Increasing Methane Concentration Research Articles

The marine methane cycle in the Canadian Arctic Archipelago during summer.

In the Arctic Ocean, methane concentrations surpassing global averages are prevalent, especially along sub-Arctic and Arctic continental shelf margins. Despite elevated dissolved methane levels, the Arctic Ocean exhibits minimal methane fluxes to the atmosphere, indicating a potential role of water column oxidation in methane processing. During the Northwest Passage Project in the summer of 2019, we integrated thermohaline, chemical, and biological data with in-situ and in-vitro methane data in Canadian Arctic Archipelago (CAA) waters. Elevated in-situ dissolved methane was prominent in near-surface Pacific waters (between 2 and 7m), particularly in meltwater regions, with av. concentrations of 5.8±2.5 nM within the upper 30m. While methane oxidation constants were generally low (av. 0.006±0.002 d-1), surface waters in Wellington Channel and Croker Bay exhibited higher rates (av. 0.01±0.0004 d-1), associated with Pacific-origin microbial taxa like Oleispira and Aurantivirga. Deeper layers (>200m) displayed lower methane concentrations (av. 3.1±1.1 nM) and oxidation rates (av. 0.005±0.001 d-1). Sea ice showed elevated dissolved methane concentrations (av. 9.2±5 nM). Waters in the western CAA exhibited a 25% increase in methane concentrations compared to ice-free areas. The overall picture suggested supersaturation of in-situ methane in shallow waters (between 2 and 50m), coupled with faster oxidation rates in meltwater and Pacific dominant layers, suggesting rapid seasonal cycling of methane and prevention of the methane migration into the atmosphere.

On the lower explosion limit of ventilation air methane under high temperatures

Regenerative thermal oxidation of Ventilation-Air-Methane is a technology for clean utilization of energy. Increasing methane concentration can enhance utilization efficiency, but pose a risk of explosion. To ensure the safe and effective utilization of VAM, critical concentration of oxidation to explosion is determined through experiments and simulations. Results indicate that GRTO model established by our group exhibits the highest prediction accuracy of 99.57%. The model was selected to study critical mechanisms of oxidation to explosion, thereby providing theoretical guidance for VAM utilization. The oxidation process can be divided into three stages: CH4 pyrolysis, rapidly generation/consumption of ·CH3/·HCO, and CO oxidation. With temperature rises from 600 °C to 800 °C and then to 1000 °C, the explosion limit of methane decreases mainly by speeding up ·H + O2⇔·O+·OH, and the ignition timing at critical limit shifts from the stage of ·CH3O generation/consumption to ·CH3 generation/consumption, and ultimately to ·OH formation/accumulation.

A Life Cycle Assessment of Methane Slip in Biogas Upgrading Based on Permeable Membrane Technology with Variable Methane Concentration in Raw Biogas

While energy-related sectors remain significant contributors to greenhouse gas (GHG) emissions, biogas production from waste through anaerobic digestion (AD) helps to increase renewable energy production. The biogas production players focus efforts on optimising the AD process to maximise the methane content in biogas, improving known technologies for biogas production and applying newly invented ones: H2 addition technology, high-pressure anaerobic digestion technology, bioelectrochemical technology, the addition of additives, and others. Though increased methane concentration in biogas gives benefits, biogas upgrading still needs to reach a much higher methane concentration to replace natural gas. There are many biogas upgrading technologies, but almost any has methane slip. This research conducted a life cycle assessment (LCA) on membrane-based biogas upgrading technology, evaluating biomethane production from biogas with variable methane concentrations. The results showed that the increase in methane concentration in the biogas slightly increases the specific electricity consumption for biogas treatment, but heightens methane slip with off-gas in the biogas upgrading unit. However, the LCA analysis showed a positive environmental impact for treating biogas with increasing methane concentrations. This way, the LCA analysis gave a broader comprehension of the environmental impact of biogas upgrading technology on GHG emissions and offered valuable insights into the environmental implications of biomethane production.

