Fluids

Research

9 pages, 3713 KiB

Open AccessArticle

Experimental and Numerical Study of Gas Injection Effect on the Methane–Air Combustion inside a Coaxial Burner

by Alexey Kiverin, Boris Kichatov, Alexey Korshunov, Vladimir Gubernov, Ivan Yakovenko and Andrey Yarkov

Fluids 2021, 6(2), 60; https://doi.org/10.3390/fluids6020060 - 01 Feb 2021

Cited by 1 | Viewed by 1408

Abstract

This paper is devoted to the analysis of the effect of gas injection on the efficiency of gaseous fuel burning. A coaxial burner with a perforated inner wall is presented in which the methane–air acceleration is observed. With the use of numerical analysis, [...] Read more.

This paper is devoted to the analysis of the effect of gas injection on the efficiency of gaseous fuel burning. A coaxial burner with a perforated inner wall is presented in which the methane–air acceleration is observed. With the use of numerical analysis, it is demonstrated that the flame acceleration is related to the flow separation from the inner wall that, in turn, leads to the reduction in heat losses to the wall as well as to vortex formation and reduction in momentum losses. On the basis of the obtained results, a new technology of efficient burning of gaseous fuels can be proposed with the use of gas and/or liquid fuel injection. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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24 pages, 553 KiB

Open AccessEditor’s ChoiceArticle

Effects of Reaction Mechanisms and Differential Diffusion in Oxy-Fuel Combustion Including Liquid Water Dilution

by Fernando Luiz Sacomano Filho, Luis Eduardo de Albuquerque Paixão e Freire de Carvalho, Jeroen Adrianus van Oijen and Guenther Carlos Krieger Filho

Fluids 2021, 6(2), 47; https://doi.org/10.3390/fluids6020047 - 21 Jan 2021

Cited by 5 | Viewed by 2562

Abstract

The influence of chemistry and differential diffusion transport modeling on methane oxy-fuel combustion is analyzed considering different diluent characteristics. Analyses are conducted in terms of numerical simulations using a detailed description of the chemistry. Herein, different reaction mechanisms are employed to represent the [...] Read more.

The influence of chemistry and differential diffusion transport modeling on methane oxy-fuel combustion is analyzed considering different diluent characteristics. Analyses are conducted in terms of numerical simulations using a detailed description of the chemistry. Herein, different reaction mechanisms are employed to represent the combustion of methane. Simulations were performed with the computational fluid dynamics (CFD) code CHEM1D following different numerical setups, freely propagating flame, counter flow flame, and propagating flame in droplet mist reactors. The employed method is validated against experimental data and simulation results available in the literature. While the counter-flow flame reactor is exclusively used in the validation stage, different scenarios have been established for propagating flame simulations, as in single- or two-phase flow configuration. These comprehend variations in diluent compositions, reaction mechanisms, and different models to account for diffusion transport. Conducted investigations show that the choice for a specific reaction mechanism can interfere with computed flame speed values, which may agree or deviate from experimental observations. The achieved outcomes from these investigations indicate that the so-called GRI 3.0 mechanism is the best option for general application purposes, as a good balance is found between accuracy and computational efforts. However, in cases where more detailed information and accuracy are required, the CRECK C1-C3 mechanism demonstrated to be the best choice from the evaluated mechanisms. Additionally, the results clearly indicate that commonly applied simplifications to general flame modeling as the unitary Lewis number and mixture averaged approach strongly interfere with the computation of flame propagation speed values for single- and two-phase flows. While the application of unitary Lewis number approach is limited to certain conditions, the mixture averaged approach demonstrated a good agreement with the complex model for flame speed computations in the various tested scenarios. Such an outcome is not limited to oxy-fuel applications, but are straightly extensible to oxy-steam and air-blown combustion. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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22 pages, 5156 KiB

Open AccessArticle

Analysis of the Aerodynamics in the Heating Section of an Anode Baking Furnace Using Non-Linear Finite Element Simulations

by Prajakta Nakate, Domenico Lahaye, Cornelis Vuik and Marco Talice

Fluids 2021, 6(1), 46; https://doi.org/10.3390/fluids6010046 - 19 Jan 2021

Cited by 3 | Viewed by 3356

Abstract

The emissions from the industrial furnaces impact the environment. Among the various factories, those having anode baking furnaces are working on reducing the pollutant emissions. The aerodynamics in the furnace influences the emissions due to the high dependence of combustion and radiation phenomena [...] Read more.

