for...

Near Field Visualization of Diesel Spray for Different Nozzle Inclination Angles in Non-Vaporizing Conditions

“…Computational Fluid Dynamics (CFD) is used to improve the understanding of the process, and obtain parameters which can be difficult to measure experimentally, but often rely on accurate experimental data in order to be validated. The current trend in diesel simulation is to do seamless calculations of internal and external flow using Large Eddy Simulation (LES) (Battistoni et al, 2016), which allows no domain interpolation of results between coupled simulations. An advantage of these models is that they simulate large scale turbulence phenomena, enabling them to reproduce local effects of complex internal flow structures, but as the level of detail gets higher, a more detailed and reliable experimental data is necessary to validate these models.…”

A quantitative analysis of nozzle surface bound fuel for diesel injectors

“…There have been numerous simulations and numerical studies that have predicted the complex fluid behaviour inside nozzle during the closing of the needle [16][17][18][19] these studies predict the breaking up of the jet into ligaments as well as rapid pressure fluctuations during this time. There is a point in which the experimental observation and numerical simulations are in very good agreement.…”

An Eulerian-Lagrangian Coupled Model for Droplets Dispersion from Nozzle Spray

“…Each cell has a portion of its volume filled by the liquid phase and the other part by the air. Continuity, momentum, energy and species, for a single-fluid mixture conservation equations, are solved in all pass time of the simulation [1,2]. On the other hand, the Lagrangian approach at one particle proposes the velocities and positions of particles simulation (solids, liquid, vapor, or scalar species) by solving a stochastic equation following the Markov chains.…”