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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "I2: Energy and Combustion Science".

Deadline for manuscript submissions: closed (28 February 2022) | Viewed by 30565

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Dr. Alexandre M. Afonso

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CEFT-Transport Phenomena Research Center, Department of Mechanical Engineering, Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal
Interests: theoretical and computational rheology; complex flows of complex fluids; electrokinetics; multiphase flow; micro-combustion
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Prof. Dr. Pedro Resende

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Department of Mechanical Engineering, School of Technology and Management (ESTG), Polytechnic Institute of Viana do Castelo (IPVC), Praça Gen. Barbosa 44, 4900-347 Viana do Castelo, Portugal
Interests: turbulence models; viscoelastic fluids; microcombustion; computer simulation; energy and CSP; systems biomass and energy conversion systems
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Prof. Dr. Mohsen Ayoobi

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Guest Editor

Division of Engineering Technology, Wayne State University, Detroit, MI 48201 USA
Interests: numerical modeling analysis; computational fluid dynamics; combustion physics, flame dynamics and instabilities; engineering education research
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Special Issue Information

Dear Colleagues,

The Guests Editors are pleased to invite submissions for a Special Issue entitled “Numerical Investigations of Combustion” in the open access journal Energies.

This Special Issue is launched to address recent advances in numerical modeling of combustion-related applications. With the recent advancements in computational capacities and the widespread applications of machine learning in engineering problems, the role of numerical methods is becoming more and more important to improve existing models or develop new models that can help researchers to better understand the underlying physics of combustion, their interaction with other physical phenomena such as turbulence, and their impacts on the performance of the related applications at both fundamental and practical levels.

This Special Issue aims to highlight the most recent advances in the development and application of such numerical methods.

Prof. Dr. Alexandre Afonso
Prof. Dr. Pedro Resende
Prof. Dr. Mohsen Ayoobi
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Laminar/turbulent combustion
Gaseous, liquid, and/or solid fuel combustion
Premixed/non-premixed and homogeneous/non-homogeneous combustion
Reaction kinetics
Combustion-related micropower generation
Internal combustion engines
Fuel reforming/alternative fuels
Other

Published Papers (13 papers)

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Editorial

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5 pages, 190 KiB

Open AccessEditorial

Numerical Investigations of Combustion—An Overview

by Mohsen Ayoobi, Pedro R. Resende and Alexandre M. Afonso

Energies 2022, 15(9), 2975; https://doi.org/10.3390/en15092975 - 19 Apr 2022

Cited by 1 | Viewed by 1367

Abstract

With the recent advancements in computational capacities and the widespread applications of machine learning in engineering problems, the role of numerical methods has been becoming more and more important to improve existing models or develop new models that can help researchers to better understand the underlying physics of combustion, their interaction with other physical phenomena such as turbulence, and their impacts on the performance of the related applications at both fundamental and practical levels [...] Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

Research

Jump to: Editorial

15 pages, 5464 KiB

Open AccessArticle

Combustion Characteristics of Premixed Hydrogen/Air in an Undulate Microchannel

by Pedro R. Resende, Leandro C. Morais, Carlos Pinho and Alexandre M. Afonso

Energies 2022, 15(2), 626; https://doi.org/10.3390/en15020626 - 17 Jan 2022

Cited by 4 | Viewed by 1624

Abstract

This work reports a numerical investigation of microcombustion in an undulate microchannel, using premixed hydrogen and air to understand the effect of the burner design on the flame in order to obtain stability of the flame. The simulations were performed for a fixed equivalence ratio and a hyperbolic temperature profile imposed at the microchannel walls in order to mimic the heat external losses occurred in experimental setups. Due to the complexity of the flow dynamics combined with the combustion behavior, the present study focuses on understanding the effect of the fuel inlet rate on the flame characteristics, keeping other parameters constant. The results presented stable flame structure regardless of the inlet velocity for this type of design, meaning that a significant reduction in the heat flux losses through the walls occurred, allowing the design of new simpler systems. The increase in inlet velocity increased the flame extension, with the flame being stretched along the microchannel. For higher velocities, flame separation was observed, with two detected different combustion zones, and the temperature profiles along the burner centerline presented a non-monotonic decrease due to the dynamics of the vortices observed in the convex regions of the undulated geometry walls. The geometry effects on the flame structure, flow field, thermal evolution and species distribution for different inlet velocities are reported and discussed. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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16 pages, 4789 KiB

