Explosion Flame Research Articles

Effect of obstruction ratio rate of change gradients on the deflagration characteristics of H2-Air premixed gases

To investigate the effect of the gradient of obstruction ratio change rate on the H2-Air premixed gas combustion explosion in the semi-confined space, Fluent software is used to simulate the explosion flame, turbulent turning and pressure wave coupling process under the conditions of obstacles with different obstruction ratios change rate. The results indicate that as the obstruction ratio's rate of change increases, flame propagation speed decreases, while pressure peak and pressure change rate increase. The flame front becomes sharper, and a positive change in obstruction ratio more significantly affects flame shape and speed than a negative change. At obstruction ratio change rates of −0.3 and −0.2, the flame front area and peak area reach their maximum values. At a change rate of 0.3, the pressure peak is 232 kPa, and the maximum pressure change is 126 kPa/ms, indicating the explosion intensity reaches its peak.

Research on Gas Explosion Pressure and Flame Propagation Characteristics in Turning Pipelines.

In order to investigate the overpressure and flame propagation characteristics of gas explosions in turning pipelines, this study designed a transparent organic glass pipeline test system with different turning angles (30°, 60°, 90°, 120°, and 150°) and conducted a series of experimental studies to analyze the explosion shock wave overpressure and flame propagation behavior. The experimental results show that with the increase of the turning angle of the pipeline, the overpressure of the explosion shock wave significantly increases. In terms of flame propagation characteristics, when the turning angle is small, the flame can adhere to the outer wall of the pipeline corner and gradually fill the entire pipeline section. When the turning angle increases, the flame forms a blank area near the outer wall of the corner, and the blank area expands with the increase in the corner. In addition, the increase in the turning angle promotes the increase in the velocity of the explosion flame front. The research results of this review are of great significance for a deeper understanding of the mechanism of gas explosions in turning pipelines and evaluating their potential hazards.

Suppression characteristics of water mist containing alkali metal compounds in natural gas explosions

The natural gas explosion in semi-constrained spaces seriously jeopardize public safety. Water mist containing additive is an important method to reduce the disaster intensity. However, in actual scenarios, the explosion usually propagates for a certain distance before entering the mist area, which is more difficult to suppress the explosion. Therefore, the self-designed experimental system was used to recognize the suppression effect of water mist containing alkali metal compounds under the simulated scenario. The results show that the flame propagation distance was significantly reduced, the shortest overfire range was decreased by 40.0 % compared with the water mist condition. The peak overpressure and pressure rise rate also showed a significant decrease, the maximum pressure drop rate reached 72.3 %. When the explosion flame entered the atomized region, the turbulent disturbance generated by the atomization accelerated the mixture of combustion zone and the unburned area, which increases the possibility of consuming free radicals. Compared with the KCl and NaCl, the mist containing K2CO3 and Na2CO3 share higher suppression capacity. This study provides scientific guidance for the practical application of water mist explosion suppression.

Piperazine pyrophosphate-functionalized Ni-MOF metal framework: Fabrication and synergistic explosion suppression mechanisms

Dust explosion suppression is crucial for ensuring safe industrial operations. To explore composite explosion suppression powders with higher performance, piperazine pyrophosphate (PAPP)-functionalized nickel-based metal–organic framework (PAPP@Ni-MOF) synergistic suppression materials were designed and synthesized. The effectiveness of this suppressant in inhibiting the explosion flame and intensity of polypropylene (PP) dust was investigated using explosion flame propagation and explosion pressure test apparatus. The results indicate that the combination of N/P elements and Ni-MOF exhibits excellent catalytic carbonization performance. Adding 50 wt% PAPP@Ni-MOF can completely inhibit the propagation of PP explosion flames and the rise in explosion pressure. The maximum propagation distance of the explosion flame was reduced by 78.07 %, the overall flame propagation speed decreased by 84.54 %, and the maximum explosion pressure was reduced by 76.87 %. Through characterization experiments, the products before and after the explosion were analyzed. Combined with molecular dynamics (MD) simulation results, the efficient synergistic explosion suppression mechanism of PAPP@Ni-MOF for PP dust was revealed from the perspectives of thermal conduction isolation, key radical recombination, and volatile gas adsorption.

