An approach is presented for predicting the upper flammability limits of hydrocarbons in air. The upper flammability limits of paraffin/air and olefin/air mixtures were determined using calculated adiabatic flame temperatures at initial temperatures of up to 500 K under atmospheric pressure. The explosion products of the various mixtures and their changes are discussed to improve the accuracy of the predicted upper flammability limits. It is found that the predicted upper flammability limits with temperature dependence agree with the experimental data. The relative error for the predicted upper flammability limits of the hydrocarbon/air is 0.13–3.40%. Moreover, the estimated upper flammability limits increase significantly with initial temperature at atmospheric pressure, which indicates that the examined hydrocarbon/air mixtures at high temperature have higher risk of explosion.

•Explosion overpressure of hydrogen/air rises locally with distance unlike methane or propane.•Maximum peak dynamic pressures of hydrogen/air explosion are reached beyond original cloud.•Peak explosion dynamic pressure of hydrogen/air cloud is of same order as overpressure.•Explosion temperatures have little difference between three mixtures examined in this study.Numerical simulations were performed to study explosion characteristics of the unconfined clouds. The examined cloud volume was 4 m × 4 m × 2 m. The build-in obstruction inside the cloud was the 8 × 8 × 4 perpendicular rod array. The obstacle volume blockage ratio was 0.74. Three gases were considered: hydrogen/air at the stoichiometric concentrations, propane/air at the stoichiometric concentrations, and methane/air at the stoichiometric concentrations. The hydrogen/air cloud explosion has higher peak overpressure and the overpressure rises locally at the nearby region of the cloud boundary. The explosion overpressures of both methane/air and propane/air are lower, compared with the hydrogen/air, and decreases with distance. The maximum peak dynamic pressure is reached beyond the original cloud, which is clearly different from the explosion peak overpressure tends. Furthermore, dynamic pressure of a cloud explosion is of the same order as overpressure. The explosion flame region for the hydrogen/air cloud is approximately 1.25 times of the original width of the cloud. The explosion flame regions for propane/air or methane/air clouds are approximately 1.4 times of the original width of the cloud. Unlike the explosion overpressures, the explosion temperatures have little difference between the three mixture examined in this study. The higher energy of explosive mixture generates a high temperature hazard effect, but the higher energy of explosive mixture may not generate a larger overpressure hazard effect in a gas explosion accident.

•The distribution of local dust concentration in the vessel can be described quantitatively.•The dispersion duration of 20 ms or 50 ms has little impact on the spatial uniformity of dust dispersion.•The distribution of dust concentration with time shows similar trend in the local position of vessel.•The local dust concentration at each measurement position reached peak at 50 ms for the two dusting time.To further study the distribution of local dust concentration, our work evaluated the dispersion quality of tracer particles in a new 20 L experimental vessel with a multi-nozzle injection system. Adopting the light extinction method and a high-speed camera system, local dust concentrations were obtained based on the measured optical transmittance through the dust cloud at various positions inside the 20 L vessel. Afterwards, the spatial uniformity of dust dispersion was examined using the obtained local concentrations. Based on the Lambert-Beer law, a quantitative description of dust local concentration in the upper, lower and central areas was obtained by experiment and calculation, respectively. Results show that the dust concentrations of central area in the vertical direction from top to bottom were higher than concentrations on the both left and right sides. The dust concentration on the right side near the vessel wall was slightly higher than that on the left. For two different dust dispersion durations of 20 ms and 50 ms, the local dust concentrations reached peak at 50 ms and then decreased with time due to the gravity impact on dust and turbulence intensity. In the dust cloud, the large-particle dust settles faster while the small-particle dust disperses better under the airflow action. After continuous dispersion, with the injection nozzles on two sides as the axis, dust concentration changes are symmetric between the upper and the lower areas. From analysis of dust concentrations for two dispersion durations, the variations of local dust concentrations at the selected seven measuring positions differ very little with one another. That is, the dispersion duration of 20 ms or 50 ms has little impact on the spatial uniformity of dust dispersion in the 20 L vessel.

