Prediction of the combustion and emission processes in Diesel engines based on a tabulated chemistry approach

Paper #:
  • 2017-01-2200

Published:
  • 2017-10-08
Abstract:
Turbulent combustion modeling in a RANS or LES context imposes the challenge of closing the chemical reaction rate on the sub-grid level. Many turbulent combustion models exist in literature. Such turbulent models have as their two main ingredients sources from chemical reactions and turbulence-chemistry interaction. The various combustion models then differ mainly by how the chemistry is calculated (level of detail, canonical flame model) and on the other hand how turbulence is assumed to affect the reaction rate on the sub-grid level (turbulence-chemistry interaction - TCI). In this work, an advanced combustion model based on tabulated chemistry is applied for 3D CFD modeling of Diesel engine cases. The combustion model is based on the Flamelet Generated Manifold (FGM) chemistry reduction technique. The underlying chemistry tabulation process uses auto-ignition trajectories of homogeneous fuel/air mixtures, which are computed with detailed chemical reaction mechanisms. The TCI modeling is based on a presumed PDF approach. The look-up tables have up to 5 dimensions: pressure, temperature, mixture fraction, mixture fraction variance and progress variable. By applying such type of model, it is possible to account for a very large number of chemical reactions within the CFD simulation. The results of the reactions are pre-tabulated and picked up from the data bases during the CFD runtime. This data fetching process is very efficient so that the 3D calculation only requires the calculation time of usually much simpler combustion models. Within the current framework also emission models have been introduced. The overall results, which will be discussed in the paper, show very good response of the modeling approach compared to measurements in production engines.
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