Volume Of Methane Research Articles

Progress in palladium-based bimetallic catalysts for lean methane combustion: Towards harsh industrial applications

<p>Significant volumes of lean methane (0.1–1.0 vol%) are released untreated into the atmosphere during industrial operations, contributing to the greenhouse effect and energy wastage. Catalytic methane combustion presents a promising avenue to mitigate these emissions. Depending on their active components, catalytic systems are predominantly categorized into noble metal-based and non-noble metal-based catalysts, with palladium (Pd)-based catalysts recognized for their superior low-temperature oxidation activity. Nevertheless, enhancing the thermal stability of Pd remains challenging, complicated by impurities such as H<sub>2</sub>O, SO<sub>2</sub> and H<sub>2</sub>S in the lean methane stream, which can cause catalyst poisoning and deactivation. Recent research has focused on the design of Pd-based bimetallic catalysts, offering improved stability, activity, and resistance to poisoning in harsh industrial conditions. This review examines advancements in improving the deactivation resistance of Pd-based bimetallic catalysts for lean methane combustion, covering active site characterization, dispersion and metal-support interactions, the role of auxiliary metals, and structural modulation strategies. It also investigates the impact of harsh industrial environments on Pd-based catalyst performance, focusing on deactivation mechanisms and mitigation strategies. Ultimately, this review identifies current research trends and challenges for Pd-based catalysts in demanding applications. By providing insights into the design of Pd-based catalysts with enhanced stability, activity, and resistance to poisoning, this review aims to guide the development of catalysts that meet industrial demands.</p>

Impact of biochar prepared at different pyrolysis temperatures on the methane production and microbial community structure of food waste anaerobic digestion

Biochars were prepared through the pyrolysis of sawdust at 300 °C, 500 °C, and 700 °C, respectively, under oxygen-limited conditions. The basic physicochemical properties of biochars were explored by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), surface area and porosity analyzer (BET), and Fourier-transform infrared spectrometer (FTIR). The effects of biochar addition on the methane yield and microbial community structure of anaerobic digestion of food waste were also investigated. SEM images showed that biochar had a honeycomb-like pore structure, EDS analysis showed that the C content in the biochar tended to increase, and the O contents tended to decrease with the increasing temperature. The specific surface area of biochars increased from 1.2014 m2/g (300 °C) to 326.8435 m2/g (700 °C). FTIR analysis showed that the number of different surface functional groups decreased with the increasing temperature. The addition of biochar could increase the cumulative methane volume by 11.63%–25.18%. High-throughput sequencing results showed that biochar addition could increase the relative abundance of Bacteroidetes, Chloroflexi, Firmicutes, Proteobacteria, and Spirochaetota, which were associated with the degradation of refractory organic matters. Meanwhile, biochar addition could enrich the relative abundance of methanogens participating in direct electron transfer (Methanosaeta and Methanosarcina), and methanogens producing methane through multiple pathways (Methanobacterium and Methanosarcina). The addition of biochar derived at 700 °C significantly increased the relative abundance of Methanobacterium and Methanosarcina from 1.96% and 0.70% (control group) to 32.68% and 64.69%, respectively and improved methane production by transforming acetoclastic/hydrogenotrophic methanogenic pathways to more metabolically diverse methanogenic pathways.

The potential Impact of bacterial probiotics on ruminal greenhouse gases production in vitro of dietary Delonix regia seeds in rams and steers.