The emissions from the industrial furnaces impact the environment. Among the various factories, those having anode baking furnaces are working on reducing the pollutant emissions. The aerodynamics in the furnace influences the emissions due to the high dependence of combustion and radiation phenomena on the mixing characteristics. Therefore, this paper aims to establish the numerical simulation results for the three-dimensional turbulent flow in a single section of an anode baking furnace with a high rate of fuel injection. The stabilized non-linear finite element approach on the Reynolds-averaged Navier-Stokes (RANS) equation is used with COMSOLMultiphysics. The turbulent viscosity ratio is highly sensitive to the mesh for the standard k-

ϵ

model. The requirements of the Cartesian and refined mesh near the jet development region is explained. The comparison of meshes generated by two meshing tools namely cfMesh and COMSOL Multiphysics default Mesher is carried out. The high numerical diffusion in the flow models due to the coarser mesh leads to convergence but deficit the precision in the results. This paper shows that the mesh generated by cfMesh with flow aligned refinement combined with the non-linear finite element solver in COMSOL Multiphysics proves to provide accurate results of turbulent quantities. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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26 pages, 42430 KiB

Open AccessArticle

Computational Study of Premixed Flame Propagation in Micro-Channels with Nonslip Walls: Effect of Wall Temperature

by Orlando J. Ugarte and V’yacheslav Akkerman

Fluids 2021, 6(1), 36; https://doi.org/10.3390/fluids6010036 - 11 Jan 2021

Cited by 3 | Viewed by 2006

Abstract

This investigation evaluates the propagation of premixed flames in narrow channels with isothermal walls. The study is based on the numerical solution of the set of fully-compressible, reacting flow equations that includes viscosity, diffusion, thermal conduction and Arrhenius chemical kinetics. Specifically, channels and [...] Read more.

This investigation evaluates the propagation of premixed flames in narrow channels with isothermal walls. The study is based on the numerical solution of the set of fully-compressible, reacting flow equations that includes viscosity, diffusion, thermal conduction and Arrhenius chemical kinetics. Specifically, channels and pipes with one extreme open and one extreme closed are considered such that a flame is sparked at the closed extreme and propagates towards the open one. The isothermal channel walls are kept at multiple constant temperatures in the range from

T_{w} = 300 K

to

1200 K

. The impact of these isothermal walls on the flame dynamics is studied for multiple radii of the channel (

R

) and for various thermal expansion ratios (

Θ

), which approximate the thermal behavior of different fuel mixtures in the system. The flame dynamics in isothermal channels is also compared to that with adiabatic walls, which were previously found to produce exponential flame acceleration at the initial stage of the burning process. The results show that the heat losses at the walls prevent strong acceleration and lead to much slower flame propagation in isothermal channels as compared to adiabatic ones. Four distinctive regimes of premixed burning in isothermal channels have been identified in the

Θ - T_{w} - R

space: (i) flame extinction; (ii) linear flame acceleration; (iii) steady or near-steady flame propagation; and (iv) flame oscillations. The physical processes in each of these regimes are discussed, and the corresponding regime diagrams are presented. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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11 pages, 22333 KiB

Open AccessArticle

Ultra-Lean Gaseous Flames in Terrestrial Gravity Conditions

by Ivan Yakovenko, Alexey Kiverin and Ksenia Melnikova

Fluids 2021, 6(1), 21; https://doi.org/10.3390/fluids6010021 - 03 Jan 2021

Cited by 8 | Viewed by 2082

Abstract

Development of the combustion process in the gaseous mixtures of near-limit composition is of great interest for fundamental aspects of combustion theory and fire-safety applications. The dynamics of ultra-lean gaseous flames in near-limit mixtures is governed by many effects, such as buoyancy, preferential [...] Read more.

