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In this paper, the experiment of titanium powder explosion was carried out by using Hartmann and 20-L spherical explosion tank. The inhibition effect of different proportions of Ca(H2PO4)2 and CaCO3 powders on titanium powder explosion was studied, and the inhibition mechanism of inhibitor on titanium powder explosion was analyzed. The experimental results show that with the increase of the proportion of inhibitors, the flame brightness becomes darker, the propagation velocity and distance decrease gradually, and the Pex and (dp/dt)ex decrease gradually. When 80% Ca(H2PO4)2 and CaCO3 were added, the average flame propagation speed decreased to 0.59 m/s and 1.08 m/s, respectively, and decreased by 87.7% and 77.4%; the Pex decreased to 0.152 MPa and 0.206 MPa, respectively, and decreased by 80% and 72.9%. The results show that both Ca(H2PO4)2 and CaCO3 have certain inhibition effect on titanium powder explosion, and the inhibition effect of Ca(H2PO4)2 is better.

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.

A vertical spill fire is one of the typical phenomena in fire scenes, which usually occurs with liquid fuel usage and storage and may pose a threat to process safety. In this study, a number of transformer oil continuous spill fire experiments were carried out on a steel experimental setup, in order to obtain the vertical spill fire characteristics of transformer oil or fuels that have similar properties as transformer oil. The flame shape, temperature and radiation data in the process of flame propagation were recorded. According to the change of the burning area, the formation and development process of a vertical spill fire can be divided into four stages. The relationship between burning area and fuel leakage rate in the quasi-stable combustion stage is analyzed and a prediction model for the burning area of a transformer oil vertical spill fire is established. The radiation model of a transformer oil vertical spill fire is established as a function of leakage rate. Based on heat transfer analysis, a mass burning rate model is derived and verified by experimental data.

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 safety issues and existing risks of ethanol-gasoline in industrial production have to be well considered and investigated. Especially when there are more than one thin doors, windows/thin walls in containers were broken once deflagrations occurred, but it appears that few researches deal with multi vented deflagrations. Hence we carried out experiments in a small cuboid container to investigate the effect of multiple vents’ numbers and distributions on vented ethanol-gasoline vapor deflagrations characteristics. Multi overpressure peak structures during multi-vented deflagrations were first observed and analyzed to reveal the complex physical process in the venting. Results show that five overpressure peaks’ structures were found ( P b , P f v , P c v , P e x t and P a c ) when multiple vents with the same area are arranged along the axis of the container’s roof. Flame propagation and overpressure buildup are mainly influenced by the 1st vent (i.e., the nearest one to the spark plug). The 1st vent also determines the number and types of overpressure peak structures. Compared with the single vent, the cases of multiple vents with the constant total vent area may cause larger P m a x , d P / d t m a x and K G even if all vents are closer to the spark plug. Consequently, the use of multiple vents does not necessarily help to improve the vent effects.

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.

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 present study proposes a localized thickened flame (LTF) model for the accurate prediction of flame propagation and autoignition timing. The unresolved-scale terms appeared in spatially-filtered governing equations due to thin flame structures are constructed under a physical constraint in which laminar flame speed is maintained. A high-order derivative is introduced to dynamically localize the effects of the LTF in the regions of unresolved propagating flame. The model is also designed such that the thickened flame is resolved by the same number of grid points for any grid size used. Therefore, a user-specified constant in the model does not need to be adjusted depending on the employed grid size. Laminar flame propagation problems are used to validate the performance of the proposed LTF model and determine the appropriate value of the user-specified constant. The results using a one-dimensional constant-volume reactor demonstrate that the LTF successfully captures the accurate flame propagation behaviors under elevated pressure conditions, while not affecting the end-gas autoignition timing, even on relatively coarse grid resolutions. The high-order derivative in the LTF serves as a dynamic parameter for detecting the thinning flame under elevated pressure conditions.