Open AccessArticle

Laminar Burning Velocities of Hydrogen-Blended Methane–Air and Natural Gas–Air Mixtures, Calculated from the Early Stage of p(t) Records in a Spherical Vessel

by Maria Mitu, Domnina Razus and Volkmar Schroeder

Energies 2021, 14(22), 7556; https://doi.org/10.3390/en14227556 - 12 Nov 2021

Cited by 60 | Viewed by 3659

Abstract

The flammable hydrogen-blended methane–air and natural gas–air mixtures raise specific safety and environmental issues in the industry and transportation; therefore, their explosion characteristics such as the explosion limits, explosion pressures, and rates of pressure rise have significant importance from a safety point of view. At the same time, the laminar burning velocities are the most useful parameters for practical applications and in basic studies for the validation of reaction mechanisms and modeling turbulent combustion. In the present study, an experimental and numerical study of the effect of hydrogen addition on the laminar burning velocity (LBV) of methane–air and natural gas–air mixtures was conducted, using mixtures with equivalence ratios within 0.90 and 1.30 and various hydrogen fractions r_H within 0.0 and 0.5. The experiments were performed in a 14 L spherical vessel with central ignition at ambient initial conditions. The LBVs were calculated from p(t) data, determined in accordance with EN 15967, by using only the early stage of flame propagation. The results show that hydrogen addition determines an increase in LBV for all examined binary flammable mixtures. The LBV variation versus the fraction of added hydrogen, r_H, follows a linear trend only at moderate hydrogen fractions. The further increase in r_H results in a stronger variation in LBV, as shown by both experimental and computed LBVs. Hydrogen addition significantly changes the thermal diffusivity of flammable CH₄–air or NG–air mixtures, the rate of heat release, and the concentration of active radical species in the flame front and contribute, thus, to LBV variation. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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16 pages, 3994 KiB

Open AccessArticle

Effects of the Multiple Injection Strategy on Combustion and Emission Characteristics of a Two-Stroke Marine Engine

by Ju-Hwan Seol, Van Chien Pham and Won-Ju Lee

Energies 2021, 14(20), 6821; https://doi.org/10.3390/en14206821 - 19 Oct 2021

Cited by 7 | Viewed by 2095

Abstract

This paper presents research on the effects of the multiple injection strategies on the combustion and emission characteristics of a two-stroke heavy-duty marine engine at full load. The ANSYS FLUENT simulation software was used to conduct three-dimensional simulations of the combustion process and emission formations inside the engine cylinder in both single- and double-injection modes to analyze the in-cylinder pressure, temperature, and emission characteristics. The simulation results were then compared and showed good agreement with the measured values reported in the engine’s sea-trial technical reports. The simulation results showed reductions in the in-cylinder pressure and temperature peaks by 6.42% and 12.76%, while NO and soot emissions were reduced up to 24.16% and 68%, respectively, in the double-injection mode in comparison with the single-injection mode. However, the double-injection strategy increased the CO₂ emission (7.58%) and ISFOC (23.55%) compared to the single-injection. These are negative effects of the double-injection strategy on the engine that the operators need to take into consideration. The results were in line with the literature reviews and would be good material for operators who want to reduce the engine exhaust gas emission in order to meet the stricter IMO emission regulations. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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16 pages, 2085 KiB

Open AccessArticle

Reactivity Model as a Tool to Compare the Combustion Process in Aviation Turbine Engines Powered by Synthetic Fuels

by Tomasz Białecki, Wojciech Dzięgielewski, Mirosław Kowalski and Andrzej Kulczycki

Energies 2021, 14(19), 6302; https://doi.org/10.3390/en14196302 - 2 Oct 2021

Cited by 5 | Viewed by 1927

Abstract

The paper aims to verify the thesis that the reactivity model, developed in earlier research, can be used to compare the fuels combustion processes in turbine engines, which is important for predicting the behavior of different alternative fuels in combustion process. Synthetic blending components from alcohol to jet and hydroprocessed esters and fatty acids technologies and their blends with conventional jet fuel were used in tests. The undertaken laboratory tests reveal the differences between the properties of the tested fuels. Bench tests were carried out on a test rig with a miniature turbojet engine, according to authorial methodology. For each blend, on selected points of rotational speed the carbon oxide concentration in the exhaust gases was recorded. The obtained results allowed the formulation of empirical power functions describing relations between carbon oxide concentration and fuel mass flow rate. Based on general assumptions, the reactivity model was adopted to compare the combustion processes of the different fuels in turbine engines. The directions of further research on the development of the proposed model were indicated. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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23 pages, 3591 KiB

