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Combined effects of obstacles and fine water mist on a methane-air explosion of a semi-closed pipe were investigated experimentally. In this study, the diameter of the water mist, the location, and the number of obstacles was considered. The results demonstrated that 5 µm water mist present a significant suppression affected while 45 µm shows a slight promotion effected on a gas explosion of the condition without obstacles. In the presence of an obstacle, however, the inhibitory effect of 5 µm water veils of mist dropped significantly during flame propagation, and the effect of 45 µm water veils of mist changed from the enhancement of inhibition, and its inhibitory effect was significant. The inhibitory effect of 45 µm water veils of mist on gas explosion weakened firstly and then enhanced with the increasing distance between obstacle location from the ignition location as well as in several obstacles.

Evolution of fuel droplet evaporation zone and its interaction with the propagating flame front are studied in this work. A general theory is developed to describe the evolutions of flame propagation speed, flame temperature, droplet evaporation onset and completion locations in ignition and propagation of spherical flames. The influences of liquid droplet mass loading, heat exchange coefficient (or evaporation rate) and Lewis number on spherical spray flame ignition are studied. Two flame regimes are considered, i.e., heterogeneous and homogeneous flames, based on the mixture condition near the flame front. The results indicate that the spray flame trajectories are considerably affected by the ignition energy addition. The critical condition for successful ignition for the fuel-rich mixture is coincidence of inner and outer flame balls from igniting kernel and propagating flame. The flame balls always exist in homogeneous mixtures, indicating that ignition failure and critical successful events occur only in purely gaseous mixture. The fuel droplets have limited effects on minimum ignition energy, which however increases monotonically with the Lewis number. Moreover, flame kernel originates from heterogeneous mixtures due to the initially dispersed droplets near the spark. The evaporative heat loss in the burned and unburned zones of homogeneous and heterogeneous spray flames is also evaluated, and the results show that for the failed flame kernels, evaporative heat loss behind and before the flame front first increases and then decreases. The evaporative heat loss before the flame front generally increases, although non-monotonicity exists, when the flame is successfully ignited and propagate outwardly. For heterogeneous flames, the ratio of the heat loss from the burned zone to the total one decreases as the flame expands.

With the coal mining toward depth, there is an increased probability of gas explosion accidents. While the propagation characteristics of gas explosion on account of goaf environment have not been ...

To study the law of influence of an explosion venting door on gas explosion characteristics and verify its venting effect and fast sealing performance, a large-sized explosion pipeline experimental system was used. The gas explosion tests were carried out under the conditions of 5.5, 7.5, 9.5, and 11.5% gas concentration. The gas explosion characteristic parameters were measured by a data acquisition system. The laws of change in characteristic parameters and the flame-proof effect were analyzed. The results showed that the pressure peak was attenuated by 42.25, 50.54, 53.27, and 52.88% under the aforementioned four working conditions. As the gas volume fraction increased, the peak explosion pressure decayed as a quadratic function, and the average closing time of the fire zone was 13 h. This showed that the explosion venting door had significant explosion venting characteristics and the function of quickly closing the fire zone. The law of temperature change was basically the same, no matter how the gas concentration changed, and the explosion venting door had no inhibitory effect on the gas explosion flame. Under the four operating conditions, the maximum average values of the flame propagation speed were 103.56, 105.73, 136.67, and 138.34 m/s. The results of the study provide theoretical support for explosion-proof technology and emergency rescue technology in coal mines.

The localized forced ignition and subsequent flame propagation have been analyzed for stoichiometric biogas-air mixtures (CH4/CO2/air blend) with different spatial distributions (uniform, Gaussian ...

In recent years, the explosion accidents of liquefied petroleum gas (LPG) have induced tremendous losses. To analyze the deflagration danger of LPG, the explosion pressure and flame propagation features of the premixed LPG-air mixture in a closed pipeline at increased initial pressures and temperatures were examined by the numerical method. It has been shown that with an increase in the initial temperature, the highest explosion pressure and explosion induction period decrease, while the maximum flame temperature increases. As the initial temperature rises, the formation of the tulip flame accelerates, and the depression of the flame front increases at the same time. The elevated initial pressure raises the highest explosion pressure and the maximum flame temperature. Nevertheless, when the initial pressure exceeds 0.5 MPa, its impact on the flame temperature slowly diminishes. In addition, the gray relational analysis approach was utilized to evaluate the correlation between the initial condition and the derived parameters. The findings indicate that the initial pressure exerts the largest influence on the four explosion parameters. The research finding is important for exposing the deflagration risk features of LPG under complicated working situations, evaluating the explosion risk of correlated procedures and devices, and formulating scientific and effective explosion-proof measures.