•Dust cloud explosion in open space and its flame propagation was examined using numerical simulation.•Dust cloud volume expands to 366.92 m3, which is 14.60 times of its initial value (25.13 m3).•Influence of the ground on flame propagation changes from inhibition to promotion during the explosion.•Variation of dust cloud expansion velocity lags behind the variation of flame velocity.•Acceleration to dust particles by the explosion is unstably confined to a certain area surrounding flame boundary.In recent years, dust explosion accidents have been reported frequently. More and more studies on dust explosions have been published. However, there are few reports concerning flame propagation and dust particle movement of a large-scale dust explosion process in open space. In this study, a large-scale corn starch dust explosion was simulated using computational fluid dynamics software. Flame propagation and particle transient movement during the explosion were monitored. The initial dust cloud, with a concentration of about 300 g m−3, is approximately an ellipsoid with a 4 m major axis (horizontal) and a 3 m minor axis (vertical); its center is at about 1.5 m distance from the ground. At the time of 700 ms when the explosion process basically finishes, the dust cloud expands to a semi ellipsoid with a 14 m major axis (vertical) and a 10 m minor axis (horizontal). The dust cloud volume expands to 366.92 m3, which is 14.60 times of its initial value (25.13 m3). During the explosion, both the flame and the dust cloud expansion are first accelerated and then decelerated, but overall, variation of dust cloud expansion velocity lags behind the variation of flame velocity. Before 400 ms, dust cloud expansion velocity is notably lower than flame velocity, then dust cloud and flame expand outwards together basically at the same speed, and the distance between dust cloud boundary and flame boundary stabilizes at around 0.5 m.

•The SMDs of 19.95 and 34.84 μm were studied in Urms ∼ 3.5–7 m/s.•The evaporation rate for smaller particles is larger than for larger particles.•The peak pressure and temperature for smaller SMDs is larger than for larger SMDs.•The concentration of Pmax is greater than Tmax regardless of particle size.•LFL and Pmax will be subject to corresponding vapor-phase concentration.In this study, we investigated the explosion parameters of vapor–liquid two-phase JP-10 (C10H16, tricycle [5.2.1.02, 6] decane)/air mixtures, and reported new experimental data obtained at various conditions. Two sets of vapor–liquid two-phase JP-10/air mixtures at different fuel concentrations, with Sauter mean diameters (SMDs) of 20 μm and 35 μm, respectively, were examined. Their explosion temperature, pressure and lower flammability limits were measured and analyzed in the current study.

In order to investigate the heterogeneous detonation characteristics of aluminum particles/JP-10/air mixtures, the gas–solid two phase flow and detonation models were established using the discrete phase model (DPM) and turbulent combustion model, and detonation properties of the aluminum particles/JP-10/air mixtures were simulated. At stoichiometric concentrations of the solid particle–gas mixtures, and four different mass ratios (100% aluminum particles/air, 60% aluminum particles/40% gaseous JP-10/air, 40% aluminum particles/60% gaseous JP-10/air, 100% gaseous JP-10/air), results reveal that obvious reaction relaxation phenomenon exists in aluminum particles detonation process, however, addition of gaseous JP-10 to aluminum particles obviously contributes to higher steady detonation propagation velocity and extended reaction zone width. Furthermore, 60% aluminum particles/40% JP-10/air mixture achieves the highest detonation velocity up to 2128 m/s, detonation pressure of 3.7 MPa, efficiently enhanced reaction zone width of 0.369 m, and the reaction times of JP-10/air and aluminum particles/air of 2.07 μs and 5.65 μs, respectively.

•50 nm titanium dust flame was characterized by discrete single burning particles.•35 μm titanium dust flame was marked by clusters of glowing burning particles.•Micro explosion occurred more seriously in nano-titanium dust flame propagation.•Oxidation reaction occurred on the liquid phase surface.•50 nm titanium combustion products contained TiO (Ti2+) and TiN (Ti3+).Particle size has significant effect on flame propagation behaviors in dust explosions. In this study, the flame propagation behaviors and microstructures in micro- and nano-titanium dust explosions were observed and compared. Results showed that flame propagation mechanisms in 50 nm and 35 μm titanium dust clouds were quite different. 50 nm titanium dust flame was characterized by discrete single glowing burning particles with smooth spherical flame front. While 35 μm titanium dust flame was marked by clusters of glowing burning particles with irregular flame front. 50 nm titanium flame velocity was fluctuated more violent and the average flame propagation velocity was faster than that of 35 μm titanium flame. In addition, micro explosion phenomenon occurred significantly in the burning process of 50 nm titanium particles. SEM photos showed that 50 nm titanium particles were approximately spherical shape with observably agglomerations before ignition. However, the combustion products exhibited complicated structures combined the spherical titanium oxides with considerable larger diameters and irregularly spliced smaller titanium oxides. 35 μm titanium particles were in irregular shape before ignition, but in spherical shape after combustion. These results indicated that oxidation reaction occurred on the liquid surface of 35 μm and 50 nm titanium particles. From X-ray photoelectron spectroscopy, it was revealed that the dominant oxidation states of 35 μm titanium combustion products was TiO2 (Ti4+), and to a much lesser extent of Ti2O3 (Ti3+). However, 50 nm titanium combustion products contained 61% TiO2 (Ti4+), 18% Ti2O3 (Ti3+), 8% TiO (Ti2+) and 13% TiN (Ti3+).

