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1

Simulation studies on the influence of other combustible gases on the characteristics of methane explosions at constant volume and high temperature

Luo Zhenmin, Liu Litao, Gao Shuaishuai, Wang Tao, Su Bin, Wang Lei, Yang Yong, Li Xiufang

Archives of Mining Sciences

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2021

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Vol. 66, no. 2

279--295

EN

Gas explosions are major disasters in coal mining, and they typically cause a large number of deaths, injuries and property losses. An appropriate understanding of the effects of combustible gases on the characteristics of methane explosions is essential to prevent and control methane explosions. FLACS software was used to simulate an explosion of a mixture of CH4 and combustible gases (C2H4, C2H6, H2, and CO) at various mixing concentrations and different temperatures (25, 60, 100, 140 and 180℃). After adding combustible gases to methane at a constant volume and atmospheric pressure, the adiabatic flame temperature linearly increases as the initial temperature increases. Under stoichiometric conditions (9.5% CH4-air mixture), the addition of C2H4 and C2H6 has a greater effect on the adiabatic flame temperature of methane than H2 and CO at different initial temperatures. Under the fuel-lean CH4-air mixture (7% CH4-air mixture) and fuel-rich mixture (11% CH4-air mixture), the addition of H2 and CO has a greater effect on the adiabatic flame temperature of methane. In contrast, the addition of combustible gases negatively affected the maximum explosion pressure of the CH4-air mixture, exhibiting a linearly decreasing trend with increasing initial temperature. As the volume fraction of the mixed gas increases, the adiabatic flame temperature and maximum explosion pressure of the stoichiometric conditions increase. In contrast, under the fuel-rich mixture, the combustible gas slightly lowered the adiabatic flame temperature and the maximum explosion pressure. When the initial temperature was 140℃, the fuel consumption time was approximately 8-10 ms earlier than that at the initial temperature of 25℃. When the volume fraction of the combustible gas was 2.0%, the consumption time of fuel reduced by approximately 10 ms compared with that observed when the volume fraction of flammable gas was 0.4%.

2

Comparative FE-studies of interface behavior of granular Cosserat materials under constant pressure and constant volume conditions

Ebrahimian B., Alsaleh M. I., Kahbasi A.

Archives of Mechanics

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2021

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Vol. 73, nr 5-6

421--470

EN

This article shows the outcomes of a systematic series of finite element (FE) calculations relevant to the shear behavior of a particulate-continuum interface system under different normal boundary conditions. In this respect, shearing of a thin and long granular Cosserat layer in the vicinity of a rigid moving wall with varied surface roughness values is analyzed under constant normal pressure and constant volume conditions. The material behavior is defined with a special elasto-plastic Cosserat model, taking into account micro-rotation, micro-curvature, couple stress, and mean particle size. The interaction between the layer of boundary particles and the surface roughness of the adjoining bottom wall is modeled by the rotation resistance of particles along the wall surface. Herein, the coupled effects of normal confining constraints imposed on the layer and the surface roughness of the bottom wall, are considered on the response of granular material under shearing. The influences of pressure level and initial void ratio are explored as well. Numerical results demonstrate that the dilatancy constraint prescribed to the interface plane in the normal direction, and the wall roughness have visible influences on the interface shear resistance as well as the deformation field formed within the layer. After large shearing, the width of the localized zone along the wall does not necessarily depend on the normal confining constraint and the applied pressure level. However, the localized zone characteristics and the interface shear response are mainly affected by the initial void ratio of the material. In addition to FE analyses, DEM-based simulations are also performed to investigate the micro-mechanical response of granular medium adjacent to a wall under shearing. FE predictions are qualitatively compared with DEM results, and reasonable agreement is observed.

3

Explosion Characteristics of Blast Furnace Gas

Skrinsky J., Veres J., Kolonicny J.