The burning velocity plays an important role in determining the safety level of new refrigerants. Based on the self-designed test system for burning velocity characteristics of flammable refrigerants, the burning velocities of R152a with different concentration were studied by vertical glass tube method. And the maximum burning velocity of R152a was analyzed, which was close to the standard recommended value. R1234yf with environmental advantages and lower flammability may form a new alternative refrigerant mixture with R152a. Therefore, the flame propagation and burning velocity characteristics of R152a+R1234yf were studied under the conditions of different component ratio and different concentration. Based on the theoretical analysis, three calculation methods for predicting the burning velocity of binary mixed flammable refrigerant were proposed for the first time. Then, three groups of predicted burning velocity of R152a+R1234yf under different composition or concentrations were calculated. Compared with the experimental data, it was found that the prediction accuracy of the component equivalent simplified method is the highest among the three methods. It was of great significance for the prediction of burning velocity and the assessment of safety level of new mixed refrigerant or flammable gas.

It studied the explosion propagation of the hybrid mixture of LDPE dust and a small amount of ethylene (below its LEL) in a closed duct, to examine the impacts of dust concentration, dust particle ...

Passive explosion suppression remains an indispensable auxiliary method for gas explosion suppression due to its low cost. To explore a new type of explosion passive suppression technology, three rectangular cavities with different width-diameter ratios were designed and laid in a large-scale methane/air explosion experiment system, and its explosion suppression performance was evaluated by measuring the changes in the explosion flame and shock wave before and after passing through the cavity. The results show that the suppression effect of the cavity is affected by its width. The larger the width-diameter ratio, the faster the attenuation of the flame and shock wave. The cavity-combined aluminum hydroxide powder effectively improves the suppression effect. When the filling amount of the powder is 140 g, the flame is quenched. However, there is an optimal powder filling degree for the suppression of the shock wave in the limited space of the cavity. In the test range, the maximum decay rate of the overpressure and impulse are 49.4 and 39.4%, respectively. This study can provide theoretical guidelines for the suppression of gas explosion.

Such Nikolay Nikolayevich Semyonov’s discoveries as branching of reaction chains and features of chain combustion mechanism at low pressures (in the absence of self-heating) were shown to play a decisive role also at high pressures, in flame propagation, and in explosion and detonation. A physicochemical mechanism was revealed that ensures high rates and accelerations of reactions, consumption of reactants within hundred-thousandths of a second, and transition of combustion to explosion and detonation. Previously unexplainable laws of all the combustion modes were explained. Chemical methods based on the laws of chain reactions were developed to control combustion, explosion, and detonation.

The localised forced ignition and subsequent flame propagation have been analysed for stoichiometric C H 4 − C O 2 − air mixtures with different spatial distributions and mean levels of C O 2 dilut...

The paper reports results of the detailed chemical modelling of isobaric deflagrations in stoichiometric H2-N2O-N2 mixtures (N2 = 20 - 60 vol%) at various initial temperatures (300 - 500 K) and various initial pressures (1 - 10 bar): laminar burning velocities, and profiles of temperature, volumetric heat release rate and species concentrations across the flame front. The dependence of the laminar burning velocity on temperature and pressure is examined by empirical power laws, for restricted ranges of pressure (or temperature) variation. For each examined composition, the laminar burning velocity correlates well with the volumetric rate of heat release and with the sum of mass fractions of reactive species in the flame front.

