scholarly journals Comparison of Combustion Models for Lifted Hydrogen Flames within RANS Framework

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 152
Author(s):  
Ali Cemal Benim ◽  
Björn Pfeiffelmann
Keyword(s):  
Reaction Mechanism ◽  
Turbulent Combustion ◽  
Reaction Mechanisms ◽  
Numerical Study ◽  
Combustion Reaction ◽  
Combustion Model ◽  
Prediction Quality ◽  
Combustion Models ◽  
Wide Range ◽  
Lift Off

Within the framework of a Reynolds averaged numerical simulation (RANS) methodology for modeling turbulence, a comparative numerical study of turbulent lifted H2/N2 flames is presented. Three different turbulent combustion models, namely, the eddy dissipation model (EDM), the eddy dissipation concept (EDC), and the composition probability density function (PDF) transport model, are considered in the analysis. A wide range of global and detailed combustion reaction mechanisms are investigated. As turbulence model, the Standard k-ε model is used, which delivered a comparatively good accuracy within an initial validation study, performed for a non-reacting H2/N2 jet. The predictions for the lifted H2/N2 flame are compared with the published measurements of other authors, and the relative performance of the turbulent combustion models and combustion reaction mechanisms are assessed. The flame lift-off height is taken as the measure of prediction quality. The results show that the latter depends remarkably on the reaction mechanism and the turbulent combustion model applied. It is observed that a substantially better prediction quality for the whole range of experimentally observed lift-off heights is provided by the PDF model, when applied in combination with a detailed reaction mechanism dedicated for hydrogen combustion.

scholarly journals Validation of Combustion Models for Lifted Hydrogen Flame

2019 ◽  
Vol 128 ◽  
pp. 01014
Author(s):  
Ali Cemal Benim ◽  
Björn Pfeiffelmann
Keyword(s):  
Turbulent Combustion ◽  
Reaction Mechanisms ◽  
Transport Model ◽  
Combustion Model ◽  
Computational Investigation ◽  
Combustion Models ◽  
Hydrogen Flame ◽  
Dissipation Model ◽  
Global Reaction ◽  
Pdf Model

Within a Reynolds Averaged Numerical Simulation (RANS) approach for turbulence modelling, a computational investigation of a turbulent lifted H2/N2 flame is presented. Various turbulent combustion models are considered including the Eddy Dissipation Model (EDM), the Eddy Dissipation Concept (EDC), and the composition Probability Density Function transport model (PDF) in combination with different detailed and global reaction mechanisms. Turbulence is modelled using the Standard k-ɛ model, which has proven to offer a good accuracy, based on a preceding validation study for an isothermal H2/N2 jet. Results are compared with the published measurements for a lifted H2/N2 flame, and the relative performance ofthe turbulent combustion models are assessed. It is observed that the prediction quality can vary largely depending on the reaction mechanism and the turbulent combustion model. The best and quite satisfactory agreement with experiments is provided by two detailed reaction mechanisms applied with a PDF model.

NOx Emissions Reduction in an Innovative Industrial Gas Turbine Combustor (GE10 Machine): A Numerical Study of the Benefits of a New Pilot-System on Flame Structure and Emissions

2005 ◽  
Author(s):  
Antonio Andreini ◽  
Bruno Facchini ◽  
Luca Mangani ◽  
Antonio Asti ◽  
Gianni Ceccherini ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Numerical Study ◽  
Flame Structure ◽  
Combustion Model ◽  
Emissions Reduction ◽  
Minimal Amount ◽  
Nox Emissions ◽  
Ambient Temperatures ◽  
Wide Range