Inżynieria Mineralna

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2018

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R. 19, nr 1

131--136

EN

The main focus of this contribution is the explosion characteristics and hazards arising from the blast furnace gas. Primarily, these are the hazards of fire and explosion induced by flammable components of blast furnace gas. In order to prevent explosions when storing and handling blast furnace gas it is necessary to know the explosion limits of individual gas components and its gas mixtures in mixture with air. However, blast furnace gas from different blast furnace can vary significantly in its composition. Therefore, for each gas composition the explosion limits would have to be determined. This would require a considerable amount of time and effort. Due to this fact, the explosion limits of blast furnace gas are frequently referred to only by the hydrogen fraction of the gas mixture in the safety-relevant literature. In reality as blast furnace gas consists of hydrogen, carbon monoxide, carbon dioxide and further residual gases the explosion limits are generally over or underestimated.

PL

Celem artykułu jest charakterystyka i zagrożenia wynikające z wybuchu gazu wielkopiecowego. Niebezpieczeństwo pożaru i wybuchu wywołane jest przez łatwopalne składniki gazu wielkopiecowego. Aby zapobiec wybuchom w trakcie powstawania gazu wielkopiecowego konieczne jest poznanie granic wybuchowości poszczególnych składników gazu i mieszanin gazowych z powietrzem. Gaz wielkopiecowy z różnych wielkich pieców może się znacznie różnić pod względem składu. W związku z tym, dla każdego składu gazu należy określić granice wybuchowości. Wymaga to znacznego czasu i wysiłek. Z tego powodu granice wybuchu gazu wielkopiecowego są często określane (w literaturze dotyczącej bezpieczeństwa) tylko przez zawartość frakcji wodorowej w mieszaninie gazowej. W rzeczywistości gaz wielkopiecowy składa się z wodoru, tlenku węgla, dwutlenku węgla i innych gazów resztkowych. Granice wybuchowości są generalnie przekroczone.

4

Comparison of sandy soil shear strength parameters obtained by various construction direct shear apparatuses

Amsiejus J., Dirgeliene N., Norkus A., Skuodis S.

Archives of Civil and Mechanical Engineering

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2014

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Vol. 14, no. 2

327--334

EN

An analysis of test results performed by common type of direct shear apparatuses shows that normal stress on the shear plane of soil sample is not equal to vertical component of distributed external load applied to the top of soil sample. Performed measurements cleared that only 65–85% of total vertical load is transmitted to the sample shear plane. Thus, determining of the soil shear strength depends on shear apparatus construction, i.e. on actual magnitude of vertical load transmitted to the shear plane. The paper presents an analysis of shear strength parameters of sand determined by two different construction of direct shear apparatuses with movable lower shear ring. The soil shear strength parameters by employing direct shear apparatus SPF-2 have been obtained under constant vertical load and measuring the vertical load at different positions, namely: at the bottom and that of at the top of soil sample, respectively. The soil strength parameters by employing the universal shear testing device ADS 1/3 were determined under two conditions, namely: by maintaining constant soil volume and that of for constant vertical load, respectively. In both cases the vertical load was measured at the top of soil sample.

5

Combustion of ethanol-air mixtures in closed vessel comparison of simulation with the use of RANS and LES method

Jaworski P., Żbikowski M., Teodorczyk A.

Archivum Combustionis

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2011

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Vol. 31 nr 4

223-232

EN

Large Eddies Simulation method (LES) has become a powerful computational tool with application to turbulent flows. It links classical Reynolds Averaged Navier-Stokes (RANS) approach and Direct Numerical Simulation (DNS). This modeling approach computes the large eddies explicitly in a time-dependent simulation using the filtered Navier-Stokes equations. LES resolves the large flow scales that depend directly on the geometry where small scales are modeled by the sub-grid-scale models. LES is expected to improve the description of the aerodynamic and combustion processes in Internal Combustion Engines. With LES it is possible to resolve the essential part of the flow energy, yielding reliable results. Proper predictions depend on the quality of sub-grid-scale (SGS) models. In this paper the computational analysis is compared with experimental results in constant volume chamber. In that way there is a possibility to see the difference in results of initial flame kernel development and laminar flame speed. The calculations were made for two different combustion models. This allows to compare the experimental and simulation results for RANS (Fire ECFM combustion model) and LES (Fire) method and make further improvement in LES combustion model for application in full engine simulation.