The experimental study on the laminar flame speeds of the CH4/H2/CO/CO2/N2 mixture was carried out in oxygen-enriched air condition. The laminar flame propagation velocities of the blended gas were measured in a range of equivalence ratios (from 0.6 to 1.4) and oxygen concentrations (from 21 to 33%) using a Bunsen flame. Comparisons between the experiments and calculations show that the GRI Mech 3.0 mechanism can well predict the laminar flame speed of the blended gas in oxygen-enriched conditions. The laminar flame propagation velocities were enhanced by the increasing oxygen concentration, while the reaction pathway of fuel changed little. The effects of each species of the CH4/H2/CO/CO2/N2 mixture on the laminar flame speeds were discussed. Results show that the laminar flame speed is promoted by the increase of H2 and CO, while the laminar flame speed is decreased by the increasing CH4, CO2, and N2 concentrations. The inhibition effect of CO2 on the laminar flame speed is bigger than that of N2, which is due to the difference in the properties of CO2 and N2.

Effects of radiation reabsorption on the burning flux of freely propagating laminar premixed flames at atmospheric and elevated pressures were numerically investigated for CH4/O2/N2/CO2 mixtures. Models with SNBCK 9 bands and 7 bands based on the spectral band lumping for H2O, CO2, CO and CH4 were developed to improve the computational efficiency. It is found that the burning flux is promoted by the upstream radiation reabsorption and with increasing CO2 concentration. Furthermore, with increasing pressure, radiation reabsorption first increases and then reduces the burning flux because of the corresponding increases of the reabsorption efficiency and the optical thickness, respectively. The blockage of radiation emission from the burnt mixture due to the increased optical thickness is dominant with the addition of the stronger radiative species CO2 at higher pressures. Extensive computation further demonstrates that, compared with the benchmark case of 367 bands, the SNBCK 9 bands lumping retains good accuracy while substantially facilitates the computational efficiency.

Experiments have been carried out in a constant volume chamber to investigate the effects of Chlorella oil addition on the laminar burning velocity and Markstein length of Chlorella oil/RP-3 kerosene blends at an initial pressure of 0.1 MPa and temperature of 450 K over a wide equivalence ratio range from 0.8 to 1.4. The result shows that at equivalence ratios of 0.9 and 1.1, with the increase of Chlorella oil addition, no cellular structure is observed in the flame propagation images. It means that the Chlorella oil addition has little effect on the flame stability under these experimental conditions; however, at an equivalence ratio of 1.3, with the increase of Chlorella oil addition from 0 to 0.5, the flame tends to be stable. It is found that the Markstein length of Chlorella oil/RP-3 blend decreases with the increase of the equivalence ratio. The blend with 0.5 Chlorella oil addition has a more rapid decrease in Markstein length compared with that of the RP-3 between the equivalence ratio from 1.1 to 1.3. The peak laminar burning velocity of Chlorella oil/RP-3 kerosene blend is obtained at the equivalence ratio of 1.1, and with the increase of Chlorella oil addition from 0 to 0.5, the laminar burning velocity increases about 20%.

In this paper the phenomenon of flame jump vis-a-vis steady propagation in biomass packed beds in counter-current mode is discussed. By analyzing the fuel flux and propagation rate data from experi...

Non-combustible solid materials play a major role as inerting agents in explosion prevention. While the importance and application of these materials are well understood, there is still a lack of information about the actual mechanisms responsible for explosion suppression. Especially, the role of inert materials with a large specific surface area and the influence of the moisture content of inert materials have not been sufficiently investigated. In this work, an experimental and computational study of the effects of inert materials on ignition and flame propagation in lycopodium–air mixtures is undertaken. The influence of a large specific surface area is studied by using Clinoptilolith as an inert material.

The flame propagation behavior and the effect of particle agglomeration are examined by changing the size of PMMA particles in laboratory-scale experiments. PMMA particles having a very narrow size distribution are used. We show that the minimum explosible concentration increases as the particle size decreases. On the other hand, the flame propagation velocity also increases as the particle size decreases. Therefore, the minimum explosible concentration and the flame propagation velocity show the opposite dependences on the particle size. It is considered that the minimum explosible concentration is strongly affected by the interparticle distance; meanwhile, the flame propagation velocity strongly depends on the specific surface area. It has to be emphasized that the severity of the explosion can be serious for very fine particles, although the minimum explosible concentration is fairly high.