Open AccessArticle

Numerical Analysis of GDI Flash Boiling Sprays Using Different Fuels

by Raul Payri, Pedro Marti-Aldaravi, Rami Abboud and Abian Bautista

Energies 2021, 14(18), 5925; https://doi.org/10.3390/en14185925 - 18 Sep 2021

Cited by 7 | Viewed by 2397

Abstract

Modeling the fuel injection process in modern gasoline direct injection engines plays a principal role in characterizing the in–cylinder mixture formation and subsequent combustion process. Flash boiling, which usually occurs when the fuel is injected into an ambient pressure below the saturation pressure of the liquid, is characterized by fast breakup and evaporation rates but could lead to undesired behaviors such as spray collapse, which significantly effects the mixture preparation. Four mono–component fuels have been used in this study with the aim of achieving various flashing behaviors utilizing the Spray G injector from the Engine Combustion Network (ECN). The numerical framework was based on a Lagrangian approach and was first validated for the baseline G1 condition. The model was compared with experimental vapor and liquid penetrations, axial gas velocity, droplet sizes and spray morphology and was then extended to the flash boiling condition for iso–octane, n–heptane, n–hexane, and n–pentane. A good agreement was achieved for most of the fuels in terms of spray development and shape, although the computed spray morphology of pentane was not able to capture the spray collapse. Overall, the adopted methodology is promising and can be used for engine combustion modeling with conventional and alternative fuels. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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16 pages, 2456 KiB

Open AccessArticle

Deflagration Characteristics of N₂-Diluted CH₄-N₂O Mixtures in the Course of the Incipient Stage of Flame Propagation

by Maria Mitu, Codina Movileanu and Venera Giurcan

Energies 2021, 14(18), 5918; https://doi.org/10.3390/en14185918 - 17 Sep 2021

Cited by 6 | Viewed by 1679

Abstract

In this study, experimental measurements in a spherical combustion bomb were performed in order to investigate the flame propagation in N₂-diluted CH₄-N₂O mixtures with stoichiometric equivalence ratio, at several initial pressures (0.5–1.75 bar) and ambient initial temperatures. Methane was chosen as a test-fuel, since it is the main component of natural gas, a fuel often used as a substitute to gasoline in engines with internal combustion and industrial plants. The method approached in this study is based on a simple examination of the cubic law of pressure rise during the early (incipient) period of flame propagation. The incipient stage defined by a pressure rise equal or smaller than the initial pressure, was divided into short time intervals. The burnt mass fractions (obtained using three different Equations) and flame radii at various moments of the flame propagation in the course of the incipient stage were calculated. The cubic law coefficients and corresponding laminar burning velocities at considered time intervals were also reported. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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19 pages, 6913 KiB

Open AccessArticle

Computational Analysis of Premixed Syngas/Air Combustion in Micro-channels: Impacts of Flow Rate and Fuel Composition

by Sunita Pokharel, Mohsen Ayoobi and V’yacheslav Akkerman

Energies 2021, 14(14), 4190; https://doi.org/10.3390/en14144190 - 11 Jul 2021

Cited by 10 | Viewed by 2280

Abstract

Due to increasing demand for clean and green energy, a need exists for fuels with low emissions, such as synthetic gas (syngas), which exhibits excellent combustion properties and has demonstrated promise in low-emission energy production, especially at microscales. However, due to complicated flame properties in microscale systems, it is of utmost importance to describe syngas combustion and comprehend its properties with respect to its boundary and inlet conditions, and its geometric characteristics. The present work studied premixed syngas combustion in a two-dimensional channel, with a length of 20 mm and a half-width of 1 mm, using computational approaches. Specifically, a fixed temperature gradient was imposed at the upper wall, from 300 K at the inlet to 1500 K at the outlet, to preheat the mixture, accounting for the conjugate heat transfer through the walls. The detailed chemistry of the ignition process was imitated using the San Diego mechanism involving 46 species and 235 reactions. For the given boundary conditions, stoichiometric premixed syngas containing various compositions of carbon monoxide, methane, and hydrogen, over a range of inlet velocities, was simulated, and various combustion phenomena, such as ignition, flame stabilization, and flames with repeated extinction and ignition (FREI), were analyzed using different metrics. The flame stability and the ignition time were found to correlate with the inlet velocity for a given syngas mixture composition. Similarly, for a given inlet velocity, the correlation of the flame properties with respect to the syngas composition was further scrutinized. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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19 pages, 8652 KiB