This study aimed to evaluate the influence of probiotic bacteria (Pediococcus acidilactici BX-B122 and Bacillus coagulans BX-B118) on methane, carbon monoxide, and hydrogen sulfide, and fermentation profile of dietary Delonix regia seeds in ruminant. Ruminal contents from slaughtered rams and steers were used as inoculum for in vitro fermentation system. The total gas, methane, carbon monoxide, and hydrogen sulfide volume, as well as pH and dry matter degradability, were quantified in three fermentation cycles. Probiotic bacteria reduced the production of methane and hydrogen sulfide, while also increasing (P < 0.05) dry matter biodegradability, short-chain fatty acids, and metabolizable energy in both rams and steers. Delonix regia seeds at 6, 12, and 18% reduced total gas production. Higher production of methane and carbon monoxide was observed in rams compared to steers. Interestingly, no impact (P > 0.05) on the pH of the ruminal contents was found in Delonix regia seeds alone or in combination with probiotics. However, higher (P < 0.05) methane conversion efficiency (i.e., ratios of methane: short-chain fatty acids, methane: metabolizable energy, and methane: organic matter) was observed in experimental diets with Delonix regia seeds compared to diets containing both Delonix regia seeds and probiotic bacteria. In conclusion, dietary inclusion of 6, 12, and 18% of Delonix regia seeds with probiotic bacteria (Pediococcus acidilactici BX-B122 and Bacillus coagulans BX-B118) can mitigate the production of methane and hydrogen sulfide, while also increasing dry matter biodegradability, short-chain fatty acids, and metabolizable energy both ruminant animals.

Assessment of the effect of browse plants’ feed formulation on Goat (&lt;i&gt;Capra aegagrus hircus&lt;/i&gt;) rumen microbial activities and &lt;i&gt;in vitro&lt;/i&gt; gas production

This study assessed the effect of browse Plants feed formulation on Goat (Capra aegagrus hircus) rumen microbial activities and in vitro gas production in Red Sokoto goat (Capra aegagrus hircus) over a period of fourteen (14) weeks. Four selected browse plants- Afzelia africana (TAa) Detarium microcarpum (TDm), Daniellia oliveri (TDo) and Khaya senegalensis (TKs) -were used to formulate diets for animal feeding. Three groups of growing Indigenous Red Sokoto goats were assigned to each of the browse plant diets (BPD), while the control group was placed on a basal diet only. Rumen fluids were collected from the goats intermittently for three (3) consecutive periods, and analyzed for pH, methylene blue-reduction time (MBRT), nitrate reduction, cellulose digestion, glucose fermentation and sedimentation activity rate. The results showed that browse plant feed formulation did not have a significant (p &gt; 0.05) effect on the pH value of the rumen contents. Significant (p &lt; 0.05) reductions in MBRT, nitrate reduction, and glucose fermentation were observed in all treatments except the control diets. However, the period for cellulose digestion significantly increased in all the browse plant-supplemented diet treatments. Furthermore, the volume of gas produced was significantly reduced by 64% (TAa), 62% (TDm), 71% (TDo), and 74% (TKs) in goats fed with browse plants as dietary supplements compared to 7% in the control (Tc). Overall, this study demonstrated that browse plant feed has the potential to significantly reduce the volume of methane produced and released by ruminant animals into the environment.

Enhanced biogas production from municipal solid waste via digestion with cow manure: A case study

Abstract Anaerobic digestion (AD) of feedstocks yields biogas, a potentially useful new energy source. This study looked into the anaerobic co-digestion of cow dung and organic garbage to produce biogas. An anaerobic biodigester, with a volume of 20 L, was used to digest organic waste (OW) and to trace the changes that occur during the AD process. It was equipped with tools that ensure complete control of the conditions affecting anaerobic biological reactions such as temperature, pH function, and mixing speed. Therefore, an anaerobic biodigester was designed to contain such biological transformations and to improve the biogas production process from OW. Based on the present investigation, the AD of OW was improved by integrating the substrate with sewage sludge or cow manure (CM) during the digestion process to provide the basic microorganisms to complete the digestion process. Feeding into the digester was a blend of 100 kg of cow dung (CM) and OW per day, diluted 1:1 with water. A gasbag was used to capture the methane that resulted. Biogas production began on the seventh day after the substrate was fed into the digester. A performance test was carried out on the produced biogas to determine its composition. For OW–CM, the generated biogas’s methane (CH4) concentration was determined to be 60%, but the rates of decline for TS and VS were 57 and 50.6%, respectively. Anaerobic biodegradation of OW–CM experiments was observed at 37°C, a mesophilic temperature. For OW–CM, the pH value was 6.7. After being adjusted to standard circumstances, the cumulative volume of methane produced which had been recorded as 4,914 mL became 3964.5 mL.