Three Decades of Wetland Methane Surface Flux Modeling by Earth System Models‐Advances, Applications, and Challenges

AbstractEarth System Models (ESMs) simulate the exchange of mass and energy between the land surface and the atmosphere, with a key focus on modeling natural greenhouse gas feedbacks. Methane is the second most important greenhouse gas after carbon dioxide. There are growing concerns over the rapidly increasing methane concentration in the atmosphere, underscoring the need for accurate global modeling of its emissions using ESMs. Of the multitude of sources of methane globally, wetlands are the largest natural emitters for methane, leading to significant efforts targeting their representation in ESMs with a special focus on their methane emissions. In this review, we first provide a historical overview of including wetland‐methane components in ESMs and how methane modeling approaches have evolved over time. Second, we discuss recent modeling advancements that show promise for improvements in methane emissions predictions, namely the coupling of surface and atmospheric modules of ESMs, the representation of microtopography and transport mechanisms, the resolution of microbial processes at different spatial‐temporal scales, and the improved mapping of wetland area extent across the different wetland types. Third, we shed light on the different challenges hindering accurate estimations of wetland‐methane emissions, as shown by the consistent discrepancy between bottom‐up and top‐down models' predictions. Finally, we emphasize that more detailed representation of biogeochemistry and dynamic hydrology while resolving the within‐wetland vegetation heterogeneity should improve model predictions, especially when coupled with expanding ground‐based measurement networks and high‐resolution remote sensing mapping of methane‐relevant variables, such as water elevation, water table depth, and methane concentration.

Characteristics and Influence Factors of Natural Desorption in Coal Bodies from Fukang Mining Area, Xinjiang, China.

Coal body desorption characteristics are one of the key factors that influence the development of coalbed methane (CBM). In this study, 91 coal core samples from 11 CBM wells in the Fukang mining area were collected from Xinjiang, China, and the coal quality, high-pressure mercury compression, gas content, and natural desorption characteristics measurements were launched. With the detailed analyses of the differences in cumulative desorption volume, desorption ratio, and on-site average desorption rate for the coal samples with different body structures and macrolithotypes, the influence of the maximum reflectance of vitrinite, microscopic coal rock composition, and coal quality and pore characteristics on CBM desorption characteristics were discussed. The results showed that the cumulative desorption volume, desorption ratio, and desorption rate of cataclastic structure-bright coal are higher than those of primary structure-semibright coal. With the increase of RO,max and vitrinite content, the adsorption capacity of coal increases, and the increased methane concentration difference during desorption leads to an increase in cumulative desorption volume and on-site average desorption rate. The higher contents of moisture and ash yield would occupy the adsorption sites and hinder gas diffusion, which would decrease the desorption of coalbed methane. The greater porosity/pore volume ratio of medium and large pores can enhance the connectivity of pores, which increases the desorption ratio and the average desorption rate, while the higher micropore porosity/pore volume ratio can increase the gas adsorption space and the cumulative desorption volume. The pore characteristics have the most significant effect on the cumulative desorption volume and desorption ratio. The results of the study can help guide coal mine gas management and CBM development from middle-and low-rank coal reservoirs in Xinjiang.

Methane Emissions from Rice Fields of the Rostov Region

On the example of the Rostov region, the results of measurements by the chamber method of methane fluxes into the atmosphere from rice fields are analyzed. In addition to measuring methane fluxes in the phases of “germination” and “full ripeness” of rice, concentrations of methane and hydrogen sulfide, Eh, pH, density and humidity were determined in the water of the rice check and various horizons of watered soils. The rate of methane flow into the atmosphere from the surface of the rice check varied in the range from 0.195 to 0.531 mg СН4/(m2 h) and in the “full ripeness” phase of rice was on average 2.1 times higher than in the “germination” phase. The rate of methane flow into the atmosphere from the surface of soils located between rice checks was on average 4.9–12.1 times lower than the rate of its flow from rice checks, varying within 0.034–0.045 mg СН4/(m2 h). It is shown that after watering rice checks in soils isolated by a layer of water, Eh values decrease and, as a consequence, there is an increase in methane concentrations in soils and its fluxes into the atmosphere. According to the assessment, the total methane emission by rice fields of the Rostov region approximately reaches 1.253 tons per day or 150 tons/year, which is 0.4–1.5% of the annual methane release by the soils of the Rostov region.

