Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model

2000 ◽  
Vol 124 (1) ◽  
pp. 58-65 ◽  
Author(s):  
W. Polifke ◽  
P. Flohr ◽  
M. Brandt
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Combustion Stability ◽  
Model Parameters ◽  
Turbulent Flame Speed ◽  
Functional Relationships

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the turbulent flame speed closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e., the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.

Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model

2000 ◽  
Author(s):  
Wolfgang Polifke ◽  
Peter Flohr ◽  
Martin Brandt
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Combustion Stability ◽  
Model Parameters ◽  
Turbulent Flame Speed ◽  
Functional Relationships

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the Turbulent Flame speed Closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e. the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.

Investigation of Flamelet Generated Manifold Reaction Source Term Closure Models Applied to an Industrial Gas Turbine

2019 ◽  
Author(s):  
George Mallouppas ◽  
Graham Goldin ◽  
Yongzhe Zhang ◽  
Piyush Thakre ◽  
Jim Rogerson
Keyword(s):  
Gas Turbine ◽  
Source Term ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Turbulent Flame Speed ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Reactor Types ◽  
Industrial Gas Turbine

Abstract Three Flamelet Generated Manifold reaction source term closure options and two different reactor types are examined with Large Eddy Simulation of an industrial gas turbine combustor operating at 3 bar. This work presents the results for the SGT-100 Dry Low Emission (DLE) gas turbine provided by Siemens Industrial Turbomachinery Ltd. The related experimental study was performed at the German Aerospace Centre, DLR, Stuttgart, Germany. The FGM model approximates the thermo-chemistry in a turbulent flame as that in a simple 0D constant pressure ignition reactors and 1D strained opposed-flow premixed reactors, parametrized by mixture fraction, progress variable, enthalpy and pressure. The first objective of this work is to compare the flame shape and position predicted by these two FGM reactor types. The Kinetic Rate (KR) model, studied in this work, uses the chemical rate from the FGM with assumed shapes, which are a Beta function for mixture fraction and delta functions for reaction progress variable and enthalpy. Another model investigated is the Turbulent Flame-Speed Closure (TFC) model with Zimont turbulent flame speed, which propagates premixed flame fronts at specified turbulent flame speeds. The Thickened Flame Model (TFM), which artificially thickens the flame to sufficiently resolve the internal flame structure on the computational grid, is also explored. Therefore, a second objective of this paper is to compare KR, TFC and TFM with the available experimental data.

Flashback and Turbulent Flame Speed Measurements in Hydrogen/Methane Flames Stabilized by a Low-Swirl Injector at Elevated Pressures and Temperatures

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
David Beerer ◽  
Vincent McDonell ◽  
Peter Therkelsen ◽  
Robert K. Cheng
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Inlet Temperature ◽  
Local Displacement ◽  
Turbulent Flame Speed ◽  
Elevated Pressures ◽  
Swirl Injector ◽  
Inlet Conditions ◽  
Displacement Speed

This paper reports flashback limits and turbulent flame local displacement speed measurements in flames stabilized by a low swirl injector operated at elevated pressures and inlet temperatures with hydrogen and methane blended fuels. The goal of this study is to understand the physics that relate turbulent flame speed to flashback events at conditions relevant to gas turbine engines. Testing was conducted in an optically accessible single nozzle combustor rig at pressures ranging from 1 to 8 atm, inlet temperatures from 290 to 600 K, and inlet bulk velocities between 20 and 60 m/s for natural gas and a 90%/10% (by volume) hydrogen/methane blend. The propensity of flashback is dependent upon the proximity of the lifted flame to the nozzle that is itself dependent upon pressure, inlet temperature, and bulk velocity. Flashback occurs when the leading edge of the flame in the core of the flow ingresses within the nozzle, even in cases when the flame is attached to the burner rim. In general the adiabatic flame temperature at flashback is proportional to the bulk velocity and inlet temperature and inversely proportional to the pressure. The unburned reactant velocity field approaching the flame was measured using a laser Doppler velocimeter with water seeding. Turbulent displacement flame speeds were found to be linearly proportional to the root mean square of the velocity fluctuations about the mean velocity. For identical inlet conditions, high-hydrogen flames had a turbulent flame local displacement speed roughly twice that of natural gas flames. Pressure, inlet temperature, and flame temperature had surprisingly little effect on the local displacement turbulent flame speed. However, the flow field is affected by changes in inlet conditions and is the link between turbulent flame speed, flame position, and flashback propensity.