Application of Low-Temperature Temporary Plugging Agents in Coalbed Methane Volume Fracturing

Currently, unconventional oil and gas fields employ volume fracturing technology, and temporary plugging and diversion techniques have become one of the main methods for increasing production. The Mixi coalbed methane block in Yibing has a formation vertical depth of 800-1000 meters and a relatively low average formation temperature of 30 degrees Celsius. The temporary plugging agents currently in use face challenges during reservoir stimulation, including difficulty in withstanding pressure differentials, poor degradability, and significant reservoir damage, resulting in unsatisfactory implementation effects. Therefore, the water-soluble temporary plugging agent RD-1 was selected as the preferred option. Laboratory performance evaluation experiments have demonstrated that this temporary plugging agent exhibits good sealing and degradation properties. Field trials have shown good temporary plugging and diversion effects, with noticeable pressure increase during plugging and significantly improved stimulation volume. It has demonstrated good applicability in coalbed methane volume fracturing, accumulating valuable experience for efficient development of this block.

Study on the influencing factors of gas-liquid two-phase explosions of hybrid methane/isoprene on the basis of bush fires

To evaluate the explosion hazard of hybrid isoprene/biogas in a primary forest environment, a 20 L spherical explosion vessel combining with a colorimetric thermometry was used to study the explosion parameters, flame structures and temperature distributions of hybrid isoprene/methane at different methane content and initial temperatures. Furthermore, the relationships between the explosion gas products and explosibility of hybrid isoprene/methane were analyzed. Experimental results showed that when the mass concentration of isoprene was 272.4 g m−3, the explosion pressure, the pressure rising rate, and the average combustion temperature reached their peak values of 0.89 MPa, 63.9 MPa s−1 and 2216 K, respectively. When the mass concentration was fixed at 272.4 g m−3, the explosibility of hybrid isoprene/methane initially enhanced and then decreased with the increasing methane volume fraction, and got the maximum values at 5 vol% methane. It was worth noting that the explosibility of hybrid methane/isoprene weakened continuously as the initial temperature increased, and it exhibited a stronger explosion power at a lower temperature. The research results would be helpful for understanding the deflagration processes and mechanisms of bush fires under various conditions, providing scientific basis for the formulation of its prevention and control measures.

Characterization of gas explosion shock wave propagation in long straight confined space

Abstract Currently, China is engaged in the construction of urban subterranean areas and the deployment of gas pipelines within these spaces. Nonetheless, the entry of gas into subterranean areas poses a definite threat of leaks and explosions. An explosion triggered by a gas pipeline leak will gravely compromise the underground space’s integrity and significantly affect nearby structures. Consequently, examining the spread properties of gas explosion shock waves in urban subterranean areas is essential. This document utilizes FLACS software to develop an extensive straight confined space gas explosion model, examining the load properties of gas explosion shock waves and deriving the propagation law and distribution patterns of blast shock wave loads across various methane volumes. Gas explosion tests confirm the precision of the numerical model. Findings from the study can supply data on load for comparable safety assessments in underground spaces, enhancing their resilience to explosions.

The effect of raw material (cow and chicken manure) and reactor type for improving and maximizing biogas production.

Biomass energy is a type of renewable energy and animal waste is one of the main resources for its production. The purpose of this study is to investigate the effect of raw material type (cow and chicken manure) and the type of reactor (digester) on the biogas produced by measuring the amount of methane in the product. Three types of digester (metal, simple PVC, and PVC with leachate rotation) with the same volume (10 L) were prepared. Equipment was installed on the digesters to measure the pH and volume of produced gas. The experiments were carried out in controlled temperature conditions (28-30 °C) and in two stages. The first experiment was to load the digesters with cow excrement, and the second experiment was to load the digesters with chicken excrement. In both experiments, the digesters were fed with 1.5 kg of animal manure and water with a ratio of 1:1. During a period of 60 days, the volume of biogas and methane produced was measured and recorded. The results showed that the amount of biogas produced from chicken waste is more than the amount obtained from cow waste. However, the amount of methane produced using cow excrement was more than that of chicken excrement. Also, the performance of PVC digester with leachate rotation was better than the other two digesters, which could be due to the mixing of raw materials in this type of digester.

