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In order to reduce the power of methane explosion in natural gas pipelines and effectively improve the explosion suppression efficiency of a single explosion suppressant, we carry out the explosion suppression of HFC‐227ea/carbon dioxide mixed gas as well as mixed gas/ultrafine water mist through a self‐built methane explosion suppression experimental platform. Based on the changes in parameters such as explosion overpressure, flame propagation velocity, and flame propagation structure, the coupling mechanism of methane explosion suppression between mixed gases and between mixed gases and ultrafine water mist is revealed, which provides scientific support for promoting the development of methane explosion suppression technology. The experimental results show that when the mixed gas HFC‐227ea/carbon dioxide and ultrafine water mist synergistically suppresses methane explosion, the addition of the mixed gas can effectively improve the suppression effect of ultrafine water mist on methane explosion. [ABSTRACT FROM AUTHOR]

In a semi-closed visualization pipeline, this experiment studied the inhibitory effect of ultra-fine pure water mist, ultra-fine water mist containing inorganic salt and ultra-fine water mist containing bacteria-inorganic salt on 9.8% methane explosion under five different quality of spray volume. Combined with the methane explosion suppression experiment, the ability of methane-oxidizing bacteria to degrade 9.8% of methane was studied in a simulated pipeline. Experiments showed that the addition of inorganic salt and the degradation of methane-oxidizing bacteria could improve the suppression explosion effect of ultra-fine water mist, and the suppression explosion effect was related to the volume of water mist. Under the same ultra-fine water mist condition, with the increase of the volume of water mist, the explosion suppression effect was improved. Compared with pure methane, pure water ultra-fine water mist, and inorganic salt ultra-fine water mist, the maximum explosion overpressure and flame propagation speed under the condition of bacteria-inorganic salt ultra-fine water mist were significantly reduced. Compared with the explosion of pure methane, due to the degradation of methane by methane-oxidizing bacteria, when the degradation time was 10 h, and the volume of ultra-fine water mist containing bacteria-inorganic salt was 12.5 mL, the maximum explosion overpressure dropped significantly from 0.663 to 0.343 MPa, a decrease of 48.27%. The appearance time of the maximum explosion overpressure was delayed from 208.8 to 222.6 ms. The peak flame velocity was 4 m s−1, which was 83.3% lower than that of 9.8% pure methane explosion. This study will contribute to the development of efficient ultrafine water mist synergistic inhibitors for the prevention of methane explosion disasters. [ABSTRACT FROM AUTHOR]

In order to explore the influence of the side duct position and venting position on the premixed combustion and explosion characteristics of methane/air, a premixed combustion and explosion experiment of methane/air and a simulation of an explosion of the same size were carried out in a tube with an internal size of 2000 mm × 110 mm × 110 mm. The results showed that the side duct could change the flame structure and accelerate the flame inside the tube. The maximum increase ratio of the flame propagation speed was 106.1%. The side duct had a certain venting effect on the explosion pressure. For different position cases, when the venting film was placed over the bottom section, the maximum overpressure first decreased and then increased. When the venting film was placed over the middle section and the top section, the maximum overpressure first increased and then decreased, and the change trend of the top section was stronger. Turbulence mostly occurred inside the side duct when the venting film of the side duct ruptured. There is no linear relationship between the maximum flame propagation velocity within the tube and the maximum turbulent kinetic energy inside the side duct. The two had a relationship that could be fitted to the Gauss function; the correlation coefficient R2 was 0.836, and the minimum value was at (4767.72, 17.918), suggesting that the side duct had the best venting effect on the flame inside the duct at this maximum turbulent kinetic energy. The analysis results of the influence of the location of the vent on the maximum flame propagation velocity inside the tube are helpful for optimizing the layout design of the underground space, reducing the combustion efficiency, and ensuring the safety of the process. [ABSTRACT FROM AUTHOR]

