An optimization-based approach to detailed chemistry tabulation: Automated progress variable definition

2013 ◽  
Vol 160 (4) ◽  
pp. 776-785 ◽  
Author(s):  
Yi-Shuai Niu ◽  
Luc Vervisch ◽  
Pham Dinh Tao
Keyword(s):  
Detailed Chemistry ◽  
Progress Variable ◽  
Variable Definition ◽  
Chemistry Tabulation

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

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 905-915
Author(s):  
Mijo Tvrdojevic ◽  
Milan Vujanovic ◽  
Peter Priesching ◽  
Ferry A. Tap ◽  
Anton Starikov ◽  
...  
Keyword(s):  
Diesel Engines ◽  
Mixture Fraction ◽  
Operating Conditions ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Fraction Mixture ◽  
Semi Empirical ◽  
Soot Model ◽  
Chemistry Tabulation

Abstract 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.

scholarly journals Comparison of Flame Propagation Statistics Based on Direct Numerical Simulation of Simple and Detailed Chemistry. Part 2: Influence of Choice of Reaction Progress Variable

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5695
Author(s):  
Felix B. Keil ◽  
Marvin Amzehnhoff ◽  
Umair Ahmed ◽  
Nilanjan Chakraborty ◽  
Markus Klein
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Flame Propagation ◽  
Flame Structure ◽  
Tangential Strain ◽  
Detailed Chemistry ◽  
Reaction Progress ◽  
Considerable Uncertainty ◽  
Progress Variable ◽  
Displacement Speed

Flame propagation statistics for turbulent, statistically planar premixed flames obtained from 3D Direct Numerical Simulations using both simple and detailed chemistry have been evaluated and compared to each other. To achieve this, a new database has been established encompassing five different conditions on the turbulent combustion regime diagram, using nearly identical numerical methods and the same initial and boundary conditions. The discussion includes interdependencies of displacement speed and its individual components as well as surface density function (i.e., magnitude of the reaction progress variable) with tangential strain rate and curvature. For the analysis of detailed chemistry Direct Numerical Simulation data, three different definitions of reaction progress variable, based on CH4,H2O and O2 mass fractions will be used. While the displacement speed statistics remain qualitatively and to a large extent quantitatively similar for simple chemistry and detailed chemistry, there are pronounced differences for its individual contributions which to a large extent depend on the definition of reaction progress variable as well as on the chosen isosurface level. It is concluded that, while detailed chemistry simulations provide more detailed information about the flame structure, the choice of the reaction progress variable definition and the choice of the resulting isosurface give rise to considerable uncertainty in the interpretation of displacement speed statistics, sometimes even showing opposing trends. Simple chemistry simulations are shown to provide (a) the global flame propagation statistics which are qualitatively similar to the corresponding results from detailed chemistry simulations, (b) remove the uncertainties with respect to the choice of reaction progress variable, and (c) are more straightforward to compare with theoretical analysis or model assumptions that are mostly based on simple chemistry assumptions.

Modeling of Turbulent Combustion of Lean Premixed Prevaporized Propane Using the CFI Combustion Model

2006 ◽  
Author(s):  
B. de Jager ◽  
J. B. W. Kok
Keyword(s):  
Gas Turbine ◽  
Source Term ◽  
Laminar Flame ◽  
Dimensional Space ◽  
Turbulent Flames ◽  
Combustion Model ◽  
Detailed Chemistry ◽  
Reaction Progress ◽  
One Dimensional ◽  
Progress Variable

In this paper combustion of propane under gas turbine conditions is investigated with a focus on the chemistry and chemical kinetics in turbulent flames. The work is aimed at efficient and accurate modeling of the chemistry of heavy hydrocarbons, ie. hydrocarbons with more than one carbon atom, as occurring in liquid fuels for gas turbine application. On the basis of one dimensional laminar flame simulations with detailed chemistry, weight factors are determined for optimal projection of species concentrations on one or several composed concentrations, using the Computational Singular Perturbation (CSP) method. This way the species concentration space of the detailed mechanism is projected on a one dimensional space spanned by the reaction progress variable for use in a turbulent simulation. In the projection process a thermochemical database is used to relate with the detailed chemistry of the laminar flame simulations. Transport equations are formulated in a RaNS code for the mean and variance of the reaction progress variable. The turbulent chemical reaction source term is calculated by presumed shape probability density function averaging of the laminar source term in the thermochemical database. The combined model is demonstrated and validated in a simulation of a turbulent premixed prevaporized swirling propane/air flame at atmospheric pressure. Experimental data are available for the temperature field, the velocity field and the unburnt hydrocarbon concentrations. The trends produced by CFI compare reasonable to the experiments.

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