Investigation and CFD simulation of coal dust explosion accident in confined space: A case study of Gaohe Coal Mine Ventilation Air Methane oxidation power plant

The study investigates a coal dust explosion accident within a confined space in Shanxi. The accident was caused by coal dust coming into contact with a high-temperature heat source under the influence of the stack effect. Based on the investigation of the coal dust explosion accident, the study uses computational fluid dynamics (CFD) simulation to reconstruct the accident scenario. The simulation results provide a detailed depiction of coal dust movement within subsurface semi-enclosed confined spaces during the ventilation diffusion stage, influenced by the stack effect, and confirm the formation of a coal dust layer at the heat source due to coal dust deposition. The simulation results of the two explosion processes indicate that excessively high coal dust concentrations within confined spaces have a negative correlation with the development of explosion flames and the peak overpressure. It resulted in a secondary explosion with a relatively low concentration of coal dust, where the peak overpressure was five times that of the primary explosion. Comparative analysis between simulation results and actual investigations the accuracy of the CFD simulation in capturing the accident process and its characteristics, providing valuable insights for preventing and controlling coal dust explosion accidents.

Development of a multiple laser-sheet imaging technique for the analysis of three-dimensional turbulent explosion flame structures

The present work describes the development of a multiple laser-sheet imaging technique for the study of turbulent, premixed flame surface structures at high Karlovitz stretch factor values. Experiments were conducted using CH4 air mixtures at 365 K and 0.5 MPa and up to a root mean square turbulence velocity of 1.5 m/s. A high-speed Nd:YAG laser capable of pulsing up to 60 kHz in conjunction with a high-speed camera and a rotating mirror was used to reconstruct time-resolved three-dimensional turbulent flames. This has, for the first time, enabled the direct measurement of wrinkled flame surface areas, along with reaction progress variable and flame brush thickness. These are important parameters for the characterization of turbulent burning rates and provide more insight into the dynamic nature of the flames and their structures. In addition, the current data aid toward direct comparison with results from combustion simulation studies.

Flame propagation mechanism of methanol fuel spray explosion in a square closed vessel

Methanol, as an important chemical raw material and clean energy source, easily forms explosive droplet clouds during its production, processing, and usage. Therefore, understanding the evolution and propagation mechanisms of methanol spray explosion flames is crucial for its widespread use and the design of safety measures. This paper studies the flame propagation behavior of methanol spray explosions using a 16.2-L visualized enclosed vessel. The results indicate that the flame structure of methanol spray explosions is similar to that of premixed gas explosions but significantly differs from traditional fossil fuels. It demonstrates homogeneous combustion characteristics primarily governed by the kinetics-controlled regime. As the methanol spray concentration increases, both the maximum flame propagation speed and the maximum explosion pressure initially increase and then decrease, reaching their peak at a concentration of 224.68 g/m3, with values of 9.96 m/s and 0.72 MPa, respectively. The heat losses during combustion exhibit a trend opposite to that of explosion pressure. Numerical simulation results indicate that the concentrations of key radicals such as O, H, and OH vary significantly between lean and rich combustion states. The increase in H radical concentration enhances the elementary reactions that suppress flame temperature and promotes chain-terminating reactions.

Hydrogen explosion characteristics in the obstructed chamber by changing blockage ratio among adjacent obstacles

Using the experimental and large eddy simulation (LES) methods, the impacts of equivalence ratio and adjacent obstacle blockage ratio on flame propagation, flame moving velocity, and explosion overpressure in a closed obstructed duct are investigated. The results indicate that the developed LES method is able to reproduce the tendency of flame propagation, flame moving velocity, and explosion overpressure of BR = 30%, 50%, 70% and BR = 70%, 50%, 30%. The early flame propagation and flame moving velocity are not affected by the first obstacle. As the explosion flame passes through the three obstacles, the flame acceleration and deceleration occur in sequence due to the decreasing cross-section and vortex-flame interaction, eventually forming three ascending peak flame moving velocity. The higher vorticity magnitude of BR = 70%, 50%, 30% and BR = 30%, 50%, 70% is mainly concentrated in the early stage and later stage of hydrogen explosion, which directly results in the fact that the flame acceleration and rise rate of explosion overpressure of BR = 70%, 50%, 30% is higher than that of BR = 30%, 50%, 70%. Additionally, the maximum value of flame moving velocity and explosion overpressure of BR = 30%, 50%, 70% is higher than that of BR = 70%, 50%, 30%.