Acceleration characteristics of composite flame in the initial stage of gas/coal dust explosion and analysis of disaster intensification

To clarify the strengthening mechanism of gas/coal dust coupling explosion disasters, a 20 L spherical explosion test system, high-speed schlieren, and PIV analysis were used to study the acceleration characteristics and pressure change of composite flames in the initial stage of gas/coal dust explosion, and the flow field characteristics were also analyzed. The results showed that methane concentration had the most important influence on the formation and development of composite flame. When the methane concentration was 7.5% and 9%, the composite flame propagation showed obvious acceleration characteristics and developed spherically, the flame boundary was clear and smooth, with the whole flame being continuous and bright white. Meanwhile, the Markstein length of composite flame is positive, and increased with the increase of methane concentration and dust particle size but decreased with the increase of coal dust mass concentration, the Markstein length for 9% gas concentration was 7 times larger than 6% gas concentration, indicating the increase of gas concentration can obviously inhibit the instability of composite flame, which prolonged the residence time of coal dust particles in the composite flame, resulting in the enhancement of the pyrolysis of coal dust and improvement of explosion intensity. The PIV test results of 9% gas/coal dust explosion showed that due to the high initial explosion intensity, the negative pressure in the center of the composite flame made most of the coal dust particles undergo centripetal movement, and a large number of coal dust particles gathered around the front of the flame. At the same time, a large number of large vortices in opposite directions were formed around the front of the flame, which promoted rapid contact between the coal dust surface and oxygen and intensified the combustion reaction. The research results can provide guidance for the prevention and control of gas/coal dust composite explosion disasters.

Evaluation of biogas production rate and leachate treatment in Landfill through a water-energy nexus framework for integrated waste management

The aim of this study was to investigate the simultaneous biogas generation and leachate treatment using municipal waste and its polluted leachate at Mashhad landfill in northeast Iran. The research focused on examining the kinetic model of CH4, CO2, CO, H2S and O2 production with and without leachate recirculation (LR) through control/test wells. The findings from both wells showed an increase in logarithmic CH4 production rate, with the coefficient related to the rate of increase in methane concentration ranging from 0/52-0/64 in the control well and 0/47-0/55 in the test well, respectively. Under LR conditions, it was observed that the CH4 production rate was slower, taking an average of 120 minutes to reach 50% concentration, compared to just 15 minutes without LR. Using first-order equations, the CH4 production coefficients were measured to be 2/17 h−1 and 0/9 h−1 for the control and test wells, respectively. The analysis of recirculated leachate revealed a significant decrease (∼30%) in the total volume of leachate with 72% COD removal, which could help manage overloaded leachate problems in the landfill. The COD removal coefficient was found to be 0/036 day−1 in the control well, whereas the test well with leachate recirculation showed a more rapid decrease from 50 g.l−1 to about 14 g.l−1 with a removal coefficient of 0/012 day−1, three times higher than the control well. Additionally, nitrogen content analysis indicated that although the amount of ammonia content increased with LR, the increase was relatively low in comparison to conditions without LR, equivalent to 1394 ppm and 1000 ppm in control and test wells, respectively. This study aligns with the water-energy-nexus concept by offering a sustainable solution for waste management and energy generation, while also addressing water management challenges associated with landfill operations.