This work reports an experimental and kinetic modeling investigation on the laminar flame propagation of three butylbenzene isomers (n-butylbenzene, iso-butylbenzene and tert-butylbenzene)/air mixtures. The experiments were performed in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 423 K, initial pressures of 1–10 atm, and equivalence ratios (ϕ) of 0.7–1.5. The laminar burning velocities of butylbenzene/O2/He mixtures were also measured at 423 K, 10 atm and ϕ = 1.5 to provide additional experimental data under conditions that the butylbenzene/air experiments are susceptible of cellular instability. Comparison among the laminar burning velocities of butylbenzenes including both the three isomers investigated in this work and sec-butylbenzene investigated in our recent work [Combust. Flame 211 (2020) 18–31] shows remarkable fuel isomeric effects, that is, iso-butylbenzene has the slowest laminar burning velocities, followed by n-butylbenzene and tert-butylbenzene, while sec-butylbenzene has the fastest laminar burning velocities. A kinetic model for butylbenzene combustion was developed to simulate the laminar flame propagation of butylbenzenes. Sensitivity analysis was performed to reveal important reactions in laminar flame propagation of butylbenzenes, including both small species reactions and fuel-specific reactions. Kinetic effects are concluded to result in the different laminar burning velocities of four butylbenzene isomers. Small species reactions control the laminar flame propagation under lean conditions, which results in small differences of laminar burning velocities. Chain termination reactions, especially fuel-specific reactions, have important contributions to inhibit the laminar flame propagation under rich conditions. The structural features of butylbenzene isomers can significantly affect the formation of some crucial radicals such as methyl, cyclopentadienyl and benzyl radicals under rich conditions, which leads to remarkable fuel isomeric effects on their laminar burning velocities, especially at high pressures.

Propagation of a H2-added strained laminar CH4/air flame in a rich-to-lean stratified mixture is numerically studied. The back-support effect, which is known to enhance the consumption speed of a flame propagating into a leaner mixture compared to that into a homogeneous mixture, is evaluated. A new method is devised to characterize unsteady reactant-to-reactant counterflow flames under transiently decreasing equivalence ratio, in order to elucidate the influence of flow strain on the back-support effect. In contrast to the conventional reactant-to-product configurations, the current configuration is more relevant to unsteady stratified flames back-supported by their own combustion products. Moreover, since H2 distribution downstream of the flame is known to play a crucial role in back-supported CH4/air flames, the influence of H2 addition in the upstream mixture is examined. The results suggest that a larger strain rate leads to a larger equivalence ratio gradient at the reaction zone through increased flow divergence, which amplifies the back-support. Meanwhile, since H2 addition in the upstream mixture does not affect the downstream H2 content, the relative increase in the consumption speed, i.e. the back-support, is suppressed with larger H2 addition. Especially, when the upstream H2 content decreases with the equivalence ratio, the H2 preferentially diffuses toward the unburned gas, which mitigates H2 accumulation in the preheat zone and further weakens the back-support.

Driven by pollutant emissions stringent regulations, engine manufacturers rely on lean combustion and aim to reduce the number of injectors, both affecting the light-round phase of ignition. This work focuses on inter-injector spray flame propagation in a linear multi-injector n-heptane/air spray burner measured at CORIA. Large Eddy Simulation (LES) are performed together with a complex chemistry description and a Lagrangian formalism of the spray in order to account for fuel droplet polydispersion. First, a non-reacting case enables to evaluate the numerical approach by comparison with measurements, and to analyse the influence of inter-injector spacing on both the flow dynamics and the local fuel distribution. Second, the comparison of numerical fully transient ignition sequences with experimental data shows that LES recovers the inter-injector spray propagation features found in the experiment such as flame propagation modes from radial to progressively arc-like, and total ignition time delay. However due to important pre-evaporation, liquid fuel does not significantly impact the overall ignition process, which exhibits the same driving mechanisms as in purely gaseous flows.

An experimental study was performed on pressure evolution and flame propagation for CH4 and its blends with C2H6, C2H4, CO, and H2 over its entire flammable range for systems with various concentra...

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.

Experiments of partial inerting on flame propagation of starch dust deflagration in a vertical duct were conducted to reveal the differences in flame structure evolutions. Particle pyrolysis and combustion behavior combined with time scale analysis are used to discuss the flame inerting mechanism. The results showed that the inerting process makes the flame front fuzzy, discrete and irregular. The thickness of flame reaction zone increases as O2 concentration decreases, while the preheat zone decreases accordingly. The pyrolysis rate always controls the flame propagation process under inerting conditions. With the decrease of O2 concentration, the control effect of pyrolysis rate is gradually weakened, and the effect of combustion reaction rate on flame propagation appears. A physical model of starch dust flame propagation under partial inerting is established, and the inerting process of dust pyrolysis and combustion on the flame structure evolution is further revealed.

