Implementation of the Semi Empirical Kinetic Soot Model Within Chemistry Tabulation Framework for Efficient Emissions Predictions in Diesel Engines

Soot prediction for diesel engines is a very important aspect of internal combustion engine emissions research, especially nowadays with very strict emission norms. Computational Fluid Dynamics (CFD) is often used in this research and optimisation of CFD models in terms of a trade-off between accuracy and computational efficiency is essential. This is especially true in the industrial environment where good predictivity is necessary for engine optimisation, but computational power is limited. To investigate soot emissions for Diesel engines, in this work CFD is coupled with chemistry tabulation framework and semi-empirical soot model. The Flamelet Generated Manifold (FGM) combustion model precomputes chemistry using detailed calculations of the 0D homogeneous reactor and then stores the species mass fractions in the table, based on six look-up variables: pressure, temperature, mixture fraction, mixture fraction variance, progress variable and progress variable variance. Data is then retrieved during online CFD simulation, enabling fast execution times while keeping the accuracy of the direct chemistry calculation. In this work, the theory behind the model is discussed as well as implementation in commercial CFD code. Also, soot modelling in the framework of tabulated chemistry is investigated: mathematical model and implementation of the kinetic soot model on the tabulation side is described, and 0D simulation results are used for verification. Then, the model is validated using real-life engine geometry under different operating conditions, where better agreement with experimental measurements is achieved, compared to the standard implementation of the kinetic soot model on the CFD side.

Multi-Dimensional Flamelet Manifolds for Laminar Partially Premixed Flame

The aim of this paper is to evaluate the performance of thermo-chemistry tabulation approaches for numerical simulation of laminar partially premixed flame by comparing with the results of detail chemistry. Two thermo-chemistry tabulation approaches are considered: the multidimensional flamelet manifolds (MFM) method and Flame Prolongation of Intrinsic low-dimensional manifold (FPI) method. The fuel streams with different equivalence ratios (ΦF=1.8,ΦF=2.464) are analyzed. In both of the equivalence ratios the results obtained from MFM method are in closer agreement with the direct calculation than FPI method. It is concluded that multi-dimensional flamelet manifolds can capture more precisely partially premixed characteristic of the multi-regime flame structure, comparing to single-dimensional flamelet model FPI.