Co Emission Modeling in a Heavy Duty Annular Combustor Operating with Natural Gas

2021 ◽  
Author(s):  
Roberto Meloni ◽  
Stefano Gori ◽  
Antonio Andreini ◽  
Pier Carlo Nassini
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Production Region ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Extinction Limit ◽  
Flamelet Generated Manifold ◽  
Annular Combustor ◽  
Definition Of ◽  
Co Emission

Abstract The present paper summarizes the development of a Large-Eddy Simulation (LES) based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the Extended Turbulent Flame Speed Closure (ETFSC) of the standard Flamelet Generated Manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to de-couple the in-flame CO production region from the post-flame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

CO Emission Modeling in a Heavy Duty Annular Combustor Operating With Natural Gas

2021 ◽  
Author(s):  
R. Meloni ◽  
S. Gori ◽  
A. Andreini ◽  
P. C. Nassini
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Production Region ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Extinction Limit ◽  
Flamelet Generated Manifold ◽  
Annular Combustor ◽  
Definition Of ◽  
Co Emission

Abstract The present paper summarizes the development of a Large-Eddy Simulation (LES) based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the Extended Turbulent Flame Speed Closure (ETFSC) of the standard Flamelet Generated Manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to de-couple the in-flame CO production region from the post-flame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

Effect of Fuel Stage Proportion on Flame Position in an Internally-Staged Combustor

2020 ◽  
Author(s):  
Tiezheng Zhao ◽  
Xiao Liu ◽  
Hongtao Zheng ◽  
Zhihao Zhang ◽  
Jialong Yang ◽  
...  
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Prediction Method ◽  
Combustion Characteristics ◽  
Turbulent Flame Speed ◽  
Pilot Fuel ◽  
High Temperature Area ◽  
Incomplete Reaction ◽  
Co Emission ◽  
Flame Position

Abstract To study the effect of fuel stage proportion on flame position and combustion characteristics of the internally-staged combustor, a detailed numerical investigation is performed in the present paper. The prediction method of flame position is established by analyzing the variations of the distribution of intermediate components and the turbulent flame speed. Meanwhile, the flame position is simulated to verify the accuracy of the prediction method. It is demonstrated that the flame position prediction model established in this paper can accurately predict the flame position under different fuel stage proportions. On this basis, special attention is paid to analyze the variation of velocity field, temperature field, distribution of intermediate components and emissions under different fuel stage proportions. As the proportion of pilot fuel stage increases slightly, the mass fraction of fuel at the combustor dome increases. In addition, the combustion characteristics change significantly with the increase in the proportion of pilot stage fuels. The flame moves downstream and the high temperature area increases as the proportion of pilot fuel increases. In particular, when the proportion of pilot stage reaches 3%, the highest flame temperature is generated due to the most concentrated reaction area, resulting in the largest emission of NOx. At the same time, due to the most complete reaction, the minimum CO emission is produced. When the proportion of pilot fuel stage reaches 1%, the NOx emission is the lowest, and the highest CO emission is generated due to the incomplete reaction.

A Novel Les-Based Process for NOx Emission Assessment in a Premixed Swirl Stabilized Combustion System

2021 ◽  
Author(s):  
Roberto Meloni ◽  
Antonio Andreini ◽  
Pier Carlo Nassini
Keyword(s):  
Turbulent Flame ◽  
Nox Emission ◽  
Percentage Error ◽  
Nox Formation ◽  
Fuel Gas ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Annular Combustor ◽  
Swirl Stabilized Combustion ◽  
The Impact

Abstract This paper presents a new CFD approach for the assessment of the NOx emission. The methodology is validated against the experimental data of a heavy-duty gas turbine annular combustor. Since the NOx formation involves time scales that are different from the fuel oxidation time, the present work defines the transport equation source terms for NOx on the basis of a dedicate NOx-Damköhler number. The latter parameter allows to properly distinguish the "in-flame" contribution from the "post-flame" one. While the former is a mix of several mechanisms (prompt, N2O-pathway, thermal), the latter is dominated by the thermal contribution. The validation phase is developed in a Large-Eddy Simulation (LES) framework where the Extended Turbulent Flame Speed model is implemented to consider the influence of both heat loss and strain rate on the progress variable source term. The accuracy of the model against the most important operability parameters of the combustor is verified. A strong focus on the fuel composition effect onto NOx is presented as well. For any simulated operating condition, the present methodology is able to provide a limited percentage error if compared with the data, considering also different combustion regimes. Leveraging this alignment, the last portion of the paper is dedicated to a detailed post processing highlighting the role of some key factors on to NOx formation. In particular, the focus will be dedicated to the impact of the fuel gas composition and the pilot split.