Research on shock wave driving technology of methane explosion

In order to improve the driving ability of the explosion wave simulation equipment, reduce the erosion effect of condensed explosives on the explosion wave simulation equipment, improve the safety of the test process, and make better use of the meteorological detonation driving method, it is necessary to optimize the source of the shock wave load in the driving section. Based on the finite volume method of FLACS, a methane detonation driving model corresponding to the test is established to explore the feasibility of using methane as an explosion source to test the structure against explosion shock wave. A methane detonation drive test was carried out to verify the accuracy of the numerical model. Finally, an engineering model for attenuation of shock wave overpressure peak value in pipeline is established by dimensional analysis, and the model coefficient is determined by numerical simulation and test data. The results show that the blast pressure is the highest when the methane volume ratio reaches 9.5 vol% in the methane-air mixture. Simply increasing oxygen content has little effect on the peak overpressure and positive pressure duration of shock wave. In the pure oxygen environment, the detonation effect can be achieved when the volume ratio of methane to oxygen is 1:2, and the incident pressure of the shock wave is proportional to the volume of the gas cloud. When the gas cloud volume is constant, a reasonable selection of methane-oxygen mixture ratio can achieve a better detonation effect, which can effectively increase the peak overpressure of the shock wave in the test section. The research results can provide technical reference for the development of new explosion wave simulation equipment.

High methane potential of oxygenic photogranules decreases after starvation

Oxygenic photogranules (OPG) are granular biofilms that can treat wastewater without external aeration, making it an advantage over activated sludge. Excess of OPG biomass can serve as energy source through anaerobic digestion. Two sequencing batch photoreactors were operated over 400 days to grow OPG. Biochemical methane potentials (BMP) were obtained from near-infrared spectroscopy. OPGs had an average BMP of 356 mL CH4·gVS-1, much higher than typical BMP from activated sludge. A partial least squares analysis could relate BMP with reactor operating conditions, like light regime, load or biomass concentration. Since organic load was the most influential parameter on BMP, three starvation experiments were set up. An average decrease of BMP by 18.4 % was observed. However, the unexpected growth of biomass during starvation resulted in a higher total methane volume. In conclusion, starvation reduces the BMP of OPGs but anaerobic digestion of OPG biomass remains a promising route for biomass valorization.

Flame propagation dynamic characteristics and mechanisms of methane–syngas–air mixtures in a semi-enclosed duct

The composition of syngas is complex, often leading to the generation of methane, which impacts the explosive characteristics of syngas. The analysis focused on the kinetic characteristics and mechanisms of flame propagation in methane–syngas–air mixtures in a semi-enclosed duct under various equivalence ratios (φ = 0.8–1.4) and methane volume ratios (R = 0 %–70 %) under ambient temperature and pressure. The results indicated that the flame speed and pressure propagation of methane–syngas–air mixtures could be divided into three stages: a stable stage, an oscillatory increase stage, and an oscillatory decrease stage. In the stable stage, as the methane proportion in the premixed gas increased, the oscillations in the flame and pressure decreased. Turbulent flow of the mixed gas was observed due to restrictions and obstructions within the duct. This led to an increase in the peak pressure and flame speed of the mixed gas, thereby resulting in an oscillatory increase stage. Distorted tulip-shaped flames were also formed in the semi-enclosed duct. The flame of the pure syngas/air mixture exhibited a hemispherical shape and a finger-shaped and slope-shaped propagation structure. When 30 %, 50 %, or 70 % of the methane in the methane–syngas–air mixtures was added, the flame exhibited a propagation structure characterized by a hemispherical shape, finger shape, slope shape, flat shape, tulip shape, or distorted tulip shape. The flame front evolved with time from a linear growth stage to a nonlinear growth stage. The flame front speed of the methane–syngas–air mixtures was closely related to the pressure and flame structure. With the increase in the methane proportion in the methane–syngas–air mixtures, the concentration of key radicals and the rate of OH* generation and consumption gradually decreased. Sensitivity analysis revealed that with increasing methane proportion in the premixed gas, the most important reaction dominating OH* consumption changed from R15 (H + O2(+M) <=> HO2(+M)) to R138 (CH4 + OH <=> CH3 + H2O) and then to R112 (2CH3(+M) <=> C2H6(+M)); moreover, the most important reaction dominating OH* generation remained R1 (H + O2 <=> O + OH). The addition of methane interrupted the hydrogen–oxygen chain reaction of the methane–syngas–air explosion process.