Development of the combustion process in the gaseous mixtures of near-limit composition is of great interest for fundamental aspects of combustion theory and fire-safety applications. The dynamics of ultra-lean gaseous flames in near-limit mixtures is governed by many effects, such as buoyancy, preferential diffusion, radiation, and instability development. Though ultra-lean combustion was extensively studied in microgravity conditions, the influence of gravity on the ultra-lean flame structure and stability is still poorly understood. The paper is devoted to deepening the knowledge of ultra-lean flame dynamics in hydrogen-air mixtures under terrestrial gravity conditions. The spatial structures of the flame developing under the effect of buoyancy forces are investigated employing detailed numerical analysis. Different modes of near-limit flame evolution are observed depending on the mixture concentration. In particular, we registered and described three distinct spatial structures: individual kernels tending to extinguish in leanest compounds, complex multi-kernel structures in marginal compositions, and stable cap-shaped flames in more chemically active mixtures. We apply the flame-bubble analogy to interpret flame dynamics. On this basis, the diagram in the Re-Fr plane is developed. That allows classifying the emerging flame structures and determine flame stability. Additionally, different ignition modes are studied, and the mechanisms determining the impact of ignition mode on the flammability limits are distinguished. Obtained results provide useful insights into the processes of flame quenching and development in near-limit hydrogen-air mixtures under real gravity conditions and can be applied in the design of contemporary fire-safety systems. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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12 pages, 488 KiB

Open AccessArticle

Stability Analysis for an Interface with a Continuous Internal Structure

by Mikhail Modestov

Fluids 2021, 6(1), 18; https://doi.org/10.3390/fluids6010018 - 01 Jan 2021

Cited by 2 | Viewed by 1578

Abstract

A general method for solving a linear stability problem of an interface with a continuous internal structure is described. Such interfaces or fronts are commonly found in various branches of physics, such as combustion and plasma physics. It extends simplified analysis of an [...] Read more.

A general method for solving a linear stability problem of an interface with a continuous internal structure is described. Such interfaces or fronts are commonly found in various branches of physics, such as combustion and plasma physics. It extends simplified analysis of an infinitely thin discontinuous front by means of numerical integration along the steady-state solution. Two examples are presented to demonstrate the application of the method for 1D pulsating instability in magnetic deflagration and 2D Darrieus–Landau instability in a laser ablation wave. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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8 pages, 1625 KiB

Open AccessArticle

An Elementary Model for a Self-Accelerating Outward Propagating Flame Subject to the Rayleigh–Taylor Instability: Transition to Detonation

by Leonid Kagan and Gregory Sivashinsky

Fluids 2020, 5(4), 196; https://doi.org/10.3390/fluids5040196 - 31 Oct 2020

Cited by 4 | Viewed by 1581

Abstract

Within the Boussinesq approximation, an elementary model for the deflagration-to-detonation transition triggered by self-acceleration of an expanding flame is formulated and explored. The self-acceleration is sustained by the intrinsic Rayleigh–Taylor instability until the Deshaies–Joulin deflagrability threshold is reached, followed by an abrupt transition [...] Read more.

Within the Boussinesq approximation, an elementary model for the deflagration-to-detonation transition triggered by self-acceleration of an expanding flame is formulated and explored. The self-acceleration is sustained by the intrinsic Rayleigh–Taylor instability until the Deshaies–Joulin deflagrability threshold is reached, followed by an abrupt transition to detonation. Emergence of the threshold is caused by positive feedback between the accelerating flame and the flame-driven pressure shock that results in the thermal runaway when the flame speed reaches a critical level. The model offers a simple mechanism that may be responsible for the transition to detonation in thermonuclear supernovae. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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29 pages, 5770 KiB

Open AccessArticle

Effects of Composition Heterogeneities on Flame Kernel Propagation: A DNS Study

by Aimad Er-raiy, Radouan Boukharfane and Matteo Parsani

Fluids 2020, 5(3), 152; https://doi.org/10.3390/fluids5030152 - 04 Sep 2020

Cited by 1 | Viewed by 2013

Abstract

In this study, a new set of direct numerical simulations is generated and used to examine the influence of mixture composition heterogeneities on the propagation of a premixed iso-octane/air spherical turbulent flame, with a representative chemical description. The dynamic effects of both turbulence [...] Read more.

