Large Eddy Simulation of a Methane Diffusion Flame: The effect of the Chemical Mechanism on NOx Emissions

This article focuses on combustion instabilities (CI) driven by entropy fluctuations which is of great importance in practical devices. A simplified geometry is introduced. It keeps the essential features of an aeronautical combustion chamber (swirler, dilution holes, and outlet nozzle), while it is simplified sufficiently to ease the analysis (rectangular vane, one row of holes of the same diameter, no diffuser at the inlet of the chamber, and circular nozzle at the outlet). A large eddy simulation (LES) is carried out on this geometry and the limit cycle of a strong CI involving the convection of an entropy spot is obtained. The behavior of the instability is analyzed using phenomenological description and classical signal analysis. One shows that the system can be better described by considering two reacting zones: a rich mainly premixed flame is located downstream of the swirler and an overall lean diffusion flame is stabilized next to the dilution holes. In a second step, dynamic mode decomposition (DMD) is used to visualize, analyze, and model the complex phasing between different processes affecting the reacting zones. Using these data, a zero-dimensional (0D) modeling of the premixed flame and of the diffusion flame is proposed. These models provide an extended understanding of the combustion process in an aeronautical combustor and could be used or adapted to address mixed acoustic-entropy CI in an acoustic code.

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Large Eddy Simulation of aTurbulent Diffusion Flame: Some Aspects of Subgrid Modelling Consistency

Flow Turbulence and Combustion ◽

10.1007/s10494-017-9813-2 ◽

2017 ◽

Vol 99 (1) ◽

pp. 209-238 ◽

Cited By ~ 2

Author(s):

J. Ventosa-Molina ◽

O. Lehmkuhl ◽

C. D. Pérez-Segarra ◽

A. Oliva

Keyword(s):

Large Eddy Simulation ◽

Diffusion Flame ◽

Eddy Simulation ◽

Large Eddy

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Large-Eddy Simulation of a Swirling Diffusion Flame Using a SOM SGS Combustion Model

Numerical Heat Transfer Part B Fundamentals ◽

10.1080/10407790500459395 ◽

2006 ◽

Vol 50 (1) ◽

pp. 41-58 ◽

Cited By ~ 31

Author(s):

L. Y. Hu ◽

L. X. Zhou ◽

J. Zhang

Keyword(s):

Large Eddy Simulation ◽

Diffusion Flame ◽

Combustion Model ◽

Eddy Simulation ◽

Large Eddy

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Mixed Acoustic-Entropy Combustion Instabilities in a Model Aeronautical Combustor: Large Eddy Simulation and Reduced Order Modeling

Volume 4A: Combustion, Fuels and Emissions ◽

10.1115/gt2017-64191 ◽

2017 ◽

Author(s):

Florent Lacombe ◽

Yoann Mery

Keyword(s):

Large Eddy Simulation ◽

Diffusion Flame ◽

Combustion Process ◽

Premixed Flame ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Combustion Instabilities ◽

Eddy Simulation ◽

Mode Decomposition ◽

Large Eddy

This article focuses on Combustion Instabilities (CI) driven by entropy fluctuations which is of great importance in practical devices. A simplified geometry is introduced. It keeps the essential features of an aeronautical combustion chamber (swirler, dilution holes, outlet nozzle) while it is simplified sufficiently to ease the analysis (rectangular vane, one row of holes of the same diameter, no diffuser at the inlet of the chamber, circular nozzle at the outlet). A Large Eddy Simulation (LES) is carried out on this geometry and the limit cycle of a strong CI involving the convection of an entropy spot is obtained. The behavior of the instability is analyzed using phenomenological description and classical signal analysis. One shows that the system can be better described by considering two reacting zones: a rich mainly premixed flame is located downstream of the swirler and an overall lean diffusion flame is stabilized next to the dilution holes. In a second step, Dynamic Mode Decomposition (DMD) is used to visualize, analyze and model the complex phasing between the different processes affecting the reacting zones. Using these data, a 0D modeling of the premixed flame and of the diffusion flame is proposed. These models provides an extended understanding of the combustion process in an aeronautical combustor and could be used or adapted to address mixed acoustic-entropy CI in an acoustic code.