Open AccessArticle

Numerical and Experimental Study of a Jet-and-Recirculation Stabilized Low Calorific Combustor for a Hybrid Power Plant

by Felix Grimm, Timo Lingstädt, Peter Kutne and Manfred Aigner

Energies 2021, 14(3), 537; https://doi.org/10.3390/en14030537 - 21 Jan 2021

Cited by 5 | Viewed by 2148

Abstract

An atmospheric prototype burner is studied with numerical and experimental tools. The burner system is designed for operation in a hybrid power plant for decentralized energy conversion. In order to realize such a coupled system, a reliable combustion system has to be established. Numerical and experimental findings in the presented study demonstrate the capabilities of the novel burner system in suitable operation conditions. In this system, a solid oxide fuel cell (SOFC) is mounted upstream of the burner in the gas turbine system. The combination of both realizes a large operational flexibility with comparably high overall efficiency. Since the combustor is operated with SOFC off-gas, several challenges arise. Low calorific combustion needs careful burner design and numerical modeling, since the heat-loss mechanisms occur to be in the order of magnitude of thermal power output. Thus, different modeling strategies are discussed in the paper. The numerical studies are compared with experimental results and high-quality simulation results complement limited measured findings with easy-to-use low fidelity RANS models. A priori measurements are employed for the selection of investigation points. It is shown that the presented combustor system is able to cover low-calorific combustion over a large range of operation conditions, despite major heat-loss effects, which are characterized by means of numerical CFD (Computational Fluid Dynamics) modeling. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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17 pages, 1224 KiB

Open AccessArticle

Numerical Investigation of the Impact of H₂ Enrichment on Lean Biogas/Air Flames: An Analytical Modelling Approach

by Filipe M. Quintino and Edgar C. Fernandes

Energies 2021, 14(2), 369; https://doi.org/10.3390/en14020369 - 11 Jan 2021

Cited by 6 | Viewed by 1764

Abstract

The transition from natural gas to renewable gases such as biogas and hydrogen creates an interchangeability challenge. The laminar flame speed

S_{L}

is a critical parameter in appliance design as it is a unique characteristic of the flame mixture. It is thus [...] Read more.

The transition from natural gas to renewable gases such as biogas and hydrogen creates an interchangeability challenge. The laminar flame speed

S_{L}

is a critical parameter in appliance design as it is a unique characteristic of the flame mixture. It is thus essential to evaluate the impact of renewable gases on

S_{L}

. In this work, 1D simulations were conducted in Cantera with the USC-Mech 2.0 kinetic mechanism. The

S_{L}

of three base biogas blends (BG100, BG90 and BG80) was computed for H₂ enrichment up to 50% in volume, equivalence ratio

0.8 \leq ϕ \leq 1.0

p = 1

atm and

T_{u} = 298

K. It was found that the effect of H₂ enrichment is higher for base blends with higher CO₂ content as the thermal-diffusive and dilution effects of carbon dioxide are mitigated by hydrogen. The introduction of H₂ also increases the H radical pool, which is linked with the increase in

S_{L}

. A new correlation to model the impact of H₂ enrichment,

S_{L} (x_{H_{2}}) = (ζ (ϕ) / S_{L}^{'} (x_{C O_{2}})) x_{H_{2}} e^{x_{H_{2}}} + S_{L}^{'} (x_{C O_{2}})

, is proposed, which exhibits good agreement with the literature data and simulations. This equation can be directly used to estimate

S_{L}

without the need for a priori adaptations of fit parameters as the contributions of CO₂ and H₂ are isolated in independent variables. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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27 pages, 5461 KiB