The effect of metal foam mesh on flame propagation of biomass-derived gas in a half-open duct was studied. The explanations are based essentially on the experimental investigations of premixed biomass-derived gas explosions carried out in a rectangular half-open combustion chamber. The initial temperature T0 and pressure P0 were 300 K and 1.0 atm, respectively. The key parameters of explosive characteristics, such as flame propagation images and explosive overpressure, were analyzed by changing the porosity, the pore density of porous metal foams, and the gas components. The results show that the use of porous metal foam has a significant inhibitory effect on the gas explosion. Although the combustion structure of the flames is similar, the action of the porous metal foam during the experiment also shows the characteristics consistent with the obstacles. When the porosity of the porous foam is 97%, the flame can be stimulated to produce turbulence, and then the shock–flame interaction generated by the reflection of the lead shock wave can enhance the explosion propagation and promote the explosion escalation. However, with the increase of hole density, the existence of the porous metal foam by momentum loss and heat loss to curb the spread of the explosion not only hindered the flow of not flammable but also extracted energy from the expansion of the combustion products at the same time. This study also confirms that the biological hydrogen and methane component has a vital role in the flame, and a reasonable hydrogen and methane ratio can improve the flame burning to get more economic value.

Flame acceleration and the deflagration to detonation transition (DDT) are important physical phenomena in combustion theories. The main objective of this work is to provide a comprehensive underst...

Deposited coal dust, when involved in a methane explosion, aggravates the severity of a mine explosion accident. Mastering the explosion flame duration and flame signal intensity, thereby allowing ...

In order to reduce the damage caused by a gas explosion in a ventilation duct, a Large Eddy Simulation (LES) model was used to simulate the hydrogen/air explosion process in the ventilation duct un...

Questions concerning the production of fire-resistant textile materials based on plasticized polyvinylchloride are examined. The parameters of fire hazard in fire-resistant samples of vinyl leather substitute in the presence of metal- and phosphorus-nitrogen-containing fire-retarding systems (flammability, resistance to the action of heat flows, flame propagation along the surface, smokeforming ability) were investigated. Recipes using phosphorus- and metal-containing fire-retarding systems were selected for the production of vinyl leather with reduced fire risk.

A kinetic model is presented for high-temperature oxidation and combustion of the refrigerants: 2,3,3,3-tetrafluoropropene (R-1234yf), 1,3,3,3-tetrafluoropropene (R-1234ze(E)), and 3,3,3-trifluorop...

To study the phenomenon of sedimentary coal dust being lifted by impact airflow after the underground methane explosion participated in the explosion, a transversal pipe network system of gas–coal ...

To study the effects of variable cross-section ducts with different configurations on the flame structure, flame propagation speed and overpressure of hydrogen/methane/air premixed gases, a series ...

Computational fluid dynamics (CFD) investigation of flame propagation and reflections of pressure waves through the fixed bed in a detonation tube (DT) is presented. A partially premixed combustion...

To evaluate the ignition sensitivity of mixed oil shale–coal dust, understand the flame propagation behavior of these mixtures during combustion and provide further reliable parameters for preventi...

The rate of flame propagation is generally understood to directly reflect the burning rate of a combustible mixture, as it is proportional to the square root of the overall reaction rate in the flame. However, in the case of heterogeneous mixtures composed of spatially separated discrete heat sources, such as suspensions of solid-fuel particles, theory suggests that the flame propagation speed may become insensitive to the reaction rate. Such a flame propagation regime, known as the “discrete flame” in the literature, is predicted to occur in suspensions of fast-burning metal particles and (or) low-conductivity gas media where the flame propagation becomes dominated by the heat transfer between fast-burning heat sources. In an attempt to experimentally confirm the existence of the discrete flame regime, flame fronts propagating in transparent glass tubes through iron particle ( d 32 = 33 µm) suspensions in low-thermal-diffusivity oxygen/xenon mixtures were studied in a high-quality microgravity environment. The experiment was performed on board the European Space Agency MAXUS-9 sounding rocket that lifted off from the Esrange Space Center (Sweden) on April 7, 2017. In total, 41 combustion runs were completed in suspensions with 20% and 40% of oxygen content during the 12 min of microgravity. While the experimentally determined combustion time of a single iron particle differs by a factor of more than three in mixtures with 20% and 40% oxygen content, the flames in these mixtures were found to propagate with practically equal speed in accordance with the predictions of the discrete flame theory.