A NaHCO3/diatomaceous earth (DE) composite powder suppressant with unique clustered structures is prepared by high-pressure impact method, using DE as the carrier and NaHCO3 as the loaded chemical suppressant. The purpose is to obtain affordable, environmentally friendly, high-efficiency power explosion suppression materials. The suppression efficiencies of the NaHCO3/DE composite powder suppressant on aluminum dust propagation and explosion pressure are tested. The results show that as the content of the NaHCO3/DE composite powder suppressant increases, the maximum flame length gradually reduces and the suppression efficiency gradually increases. Addition of 60 wt% of the NaHCO3/DE composite powder suppressant suppress aluminum dust flame propagation and addition of 100 wt% of the NaHCO3/DE composite powder suppressant can fully suppress aluminum dust explosion. Comparison with pure NaHCO3 and pure DE reveals that NaHCO3/DE composite powder suppressant is more effective in suppressing aluminum dust flame propagation and aluminum dust explosion pressure than either of the two powders alone. The suppression mechanism of the NaHCO3/DE composite powder suppressant is established: On the one hand, reaction is suppressed by the decomposition of NaHCO3 and the product of this decomposition; on the other hand, as DE is rich in porous structures, when the loaded NaHCO3 powder separates from DE, the porous structures will not only limit flame propagation, but will also well adsorb the substances generated from explosion reaction.

Experiments were performed to carefully characterize the influence of ambient temperature and incident heat flux on the horizontal flame spread over wires and cables. Results show that the flame spreads evenly along the wire, and the flame spread rate slightly increases with the ambient temperature increasing with a maximum increase of 16 %. However, the change of the flame front position with time for the cable presents a piecewise linear function, and an accelerating process exists. As the incident heat flux increases, the flame spread rate increases significantly with a maximum increase of 110 % and 113 % for both single and double cable. There is no spreading flame over the cable below a lower limit of the incident heat flux. The fastest flame spread along the cable occurs when the incident heat flux causes the flame to extend to the end of the fuel instantly. Compared to the single cable, the flame spread rate of double cable is increased by 13.6%–16.2% due to the enhanced heat feedback by the flame interaction effect. The difference in flame spread behavior in this work may be ascribed to different physical configurations, chemical compositions, reaction mechanisms, and heat transfer mechanisms.

In order to evaluate the explosion characteristics of biogas (i.e., the mixture of CH4 and CO2), experiments were conducted in a duct with a length-to-width ratio of 10. The ignition was activated at the closed end while the opposite end was sealed by a PVC film of varying thickness. The effect of PVC film thickness and methane fraction in biogas was studied. The results show that there were three possible pressure peaks (Pb, Pmfa, Pext), due to the film failure, the attainment of maximum flame area and the external explosion, respectively. The pressure profile pattern was dependent on the combination of film thickness and methane fraction. Two pressure peaks Pb and Pmfa were observed for the PVC film thickness δ ≤ 0.033 mm. However, the pressure peak Pmfa was absent for the film thickness δ ≥ 0.055 mm because the PVC film did not rupture in these cases when the flame had touched the sidewall. In other words, the maximum flame area was achieved prior to the moment of venting. It signifies that in the absence of explosion venting, the flame quenching due to the sidewalls alone was insufficient to induce an individual pressure peak Pmfa. The third pressure peak Pext was low for the biogas explosion in the current configuration. The film thickness exerted a greater impact on bursting pressure Pb than did the methane fraction, at least for the range of film thicknesses and methane concentrations considered. Additionally, the individual effect of the film thickness or the methane fraction was less influenced by each other. The existing theories were accurate to predict the characteristic times of the flame propagation for δ = 0.011 mm but not for δ ≥ 0.033 mm. The PVC film thickness affected the explosion overpressure more, whereas the CH4 fraction in biogas affected the flame front velocity more remarkably.

The minimum explosible concentration (MEC) and flame propagation behaviors of propane/L-leucine powder hybrid mixtures were experimentally investigated. The results of the experiment demonstrated that the MEC values decreased as the propane concentration increased. Additionally, the findings of the analysis proved that the flame propagation limitation in dust explosions increased with the increase in propane concentration. The results indicated two things. First, the flame speed of stoichiometric propane-air/L-leucine powder hybrid mixtures in the initial period of propagation was almost constant notwithstanding an increase in the L-leucine concentration. Second, the dimensionless flame speed was close to unity because the speed of the hybrid mixture was strongly affected by the propane–air premixed flame speed, although the flame speed increased with the increase in propane concentration. Further, it was found that the separate propagating flames of dust/gas hybrid mixtures had a considerable difference in flame speeds were observed.

