Group Combustion of a Cylindrical Cloud of Char/Carbon Particles

1988 ◽  
Vol 110 (1) ◽  
pp. 190-200 ◽  
Author(s):  
K. Annamalai ◽  
S. Ramalingam ◽  
T. Dahdah ◽  
D. Chi
Keyword(s):  
Experimental Data ◽  
Collective Behavior ◽  
A Priori ◽  
Individual Particle ◽  
Combustion Model ◽  
Carbon Particles ◽  
Particle Combustion ◽  
Combustion Models ◽  
Coal Particles ◽  
Group Combustion

Extensive experiments were carried out in the past in order to obtain kinetics data on the pyrolysis of coal particles and the char reactions. The literature survey distinctively reveals two kinds of studies: (i) Individual Particle Combustion (IPC) and (ii) Combustion of Particle Streams or Clouds. The experimental data obtained with particle streams are normally interpreted using IPC models with the a priori assumption that the cloud is dilute. But the term “dilute” is rarely quantified and justified considering the collective behavior of a cloud of particles. The group combustion model accounts for the reduction in burning rate due to the collective behavior of a large number of particles. While the spherical group combustion model may be employed for coal/char spray combustion modeling, the cylindrical group combustion model is more useful in interpreting the experimental data obtained with a monosized stream of particles. Hence a cylindrical group combustion model is presented here. As in the case of spherical group combustion models, there exist three modes of combustion: (i) Individual Particle Combustion (IPC), (ii) Group Combustion (GC), and (iii) Sheath Combustion (SC). Within the range of parameters studied, it appears that the cylindrical and spherical cloud combustion models yield similar results on nondimensional cloud burning rates and on the combustion modes of a cloud of particles. The results from group theory are then used to identify the mode of combustion (IPC, GC, or SC) and to interpret the experimental data.

Group Ignition of a Cloud of Coal Particles

1991 ◽  
Vol 113 (3) ◽  
pp. 677-687 ◽  
Author(s):  
W. Ryan ◽  
K. Annamalai
Keyword(s):  
Initial Conditions ◽  
Numerical Study ◽  
Ignition Time ◽  
Volatile Matter ◽  
Combustion Model ◽  
Ambient Conditions ◽  
Experimental Conditions ◽  
Coal Particles ◽  
Group Combustion ◽  
Ignition Characteristics

Ignition of an isolated single coal particle is known to occur either heterogeneously or homogeneously. While single-particle studies may be useful for dilute coal sprays, their application to burners is limited since ignition occurs in the vicinity of the burners where the spray is dense. Rather than considering an isolated particle, one must consider a collection of particles in order to determine the change in ignition characteristics resulting from particle interactions. Thus, group combustion models have been developed essentially to predict the ignition and combustion characteristics of a larger number of interacting drops/particles. This paper presents results of the ignition characteristics of a spherical cloud of uniformly distributed coal particles in quiescent surroundings using a simple group combustion model. For the conditions studied, the results are as follows: (1) Ignition is heterogeneous if the cloud is dilute and homogeneous if the cloud is dense under the same ambient conditions; (2) there is a minimum ignition time for a given set of initial conditions corresponding to a certain cloud denseness; (3) ignition time is less sensitive to the denseness of the cloud at higher ambient temperatures; and (4) decreased proximate volatile matter can result in either increased or decreased ignition time depending on the cloud denseness (ignition mode). Qualitative comparisons to experimental data are given; however, these comparisons should be approached with caution since the experimental conditions and geometries may be vastly different than those used in the numerical study presented here.