Ignition energy, explosion flame propagation, and particle movement process of coal dust cloud in vertical Hartmann tube

To discuss the ignition energy, explosion flame propagation, and particle movement process of coal dust in vertical glass tube, experimental analysis and numerical simulation methods are used to carry out research. The experimental research results show that the optimal ignition delay time is 1 s, under this condition, the dust cloud near the ignition electrode has the highest turbulence, making it easier to ignite. When the dust cloud mass concentration is 2500 g/m3, the ignition energy is the smallest, resulting in the highest risk of explosion. The simulation results show that the propagation speed of flame is 4 m/s, due to the small amount of suspended dust used, the intensity of the explosion is not significant. The further away from the explosion source, the more energy is lost, the lower the temperature of the flame. Within 30∼50 ms after the ignition, the temperature near the explosion source rapidly increases, from 900 K to 1300 K. During the period of 0.2–0.5 s after dust injection, most particles move upwards along the tube. At 1 s after the dust injection, most particles move downwards and gather near the ignition electrode, forming a suspended dust cloud that is easily ignited, which is consistent with the optimal ignition delay time of 1 s obtained from the experiment.

Simulation and Experimental Verification of Dispersion and Explosion of Hydrogen–Methane Mixture in a Domestic Kitchen

Hydrogen is a carbon-free energy source that can be obtained from various sources. The blending of hydrogen represents a transitional phase in the shift from natural gas systems to hydrogen-based systems. However, concerns about the safety implications of introducing hydrogen have led to extensive discussions. This paper utilizes Fluent 17.0 numerical simulation software to simulate the leakage of hydrogen-blended natural gas in a closed domestic kitchen and analyze the concentration distribution and its variation pattern after a leakage. An experimental platform is set up, and a mixture of nitrogen and helium gas is used as a substitute for hydrogen-blended natural gas for the simulations and experiments. The simulation results demonstrate that the leaked gas spreads and accumulates towards the top of the space, gradually filling the entire area as the leak persists. As the hydrogen content in the leaked gas increases, the dispersion capacity of the gas in the confined space also increases. Furthermore, as the flow rate of the leaked gas increases, the average concentration of the leaked gas rises, and the gas stratification in the confined kitchen diminishes. The concentration distribution observed in the experiments aligns with the simulation results. After establishing the feasibility conditions of the model, the dispersion of the hydrogen-blended natural gas in the kitchen is further simulated. The results suggest that blending hydrogen into the gas enhances the dispersion of the gas after a leak, leading to a wider distribution within the kitchen and an increased risk in the event of a leak. Additionally, this paper employs the CASD module of FLACS 11.0 software to construct a three-dimensional geometric model of the domestic kitchen for simulation studies on the explosion of hydrogen-blended natural gas in a confined space. By adjusting the hydrogen ratio in the combustible gases present in the space and examining the variations in hydrogen concentration and external conditions, such as opening or closing the door, the influence on parameters including the peak explosion pressure, explosion overpressure, explosion flame temperature, and explosion response time are examined. Furthermore, the extent of the explosion area is determined, and the effect of hydrogen on the blast is clarified.

Effects of methane concentration on flame propagation mechanisms and dynamic characteristics of methane/coal dust explosions

The study explores the flame propagation and explosion dynamic behavior of gas/powder two-phase compound explosions, taking methane and coal dust mixture as the research object. The influence of different methane concentrations on the compound explosion characteristics was researched. The vertical pipeline, high-speed camera, ion current probe, and pressure sensor be used to test the propagation behaviors, microstructure characteristics, and explosion dynamics of compound explosion flames. The function of methane concentration on the propagation behaviors, combustion reaction zone thickness, flame temperature, propagation velocity, and explosion pressure of compound flame was revealed, and the propagation mechanisms of gas/powder compound explosion flames were explained. The experimental research discovered that the compound flame of methane/coal dust explosion presents a white luminous zone with uniform distribution and appears to have an approximate homogeneous combustion state. The explosion dynamics parameters all showed a trend of first increased and then decreased as the methane concentration increased, but the reaction zone thickness of the combustion first reduced and then increased. In addition, the dominant position of homogeneous or heterogeneous combustion in the combustion reaction zone will also switch with the change in methane concentration. The compound flame is similar to premixed gas combustion under optimal methane concentration, the combustion zone thickness (δ) and preheating zone thickness (β) are the smallest, and the compound explosion shows powerful performance. In addition, the flame propagation mechanisms of methane/coal dust compound explosion were elucidated based on the theory of heat.