One of the driving requirements in gas turbine design is emissions reduction. In the mature markets (especially the North America), permits to install new gas turbines are granted provided emissions meet more and more restrictive requirements, in a wide range of ambient temperatures and loads. To meet such requirements, design techniques have to take advantage also of the most recent CFD tools. As a successful example of this, this paper reports the results of a reactive 3D numerical study of a single-can combustor for the GE10 machine, recently updated by GE-Energy. This work aims to evaluate the benefits on the flame shape and on NOx emissions of a new pilot-system located on the upper part of the liner. The former GE10 combustor is equipped with fuel-injecting-holes realizing purely diffusive pilot-flames. To reduce NOx emissions from the current 25 ppmvd@15%O2 to less than 15 ppmvd@15%O2 (in the ambient temperature range from −28.9°C to +37.8°C and in the load range from 50% and 100%), the new version of the combustor is equipped with 4 swirler-burners realizing lean-premixed pilot flames; these flames in turn are stabilized by a minimal amount of lean-diffusive sub-pilot-fuel. The overall goal of this new configuration is the reduction of the fraction of fuel burnt in diffusive flames, lowering peak temperatures and therefore NOx emissions. To analyse the new flame structure and to check the emissions reduction, a reactive RANS study was performed using STAR-CD™ package. A user-defined combustion model was used, while to estimate NOx emissions a specific scheme was also developed. Three different ambient temperatures (ISO, −28.9°C and 37.8°C) were simulated. Results were then compared with experimental measurements (taken both from the engine and from the rig), resulting in reasonable agreement. Finally, an additional simulation with an advanced combustion model, based on the laminar flamelet approach, was performed. The model is based on the G-Equation scheme but was modified to study partially premixed flames. A geometric procedure to solve G-Equation was implemented as add-on in STAR-CD™.

Numerical Simulation of Swirl-Stabilized Premixed Flames With a Turbulent Combustion Model Based on a Systematically Reduced Six-Step Reaction Mechanism

2000 ◽  
Vol 123 (4) ◽  
pp. 832-838 ◽  
Author(s):  
D. E. Bohn ◽  
J. Lepers
Keyword(s):  
Reaction Mechanism ◽  
Turbulent Combustion ◽  
Atmospheric Pressure ◽  
Elevated Pressure ◽  
Combustion Model ◽  
Direct Computation ◽  
Nox Formation ◽  
Gas Combustion ◽  
Fuel Gas ◽  
No Formation

This paper presents the application of a detailed combustion model for turbulent premixed combustion to a swirl-stabilized premix burner. Computations are carried out for atmospheric pressure and elevated pressure of 9 atm. Results of computations for atmospheric pressure are compared to experimental data. The combustion model is of the joint-pdf type. The model is based on the characteristics of turbulent combustion under conditions typical for gas turbine burners. It incorporates a systematically reduced six-step reaction mechanism yielding direct computation of radical concentrations via transport equations or steady-state assumptions. The model is able to simulate combustion of fuel gases containing methane, carbon monoxide, hydrogen, carbon dioxide, and water. It is therefore applicable to both methane and low-BTU fuel gas combustion. Based on computed radical concentrations, a post-processor for NOx formation is applied. This post-processor considers thermal formation of nitrogen oxides and NO formation via the nitrous oxide path.

scholarly journals A Data-Driven Methodology for the Simulation of Turbulent Flame Speed across Engine-Relevant Combustion Regimes

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4210
Author(s):  
Alessandro d’Adamo ◽  
Clara Iacovano ◽  
Stefano Fontanesi
Keyword(s):  
Turbulent Combustion ◽  
Internal Combustion Engines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Data Driven ◽  
Combustion Model ◽  
Virtual Design ◽  
Turbulent Flame Speed ◽  
Combustion Models ◽  
Combustion Regimes

Turbulent combustion modelling in internal combustion engines (ICEs) is a challenging task. It is commonly synthetized by incorporating the interaction between chemical reactions and turbulent eddies into a unique term, namely turbulent flame speed sT. The task is very complex considering the variety of turbulent and chemical scales resulting from engine load/speed variations. In this scenario, advanced turbulent combustion models are asked to predict accurate burn rates under a wide range of turbulence–flame interaction regimes. The framework is further complicated by the difficulty in unambiguously evaluating in-cylinder turbulence and by the poor coherence of turbulent flame speed (sT) measurements in the literature. Finally, the simulated sT from combustion models is found to be rarely assessed in a rigorous manner. A methodology is presented to objectively measure the simulated sT by a generic combustion model over a range of engine-relevant combustion regimes, from Da = 0.5 to Da = 75 (i.e., from the thin reaction regime to wrinkled flamelets). A test case is proposed to assess steady-state burn rates under specified turbulence in a RANS modelling framework. The methodology is applied to a widely adopted combustion model (ECFM-3Z) and the comparison of the simulated sT with experimental datasets allows to identify modelling improvement areas. Dynamic functions are proposed based on turbulence intensity and Damköhler number. Finally, simulations using the improved flame speed are carried out and a satisfactory agreement of the simulation results with the experimental/theoretical correlations is found. This confirms the effectiveness and the general applicability of the methodology to any model. The use of grid/time resolution typical of ICE combustion simulations strengthens the relevance of the proposed dynamic functions. The presented analysis allows to improve the adherence of the simulated burn rate to that of literature turbulent flames, and it unfolds the innovative possibility to objectively test combustion models under any prescribed turbulence/flame interaction regime. The solid data-driven representation of turbulent combustion physics is expected to reduce the tuning effort in ICE combustion simulations, providing modelling robustness in a very critical area for virtual design of innovative combustion systems.