Impact of Flame Stretch and Heat Loss on Heat Release Distributions in Gas Turbine Combustors: Model Comparison and Validation

2016 ◽  
Author(s):  
Noah Klarmann ◽  
Thomas Sattelmayer ◽  
Weiqun Geng ◽  
Benjamin Timo Zoller ◽  
Fulvio Magni
Keyword(s):  
Experimental Data ◽  
Heat Loss ◽  
Model Comparison ◽  
Turbulent Flame ◽  
Combustion Process ◽  
Combustion Model ◽  
Qualitative Comparison ◽  
Combustion Models ◽  
Flamelet Generated Manifold ◽  
Flame Stretch

The work presented in this paper comprises the application of an extension for the Flamelet Generated Manifold model which allows to consider elevated flame stretch rates and heat loss. This approach does not require further table dimensions. Hence, the numerical overhead is negligible, preserving the industrial applicability. A validation is performed in which stretch and heat loss dependent distributions are obtained from the combustion model to compare them to experimental data from an atmospheric single burner test rig operating at lean conditions. The reaction mechanism is extended by OH*-kinetics which allows the comparison of numerical OH*-concentrations with experimentally obtained OH*-chemiluminescence. Improvement compared to the Flamelet Generated Manifold model without extension regarding the shape and position of the turbulent flame brush can be shown and are substantiated by the validation of species distributions which better fit the experimental in situ measurements when the extension is used. These improvements are mandatory to enable subsequent modeling of emissions or thermoacoustics where high accuracy is required. In addition to the validation, a qualitative comparison of further combustion models is performed in which the experimental data serve as a benchmark to evaluate the accuracy. Most combustion models typically simplify the combustion process as flame stretch or non-adiabatic effects are not captured. It turns out that the tested combustion models show improvement when stretch or heat loss is considered by model corrections. However, satisfactory results could only be achieved by considering both effects employing the extension for the Flamelet Generated Manifold model.

Coal Particles Combustion Model and Micro Feeding Technology in Drop Tube Furnace

2011 ◽  
Vol 236-238 ◽  
pp. 680-683 ◽  
Author(s):  
Zheng Zhong Ma ◽  
Xiang Xu ◽  
Yun Han Xiao
Keyword(s):  
Design Principle ◽  
Tube Furnace ◽  
Combustion Model ◽  
Drop Tube ◽  
Test Results ◽  
Drop Tube Furnace ◽  
Coal Particles ◽  
Group Combustion ◽  
Feeding Technology

For investigation of wide use of drop tube furnace (DTF), the design and characterization of DTF and shaftless screw microfeeder are presented. With a developed group combustion model, a introduced non-dimensional number is to characterize the combustion zone of coal particles in DTF. Calculated relation is proposed to be operation criteria of DTF and design principle of feeder. It is found that the test results of coal feeder show good performance for micro feeding.

Including Heat Loss and Quench Effects in Algebraic Models for Large Eddy Simulation of Premixed Combustion

2012 ◽  
Author(s):  
Roman Keppeler ◽  
Michael Pfitzner ◽  
Luis Tay Wo Chong ◽  
Thomas Komarek ◽  
Wolfgang Polifke
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Heat Loss ◽  
Combustion Model ◽  
Algebraic Models ◽  
Combustion Models ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Interaction ◽  
Swirl Flame

In technically relevant combustion devices, combustion can take place in the vicinity of walls which can significantly affect the reaction and the heat transfer. However, only few studies focus on modelling of flame-wall interaction (FWI) for algebraic combustion models and virtually none consider FWI for algebraic Large Eddy Simulation combustion models. In the present work heat loss models, as previously published in the literature, are employed to extend a LES algebraic combustion model. The performance of the FWI models is evaluated by simulations of a nonadiabatic swirl flame. The simulation results are compared with experimental data of velocity field and heat release. The extent of the quenching zone and heat loss effects are determined in the simulations and compared with data from direct numerical simulations. Comparison of simulation and experimental data shows a significant improvement when heat loss effects are incorporated. Also the characteristic Peclet numbers are correctly predicted by FWI models.