A Novel LES-Based Process for NOx Emission Assessment in a Premixed Swirl Stabilized Combustion System

2021 ◽  
Author(s):  
R. Meloni ◽  
A. Andreini ◽  
P. C. Nassini
Keyword(s):  
Turbulent Flame ◽  
Nox Emission ◽  
Percentage Error ◽  
Nox Formation ◽  
Fuel Gas ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Annular Combustor ◽  
Swirl Stabilized Combustion ◽  
The Impact

Abstract This paper presents a new CFD approach for the assessment of the NOx emission. The methodology is validated against the experimental data of a heavy-duty gas turbine annular combustor. Since the NOx formation involves time scales that are different from the fuel oxidation time, the present work defines the transport equation source terms for NOx on the basis of a dedicate NOx-Damköhler number. The latter parameter allows to properly distinguish the “in-flame” contribution from the “post-flame” one. While the former is a mix of several mechanisms (prompt, N2O-pathway thermal), the latter is dominated by the thermal contribution. The validation phase is developed in a Large-Eddy Simulation (LES) framework where the Extended Turbulent Flame Speed model is implemented to consider the influence of both heat loss and strain rate on the progress variable source term. The accuracy of the model against the most important operability parameters of the combustor is verified. A strong focus on the fuel composition effect onto NOx is presented as well. For any simulated operating condition, the present methodology is able to provide a limited percentage error if compared with the data, considering also different combustion regimes. Leveraging this alignment, the last portion of the paper is dedicated to a detailed post processing highlighting the role of some key factors on to NOx formation. In particular, the focus will be dedicated to the impact of the fuel gas composition and the pilot split.

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.

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.

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 CO With Flamelet-Generated Manifolds: Part 2 — Application

2012 ◽  
Author(s):  
Graham Goldin ◽  
Zhuyin Ren ◽  
Hendrik Forkel ◽  
Liuyan Lu ◽  
Venkat Tangirala ◽  
...  
Keyword(s):  
Reaction Rate ◽  
Source Term ◽  
Turbulent Flame ◽  
Leading Edge ◽  
Flame Speed ◽  
Reaction Progress ◽  
Turbulent Flame Speed ◽  
Flamelet Generated Manifold ◽  
The Mean ◽  
Flame Brush

Conventional Flamelet Generated Manifold (FGM) closure of the mean progress variable reaction rate assumes PDF shapes to account for turbulent fluctuations. The FGM parameters are commonly assumed to be statistically independent, and the marginal PDFs invariably require second moments, which are difficult to model accurately and have limited coefficients that can be adjusted to calibrate the simulation. A new model is presented which locates the flame brush with a turbulent flame speed model, and applies the FGM kinetic rate to model kinetically limited processes, such as CO quenching, behind the flame-front. The model is applied to 3D RANS simulations of an equivalence ratio sweep in the GE Entitlement Rig perfectly premixed combustor experiment. Calculating the mean FGM reaction progress source term with standard assumed shape PDFs leads to a narrow flame brush and equilibrium CO outlet emissions. By limiting the mean FGM reaction progress source term by the turbulent flame speed model, the flame brush is broadened and super-equilibrium CO is predicted at the outlet. Good agreement with measurement is obtained with default model coefficients. Since the majority of the mean reaction progress source term is limited by the turbulent flame speed reaction rate, it is demonstrated that the model is relatively insensitive to assumed shape PDFs for the FGM rate, as well as the parameter used to determine the turbulent flame leading edge.

Reynolds-Averaged Navier–Stokes and Large-Eddy Simulation Investigation of Lean Premixed Gas Turbine Combustor

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Sunil Patil ◽  
Federico Montanari
Keyword(s):  
Heat Loss ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Navier Stokes ◽  
M Cells ◽  
Turbulent Flame Speed ◽  
Flamelet Generated Manifold ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulations (LES) of a Siemens scaled combustor are compared against comprehensive experimental data. The steady RANS simulation modeled one quarter of the geometry with 8 M polyhedral cells using the shear stress transport (SST) k-ω model. Unsteady LES were performed on the quarter geometry (90 deg, 8 M cells) as well as the full geometry (360 deg, 32 M cells) using the wall-adapting local eddy-viscosity (WALE) subgrid 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 thermochemistry 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 overpredict the turbulent mixing in the inner recirculation zone, causing flatter profiles than measurements. This overmixing is exacerbated in the 90 deg 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.

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