ADVANCES IN COMBUSTION MODELING IN STAR-CD: a new technique for automatic grid and mesh motion generation applied to Diesel combustion and Emissions analysis

The ECFM CLE-H is a new approach developed by CORIA [1] [2], [3] to simulate the different phases of Diesel combustion; auto-ignition, premixed and diffusion flame burning. The original proposal was based on two modelling for the two flame structures: premixed and diffusion flame. Particular emphasis was put on improving modelling for the diffusion combustion. The combustion model split the flame front in three zones: non-reactive zone, premixed zone and un-premixed zone. For each zone, a specific combustion model is attached based on flame structure analysis. CLE-H stands for Combustion Limited by Equilibrium Enthalpy; model uses an equilibrium fuel mass fraction to compute the average heat release rate. This equilibrium fuel mass fraction has been calculated a priori from complex chemistry calculations for fuel to limit burning rates. A presumed Beta-shape PDF is adopted to average the equilibrium at equilibrium. Auto-ignition is modelled from tabulated fully detailed chemistry. The tabulation strategy TKI proposed by IFP [4] is used. This model was completed with a soot model. This soot model is based from look up table established from a detailed chemistry mechanism and an original sectional method. The complete model is implemented in Version 4 of STAR-CD allowing a higher flexibility in meshing including general polyhedral cells. This new technique fully automates the simulation process and preserves a high mesh quality during the grid motion. To evaluate the model, results were compared with extensive data from DI Engines in production at full and part load. The results show that the models give realistic Heat Release History, Indicated Power and NOx emissions.