Three-Stream Flamelet Model for Industrial Applications

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Dirk Riechelmann ◽  
Masahiro Uchida
Keyword(s):  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Industrial Applications ◽  
Exhaust Gas ◽  
Water Steam ◽  
Flamelet Model ◽  
Jet Diffusion Flames ◽  
Key Points ◽  
Lift Off

Efficient turbulent combustion models are typically designed for the numerical simulation of two-stream problems, namely, the combustion of fuel in air. There are applications, however, where large amounts of a diluent such as water steam or recirculated exhaust gas is supplied to the combustor independent of fuel and air supplies. In such cases, classical approaches become quite time-consuming. In the present paper, a new three-stream flamelet model is presented, which is essentially an extension of the two-stream flamelet model for diffusion flames. Key points of the approach are the introduction of a second mixture fraction variable and the efficient establishment of the flamelet library. After presentation of the theory, the applicability of the new model is demonstrated by comparison with experimental results for the lift-off height of jet diffusion flames.

Mixing Models for Large-Eddy Simulation of Nonpremixed Turbulent Combustion

2000 ◽  
Vol 123 (2) ◽  
pp. 341-346 ◽  
Author(s):  
S. M. deBruynKops ◽  
J. J. Riley
Keyword(s):  
Turbulent Combustion ◽  
Dissipation Rate ◽  
Mixture Fraction ◽  
Reaction Rates ◽  
Large Eddy Simulations ◽  
Scalar Dissipation ◽  
Mixing Models ◽  
Mixing Rate ◽  
Flamelet Model ◽  
Large Eddy

The application of mixture fraction based models to large-eddy simulations (LES) of nonpremixed turbulent combustion requires information about mixing at length scales not resolved on the LES grid. For instance, the large-eddy laminar flamelet model (LELFM) takes the subgrid-scale variance and the filtered dissipation rate of the mixture fraction as inputs. Since chemical reaction rates in nonpremixed turbulence are largely governed by the mixing rate, accurate mixing models are required if mixture fraction methods are to be successfully used to predict species concentrations in large-eddy simulations. In this paper, several models for the SGS scalar variance and the filtered scalar dissipation rate are systematically evaluated a priori using benchmark data from a DNS in homogeneous, isotropic, isothermal turbulence. The mixing models are also evaluated a posteriori by applying them to actual LES data of the same flow. Predictions from the models that depend on an assumed form for the scalar energy spectrum are very good for the flow considered, and are better than those from models that rely on other assumptions.

Flamelet Studies of Reduced and Detailed Kinetic Mechanisms for Methane/Air Diffusion Flames

2000 ◽  
Author(s):  
Foluso Ladeinde ◽  
Xiaodan Cai ◽  
Balu Sekar
Keyword(s):  
Dissipation Rate ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Intermediate Species ◽  
Flamelet Model ◽  
Mass Fractions ◽  
Kinetic Mechanisms ◽  
Moderate Effect ◽  
Extinction Strain Rate ◽  
Air Diffusion

We adopt a steady-state flamelet model in this paper to study the performance of reduced and detailed kinetic mechanisms for methane/air diffusion flames. Through the numerical calculations, we investigate the sensitivity of the main and intermediate species mass fractions to the mixture fraction dissipation rate, χ. Our results seem to suggest a weak to moderate effect of χ on the calculated species mass fraction. It has also been shown in this paper that the current flamelet calculations fail to predict the extinction strain rate.

A Mixture Fraction-Based Model and Axial Thermal Positions for Buoyancy/Momentum-Controlled Jet Diffusion Flames

2018 ◽  
Vol 192 (1) ◽  
pp. 62-77
Author(s):  
Kun Wang ◽  
Jun Fang ◽  
Jingwu Wang ◽  
Sumei Zheng ◽  
Luyao Zhao ◽  
...  
Keyword(s):  
Diffusion Flames ◽  
Mixture Fraction ◽  
Jet Diffusion Flames

A Skewed PDF Combustion Model for Jet Diffusion Flames

1990 ◽  
Vol 112 (4) ◽  
pp. 1002-1007 ◽  
Author(s):  
M. M. M. Abou-Ellail ◽  
H. Salem
Keyword(s):  
Diffusion Flames ◽  
Mixture Fraction ◽  
Beta Function ◽  
Delta Function ◽  
Turbulent Jet ◽  
Combustion Model ◽  
Jet Diffusion Flames ◽  
Numerical Predictions ◽  
Methane Flame ◽  
The Mean

A combustion model based on restricted chemical equilibrium is described. A transport equation for the skewness of the mixture fraction is derived. It contains two adjustable constants. The computed values of the mean mixture fraction (f) and its variance and skewness (g and s) for a jet diffusion methane flame are used to obtain the shape of a skewed pdf. The skewed pdf is split into a turbulent part (beta function) and a nonturbulent part (delta function) at f = 0. The contribution of each part is directly related to the values of f, g, and s. The inclusion of intermittency in the skewed pdf appreciably improves the numerical predictions obtained for a turbulent jet diffusion methane flame for which experimental data are available.