Study on the effects of confined space opening pressure and ignition energy on the explosion flame of AlSi10Mg dust

A series of dust explosion experiments were conducted using a minimum ignition energy experimental device to investigate the explosion flame of AlSi10Mg dust and its influencing factors. The microscopic morphology of the AlSi10Mg dust explosion flame was captured using a high-speed camera, and the effects on flame characteristics were observed by varying the confined space opening pressure and ignition energy. The results indicated that when the Hartmann tube was in a closed state, the maximum instantaneous rate of flame initially increased and then decreased with increased opening pressure. Conversely, the maximum instantaneous flame rate decreased initially and then increased with an increased ignition energy. The experimental results were valuable for preventing dust explosions in industrial production.

Pressure and Flame Propagation Characteristics of Suspended Coal Dust Explosions Induced by Gas Explosions.

In order to explore the pressure and flame propagation characteristics of gas-coal dust composite explosions, a semiclosed pipeline explosion test platform was built. The shock wave overpressure and explosion flame propagation law of different concentrations of suspended coal dust participating in gas explosions were studied in depth through experiments, and the coal dust motion law was simulated and analyzed based on Fluent software. The experimental results show that the peak pressure of gas-coal dust composite explosion is significantly higher than that of single-phase gas explosion, and the pressure peak increase ratio at the pipeline outlet is the highest; as the suspended coal dust concentration increases, the pressure rise rate at point 3 gradually decreases. Under the condition of 600 g/m3 coal dust participating in the explosion, the explosion pressure increase speed reduction ratio is 25.65%, the pressure wave secondary peak decreases, and the fluctuation frequency increases. When the explosion flame front passes through the suspended coal dust area, the flame shape changes from 'v' shape to 'finger' shape and propagates forward. The gas-coal dust composite explosion flame propagation speed shows a secondary acceleration phenomenon, after the flame front passes through the coal dust suspension area. As the coal dust concentration increases, the explosion core area moves away from the flame front. The coal dust cloud moves to the right, showing a concave rectangle; the larger the coal dust concentration, the smaller the moving speed. The experimental results and analysis provide an experimental basis for further exploring the mechanism and dynamic mechanism of gas-coal dust coupling explosion.

Shear-stiffening porous material with impact-hardening functionality: Application in hydrogen explosion safety protection

In this study, a shear-stiffening composite porous material (PU@CS) was developed using the dipping-drying technique, with polyurethane (PU) as the substrate. PU@CS not only overcomes the cold flow drawbacks of shear-stiffening gel (SSG) but also significantly enhances the mechanical properties of PU (with a one-order-of-magnitude increase in maximum storage modulus). The introduction of multi-walled carbon nanotubes (MWCNTs) overcomes the electrostatic aggregation drawback of PU. Due to its outstanding shear hardening effect, PU@CS exhibits superior explosion-proof compared to PU, and when filled to a length of 50 cm, it achieves complete quenching of hydrogen gas explosion flames, with a maximum explosion overpressure attenuation ratio of 87.2%. This work provides data support for the application of SSG in the field of explosion protection.

A novel gel dry water: Preparation and application in methane-air explosion

To weaken the adverse effects of methane-air explosions on industrial processes and the environment, the development of highly effective explosion inhibitors is imperative. In this study, a novel ammonium polyphosphate gel dry water (AGDW) powder was synthesized by incorporating superabsorbent polymer (SAP) and ammonium polyphosphate (APP) as additives. The addition of SAP significantly enhanced the physical properties such as stability and water retention of AGDW powder, while APP improved its suppression effects. The suppression effect of AGDW powder on methane-air explosions was investigated in a square explosion pipeline. Experimental results revealed that 4 g AGDW powder with 15 wt% APP completely hindered the propagation of the explosion flame, resulting in a 91.2% reduction in peak temperature and completed elimination of the pressure reflection wave. Increasing the spraying pressure from 0.2 MPa to 0.4 MPa, 2 g AGDW powder with 5 wt% APP was sufficient to suppress the explosion completely. The suppression mechanism of AGDW powder on methane-air explosions was comprehensively elucidated from the cooling effect, diluting effect, and interrupting the chain reaction. This work sheds light on the preparation and application of novel dry water powders and provides a feasible solution for ensuring process safety and controlling gas explosions.