Multidimensional Modeling of Premixed Turbulent Combustion: Modeling and Testing of a Small Spark-Ignition Engine

2001 ◽  
Author(s):  
Gustavo Fontana ◽  
Enzo Galloni ◽  
Elio Jannelli
Keyword(s):  
Turbulent Combustion ◽  
Combustion Process ◽  
Spark Ignition ◽  
Measured Data ◽  
Spark Ignition Engine ◽  
Combustion Model ◽  
Engine Operation ◽  
Premixed Turbulent Combustion ◽  
Combustion Models ◽  
Good Reproduction

Abstract Combustion models, used in spark-ignition engine modeling, are reviewed. Different approaches for representing the main combustion features are reported. Limitations in simulating such a complex phenomenon as turbulent combustion in engines are highlighted as well. In order to compare different combustion models, the multidimensional program KIVA-3V has been used. The behavior of an actual spark-ignition engine has been investigated. In particular, simulation results, using simple chemical kinetics and mixing-controlled models, are compared. The results obtained, compared to measured data, confirm that different combustion models can lead to a satisfactory prediction of engine performances. But, in many cases, these models require experimental data for determining the model characteristic constants. A hybrid combustion model is proposed. It is able to provide a good reproduction of engine combustion process and, in particular, the model seems to be less sensitive to the engine operation. The computation results are compared to the measured data.

Reduced Reaction Mechanisms for Methane and Syngas Combustion in Gas Turbines

2005 ◽  
Author(s):  
N. Slavinskaya ◽  
M. Braun-Unkhoff ◽  
P. Frank
Keyword(s):  
Heat Release ◽  
Turbulent Combustion ◽  
Reaction Mechanisms ◽  
Gas Turbines ◽  
Laminar Flame ◽  
Laminar Flame Speed ◽  
Preheat Temperature ◽  
Reduced Mechanism ◽  
Wide Range ◽  
Syngas Combustion

Two reduced reaction mechanisms were established which predict reliably for pressures up to about 20 bar the heat release for different syngas mixtures including initial concentrations of methane. The mechanisms were validated on the base of laminar flame speed data covering a wide range of preheat temperature, pressure and fuel-air mixtures. Additionally, a global reduced mechanism for syngas, which comprises only two steps, was developed and validated, too. This global reduced and validated mechanism can be incorporated into CFD codes for modelling turbulent combustion in stationary gas turbines.

Comparison of Representative Interactive Flamelet and Detailed Chemistry Based Combustion Models for Internal Combustion Engines

2014 ◽  
Author(s):  
M. Wang ◽  
M. Raju ◽  
E. Pomraning ◽  
P. Kundu ◽  
Y. Pei ◽  
...  
Keyword(s):  
Diesel Engine ◽  
Internal Combustion Engines ◽  
Mixture Fraction ◽  
Spray Cooling ◽  
Combustion Model ◽  
Combustion Engines ◽  
Detailed Chemistry ◽  
Combustion Models ◽  
Computational Fluid Dynamics Cfd ◽  
Lift Off

Representative Interactive Flamelet (RIF) and Detailed Chemistry based combustion models are two commonly used combustion models for non-premixed diesel engine simulations. RIF performs transient chemistry calculations on a one-dimensional grid based on the mixture fraction coordinate. Hence, the chemistry calculations are essentially decoupled from the computational fluid dynamics (CFD) grid. The detailed chemistry model, on the other hand, solves transient chemistry in the 3D CFD domain. An efficient parallelization strategy is used for the computation of the multiple flamelets RIF model. The multiple flamelets RIF and detailed chemistry combustion models are applied for modeling a constant volume spray combustion case and a diesel engine case, with a view to compare the differences between the two models. Results for ignition delay, flame lift-off length, cylinder pressure, and emissions are compared with experimental data. The effect of number of flamelets is evaluated. Finally, the effect of spray cooling is investigated based on the results from the RIF model and the detailed chemistry based combustion model.