Study of On-Site Upgraded Livestock Biogas Production and Carbon Emission Reduction By Substituting Coals For Thermal Power Generation

The objective of this project is to integrate a farm-scale bio-desulfurization facility with a novel biogas hollow fibre adsorption module for biogas desulfurization and bio-natural gas production. In this study, the desulfurization experimental results showed that the bio-desulfurization system can remove 96.7 ± 6% of H2S from the biogas after an approximately two-month enrichment period. The average CH4, N2, and CO2 concentrations in raw biogas were 63.4, 15.2, and 21.1%, respectively. As for biogas upgrading experiments, the inlet biogas flow rates were applied from 5 to 20 L/min. The removal efficiency of CO2 under all biogas flow rates was 100%. Meanwhile, methane was promoted from 60% to nearly 94% (i.e. 57% increase in methane concentration). The replacement of anthracite and coking coal by upgraded biogas might reduce 44.4% and 42.5% of CO2 equivalent, respectively. The achievement of this project pursues the mitigation of carbon dioxide emissions by using upgraded pig biogas which can be enlarged and extended to all decentralized pig farms worldwide.

Study of on-site upgraded livestock biogas production and carbon emission reduction by substituting coals for thermal power generation

The objective of this project is to integrate a farm-scale bio-desulfurization facility with a novel biogas hollow fibre adsorption module for biogas desulfurization and bio-natural gas production. In this study, the desulfurization experimental results showed that the bio-desulfurization system can remove 96.7 ± 6% of H2S from the biogas after an approximately two-month enrichment period. The average CH4, N2, and CO2 concentrations in raw biogas were 63.4, 15.2, and 21.1%, respectively. As for biogas upgrading experiments, the inlet biogas flow rates were applied from 5 to 20 L/min. The removal efficiency of CO2 under all biogas flow rates was 100%. Meanwhile, methane was promoted from 60% to nearly 94% (i.e. 57% increase in methane concentration). The replacement of anthracite and coking coal by upgraded biogas might reduce 44.4% and 42.5% of CO2 equivalent, respectively. The achievement of this project pursues the mitigation of carbon dioxide emissions by using upgraded pig biogas which can be enlarged and extended to all decentralized pig farms worldwide.

Synthesis of Polycrystalline Diamond Films in Microwave Plasma at Ultrahigh Concentrations of Methane

Polycrystalline diamond (PCD) films are usually grown by chemical vapor deposition (CVD) in hydrogen–methane mixtures. The synthesis conditions determine the structure and quality of the grown material. Here, we report the complex effect of the microwave plasma CVD conditions on the morphology, growth rate and phase composition of the resulting PCD films. Specifically, we focus on the factors of (i) increased methane concentrations (νc) that are varied over a wide range of 4%–100% (i.e., pure methane gas) and (ii) substrate temperatures (Ts) varied between 700–1050 °C. Using scanning electron microscopy, X-ray diffraction and Raman spectroscopy, we show that diamond growth is possible even at ultrahigh methane concentrations, including νc = 100%, which requires relatively low synthesis temperatures of Ts < 800 °C. In general, lower substrate temperatures tend to facilitate the formation of higher-quality PCD films; however, this comes at the cost of lower growth rates. The growth rate of PCD coatings has a non-linear trend: for samples grown at Ts = 800 °C, the growth rate increases from 0.6 µm/h at νc = 4% to 3.4 µm/h at νc = 20% and then falls to 0.6 µm/h at νc = 100%. This research is a step toward control over the nature of the CVD-grown PCD material, which is essential for the precise and flexible production of diamond for various applications.