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Large Eddy Simulation of Autoignition in a Turbulent Hydrogen Jet Flame Using a Progress Variable Approach

Journal of Combustion ◽

10.1155/2012/780370 ◽

2012 ◽

Vol 2012 ◽

pp. 1-11 ◽

Cited By ~ 2

Author(s):

Rohit Kulkarni ◽

Wolfgang Polifke

Keyword(s):

Large Eddy Simulation ◽

Mixture Fraction ◽

Chemical Mechanism ◽

Model Parameters ◽

Jet Flame ◽

Progress Variable ◽

Eddy Simulation ◽

Variable Approach ◽

Tabulated Chemistry ◽

Large Eddy

The potential of a progress variable formulation for predicting autoignition and subsequent kernel development in a nonpremixed jet flame is explored in the LES (Large Eddy Simulation) context. The chemistry is tabulated as a function of mixture fraction and a composite progress variable, which is defined as a combination of an intermediate and a product species. Transport equations are solved for mixture fraction and progress variable. The filtered mean source term for the progress variable is closed using a probability density function of presumed shape for the mixture fraction. Subgrid fluctuations of the progress variable conditioned on the mixture fraction are neglected. A diluted hydrogen jet issuing into a turbulent coflow of preheated air is chosen as a test case. The model predicts ignition lengths and subsequent kernel growth in good agreement with experiment without any adjustment of model parameters. The autoignition length predicted by the model depends noticeably on the chemical mechanism which the tabulated chemistry is based on. Compared to models using detailed chemistry, significant reduction in computational costs can be realized with the progress variable formulation.

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Large-Eddy Simulation of a Reacting Jet in Cross Flow With NOx Prediction

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4034447 ◽

2016 ◽

Vol 139 (3) ◽

Cited By ~ 6

Author(s):

Johannes Weinzierl ◽

Michael Kolb ◽

Denise Ahrens ◽

Christoph Hirsch ◽

Thomas Sattelmayer

Keyword(s):

Large Eddy Simulation ◽

Cross Flow ◽

Nox Emissions ◽

Staged Combustion ◽

Nox Formation ◽

Full Load ◽

Eddy Simulation ◽

Jet In Cross Flow ◽

Large Eddy ◽

Combustion Systems

The reduction of full and part load emissions and the increase of the turndown ratio are important goals for gas turbine combustor development. Combustion techniques, which generate lower NOx emissions than unstaged premixed combustion in the full load range, and which have the potential of reducing minimum load while complying with emission legislation, are of high technical interest. Therefore, axial-staged combustion systems have been designed, either with or without expansion in a turbine stage between both stages. In its simpler form without intermediate expansion stage, a flow of hot combustion products is generated in the first stage of the premixed combustor, which interacts with the jets of premixed gas injected into the second stage. The level of NOx formation during combustion of the premixed jets in the hot cross flow determines the advantage of axially staged combustion regarding full load NOx emission reduction. Employing large-eddy simulation in openfoam, a tool has been developed, which allows to investigate staged combustion systems including not only temperature distribution but also NOx emissions under engine conditions. To be able to compute NOx formation correctly, the combustion process has to be captured with sufficient level of accuracy. This is achieved by the partially stirred reactor model. It is combined with a newly developed NOx model, which is a combination of a tabulation technique for the NOx source term based on mixture fraction and progress variable and a partial equilibrium approach. The NOx model is successfully validated with generic burner stabilized flame data and with measurements from a large-scale reacting jet in cross flow experiment. The new NOx model is finally used to compute a reacting jet in cross flow under engine conditions to investigate the NOx formation of staged combustion in detail. The comparison between the atmospheric and the pressurized configuration gives valuable insight in the NOx formation process. It can be shown that the NOx formation within a reacting jet in cross flow configuration is reduced and not only diluted.

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