Evaluation of Different Tabulation Techniques Dedicated to the Prediction of the Combustion and Pollutants Emissions on a Diesel Engine with 3D CFD

In this paper three turbulent combustion models with different underlying hypothesis are compared with measurements from an extensive experimental database. The reference model is ECFM3Z, with the Tabulated Kinetics of Ignition (TKI) model for auto-ignition modeling, together with the CO reduced kinetics (CORK) model and the extended Zeldovich model for the nitrogen oxides. The VVTHC (Variable Volume Tabulated Homogeneous Chemistry) model predicts both the heat release and species evolutions (including CO). The most evolved model proposed is the ADF-PCM (Approximated Diffusion Flame-Presumed Conditional Moment) approach, based on the laminar flamelet equation of the progress variable. ADF-PCM and VVTHC are tabulated models based on a progress variable approach and are then coupled to the tabulated NO model NORA based on relaxation (NO Relaxation Approach). All the present combustion models are coupled to a phenomenological soot kinetics PSK approach. These models are implemented in the 3D solver IFP-C3D, tested and validated on a large experimental database (40 engine operating points) measured on a Diesel engine. This database has been specifically designed for model validation and includes part load and full load operating points with variations of dilution levels and injection strategies. While the standard approach exhibits a good prediction of cylinder pressure and combustion timings, prediction of CO or unburned hydrocarbons (uHC) are not satisfactory. The numerical results obtained with VVTHC and ADF-PCM show the best agreement with the experimental measurements over the whole database. The most evolved model, ADF-PCM, which accounts for the limitation of the reaction rate in high strain rates regions, allows an improved and accurate prediction of high dilution operating points.