Wetting characteristics of ethane droplet – A molecular dynamics study

The wettability significantly affects condensation heat transfer of alkanes on the surface. When designing high-efficiency heat exchangers, it is necessary to grasp the wetting patterns of alkanes. Therefore, the wetting characteristics of ethane droplets on the surface are investigated based on molecular dynamics simulation. The results show that the contact angle of pure ethane droplet reduces as the surface potential energy depth parameter ε increases. The contact angle of pure ethane is larger than that of pure methane under the same ε, and the difference augments with the increasing ε. The enhanced molecular thermal motion caused by the rise in temperature produces different orientation outcomes on different VDW-functioned surfaces. The cumulative effect of molecular movement leads to a macroscopic displacement of the droplet, which makes the contact angle of pure ethane augment on hydrophobic surface, remain constant on neutral surface, and decrease on hydrophilic surface, meaning that the rise in temperature will strengthen the wetting tendency of pure ethane droplet. The addition of methane to ethane droplet acts as a “lubricant”, resulting in local molecular activation and an increase in diffusion. The contact angles of mixed droplets on hydrophobic, neutral, and hydrophilic surfaces all decrease linearly with the increasing methane concentration. And the larger the contact angle gap between methane and ethane on the same surface, the larger the decrease in the contact angle of mixed droplets. This paper investigates the wetting characteristics and corresponding mechanisms of alkane droplets from a microscopic aspect, aiming to guide the design and development of high-efficiency heat exchangers.

Assessing Leachate Migration and Gas Emissions in Landfill Sites Using Seismic and Electrical Resistivity Tomography (ERT) Methods

Other environmental concerns include the permeation of non-sanitary fill-related leachate or gas. This paper will validate these concerns using seismic and electrical resistivity tomography (ERT) techniques. We collect data at different depths of the dump sites using survey methods such as seismic and electrical resistivity tomography. We implemented the seismic reflection approach for the comprehensive seismic wave velocity studies and applied the ERT method to determine the electrical resistivity. We also used the chemical analysis laboratory to quantify the amount of leachate present in the water samples. The data analysis yielded several significant conclusions. At a depth of 75 meters, electrical resistivity fell from 120.123 Ohm-m to 5 meters. P-wave velocity dropped throughout the same depth range, from 1500.123 m/s to 1150.456 m/s. The leachate conductivity increased from 1.234 mS/cm to 4.234 mS/cm, suggesting that the deeper depths had higher pollutant levels. We observed a linear increase in methane concentrations with water depth, rising from 10.123 ppm to 24.456 ppm. The joint use of seismic and ERT was necessary because, while seismic studies aid in understanding the subsurface conditions of a landfill and their temporal changes, only seismic and ERT can evaluate properties such as soil properties, leachate dispersion, and methane emissions. These results improve our knowledge of landfill dynamics and open the door to more practical management approaches, adding to the corpus of existing information.

The ignition characteristics of dual-fuel spray at different ambient methane concentrations under engine-like conditions

In the present study, dual-fuel ignition process of pilot diesel spray injection into a natural gas-air mixture under engine-like conditions is numerically investigated via large-eddy simulation (LES). Methane and n-dodecane are considered as surrogates for natural gas and diesel fuels, respectively. This study aims to provide understandings of kinetic interactions for dual-fuel spray during the ignition process. The effects of ambient methane concentration on the ignition delay times (IDTs), product distributions, and heat release rates (HRRs) during dual-fuel ignition process are emphasized. The results show that methane prolongs the IDT of n-dodecane, especially for the first-stage IDT. Kinetic analyses reveal that the competition for OH between the dehydrogenation reactions of methane (CH4 + OH <=> CH3 + H2O) and n-dodecane (RH + OH <=> R + H2O) results in the increasing first-stage IDT of pilot spray. Moreover, it is found that the retarding effect positively correlates with the methane concentration. For product distributions, it is observed that the transition of CH2O from fuel-lean to fuel-rich regions is inhibited in the first-stage ignition. In the second-stage ignition, the concentration of CO is decreased as the methane concentration increases and the area with high CO concentration is gradually shifted to the downstream of the spray. In addition, HRRs of low-temperature exothermic reactions appear at the radial periphery as well as the head of the spray front; HRRs of high-temperature exothermic reactions are gradually shifted from the head to the center of the spray with the increase of ambient methane concentration. The HRRs of low- and high-temperature reactions are decreased with increasing ambient methane concentration, and the major reactions for heat release at various ambient methane concentrations are different.