Design Analysis of a Micro Gas Turbine Combustion Chamber Burning Natural Gas

2012 ◽  
Author(s):  
André Perpignan V. de Campos ◽  
Fernando L. Sacomano Filho ◽  
Guenther C. Krieger Filho
Keyword(s):  
Experimental Data ◽  
Natural Gas ◽  
Combustion Chamber ◽  
Gas Turbines ◽  
Low Cost ◽  
Mixture Fraction ◽  
Combustion Model ◽  
Inlet Temperature ◽  
Gas Combustion ◽  
Micro Turbine

Gas turbines are reliable energy conversion systems since they are able to operate with variable fuels and independently from seasonal natural changes. Within that reality, micro gas turbines have been increasing the importance of its usage on the onsite generation. Comparatively, less research has been done, leaving more room for improvements in this class of gas turbines. Focusing on the study of a flexible micro turbine set, this work is part of the development of a low cost electric generation micro turbine, which is capable of burning natural gas, LPG and ethanol. It is composed of an originally automotive turbocompressor, a combustion chamber specifically designed for this application, as well as a single stage axial power turbine. The combustion chamber is a reversed flow type and has a swirl stabilized combustor. This paper is dedicated to the diagnosis of the natural gas combustion in this chamber using computational fluid dynamics techniques compared to measured experimental data of temperature inside the combustion chamber. The study emphasizes the near inner wall temperature, turbine inlet temperature and dilution holes effectiveness. The calculation was conducted with the Reynolds Stress turbulence model coupled with the conventional β-PDF equilibrium along with mixture fraction transport combustion model. Thermal radiation was also considered. Reasonable agreement between experimental data and computational simulations was achieved, providing confidence on the phenomena observed on the simulations, which enabled the design improvement suggestions and analysis included in this work.

scholarly journals Extracting real-crack properties from non-linear elastic behaviour of rocks: abundance of cracks with dominating normal compliance and rocks with negative Poisson ratios

2017 ◽  
Vol 24 (3) ◽  
pp. 543-551 ◽  
Author(s):  
Vladimir Y. Zaitsev ◽  
Andrey V. Radostin ◽  
Elena Pasternak ◽  
Arcady Dyskin
Keyword(s):  
Experimental Data ◽  
Poisson Ratio ◽  
A Priori ◽  
Elastic Behaviour ◽  
Crack Model ◽  
Normal Compliance ◽  
S Wave ◽  
Linear Elastic ◽  
Non Linear ◽  
Linear Elastic Behaviour

Abstract. Results of examination of experimental data on non-linear elasticity of rocks using experimentally determined pressure dependences of P- and S-wave velocities from various literature sources are presented. Overall, over 90 rock samples are considered. Interpretation of the data is performed using an effective-medium description in which cracks are considered as compliant defects with explicitly introduced shear and normal compliances without specifying a particular crack model with an a priori given ratio of the compliances. Comparison with the experimental data indicated abundance (∼ 80 %) of cracks with the normal-to-shear compliance ratios that significantly exceed the values typical of conventionally used crack models (such as penny-shaped cuts or thin ellipsoidal cracks). Correspondingly, rocks with such cracks demonstrate a strongly decreased Poisson ratio including a significant (∼ 45 %) portion of rocks exhibiting negative Poisson ratios at lower pressures, for which the concentration of not yet closed cracks is maximal. The obtained results indicate the necessity for further development of crack models to account for the revealed numerous examples of cracks with strong domination of normal compliance. Discovering such a significant number of naturally auxetic rocks is in contrast to the conventional viewpoint that occurrence of a negative Poisson ratio is an exotic fact that is mostly discussed for artificial structures.

scholarly journals Simulation of a GOx-GCH4 Rocket Combustor and the Effect of the GEKO Turbulence Model Coefficients

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 341
Author(s):  
Evgeny Strokach ◽  
Victor Zhukov ◽  
Igor Borovik ◽  
Andrej Sternin ◽  
Oscar J. Haidn
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Turbulence Model ◽  
Chemical Kinetic ◽  
Wall Heat Flux ◽  
Combustion Model ◽  
Combustion Chambers ◽  
Separation Parameter ◽  
Kinetic Mechanisms ◽  
Stable Performance