The explosion of combustible gas is an urgent problem to be solved in production safety accidents. In this paper, the experiment of methanotroph degradation of CH4 and the experiment of the water mist containing methanotroph-inorganic salt inhibiting the methane explosion were carried out respectively based on a self-designed and built semi-closed small-scale experimental platform. We studied different volumes of the water mist containing methanotroph-inorganic salt to inhibit 5%, 8%, 9.5%, 12%, 15% methane explosion, and analyzed the relationship between time and relevant experimental parameters such as flame structure, flame average propagation velocity, maximum explosion overpressure, and average pressure rise rate, etc. The result showed that the water mist containing methanotroph-inorganic salt had a quite restrain effect on the methane explosion. At the same time, for first spray, when the degradation time is constant, with the increase of spraying volume, the explosion suppression effect is better. And when the spraying volume remains the same, the longer the degradation time is, the better the explosion suppression effect. As for the secondary spray, when spraying volume remains the same, the explosion suppression effect under the condition of Degradation with spray + explosion suppression with spray is superior to that of direct explosion suppression, whose reason is that the first spray mainly plays the biodegradation role of methanotroph, while the secondary spray mainly plays the physicochemical synergistic explosion inhibition role of the water mist containing methanotroph-inorganic salt. [ABSTRACT FROM AUTHOR]

The accidental methane explosion accident will not only pose a serious threat to the safety of industrial processes, but also cause serious environmental pollution with excessive carbon emissions and greenhouse effect. Therefore, this paper has studied the inhibition effect of modified ABC powder driven by heptafluoropropane on methane explosion. Multiple methane explosion suppression experiments were carried out using a 3.2 L horizontal experimental pipeline under various working condition. The experimental results demonstrate that the modified ABC powder has a certain inhibitory effect on methane explosions, but the explosive suppression effect of the powder improves when heptafluoropropane is used as the driving gas. When 3∼4 % heptafluoropropane is used as the driving gas, the flame is obviously inhibited. The deformation degree of flame shape is the largest at 4 % concentration. The flame totally folds inward at this point, forming an uneven finger flame. When 4 % concentration of heptafluoropropane drives the powder, there is a critical value of the concentration of the powder, which is 0.06 g/L. According to the characterization results, the average particle size of the modified ABC powder is less than 5 µm. It has good dispersibility and pyrolysis effect and is not easy to agglomerate. Under the driving action of heptafluoropropane, the powder will form aerosol, which can fully contact and react with the flame. The inert gas around the powder will reduce the forward speed of the flame and ensure that the flame and powder can fully contact and react. The combination of the two has a good synergistic effect and can effectively inhibit methane explosion. [Display omitted] [ABSTRACT FROM AUTHOR]

Methane/air is a widely used fuel. The effects of equivalent ratio (0.8–1.2) and initial pressure (1.0 atm–1.2 atm) on the flame propagation process and explosion overpressure of methane/air premixed gas were studied using a high-speed camera and pressure sensor in a rectangular closed container. Four flame modes in the late propagation stage are distinguished according to the different modes of secondary cup movement. The flame propagation velocity and structure evolution are analyzed by defining the characteristic times. The relationship between the flame structure evolution and the growth of flame propagation velocity and explosion overpressure is revealed. The results show that, in lean combustion, the maximum flame propagation velocity increases with initial pressure increase, and the explosion overpressure fluctuates more significantly. However, the opposite is true with fuel-rich combustion. The interaction between pressure waves and flame fronts can enhance the growth of explosion overpressure in fuel-rich combustion but can inhibit the growth in lean combustion. This work can provide more data support and reference for the application prospect and safe application of methane. • Different growth modes of overpressure and flame propagation velocity are analyzed. • The four types of flame structure after distorted tulip flames are distinguished. • The effects of flame instability on flame propagation are analyzed. [ABSTRACT FROM AUTHOR]