Impact of pH in the first-stage of a two-stage anaerobic digestion on metabolic pathways and methane production

The present study focuses on the use of cow manure, slaughterhouse sludge, cheese whey and green beans in a two-stage batch anaerobic process. The effect of pH regulation (4.5 to 7) on metabolic pathways and microbial community involved was studied in the first-stage of the process under mesophilic condition. At a pH lower than 5, fermentation occurred and led to an accumulation of lactic acid with a dominance of Lactobacillus. A pH >5.5 led to dark fermentation. Temporarily lactic acid production was converted in volatile fatty acids. Streptococcus and Enterococcus were involved in lactic conversion at pH 5.5 and 7, respectively. A weak hydrogen production was monitored at these pH ranges. Regardless of fatty acids produced in the first-stage, dark or lactic fermentation did not lead to higher methane production in the second-stage. However, dark fermentation increased methane concentration in biogas from 63.1 % in a single-stage to 83.6 %.

Geoenvironmental aspects of mine methane emissions

&#x0D; &#x0D; &#x0D; The purpose of the work is to reveal the regularities of the influence of the gaseous phase on the process of filtering carbonated liquid and to characterize the physi-cochemical processes during the implementation of the method of reducing mine methane emissions. The development of minerals can be accompanied by the release of a large amount of methane into the mined-out space. This leads to atmospheric air pollution and consequently to ecological disturbances. This causes methane emissions to the mined-out space and to the surface of the earth cause by the filtration processes of gases and liquids in the rocks. The intensity of fluid filtration through crack and pore systems depends on the content and properties of the fluids and the reservoir properties of the rocks. It is known that methane release to the atmosphere can be observed after mines have been mothballed. This is a problem for many countries around the world where coal and oil and gas fields are being exploited. Investment in methane production and utilization projects is therefore important. Research on fluids filtration processes allow for the development of effective methane recovery methods, and ways to reduce methane emission speed. The result is the reduced air pollution and an improved environmental situation. The paper presents the filtration properties of rocks with different structures and textures. Filtration of carbonated liquid (water-methane) in fractures and pores is considered. It found that an increase in methane concentration in the carbonated liquid leads to a decrease in the phase permeability coefficient for water and an increase for methane. This character of change in phase permeability leads to methane accumulation in crack and pores. The dependence of the average carbonated liquid filtration rate in a rectilinear fracture on the methane concentration and the fracture axis angle of inclination is obtained. The average ascending filtration speed of the carbonated liquid is determined to be greater than the average descending filtration speed. This is due to the effect of the ejection force that acts on the gas bubbles in the liquid. The authors propose a method of blocking methane seepage by physicochemical treatment of the rock mass. The methane blocking effect is achieved by creating a gas-tight zone in areas with a high risk of methane migration to the ground surface. The result is a reduction in methane emissions to the mined-out space and the environment. When the method is realized, the solid product of the polymer solution enters cracks with a disclosure greater than 6 μm or pore channels with an average diameter of 6 μm. At the same time, the water released by the destabi- lization of the polymer solution blocks the methane in small cracks and pores. In pore channels with an average diameter of less than 25 μm, there is a sharp increase in the dynamic viscosity of the polymer solution. This effect is due to an increase in the intermolecular interaction forces between the polymer solution and the walls of the filtration channels. Coagulation and destabilization of the polymer solution in cracks and pores is due to the separation of large agglomerates of macromolecules.&#x0D; &#x0D; &#x0D;

The influence of gasifier operating parameters on syngas composition of coal-fired power plant with CO2 capture