In this study, a single injector methane-oxygen rocket combustor is numerically studied. The simulations included in this study are based on the hardware and experimental data from the Technical University of Munich. The focus is on the recently developed generalized k–ω turbulence model (GEKO) and the effect of its adjustable coefficients on the pressure and on wall heat flux profiles, which are compared with the experimental data. It was found that the coefficients of ‘jet’, ‘near-wall’, and ‘mixing’ have a major impact, whereas the opposite can be deduced about the ‘separation’ parameter Csep, which highly influences the pressure and wall heat flux distributions due to the changes in the eddy-viscosity field. The simulation results are compared with the standard k–ε model, displaying a qualitatively and quantitatively similar behavior to the GEKO model at a Csep equal to unity. The default GEKO model shows a stable performance for three oxidizer-to-fuel ratios, enhancing the reliability of its use. The simulations are conducted using two chemical kinetic mechanisms: Zhukov and Kong and the more detailed RAMEC. The influence of the combustion model is of the same order as the influence of the turbulence model. In general, the numerical results present a good or satisfactory agreement with the experiment, and both GEKO at Csep = 1 or the standard k–ε model can be recommended for usage in the CFD simulations of rocket combustion chambers, as well as the Zhukov–Kong mechanism in conjunction with the flamelet approach.

scholarly journals A-Priori Validation of Scalar Dissipation Rate Models for Turbulent Non-Premixed Flames

2020 ◽  
Author(s):  
M. P. Sitte ◽  
C. Turquand d’Auzay ◽  
A. Giusti ◽  
E. Mastorakos ◽  
N. Chakraborty
Keyword(s):  
Dissipation Rate ◽  
A Priori ◽  
Turbulent Flames ◽  
Large Eddy Simulations ◽  
Moment Closure ◽  
Scalar Dissipation ◽  
Combustion Model ◽  
Scalar Dissipation Rate ◽  
Jet Flame ◽  
Large Eddy

Abstract The modelling of scalar dissipation rate in conditional methods for large-eddy simulations is investigated based on a priori direct numerical simulation analysis using a dataset representing an igniting non-premixed planar jet flame. The main objective is to provide a comprehensive assessment of models typically used for large-eddy simulations of non-premixed turbulent flames with the Conditional Moment Closure combustion model. The linear relaxation model gives a good estimate of the Favre-filtered scalar dissipation rate throughout the ignition with a value of the related constant close to the one deduced from theoretical arguments. Such value of the constant is one order of magnitude higher than typical values used in Reynolds-averaged approaches. The amplitude mapping closure model provides a satisfactory estimate of the conditionally filtered scalar dissipation rate even in flows characterised by shear driven turbulence and strong density variation.

Application of Various Combustion Models to a Generic Combustor

2003 ◽  
Author(s):  
Lei-Yong Jiang ◽  
Ian Campbell
Keyword(s):  
Experimental Tests ◽  
Combustion Model ◽  
Discrete Ordinates ◽  
Experimental Measurements ◽  
Finite Rate ◽  
Zone Length ◽  
Combustion Models ◽  
The Mean ◽  
Heat Transfers ◽  
Good Agreement

The flow-field of a generic gas combustor with interior and exterior conjugate heat transfers was numerically studied. Results obtained from three combustion models, combined with the re-normalization group (RNG) k-ε turbulence model, discrete ordinates radiation model, and partial equilibrium NOx model are presented and discussed. The numerical results are compared with a comprehensive database obtained from a series of experimental tests. The flow patterns and the recirculation zone length are excellently predicted, and the mean axial velocities are in fairly good agreement with the experimental measurements, particularly at downstream sections for all three combustion models. The mean temperature profiles are also fairly well captured by the probability density function (PDF) and eddy dissipation (EDS) combustion models. The EDS-finite-rate combustion model fails to provide acceptable temperature field. In general, the PDF shows some superiority over the EDS and EDS-finite-rate models. NOx levels predicted by the EDS model are in reasonable agreement with the experimental measurements.

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