In this study, a new set of direct numerical simulations is generated and used to examine the influence of mixture composition heterogeneities on the propagation of a premixed iso-octane/air spherical turbulent flame, with a representative chemical description. The dynamic effects of both turbulence and combustion heterogeneities are considered, and their competition is assessed. The results of the turbulent homogeneous case are compared with those of heterogeneous cases which are characterized by multiple stratification length scales and segregation rates in the regime of a wrinkled flame. The comparison reveals that stratification does not alter turbulent flame behaviors such as the preferential alignment of the convex flame front with the direction of the compression. However, we find that the overall flame front propagation is slower in the presence of heterogeneities because of the differential on speed propagation. Furthermore, analysis of different displacement speed components is performed by taking multi-species formalism into account. This analysis shows that the global flame propagation front slows down due to the heterogeneities caused by the reaction mechanism and the differential diffusion accompanied by flame surface density variations. Quantification of the effects of each of these mechanisms shows that their intensity increases with the increase in stratification’s length scale and segregation rate. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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14 pages, 5521 KiB

Open AccessArticle

Scale-Resolving Simulation of a Propane-Fuelled Industrial Gas Turbine Combustor Using Finite-Rate Tabulated Chemistry

by Kai Zhang, Ali Ghobadian and Jamshid M. Nouri

Fluids 2020, 5(3), 126; https://doi.org/10.3390/fluids5030126 - 29 Jul 2020

Cited by 5 | Viewed by 2700

Abstract

The scale-resolving simulation of a practical gas turbine combustor is performed using a partially premixed finite-rate chemistry combustion model. The combustion model assumes finite-rate chemistry by limiting the chemical reaction rate with flame speed. A comparison of the numerical results with the experimental [...] Read more.

The scale-resolving simulation of a practical gas turbine combustor is performed using a partially premixed finite-rate chemistry combustion model. The combustion model assumes finite-rate chemistry by limiting the chemical reaction rate with flame speed. A comparison of the numerical results with the experimental temperature and species mole fraction clearly showed the superiority of the shear stress transport, K-omega, scale adaptive turbulence model (SSTKWSAS). The model outperforms large eddy simulation (LES) in the primary region of the combustor, probably for two reasons. First, the lower amount of mesh employed in the simulation for the industrial-size combustor does not fit the LES’s explicit mesh size dependency requirement, while it is sufficient for the SSTKWSAS simulation. Second, coupling the finite-rate chemistry method with the SSTKWSAS model provides a more reasonable rate of chemical reaction than that predicted by the fast chemistry method used in LES simulation. Other than comparing with the LES data available in the literature, the SSTKWSAS-predicted result is also compared comprehensively with that obtained from the model based on the unsteady Reynolds-averaged Navier–Stokes (URANS) simulation approach. The superiority of the SSTKWSAS model in resolving large eddies is highlighted. Overall, the present study emphasizes the effectiveness and efficiency of coupling a partially premixed combustion model with a scale-resolving simulation method in predicting a swirl-stabilized, multi-jets turbulent flame in a practical, complex gas turbine combustor configuration. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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25 pages, 7566 KiB

Open AccessArticle

Analysis of Gaseous and Gaseous-Dusty, Premixed Flame Propagation in Obstructed Passages with Tightly Placed Obstacles

by Furkan Kodakoglu, Sinan Demir, Damir Valiev and V’yacheslav Akkerman

Fluids 2020, 5(3), 115; https://doi.org/10.3390/fluids5030115 - 17 Jul 2020

Cited by 3 | Viewed by 1876

Abstract

A recent predictive scenario of premixed flame propagation in unobstructed passages is extended to account for obstructions that can be encountered in facilities dealing with explosive materials such as in coalmines. Specifically, the theory of globally-spherical, self-accelerating premixed expanding flames and that of [...] Read more.

A recent predictive scenario of premixed flame propagation in unobstructed passages is extended to account for obstructions that can be encountered in facilities dealing with explosive materials such as in coalmines. Specifically, the theory of globally-spherical, self-accelerating premixed expanding flames and that of flame acceleration in obstructed conduits are combined to form a new analytical formulation. The coalmining configuration is imitated by two-dimensional and cylindrical passages of high aspect ratio, with a comb-shaped array of tightly placed obstacles attached to the walls. It is assumed that the spacing between the obstacles is much less or, at least, does not exceed the obstacle height. The passage has one extreme open end such that a flame is ignited at a closed end and propagates to an exit. The key stages of the flame evolution such as the velocity of the flame front and the run-up distance are scrutinized for variety of the flame and mining parameters. Starting with gaseous methane-air and propane-air flames, the analysis is subsequently extended to gaseous-dusty environments. Specifically, the coal (combustible, i.e., facilitating the fire) and inert (such as sand, moderating the process) dust and their combinations are considered, and the impact of the size and concentration of the dust particles on flame acceleration is quantified. Overall, the influence of both the obstacles and the combustion instability on the fire scenario is substantial, and it gets stronger with the blockage ratio. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

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