Open AccessArticle

An Artificial Neural Network for the Low-Cost Prediction of Soot Emissions

by Mehdi Jadidi, Stevan Kostic, Leonardo Zimmer and Seth B. Dworkin

Energies 2020, 13(18), 4787; https://doi.org/10.3390/en13184787 - 14 Sep 2020

Cited by 16 | Viewed by 2943

Abstract

Soot formation in combustion systems is a growing concern due to its adverse environmental and health effects. It is considered to be a tremendously complicated phenomenon which includes multiphase flow, thermodynamics, heat transfer, chemical kinetics, and particle dynamics. Although various numerical approaches have been developed for the detailed modeling of soot evolution, most industrial device simulations neglect or rudimentarily approximate soot formation due to its high computational cost. Developing accurate, easy to use, and computationally inexpensive numerical techniques to predict or estimate soot concentrations is a major objective of the combustion industry. In the present study, a supervised Artificial Neural Network (ANN) technique is applied to predict the soot concentration fields in ethylene/air laminar diffusion flames accurately with a low computational cost. To gather validated data, eight different flames with various equivalence ratios, inlet velocities, and burner geometries are modeled using the CoFlame code (a computational fluid dynamics (CFD) parallel combustion and soot model) and the Lagrangian histories of soot-containing fluid parcels are computed and stored. Then, an ANN model is developed and optimized using the Levenberg-Marquardt approach. Two different scenarios are introduced to validate the network performance; testing the prediction capabilities of the network for the same eight flames that are used to train the network, and for two new flames that are not within the training data set. It is shown that for both of these cases the ANN is able to predict the overall soot concentration field very well with a relatively low integrated error. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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19 pages, 6082 KiB

Open AccessArticle

Acceleration of Premixed Flames in Obstructed Pipes with Both Extremes Open

by Abdulafeez Adebiyi, Olatunde Abidakun and V’yacheslav Akkerman

Energies 2020, 13(16), 4094; https://doi.org/10.3390/en13164094 - 7 Aug 2020

Cited by 4 | Viewed by 2045

Abstract

Premixed flame propagation in obstructed channels with both extremes open is studied by means of computational simulations of the reacting flow equations with a fully-compressible hydrodynamics, transport properties (heat conduction, diffusion and viscosity) and an Arrhenius chemical kinetics. The aim of this paper is to distinguish and scrutinize various regimes of flame propagation in this configuration depending on the geometrical and thermal-chemical parameters. The parametric study includes various channel widths, blockage ratios, and thermal expansion ratios. It is found that the interplay of these three critical parameters determines a regime of flame propagation. Specifically, either a flame propagates quasi-steady, without acceleration, or it experiences three consecutive distinctive phases (quasi-steady propagation, acceleration and saturation). This study is mainly focused on the flame acceleration regime. The accelerating phase is exponential in nature, which correlates well with the theoretical prediction from the literature. The accelerating trend also qualitatively resembles that from semi-open channels, but acceleration is substantially weaker when both extremes are open. Likewise, the identified regime of quasi-steady propagation fits the regime of flame oscillations, found for the low Reynolds number flames. In addition, the machine learning logistic regression algorithm is employed to characterize and differentiate the parametric domains of accelerating and non-accelerating flames. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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15 pages, 1936 KiB

Open AccessArticle

Numerical Investigation of the Required Quantity of Inert Gas Agents in Fire Suppression Systems

by Xiaoqin Hu, Arjen Kraaijeveld and Torgrim Log

Energies 2020, 13(10), 2536; https://doi.org/10.3390/en13102536 - 16 May 2020

Cited by 6 | Viewed by 2910

Abstract

Inert gas agents have the potential to be widely used in fire suppression systems due to health and safety concerns associated with active chemicals. To suppress fire while minimizing hypoxic effects in an occupied area, the discharge quantity of inert gas agents should be carefully designed to dilute the oxygen concentration to a specific threshold level. In this study, the general expressions between oxygen concentration, the discharge rate of inert gas agents, and the ventilation rate of the air-agent mixture are derived first. Then, explicit formulas to calculate the discharge/ventilation rate and the required quantity of inert gas agents are given if the discharge rate and ventilation rate both are constants. To investigate the dilution and fire extinguishing efficiencies of inert gas agents, two scenarios with a discharge of inert gas agents into an enclosure are modeled using the Fire Dynamic Simulator (FDS). The simulation results show that the average oxygen mass fraction approximately reaches the design level at the end of the discharge period. Variation in oxygen concentration along the enclosure height is analyzed. For the scenario with a fire source, oxygen mass fraction decreases fast as oxygen is consumed by the combustion process. Thus, the fire is extinguished a little earlier than the end of the discharge period. Full article

(This article belongs to the Special Issue Numerical Investigations of Combustion)

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