This work investigated the influence of the operating parameters of the gasifier (pressure, temperature of the syngas at the outlet of the gasifier and the O2/CO2 ratio in the blast) on the composition of the syngas in relation to the Allam cycles and oxy-fuel IGCC. Thermodynamic modeling of the operation of Shell (Allam cycle) and MHI (oxy-fuel IGCC cycle) gasifiers by the entropy maximization method was carried out. For the Shell gasifier, a significant increase in methane concentration with an increase in pressure to 40 MPa has been revealed; it indicates the need to make changes to the syngas gas cleaning system. The optimal temperature at the outlet of the gasifier (1100°C) has been found for the MHI gasifier. At this temperature, there were high values of CO and H2, and, hence, the heating value of syngas. For both gasifiers, the most theoretically reasonable ratio of O2/CO2 in blast was 0.3, at which CO reached almost maximum values and decreased its growth rate.

Effect of magneto-active filling on the effectiveness of methane fermentation of dairy wastewaters

ABSTRACT The goal of this study was to determine the effectiveness of methane fermentation in dairy wastewaters in terms of the volume and qualitative composition of biogas produced in an anaerobic reactor with magneto-active filling (MAF) mounted in the zone of hydrolysis and acidogenesis. Experiments were conducted on the fractional-technical scale in a vertical fermentation reactor with a labyrinth flow. Synthetic dairy wastewaters prepared based on milk powder were used as a substrate. The analyzed filling was made of plastic covered with iron and copper powders and was additionally equipped with fluid magnetizers (FM) in the form of neodymium magnets. The study demonstrated that MAF incorporation into the technological system significantly improved the effectiveness of biogas production, increased methane concentration and lowered the content of hydrogen sulfide in gaseous metabolites of fermentative bacteria. A significant increase was also observed in the effectiveness of COD removal from dairy wastewaters. The reported experiments proved a correlation between the effectiveness of methane fermentation and the number of MAF elements introduced into the anaerobic reactor.

Large-scale experimental and simulation study on gas explosion venting load characteristics of urban shallow buried pipe trenches

In this study, a series of explosion venting tests on a large-scale test system (30 m length) and numerical simulations were conducted to evaluate the venting behavior and venting load of a gas explosion in an urban shallow buried pipe trench according to the methane concentration, location and the existence of the vents. The time history characteristics of the gas explosion overpressure, load distribution law, and explosion venting mechanism of vents in the trench were considered. The results showed that the overpressure–time history curve of the gas explosion in the trench with top vents has a single peak. The explosion overpressure initially increased and then decreased with increasing methane concentration, and the maximum overpressure was observed at a methane concentration of 9.5 vol%. The change rate in the overpressure–time history curve decreased upstream of each vent and increased downstream. In addition, the peak overpressure suddenly dropped upstream and jumped downstream of each vent. Adding vents to the top of the pipe trench significantly reduced the upstream overpressure and overall impulse, and the overpressure attenuated to a greater degree.

Experimental and numerical study on pressure dynamic and venting characteristic of methane-air explosion in the tube with effect of methane concentration and vent burst pressure

This paper presents the experiments and numerical simulation of vented methane-air explosion. The influence of methane concentration and vent burst pressure on the internal pressure dynamic and venting characteristic is investigated. The pressure oscillation is hardly noticed in the internal pressure curve as the case of concentration is 7 vol%. But for the case of concentration is from 9 vol% to 13 vol%, the pressure oscillation is obvious in the internal pressure curves. Two internal temperature peaks are found in the three simulated temperature curves. The duration of internal temperature curve will increase with the increase of methane concentration. The methane concentration and vent burst pressure have the influence on the variation curve of the internal fuel concentration. When the methane concentration is 7 vol%, it is worth noting that the internal fuel concentration drops rapidly to zero after vent opening. And when the methane concentration is 9 vol% or 11 vol%, the internal fuel concentration has a dramatic decrease and then maintains a slow descent after vent opening. The internal pressure curves with different concentrations all present two typical pressure peaks. The first pressure peak is more noteworthy than anther one under higher vent burst pressure conditions; the second pressure peak is more important under lower vent burst pressure conditions.