Large Eddy Simulations of Diesel Combustion Chambers

摘要

This report presents findings of a systematic study of turbulence predictions for diesel combustion chambers. Particular topics covered include (1) turbulence models for Reynolds averaged Navier-Stokes solutions, (2) turbulence scale analysis, (3) efficiency and accuracy improvements of the KIVA codes, (4) large eddy simulations(LES) of in-cylinder turbulence with and without combustion, (5) sub-grid scale models for LES, and (6) combustion models for diffusion flames. The generation of the turbulence during the intake stroke and its subsequent decay during the compression stroke was predicted successfully. The turbulence induced by the piston-bowl geometry alone was investigated. It was found that significant turbulence can be generated during the compression stroke from the re-entry flow in the squish area. Simulations with spray combustion indicated an augmentation of the turbulence intensity corresponding to start of ignition. These findings are in good qualitative agreement with experimental observation. A quantitative analysis of the results in comparison with experiments will require simulations of many cycles to account for cycle-to-cycle variations. This could be possible with use of computers with parallel processors. To this end a successful attempt was made to transform KIVA to run on several parallel platforms including a locally built Beowulf Workstation cluster. initial runs with fixed grids could handle up to four million nodes. This holds promising prospects for future LES of in-cylinder combustion/turbulence in internal combustion engines.