Study on inhomogeneous hydrogen–air mixture flame acceleration and deflagration-to-detonation transition

This paper discusses the effect of obstacle spacing on flame acceleration (FA) and deflagration-to-detonation transition (DDT) in inhomogeneous hydrogen–air mixture using the OpenFOAM open-source code and large eddy simulation technology based on the unsteady compressible reacting flow Navier–Stokes equation and the detailed chemical reaction mechanism of 9 species and 21 steps. The results show that the obstacle spacing has a more significant impact on the rapid deflagration state, manifested as an inverse relationship between the flame propagation speed and the obstacle spacing due to the negative correlation between the interference intensity of obstacles to the flow within a unit channel length and the obstacle spacing. In addition, under all conditions considered in this paper, the main mechanisms of FA and DDT are the same. Further analysis reveals that the detonation initiation dynamics portrayed in this study seem more aligned with the mechanisms proposed by Liberman and akin to the shock wave amplification mechanism of coherent energy release models. As the obstacle spacing increases, the run-up distance and the acceleration time of supersonic flames and DDT also increase. This paper also observes that the flame structure during explosion flame propagation has typical self-similarity, and the turbulence level in the obstacle area is higher, resulting in a larger fractal dimension. During flame acceleration, there is a mode transition from the “thin reaction zone” to the “broken reaction zone.”

Study on the propagation characteristics of methane-air explosion under the promotion of crushed gangue

Methane-air explosion is one of the major disasters in industrial process. The explosion strength could be influenced by the crushed coal gangue, which is widely distributed in coal mine gob and roadway. To understand the influence of the coal gangue on gas explosion, an experimental system with a 0.2 × 0.2 × 3.0 m3 pipeline was designed and explosion experiments of coal gangue with 5 blockage length-diameter ratios (ratio of axial blockage length to pipeline equivalent diameter) were carried out. The results show that coal gangue can cause significant disturbances to the flame front, resulting in a violent acceleration of the explosion flame. The overpressure ratio presents a negative exponential function distribution with the blockage length-diameter ratio. The influence range increases with the blockage length-diameter ratio under the condition of rich fuel, and reaches the maximum when equivalent ratio is 1.237. The explosion intensity is more sensitive to the blockage length-diameter ratio for the equivalent ratio equals 1.0 and 1.237. The formation of high-intensity explosion should be avoided by controlling the accumulation state of the overlying rock in coal mining.

Explosion characteristics of wood dust and its suppression in typical powder-related environments

To reduce the explosion hazard caused by wood dust, the effects of dust concentration and ammonium polyphosphate (APP) on the explosion of wood dust were carried out in a vertical combustion pipeline and the suppression mechanism was revealed. The explosion intensity of the wood dust increased and then decreased with increasing concentration, and the bottom of the pipeline remained bright due to continuous ignition. APP could effectively suppress the propagation of wood dust explosion flame. When the mass fraction of APP was 10%, there was no obvious flame, and the flame pressure dropped by up to 98%. The effect of APP on wood dust pyrolysis was analyzed using TG-DSC, and the explosion products were characterized by physicochemical analysis using EDS. The results showed that APP could improve the stability of the carbon layer on the surface of wood dust particles, and its decomposition products could enhance the thermal shielding and oxygen isolation effects of the particle surface protective layer. In addition, the APP significantly suppressed wood dust explosion by absorbing heat from the reaction zone, capturing and consuming free radicals, and reducing the oxygen concentration per unit volume.

Experimental and numerical simulation study of the influence of CF3CHFCF3 on characteristic of hydrogen/methane/air explosion

The effect of CF3CHFCF3 on the explosion of hydrogen/methane/air mixtures at low hydrogen doping ratios (XH2=10 %) has been investigated on a closed visualisation experimental platform. Different equivalence ratios (? = 0.8, 1 and 1.2) and CF3CHFCF3 concentrations (XCF3CHFCF3= 0% -5%) were considered. The results showed that the suppression effect of CF3CHFCF3 on the mixture was good under the conditions of different equivalence ratios. After the addition of CF3CHFCF3, both of the maximum explosion pressure and the maximum pressure rise rate decrease, which shows CF3CHFCF3 has an inhibitory effect on the explosion. However, pressure peak occurs earlier indicates that CF3CHFCF3 accelerated the progression of the explosion and facilitates its occurrence. The simulation results indicate that CF3CHFCF3 changes the mole fractions of the major species and increases the consumption of the O, H, and OH radicals. Besides, the results of sensitivity analyses show that CF3CHFCF3 not only play an inhibitory role but also enhances the laminar flame speed of the explosion flame. Meanwhile, the effect of CF3CHFCF3 on the reaction H + CH3 (+M) <=> CH4 (+M) is different under different equivalence ratios. This study can provide theoretical support for the safe use of hydrogen/methane/air mixtures.

Development of Multispectral Thermal Imager for Measuring the Temperature of Long-distance Explosion Flames

Development of Multispectral Thermal Imager for Measuring the Temperature of Long-distance Explosion Flames