Fuel Variation Effects in Propagation and Stabilization of Turbulent Counter-Flow Premixed Flames

2018 ◽  
Author(s):  
Ehsan Abbasi-Atibeh ◽  
Sandeep Jella ◽  
Jeffrey M. Bergthorson
Keyword(s):  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Mass Diffusion ◽  
Flame Stabilization ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Flame Surface ◽  
Differential Diffusion ◽  
Turbulent Flame Speed

Sensitivity to stretch and differential diffusion of chemical species are known to influence premixed flame propagation, even in the turbulent environment where mass diffusion can be greatly enhanced. In this context, it is convenient to characterize flames by their Lewis number (Le), a ratio of thermal-to-mass diffusion. The work reported in this paper describes a study of flame stabilization characteristics when the Le is varied. The test data is comprised of Le ≪ 1 (Hydrogen), Le ≈ 1 (Methane), and Le > 1 (Propane) flames stabilized at various turbulence levels. The experiments were carried out in a Hot exhaust Opposed-flow Turbulent Flame Rig (HOTFR), which consists of two axially-opposed, symmetric turbulent round jets. The stagnation plane between the two jets allows the aerodynamic stabilization of a flame, and clearly identifies fuel influences on turbulent flames. Furthermore, high-speed Particle Image Velocimetry (PIV), using oil droplet seeding, allowed simultaneous recordings of velocity (mean and rms) and flame surface position. These experiments, along with data processing tools developed through this study, illustrated that in the mixtures with Le ≪ 1, turbulent flame speed increases considerably compared to the laminar flame speed due to differential diffusion effects, where higher burning rates compensate for the steepening average velocity gradient, and keeps these flames almost stationary as bulk flow velocity increases. These experiments are suitable for validating the ability of turbulent combustion models to predict lifted, aerodynamically-stabilized flames. In the final part of this paper, we model the three fuels at two turbulence intensities using the FGM model in a RANS context. Computations reveal that the qualitative flame stabilization trends reproduce the effects of turbulence intensity, however, more accurate predictions are required to capture the influences of fuel variations and differential diffusion.

scholarly journals Evaluation of Reduced Kinetics in Simulation of Gasified Biomass Gas Combustion

2013 ◽  
Author(s):  
Xiaoxiang Zhang ◽  
Nur Farizan Munjat ◽  
Jeevan Jayasuriya ◽  
Reza Fakhrai ◽  
Torsten Fransson
Keyword(s):  
Gas Turbine ◽  
Chemical Kinetics ◽  
Cfd Simulation ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Turbulent Flame Speed ◽  
Operation Conditions ◽  
Simulation Results ◽  
Gas Turbine Combustion

It is essentially important to use appropriate chemical kinetic models in the simulation process of gas turbine combustion. To integrate the detailed kinetics into complex combustion simulations has proven to be a computationally expensive task with tens to thousands of elementary reaction steps. It has been suggested that an appropriate simplified kinetics which are computationally efficient could be used instead. Therefore reduced kinetics are often used in CFD simulation of gas turbine combustion. At the same time, simplified kinetics for specific fuels and operation conditions need to be carefully selected to fulfill the accuracy requirements. The applicability of several simplified kinetics for premixed Gasified Biomass Gas (GBG) and air combustion are evaluated in this paper. The current work is motivated by the growing demand of gasified biomass gas (GBG) fueled combustion. Even though simplified kinetic schemes developed for hydrocarbon combustions are published by various researchers, there is little research has been found in literature to evaluate the ability of the simplified chemical kinetics for the GBG combustion. The numerical Simulation tool “CANTERA” is used in the current study for the comparison of both detailed and simplified chemical kinetics. A simulated gas mixture of CO/H2/CH4/CO2/N2 is used for the current evaluation, since the fluctuation of GBG components may have an unpredictable influence on the simulation results. The laminar flame speed has an important influence with flame stability, extinction limits and turbulent flame speed, here it is chosen as an indicator for validation. The simulation results are compared with the experimental data from the previous study [1] which is done by our colleagues. Water vapour which has shown a dilution effect in the experimental study are also put into concern for further validation. As the results indicate, the reduced kinetics which are developed for hydrocarbon or hydrogen combustion need to be highly optimized before using them for GBG combustion. Further optimization of the reduced kinetics is done for GBG and moderate results are achieved using the optimized kinetics compared with the detailed combustion kinetics.

A Comparison of RANS and LES of an Industrial Lean Premixed Burner

2014 ◽  
Author(s):  
Graham Goldin ◽  
Federico Montanari ◽  
Sunil Patil
Keyword(s):  
Heat Loss ◽  
Radiation Effects ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Source Model ◽  
Flame Speed ◽  
Turbulent Flame Speed ◽  
Flamelet Generated Manifold ◽  
Rans Simulations ◽  
Polyhedral Cells

LES and RANS simulations of a Siemens scaled combustor are compared against comprehensive experimental data. The steady RANS simulation modeled one quarter of the geometry with 8M polyhedral cells using the SST-k-ω model. Unsteady LES simulations were performed on the quarter geometry (90°, 8M cells) as well as the full geometry (360°, 32M cells) using the WALE sub-grid model and dynamic evaluation of model coefficients. Aside from the turbulence model, all other models are identical for the RANS and LES. Combustion was modeled with the Flamelet Generated Manifold (FGM) model, which represents the thermo-chemistry by mixture fraction and reaction progress. RANS simulations are performed using Zimont and Peters turbulent flame speed (TFS) expressions with default model constants, as well as the kinetic rate from the FGM. The flame speed stalls near the wall with the TFS models, predicting a flame brush that extends to the combustor outlet, which is inconsistent with measurements. The FGM kinetic source model shows improved flame position predictions. The LES predictions of mean and rms axial velocity, mixture fraction and temperature do not show improvement over the RANS. All three simulations over-predict the turbulent mixing in the inner recirculation zone, causing flatter profiles than measurements. This over-mixing is exacerbated in the 900 case. The experiments show evidence of heat loss and the adiabatic simulations presented here might be improved by including wall heat-loss and radiation effects.