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 ...

Mechanisms governing the gasification to combustion regime transition in counter-current packed bed biomass systems are investigated in the current work. Single-particle experiments are performed w...

The suppression effect of expandable graphites (EGs) on 5 μm aluminum dust explosions was systematically studied in an open-space dust apparatus. Flame propagation behaviors showed that flame structures became more discrete and more irregular after the addition of EGs. The flame propagation velocities declined variously owing to the suppression effect of EGs. Meanwhile, the optimum suppression concentration for each EG was determined. It was proved that the suppression effect was improved remarkably by increasing the expandable ratios of EGs. Moreover, expandable ratios of EGs had a preferable influence on the suppression effect in comparison with size distributions. Scanning electron microscopy demonstrated that the volumes of EGs increased by several hundred times when encountered with high temperature and the surface got fluffy and multihole. Based on above results, the suppression mechanism of EG for aluminum dust explosions was summarized in this paper in detail.

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 ...

Dust explosion accidents frequently occur in dedusting pipes of wheat dust, causing huge casualties and property losses. In this paper, a vertical pipeline of combustion experimental platform was established to obtain the effects of working conditions and double-layer wire mesh parameters on wheat dust flame propagation. The results show that the double-layer wire mesh has an obvious suppression effect on the flame propagation of wheat dust. At the combination of the same mesh number, both the peak flame temperature and the maximum flame propagation velocity decreased with the increasing of the mesh number, and the flame quenching phenomenon occurs at 80 mesh. At the combination of different mesh numbers, the flame temperature at the upper-density and lower-sparseness combination is lower than that at the upper-sparseness and lower-density combination under all working conditions. The flame temperature difference (ΔT) gradually increases with the increasing of mesh number difference, and the maximum ΔT appears at the mesh difference of 40 mesh. As the separation distance increases, the flame temperature rises, and the suppression effect is best at the separation distance of 1 cm. The peak combustion pressure is negatively linear with the separation distance.

Dust explosions have been often reported in many industries that handle or process combustible dusts, with great losses to life and property. This explosion risk could be amplified under some extreme conditions like high-temperature environments. In this work, we develop a 2D numerical method to investigate explosion characteristics of corn starch cloud with an emphasis on the roles of high-temperature environments. The particle tracking trajectories and devolatilization evolution at high-temperature environments are described. The dust explosion severity characteristics including maximum explosion pressure (Pex) and maximum rate of pressure rise (dp/dt)max, are also investigated. In addition, the characterized devolatilization and explosion time are applied to analyze dust explosion behavior and flame propagation. The devolatilization evolution of dust cloud and flame propagation modes are found to vary with ambient temperature. And three ignition modes are observed after ignition. The simulation also provides a satisfactory prediction for dust explosion behavior at high-temperature environments.

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...

Laminar burning velocities of fuel mixtures of methane/ethane/propane with the compositions 100/0/0, 80/20/0, 80/0/20 and 80/10/10 vol% burning with air were determined experimentally using the heat flux method at 1 atm and initial gas temperatures 298, 318 and 338 K. The mixtures were selected as surrogates for natural gas, with the aim to investigate the effect of heavier hydrocarbons on the laminar burning velocity of the main component, methane. It was found, in agreement with the literature data, that the heavier hydrocarbons increase laminar burning velocity compared to that of methane + air flames. A common correlation for the temperature dependence of the burning velocity S L = S L0 (T/T 0 ) α , where T 0 is a reference temperature and S L0 is the laminar burning velocity at this temperature, was used to interpret new measurements. The power exponents, α, were derived from the experimental data for methane and three surrogates for natural gas. It was found that the temperature dependence of the burning velocities is practically identical for all mixtures studied. The measurements have been compared with the modelling using two kinetic schemes: recent version of the Aramco mech 2.0 and an updated version of a model developed by the authors. Both kinetic mechanisms show systematic trends in slight over- and under-prediction of the burning velocities, respectively, for all fuel blends. However, the temperature dependence of the burning velocities is accurately reproduced by these two models. Further analysis indicates that even though rate constants of the reactions determining flame propagation are somewhat different for the two mechanisms, the power exponents α are not sensitive to the differences. This indicates that, detailed kinetic schemes capable in predicting burning velocities at a specific initial mixture temperature are able to operate at higher temperatures as well, at least from lean to moderately rich natural gas mixtures.

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...

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