Pressure Dependence of the Stability Limits and the NOX Exhaust Gas Concentrations in Case of Swirl-Stabilized, Diffusion Flames Burning in a Lift-Off Regime

2009 ◽  
Author(s):  
Plamen Kasabov ◽  
Nikolaos Zarzalis
Keyword(s):  
Reaction Zone ◽  
Diffusion Flames ◽  
Sudden Change ◽  
Measurement Data ◽  
Exhaust Gas ◽  
Stabilization Mechanism ◽  
Lifted Flames ◽  
Lift Off ◽  
Stability Limits ◽  
The Impact

The present study deals with confined, swirl-stabilized, diffusion flames burning in a lift-off regime and is meant to be a meaningful extension of our previous work [1]. The unique features of these hybrid flames originate from the presence of the so called lift-off zone located between the burner exit and the reaction zone. In the lift-off zone, surrounded by hot recirculating exhaust gases, the liquid fuel heats up and will reach a certain degree of prevaporation and premixing before entering the reaction zone. For that reason lifted flames posses some of the advantages of the premixed flames, for example in respect of emissions, but lack their major drawbacks, such as susceptibility to flashback and combustion noise. The investigations were motivated by the high NOX reduction potential of the lifted flames and the scarce information about their emission characteristics, flame behaviour and stability limits for gas turbine typical conditions especially when operated with liquid fuels. In order to gain a deeper understanding of the stabilization mechanism of lifted flames, several process parameters were varied within this study. The impact of the pressure (up to 18bar), of the air preheating and of the stoichiometry on the NOX emissions and on the lean blowout limits was investigated and discussed. The lift-off burning mode was achieved by utilizing a modified airblast nozzle and kerosene serving as a fuel. To acquire measurement data for a set of Reynolds numbers and residence times, four nozzles with similar geometries, but different scaling factors were employed. All main components of the exhaust gas were detected by means of conventional gas analysis. The NOX concentrations for the whole measured pressure range and for adiabatic flame temperatures up to 1800K does not exceed 20ppm normalized for 15% O2. The carbon monoxide concentration served as indicator for the presence of flame instabilities. The evaluation of the gathered data revealed some interesting phenomena. For example a sudden change in the nitrogen oxides concentration plotted over the equivalence ratio allows to distinguish between two burning modes: lift-off and detached flame. Another interesting finding is a maximum in the profile of the LBO limits as a function of the operational pressure, signifying a change in the predominant stabilization mechanism.

Numerical Simulation of Jet Diffusion Flames With Radiative Heat Transfer Modeling

2005 ◽  
Author(s):  
Mario Baburic´ ◽  
Reinhard Tatschl ◽  
Neven Duic´
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Radiative Heat Transfer ◽  
Diffusion Flame ◽  
Radiative Heat ◽  
Diffusion Flames ◽  
Flamelet Model ◽  
Jet Flame ◽  
Combustion Modeling ◽  
Jet Diffusion Flames

Beside appropriate turbulence and combustion modeling, the problem of an accurate prediction of turbulent diffusion flames usually requires accurate radiative heat transfer predictions as well. In this paper it is shown that the inclusion of radiation modeling into the overall numerical simulation is important if accurate temperature profiles are needed. Two different jet diffusion flame configurations are simulated in this work — a diluted hydrogen jet flame (80% H2 and 20% He by volume) [1–4], and a piloted methane jet diffusion flame (flame D) [5, 6]. The predictions are compared to experimental data. Radiation is modeled by a conservative discrete transfer radiation method (DTRM) [7, 8]. Turbulence is modeled by a classical k-ε and by a hybrid procedure, as proposed in [9]. Combustion modeling is based on the stationary laminar flamelet model (SLFM) [10], where the combustion/turbulence interaction is accomplished via the presumed β probability density function (β-PDF).

Sign in / Sign up

Export Citation Format

Share Document