A New Assumed PDF Turbulent Combustion Model for Multi-Step Chemistry

2005 ◽  
Author(s):  
Baifang Zuo ◽  
David L. Black ◽  
Clifford E. Smith
Keyword(s):  
Monte Carlo ◽  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Main Stream ◽  
Wide Range ◽  
Partially Premixed

The effect of turbulence on chemical reactions is known to be important in many gas turbine combustor applications. There are only a few established models that can capture turbulence-combustion interaction in CFD codes, and all of these models are either very expensive (e.g. Monte Carlo PDF model) or limited in what types of flames can be analyzed (e.g. laminar flamelet). Assumed PDF models have been a popular choice because they are inexpensive and can handle all flame types (e.g. diffusion, premixed and partially premixed). However, assumed PDF models are typically restricted to single, one-step global mechanisms; or are a function of species and quickly become computationally expensive. CFD Research Corporation has recently developed and validated a new assumed PDF turbulence chemistry interaction model for multi-step chemistry. The model adopts an assumed, two-variable joint-PDF to model a wide-range of turbulent reacting flows. The two variables defining the PDF are the mixture fraction and reaction progress, representing species diffusion and flame propagation. A significant advantage of this new approach is its wide range of applicability for premixed, diffusion, and partially premixed flames. Allowing more detailed chemistry for species and combustion predictions enables complex chemical reaction processes including pollutant formation, flame ignition, and flame quenching to be studied. The model is also computationally efficient, with only a minor increase in computational expense with either species or number of global reaction steps. The newly developed model was first validated using a diffusion flame from a piloted burner developed at the University of Sydney. Three different methane bulk jet velocities were used to investigate the model’s behavior on turbulent diffusion flames. Simulation data were compared with the experimental measurements and the simulation results performed by Pope (Masri and Pope, 1990) using a velocity-composition joint PDF transport equation solved by the Monte Carlo method. To validate the model on premixed flames, the data of Moreau et al. (Moreau et al., 1974, 1976, 1977) were used. Data were collected on a mixing layer stabilized burner, where the main flow into the combustor was a premixed mixture of methane and air. Parallel to the main stream, a pilot stream of hot combustion products at 2000 K was injected for flame stabilization. The results demonstrate the wide applicability of the new model for practical, turbulent combustion applications.

scholarly journals Field modeling of the fire dynamics as an answer to the question about the fire alarm performance

2020 ◽  
Vol 29 (5) ◽  
pp. 40-50
Author(s):  
I. R. Khasanov ◽  
A. V. Karpov ◽  
S. F. Lobova ◽  
N. V. Petrova
Keyword(s):  
Numerical Study ◽  
Combustion Model ◽  
Smoke Detector ◽  
Fire Load ◽  
Fire Dynamics ◽  
Fire Alarm ◽  
Combustion Models ◽  
Field Modeling ◽  
Smoke Detectors ◽  
The Impact

Introduction. The performance of a fire alarm needs to be analyzed to answer the question about its compliance with fire safety requirements. This type of research is frequently performed in the course of a forensic fire investigation. Therefore, it is necessary to identify conditions of fire escalation and safe evacuation of people to assess the fire alarm performance.Purposes and objectives. The purpose of this work is the numerical study of the impact, produced by mathematical models of combustion, characteristics of fire loads and locations of fire beds, on fire alarm performance. Methods. Fire dynamics was field modeled to achieve the goal of this research. The analysis of flame propagation was performed with regard for various fire bed locations to simulate the fire alarm operation.Results and discussion. The fulfillment of safe evacuation conditions for cases of irregular arrangement of smoke detectors was analyzed to develop and test the algorithm for the calculation of the evacuation start time. It is shown that the estimated time of fire detection depends on combustion models employed (their average or complex level), the size of the computational grid, fire load specifications and the location of the fire bed.Conclusions. It is shown that the results of the field modeling of fire propagation and detection time are influenced by combustion models used, fire load specifications and the location of the fire bed in relation to smoke detectors. If the fire alarm fails to perform its functions and, consequently, safe evacuation conditions are not fulfilled, it is necessary either to improve the combustion model or to compare the modeling results obtained for actual and standard smoke detector location patterns.

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