• The coupling mechanism of heptafluoropropane synergistic barriers to methane air explosions is revealed in this article. • Explain the suppression of methane explosions in terms of thermal decomposition during the reaction process. • The flame and the inhibitory effect of C 3 HF 7 for CH 4 explosion is affected by obstacles. • The different intensities of vortex and turbulent flames will result in different inhibitory effects of C 3 HF 7. The influence of heptafluoropropane（CF 3 CHFCF 3 ） with different barrier arrangements on the prevention of methane-air explosions in semi-closed pipes is examined in this research. Using high-speed photography and pressure sensors, the propagation traits and pressure data of flames were captured on the self-built explosion test platform. The findings demonstrate that, in the absence of barriers, a 1% concentration of CF 3 CHFCF 3 promotes the spread of methane explosions, with an 8.6% reduces in flame propagation time. However, as CF 3 CHFCF 3 concentration rises, the strength of the inhibition of methane explosions weakens with increasing concentration, and at a concentration of CF 3 CHFCF 3 greater than 5%, the explosions are completely inhibited. When barriers of different arrangements are introduced, the inhibition impact of CF 3 CHFCF 3 on methane explosion is improved. In these barriers, the maximum boosting rate and peak explosion overpressure are decreased by 28.81% and 97.27%, respectively. The staggered arrangement of barriers provides a higher coupling effect when the concentration of CF 3 CHFCF 3 is between 1% and 3%, while the symmetrical arrangement of barriers has the optimum coupling effect when the concentration is between 4% and 5%. [ABSTRACT FROM AUTHOR]

This paper changed ABC powder and performed a comparison on the suppression of methane explosions between pure modified powder under various operating circumstances and cold aerosols induced by various inert gases (argon, CO 2). The results show that the maximum explosion pressure and flame velocity greatly decrease when inert gases act as catalytic gases. Different inert catalytic gases have various inhibitory effects on cold aerosols. Argon can delay the arrival of explosion overpressure. CO 2 gas can produce bidirectional inhibitory effects from inerting and free radical chain reactions. It not only delays the occurrence of explosion overpressure, but also enhances explosion suppression ability. The most effective inhibitor is the cold aerosol, which contains 0.06 g/L of modified powder and 24% CO 2 gas. Finally, under the influence of inert gases (argon, CO 2), the modified ABC powder creates a cold aerosol that can more effectively suppress methane explosions. [Display omitted] • Modified ABC powder has better pyrolysis effect and heat absorption ability. • A cold aerosol explosion suppressor has been developed. • Argon and CO 2 can delay the arrival of explosive overpressure. • CO 2 can enhance the powder's explosion suppression ability. • This material can provide experience in reducing methane explosion accidents. [ABSTRACT FROM AUTHOR]

The comprehensive effects of obstacles with different slit and heptafluoropropane on the methane-air explosion characteristics were studied by visual explosion experiment platform. The volume fraction of heptafluoropropane and the number of slits of obstacles were considered. The results show that in the absence of obstacles, 1% concentration of heptafluoropropane accelerates flame propagation. When the concentration of heptafluoropropane is 3%, the explosion overpressure increases by 24.2%, and when 5% heptafluoropropane is used, the overpressure decreases by 10.6%. With the addition of obstacles, the coupling effect of the inhibitor and the obstacle improves the inhibition effect of heptafluoropropane. For obstacles with 2, 3, and 4 slits, 1% concentration of heptafluoropropane failed to significantly accelerate the flame propagation process under obstacle conditions. When the concentration of heptafluoropropane is 3%, the explosion overpressure increases by 9.5%, 5.4%, and 7.5%, respectively. The overpressure decreased by 18.7%, 25.7%, and 20.6% when 5% heptafluoropropane is added. The coupling mechanism significantly enhances the suppression effect of heptafluoropropane on methane explosion under various obstacle conditions. • The coupling effect enhances the inhibitory effect of heptafluoropropane. • Heptafluoropropane does not accelerate flame propagation downstream of obstacles. • The suppression effect of heptafluoropropane on explosion overpressure is enhanced. • The coupling mechanism between obstacles and heptafluoropropane was analyzed. [ABSTRACT FROM AUTHOR]