Analysis of the Effects of Structural Parameters on the Thermal Performance and System Stability of Ventilation Air Methane-Fueled Reverse-Flow Oxidation Reactors

Ventilation air methane (VAM) from coal mining is a low-grade energy source that can be used in combustion systems to tackle the energy crisis. This work presents a numerical analysis of the thermal and stabilization performance of a VAM-fueled thermal reversal reactor with three fixed beds. The effects of the combustion chamber/regenerator height ratio (β), heat storage materials, and porosity on the oxidation characteristics are evaluated in detail. It is shown that the regenerator temperature tends to vary monotonically with β due to the coupling effect of the gas residence time and heat transfer intensity. The optimal β is determined to be 4/6, above which the system may destabilize. Furthermore, it is found that regardless of the methane volume fraction, the regenerator with mullite inserted has the highest temperature among the heat storage materials investigated. In contrast, the temperature gradually decreases and the system becomes unstable as SiC is adopted, signifying the importance of choosing proper thermal diffusivity. Further analysis reveals that the porosity of the heat storage materials has little effect on the system stability. Decreasing the porosity can effectively reduce the oscillation amplitude of the regenerator temperature, but it also results in greater pressure losses.

Harvest age of Urochloa hybrids regarding yield, chemical composition, and in vitro biogas production

Objective: To evaluate the chemical composition, fermentation, and in vitro biogas production of the Cayman and Cobra cultivars, at different cutting ages.&#x0D; Design/Methodology/Approach: Dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HEM), and cellulose (CEL) were determined at 28, 35, 42, and 49 cutting days. In vitro dry matter degradation (IVDMD), pH, and concentration of volatile fatty acids (VFA) were determined during fermentation. The biogas volume was estimated at 6, 12, 24, 48, and 72 hours; the volume of methane (CH4) and carbon dioxide (CO2) in the Cobra and Cayman forages was determined at 72 hours. A completely randomized design was used for the experiment.&#x0D; Results: There were no differences (P&gt;0.05) in DM production during the different cutting ages. CP was higher (P&lt;0.05) in both cultivars, at 28 and 35 days after the cutting. The NDF, ADF, HEM, and CEL percentages were different in both cultivars. IVDMD was higher (P&lt;0.05) between day 28 and day 42. Finally, CH4 production was lower (P&lt;0.05) at 28 and 35 days after the cutting.&#x0D; Study Limitations/Implications: The chemical composition of pastures is influenced by climate and, therefore, further analysis must be carried out during different periods or seasons of the year.&#x0D; Findings/Conclusions: The optimal cutting age of the Cobra and Cayman cultivars under drought conditions is between day 28 and day 35 of regrowth. During that period, they have the best chemical and fermentation characteristics.