A pipeline explosion system with different bending angles (45°, 60°, 90°, 120°, and 135°) was constructed to investigate the influences of the pipeline’s bending angles on the propagation law of co...

The transition to low global-warming potential (GWP) refrigerants is ongoing. Since a large part of Low-GWP refrigerants is combustible, fundamental flammability parameters have been studied. Howev...

In order to reveal the influence of pipe section size effect on hydrogen detonation characteristics, Large Eddy Simulation (LES) model was used to numerically investigate the hydrogen/air detonatio...

A novel comprehensive analysis based on the matched asymptotic expansions method is curried out for a problem of flame propagation in narrow channels with heat-losses using the activation energy as a large parameter. The novelty consists in presentation of the results, namely the dependence of the flame velocity versus the heat-loss intensity, in a parametric form. Comparison with the numerical calculations reveals that the asymptotic results becomes in close agreement at relatively low values of the expansion parameter in such a manner extending a practical implementation of the method. The analysis may be of utility to flame-sheet model applications increasing its accuracy in general combustion studies.

This numerical study investigates the combustion modes in the second stage of a sequential combustor at atmospheric and high pressure. The sequential burner (SB) features a mixing section with fuel injection into a hot vitiated crossflow. Depending on the dominant combustion mode, a recirculation zone assists flame anchoring in the combustion chamber. The flame is located sufficiently downstream of the injector resulting in partially-premixed conditions. First, combustion regime maps are obtained from 0-D and 1-D simulations showing the co-existence of three combustion modes: autoignition, flame propagation and flame propagation assisted by autoignition. These regime maps can be used to understand the combustion modes at play in turbulent sequential combustors, as shown with 3-D large eddy simulations (LES) with semi-detailed chemistry. In addition to the simulation of steady-state combustion at three different operating conditions, transient simulations are performed: (i) ignition of the combustor with autoignition as the dominant mode, (ii) ignition that is initiated by autoignition and that is followed by a transition to a propagation stabilized flame, and (iii) a transient change of the inlet temperature (decrease by 150 K) resulting into a change of the combustion regime. These results show the importance of the recirculation zone for the ignition and the anchoring of a propagating type flame. On the contrary, the autoignition flame stabilizes due to continuous self-ignition of the mixture and the recirculation zone does not play an important role for the flame anchoring. These findings are important for the design and operation of practical sequential combustion systems.

Deflagration of fire and explosion caused by ignition of a methane-air mixture is a major safety concern in industrial settings, such as the mining and petrochemical industries. The aim of this stu...

The laminar burning velocities and propagation speeds of stoichiometric n-butane-air mixture were obtained for outwardly propagating spherical flames by measurements of pressure rise during the early stage of propagation in a spherical vessel. The experiments were carried out at various initial pressures within 0.3 and 1.2 bar, and various initial temperatures within 298 and 423 K. The experimental laminar burning velocities were compared with those provided by the detailed kinetic modelling based on Warnatz mechanism for combustion of C1-C4 hydrocarbons, using INSFLA package. The baric and thermal coefficients of laminar burning velocities, calculated from their dependence on initial temperature and pressure, were compared with coefficients characteristic for other fuel-air mixtures. The overall activation parameters (reaction order and activation energy) are reported and discussed in comparison with similar data characteristic for alkane-air flames.

Flame propagation in a closed vessel containing a stoichiometric propane–air mixture and partially filled with a porous medium has been experimentally studied. It has been shown that the flammability limit in the porous medium is determined by the current pressure at the time the flame approaches it and by the transition processes occurring as the wave enters the porous medium. The dynamic limit phenomenon—the flammability limit in the porous medium associated with a continuous pressure drop—has been investigated. It has been found that the range of initial pressures in which the dynamic limit is observed is determined not only by the change in the number of moles in the gas phase, as during flame propagation in vessels completely filled with a porous medium, but also by gas cooling in the free space. The dynamic limit can occur in a significantly wider range of initial pressures than that due to a change in the number of moles. This range is mainly determined by heat exchange between the gas and the walls of the vessel in the region free from the porous medium.