Three-dimensional computational fluid dynamics simulation of hydrogen engines using a turbulent flame speed closure combustion model

2012 ◽  
Vol 13 (5) ◽  
pp. 464-481 ◽  
Author(s):  
Udo Gerke ◽  
Konstantinos Boulouchos
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Three Dimensional ◽  
Flame Speed ◽  
Combustion Model ◽  
Laminar Flame Speed ◽  
Release Rates ◽  
Turbulent Flame Speed

The mixture formation and combustion process of a hydrogen direct-injection internal combustion engine is computed using a modified version of a commercial three-dimensional computational fluid dynamics code. The aim of the work is the evaluation of hydrogen laminar flame speed correlations and turbulent flame speed closures with respect to combustion of premixed and stratified mixtures at various levels of air-to-fuel equivalence ratio. Heat-release rates derived from in-cylinder pressure traces are used for the validation of the combustion simulations. A turbulent combustion model with closures for a turbulent flame speed is investigated. The value of the computed heat-release rates mainly depends on the quality of laminar burning velocities and standard of turbulence quantities provided to the combustion model. Combustion simulations performed with experimentally derived laminar flame speed data give better results than those using laminar flame speeds obtained from a kinetic scheme. However, experimental data of hydrogen laminar flame speeds found in the literature are limited regarding the range of pressures, temperatures and air-to-fuel equivalence ratios, and do not comply with the demand of high-pressure engine-relevant conditions.

scholarly journals Investigation of Hydrogen Content and Dilution Effect on Syngas/Air Premixed Turbulent Flame Using OH Planar Laser-Induced Fluorescence

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1894
Author(s):  
Li Yang ◽  
Wubin Weng ◽  
Yanqun Zhu ◽  
Yong He ◽  
Zhihua Wang ◽  
...  
Keyword(s):  
Hydrogen Content ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Laser Induced Fluorescence ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
High Hydrogen ◽  
Turbulent Flame Speed ◽  
Planar Laser Induced Fluorescence ◽  
Planar Laser

Syngas produced by gasification, which contains a high hydrogen content, has significant potential. The variation in the hydrogen content and dilution combustion are effective means to improve the steady combustion of syngas and reduce NOx emissions. OH planar laser-induced fluorescence technology (OH-PLIF) was applied in the present investigation of the turbulence of a premixed flame of syngas with varied compositions of H2/CO. The flame front structure and turbulent flame velocities of syngas with varied compositions and turbulent intensities were analyzed and calculated. Results showed that the trend in the turbulent flame speed with different hydrogen proportions and dilutions was similar to that of the laminar flame speed of the corresponding syngas. A higher hydrogen proportion induced a higher turbulent flame speed, higher OH concentration, and a smaller flame. Dilution had the opposite effect. Increasing the Reynolds number also increased the turbulent flame speed and OH concentration. In addition, the effect of the turbulence on the combustion of syngas was independent of the composition of syngas after the analysis of the ratio between the turbulent flame speed and the corresponding laminar flame speed, for the turbulent flames under low turbulent intensity. These research results provide a theoretical basis for the practical application of syngas with a complex composition in gas turbine power generation.

An Optimized Correlation for Turbulent Flame Speed for C1-C3 Fuels at Engines-Relevant Conditions

2020 ◽  
Author(s):  
Eoin M. Burke ◽  
Sajjad Yousefian ◽  
Felix Güthe ◽  
Rory F. D. Monaghan
Keyword(s):  
Entire Range ◽  
State Of The Art ◽  
Velocity Ratio ◽  
Turbulent Flame ◽  
Search Method ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Percentage Error ◽  
Turbulent Flame Speed ◽  
Wide Range

Abstract The aim of this work is to examine the state-of-the-art turbulent flame speed (ST) correlations and optimize their adjustable parameters to best match a wide range experimental turbulent premixed combustion results. Four correlations based on previous works by Zimont, Kobayashi, Ronney and Muppala have been selected for the present study. Using a Matlab-based Nelder-Mead simplex direct search method, each correlation’s adjustable parameters are optimized such that their mean absolute percentage error (MAPE) is minimized. In addition to the literature correlations, a new empirical correlation is developed using the same search method to define constants and powers in the expression. Two sets of optimized parameters are proposed to account for atmospheric and elevated (0.2–3.0 MPa) pressure flames. Each correlation is tested further, examining their ability to match ST trends for varying equivalence ratio (φ) and turbulent velocity ratio (u′/SL). It was found that a minimum of two correlations and two sets of adjustable parameters are required to accurately account for the entire range of data, thus showing that there is currently no turbulent flame speed correlation that is applicable across all engine-relevant conditions.

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