Numerical simulation of internal sprays in a constant chamber using large eddy simulation techniques 2019-01-0213
For the direct injection diesel engines, physics of fuel injection, spray breakup and spray vaporization events are the key things of in-cylinder combustions for internal combustion engines. To capture instantaneous flow fields and internal jet spray characteristics, large eddy simulation (LES) technique is chosen to provide the large scale mixing of spray jets. The present work describes numerical simulation of internal spray structure in a constant volume chamber and compares the performance of two sub-grid stress (SGS) models against available experiment data. The Smargorinsky model and the dynamics sub-grid stress model based LES are implemented in the commercial code called ANSYS Forte. The predicted results from both sub-grid stress models are also compared with the Reynolds Average Navier-Stokes (RANS) turbulence model which is normally used in engine simulation. The model validations are performed against available measurement data from Sandia National Laboratory, USA. A similar experimental dimension of the constant volume chambers without moving boundaries is constructed while the solution adaptive mesh refinement is applied. The spray test case is simulated with n-heptane diesel fuel under non-reacting condition and the minimum grid size is 250 µm in this study. Spray H conditions in the database is used and the effects of different SGS models based LES are investigated. With the global characteristics of spray jets, the simulated vapor and liquid penetration are agree well with experimental data, while the radial mixture fraction profiles at different location provides the same trends with the measurement data. The contours of fuel vapor mass fraction, jets temperature and jets velocity from both SGS models are also compared and discussed. The investigation reveals that predicted results from the dynamics SGS model based LES is a better technique to provide the local information of the instantaneous fuel vapor distribution. The transient behaviors of spray temperature and velocity are improved by the dynamic model. However, the improved prediction by LES techniques is lead to the increase of computational time.