The present work was aimed to develop the flame retardant textiles for prevention of second-degree burn injuries from low intensity heat flux accidents. The different concentration of casein suspension was applied on cotton fabrics and their thermo-oxidative properties, flame retardant behavior as well as physiological comfort were examined. From thermo gravimetric analysis, the percentage increase in char residue indicated improvement in thermo-oxidative properties. The maximum improvement in flame retardant behavior was found in case of 30 w/v% casein suspension due to higher production of thermally stable char. Their SEM micrographs also showed the formation of stronger and coherent char with presence of local intumescence. Furthermore, for estimating small differences in burn length and burn area, the flame propagation was studied in detail using the image analysis. The lower concentration of casein below 20 w/v% was found to provide adequate flame retardancy with acceptable physiological comfort and mechanical properties. Finally, the short term durability of casein treatment was verified under the effect of washing and ageing conditions.

Unsteady numerical simulations with detailed kinetic chemistry have been reported for premixed H2-air flames in straight mesoscale tubes of various diameters to understand the effect of wall heat t...

Flame acceleration and flame–shock interactions are important physical phenomena in combustion science. The primary contribution of this work is to observe different combustion phenomena in the fla...

Symmetric to asymmetric transitions of laminar-premixed methane-air flames anchoring in symmetric sudden expansion channels are explored. Numerical and experimental studies on flame anchoring pheno...

To reduce the size inconvenience of airbag systems employed in human-body protection devices while maintaining comparable gas generation performance, a new family of gas-generating energetic compos- ites are proposed mixing Al/CuO nanothermite with copper complex (Cu(NH3 )4 (NO3 )2 ) known for its propensity to generate gases (0.03 mol/g) such as N2 , O2 , N2 O through exothermic chemical decomposi- tion (300 J/g). The aluminum (Al)/Copper oxide (CuO) couple, known as the most widely studied nanoma- terial for thermite reactions, releasing a high energy, mostly heat, through chemical reaction, is employed as a source of heat to trigger and sustain the decomposition of Cu(NH3 )4 (NO3 )2 complex. This work per- mits developing a new family of gas-generating energetic composites that takes advantage of specific chemical and thermal properties of both materials. We demonstrate its capability to tune the pressuriza- tion rate, burn rate and pressure peak by varying the Al/CuO over Cu(NH3 )(NO2 )2 mass ratio. The peak pressure of Cu(NH3 )4 (NO3 )2 /Al/CuO energetic composites reaches 12 MPa/g.cm3 in a close volume, which is 3.3 higher than that of traditional Al/CuO nanothermite. They achieve much longer high-pressure dura- tion ( ∼30 ms). They also exhibit very intense burning with velocity reaching hundreds of m/s in opening burning experiments. These new materials appear very promising for green gas generation.

Obstacles are unavoidable in coalmine laneways and combustible gas pipeline. However, the obstacles may enhance the intensity of explosion, or change the propagation characteristic. The present pap...

The effect of H2/CO addition on flame dynamics of propane-air mixtures in a stepped microcombustor with heat recirculation was investigated experimentally. Unstable flame propagation regimes and their transition modes were observed for a range of mixture velocities (5���8 m/s) and equivalence ratios (0.6���0.95). Up to 60% H2 addition to lean propane-air mixtures helps improve the flame stability range in the combustor. The suppression of these flame instabilities with H2 addition is attributed to the increase in the overall mixture reactivity and burning velocity. The enhancement in OH intensity with H2 addition indicated a change in the elementary reactions, thereby affecting the flame dynamics. Contrary to H2 addition, CO addition does not show any noticeable effect on the formation of stable flame modes. The change in mixture properties and burning velocity leads to a change in the flame behavior and alters the heat release rate due to H2 addition to propane-air mixtures. A higher percentage of H2 addition led to the reappearance of the unstable (rotating) flames in the microcombustor. Intrinsic flame instabilities appeared at higher H2 percentages due to differential diffusion and increased thermal-wall coupling effects.