Sustainable paddy residues management through mushroom cultivation in India

AbstractFarmers' open‐field burning of paddy straw and the indoor burning of paddy residues as domestic fuels are significant environmental concerns since they emit dangerous pollutants. The worldwide burning of paddy residues totals 90 million tons (MT). Around 24 MT emanated from India, accounting for approximately 27% of the world's paddy straw burning. Burning residues emit smog particles, polyaromatic amines, nitrous oxides, sulfur dioxide, carbon dioxide, and carbon monoxide, methane, seriously degrading the air quality and risking human health. The combustion of dry paddy straw emits massive volumes of methane and nitrous oxide, 65 and 1.6 kilotons, respectively. This study analyzes the consequences of burning paddy residue outdoors and indoors by reviewing the relevant literature and data. Open‐field burning causes air pollution, damages soil health, and harms human health. Indoor burning of paddy residues as domestic fuels harms women's and children's health in rural areas. To mitigate the adverse effects of this practice, we magnified our research using the various literature and recent statistics to link with mushroom cultivation as an alternative to paddy residue burning. Recently, India produced almost 240,000 tons of mushrooms; Odisha, Maharashtra, and Bihar are the three leading states for mushroom production. The cultivation of mushrooms is considered advantageous for both health and the environment. This study has concentrated on mushrooms' economic potential, medicinal value, and health benefits.

Tools available for methane recovery from mines belonging to C.E.H. Petroşani

Mine gas is present both in coals and in the surrounding rocks and basically consists of methane (some-times almost 100%) mixed with carbon dioxide (up to 5%) with nitrogen (a few percent) and traces of carbon monoxide. The genesis of mine gas can be related to the biochemical transformation of vegetation during the carbonization process. The degassing of coal bed has been established as an active method of reducing methane emissions due to the need to ensure the exploitation of the bed with high productivity and in safe conditions. The methane gas existing in the coal bed is captured through various types of drilling executed for this purpose, being directed through a system of pipes to the surface to the central degassing station from where it can be taken and directed for use for a specific purpose. From an economic point of view, it has been proven that methane recovery from coal mines is again a profitable activity for both the mining company and a possible investor. The volume of methane from the coal deposits in Jiu Valley is very large and can provide large quantities for the recovery of this gas. At the same time, there was already a market for this product in Jiu Valley made up of industrial and individual consumers.

Mechanism of desorption hysteresis in coalbed methane: Insights from microscopic pore properties and adsorption theory

Desorption hysteresis, a phenomenon frequently observed in coal–methane desorption experiments, holds significant implications for coalbed methane extraction due to its influence on the volume of methane involved in migration. Yet, the precise mechanism behind desorption hysteresis remains incompletely understood. This study endeavors to elucidate the underlying mechanism of desorption hysteresis by considering pore characteristics and applying adsorption theory. The pore morphology was assessed using the physisorption method, and ad/desorption isotherms were measured using high-pressure volumetric methods, with the desorption hysteresis index (DHI) utilized to quantify the degree of hysteresis. The results pointed to the pivotal role of micropores (&amp;lt;1.5 nm) in the occurrence of desorption hysteresis. Enhanced specific surface area and pore volume, in conjunction with a decrease in the fractal dimension Ds of micropores, were found to correspond to higher DHI values. Conversely, an increase in meso/macropores (&amp;gt;1.5 nm) corresponded to reduced DHI. The Frenkel–Halsey–Hill fractal dimension showed no substantial correlation with DHI. In light of these findings, it is concluded that micropores, acting as gas entrapment spaces, primarily govern desorption hysteresis, while meso/macropores serve as migration pathways with lesser influence. Micropores exhibit robust adsorption capacity, leading methane molecules to preferentially occupy these spaces. However, during desorption, insufficient potential energy impedes the release of methane molecules from the coal surface, causing desorption hysteresis. These insights offer a fresh perspective on understanding the mechanism of desorption hysteresis in coal, which may prove valuable in optimizing methane extraction.