• The effect of obstacle location on premixed H 2 /CO/air explosion dynamics was studied. • The flame will invert and deform after it propagates though the obstacle channel. • Turbulent finger-shaped flame inversion is a pure hydrodynamic phenomenon. • Tulip flame's deformation and oscillation is caused by the pressure waves. • The maximum explosion severity is attained at OL = 400 mm. An experimental study was presented to investigate the effect of obstacle location (OL) on explosion dynamics of premixed H 2 /CO/air mixtures. A fence-type obstacle providing the blockage ratio of 0.5 was mounted in the closed duct, and the distance from the ignition end increased from 100 mm to 600 mm. Therefore, the effect of the obstacle on flame exponential acceleration stage, flame deceleration stage, and tulip flame stage had been comprehensively discussed. When OL ≤ 400 mm, the turbulent finger-shaped flame front will invert into the tulip shape after the flame propagates through the obstacle channel. The competition between the flamelets' backward movements induced by the vortex motion and forward movement induced by the squish flow causes the turbulent finger-shaped flame front's inversion. The pressure dynamics are discussed in conjunction with flame tip dynamics. The prominent flame deformation and oscillation after the tulip flame is caused by the interaction of flame and pressure waves. However, the pressure waves make no difference on the finger-shaped flame front inversion. This indicates that the flame front inversion after the obstacle is a pure hydrodynamic phenomenon. What's more, for a given hydrogen volume fraction, the flame duration time first decreases and then decreases with obstacle location, the maximum flame tip speed and the maximum overpressure first increases and then decreases with obstacle location, and the maximum explosion severity occurs at OL = 400 mm. [ABSTRACT FROM AUTHOR]

An experimental investigation on explosion behavior of non-uniform methane/air explosion in obstructed duct with different blockage ratios is conducted. The methane/air mixture that the methane concentration decreases from top to bottom and from ignition end to opposite end of duct is tested. The results show that the vertical concentration gradient of methane upstream along the obstacle increases with blockage ratio. After ignition, the flame speed and overpressure increase exponentially when the flame propagates with a finger-liked shape. In the poorly mixed methane/air, the flame speed and overpressure reduce with the appearance of pronounced triple flame. The flame in duct without obstacle propagates with triple shape until it approaches the vent. In the obstructed duct, the flame speed increases again after the flame passes the obstacle and then the triple flame disappears as the flame becomes turbulent. In the more evenly mixed methane/air, the flame speed decreases with the disappearance of finger shaped flame. The flame speed decreases continuously in duct without obstacle but increases again when the flame passes the obstacle in obstructed duct, in which an incomplete mushroom-shape flame forms downstream the obstacle. Generally, both the flame speed and overpressure are larger in methane/air that mixes more fully. • The explosion behavior of non-uniform methane/air mixture in an obstructed duct is investigated. • There is no mushroom shaped flame in the poorly mixed methane/air after flame passes through the obstacle. • The flame propagates with a faster speed in the more evenly mixed methane/air. • The maximum overpressure increases significantly with diffusion time and blockage ratio. [ABSTRACT FROM AUTHOR]

Through visual explosion experiment platform, this study conducted comparative experiments on methane-air premixed gas with a methane volume fraction of 9.5 % under different working conditions. The experiment studied the effect of active explosion suppression (spraying modified attapulgite powder) and explosion venting (setting the outlet blockage ratios) on methane explosion. The results showed that when the amount of powder injection was constant, the outlet blockage ratios of the pipeline was positively correlated with the peak explosion overpressure and the explosion index, but was negatively correlated with the peak flame propagation velocity. When the outlet blockage ratio was constant, the amount of powder spraying was negatively correlated with the peak value of explosion overpressure and the peak value of flame propagation velocity. When the outlet blockage ratio was 0, the explosion precursor shock wave broke through the PVC plastic film, which made the influx of a large amount of fresh air promote the generation of turbulence in the pipeline, and a "tulip-shaped" flame front appeared. The combination of active explosion suppression and explosion venting showed different effects on the explosion overpressure and flame propagation characteristics of methane explosion. Finally, this study conducted an in-depth discussion on the complex mechanism contained in it. [Display omitted] • The characterization characteristics of the powder were obtained. • The influence on pressure and flame propagation is analyzed. • The mechanism of explosion suppression and explosion venting is studied. [ABSTRACT FROM AUTHOR]