Experimental simulation and kinetic modeling of bioenergy potential of Eichornia crassipes biomass from the Volta River basin of Ghana under mesophilic conditions

The study presents the results of the laboratory experiment performed on the anaerobic digestion of water hyacinth biomass harvested from the Volta River basin of Ghana and Fruit waste sludge as the inoculum. Batch mode of experiment was performed under mesophilic conditions (29 ± 3 °C) with a hydraulic retention time of 61 days. The experimental setup was made up of three (3) fermenter bottles of 5.0 L capacity namely F1, F2 and F3. F1 served as the control whiles F2 and F3 served as the test fermenter bottles. Each of the fermenter bottles was fitted with BlueSens methane sensor and BlueVcount flowmeter for the measurement of methane composition and biogas volumes, respectively. The Theoretical Biomethane Potential (BMP) of the water hyacinth biomass was estimated to be 422.23 ml/gVS. The experimental BMP was determined to be 402.62 ml CH4/gVS and 356.03 ml CH4/gVS for F2 and F3, respectively. Consequently, a biodegradability value of 95.36 and 84.32 % was obtained from F2 and F3, respectively. Moreover, the F2 fermenter bottle recorded a cumulative net methane and biogas volumes of 5576.3 ml and 12,014 ml, respectively. Likewise, a total net cumulative methane and biogas volumes of 4931.0 ml and 11,384 ml were produced from the F3 fermenter bottle. Using the First order kinetic model, an average value of hydrolysis constant for water hyacinth biomass was determined as 0.051 day−1. Furthermore, the modified Gompertz model, the logistic function model and Transference function models were used to fit the experimental cumulative biogas and methane production data. The outcome of the study shows that, the production of biogas from water hyacinth biomass harvested the Volta River basin of Ghana could offer sustainable control solutions to its invasion on water bodies whiles providing a cheap and reliable means of biofuel to the riparian communities.

Study on the explosion characteristics and flame propagation of hydrogen-methane-air mixtures in a closed vessel

In this study, the examination of the explosion pressure and flame propagation characteristics were investigated for premixed CH4–H2-air mixtures, with varying equivalence ratios (φ = 0.8–1.5) and methane volume ratios (R = 0–100%). This investigation was conducted employing a 20 L explosion vessel and a high-speed ripple shadow meter, while maintaining ambient temperature and pressure. The most critical primitive reactions effecting the formation and consumption of OH* were obtained by normalisation through rate analysis. The result found that as the R increased at the same φ, the premixed system exhibited a gradually decreased in the Pmax, (dP/dt)max, and KG. The increase in the R caused the flame structure to stabilise, extending the flame front distance and the time to reach the wall. The reaction process was divided into three phases based on the R: 0 < R<40% (dominated by hydrogen combustion), 40% < R<80% (dominated by methane and hydrogen co-combustion), and 80% < R<100% (dominated by methane combustion). The analysis of OH* production rate showed that R84 and R38 were the most dominant reactions promoting the OH* production and consumption, respectively. As R was increased, both the production and consumption rates of OH* decreased resulting in a weakening of the explosive reaction's intensity.

Effect of relative humidity on methane explosion characteristics of curved pipes in pipe gallery

To explore the influence of relative humidity on the explosion characteristics of methane-premixed gas in the urban underground pipe corridor. The experiment took a 30° bend pipe as an example, and the relative humidity in the pipe had been set to 50% RH, 70% RH, and 90% RH while changing the methane volume fraction to 7%, 9.5%, and 12% to study its influence on the explosion characteristics. When the methane volume fraction is 9.5%, the relative humidity under the same conditions is set in the straight pipe to compare the parameter changes of flame morphology and explosion pressure. The results show that when the methane in the bend is entirely burned, the flame propagation time is delayed by 32.64% by the influence of relative humidity, the flame is hindered by the wall of the bend, the phenomenon of multiple enhancement occurs, and the flame in the straight pipe decays monotonically with the increase of relative humidity. The relative humidity stabilizes the explosion pressure; the relative humidity of 70% RH in the bend has the best impact on suppressing the explosion pressure, and the relative humidity of 90% RH in the straight pipe dramatically reduces the explosion pressure range. In the bending pipe, the relative humidity inhibited the flame propagation velocity, and the flame propagation velocity at 70% RH and 90% RH decreased by 15.46% and 10.65%, respectively, compared with 50% RH.