•Flame speed of H2/air is faster than CH4/air at stoichiometric concentrations.•Flame duration of CH4/air is longer than H2/air at stoichiometric concentrations.•Peak maximums and (dp/dt)max of CH4/air explosion reach peak beyond premixed zone.•Peak maximums and (dp/dt)max of H2/air explosion reach peak at barrier's end.•Maximum pressures and (dp/dt)max of H2/air and CH4/air rise as volume increases.Hydrogen and methane that are largely different in gas activity are two common explosion hazards. Understanding their explosion characteristics is the foundation for acknowledging explosion hazard effects of hydrogen and methane. In this study, the explosion experiments of hydrogen/air and methane/air for different gas volumes have been carried out in a closed tube. The objectives of this study are to examine the explosion characteristics of hydrogen and methane at the stoichiometric concentrations and to acknowledge explosion hazard effects based on the experimental data in the tube. According to the experimental results, the flame propagation speed of hydrogen/air explosion is higher than that of methane/air, while the flame duration of methane/air is longer than that of hydrogen/air. It is indicated that the higher reactive hydrogen can cause massive burst damage, while the lower reactive methane can lead to a lasting harm. In the experimental tube, peak overpressures and maximum rates of pressure rise (dp/dt)max of hydrogen/air explosion for different gas volumes change greatly along the axial direction of the tube and reach the maximums at the end of the obstacles region. The pressure maximums are up to more than 1.5 MPa. While peak overpressures and (dp/dt)max of methane/air explosion change relatively slowly along the axial direction of the tube and their maximums appear beyond the original premixed gas zone. The pressure maximums just reach about 0.38 MPa. For all premixed zones, peak overpressures, maximum rates of pressure rise (dp/dt)max of hydrogen/air explosion and speeds of shock wave are significantly larger than those of methane/air, except for 1.5 m premixed zone for which peak overpressures, (dp/dt)max and speeds of shock wave of hydrogen/air and methane/air are very close relatively beyond the premixed gas zone due to too little combustible gas volume. As the combustible gas volume increases, maximum pressures and maximum rates of pressure rise of hydrogen/air explosion rise more significantly than those of methane/air because of different gas activity and flame acceleration characteristic.

•Lower flammability limits of hydrogen–air decrease as initial pressures increase from 0.1 to 0.4 MPa.•Decrement of LFL with initial temperature from 21 to 90 °C at 0.4 MPa is less than 0.25%.•Lower flammability limit of hydrogen–air at 0.1 and 0.4 MPa are 4 and 1.25%(V/V) respectively.•Upper flammability limits of hydrogen–air increase with initial pressure and temperature.•Upper flammability limit of hydrogen–air at 90 °C and 0.4 MPa is 93%(V/V).This paper presents data on the lower and upper flammability limits of hydrogen–air mixtures at elevated temperature and pressure. A 5-L explosion vessel, an ignition system, and a transient pressure measurement sub-system were used in this study. Through a series of experiments carried out, the lower and upper flammability limits of hydrogen–air mixtures at different initial pressures and temperatures have been studied and the influence of initial temperature and pressure on the lower and upper flammability limits of hydrogen–air mixtures has been analysed and discussed. It was found that the decrement of the LFLs of hydrogen–air with the initial temperature from 21 to 90 °C at the initial pressure of 0.1 MPa is less than 1%, the decrement of the LFLs with the initial temperature from 21 to 90 °C at 0.2 MPa is less than 1%, the decrement of the LFLs with the initial temperature from 21 to 90°Cat 0.3 MPa is less than 0.66%, and the decrement of the LFLs with the initial temperature from 21 to 90 °C at 0.4 MPa is less than 0.25%. The lower flammability limits of hydrogen–air mixtures at the pressures of 0.1 and 0.4 MPa are 4 and 1.25%(V/V), respectively. The upper flammability limits of the hydrogen–air mixtures increase with the initial pressure and temperature. The upper flammability limit of the hydrogen–air mixtures at 90 °C and 0.4 MPa reaches 93%(V/V) which is much higher than that (76%(V/V)) at 21 °C and 0.1 MPa.

•Model predicting flammability limits at various initial pressures was created.•FLs of mixtures with lower H2/O2 ratios are different from LFLs of hydrogen in oxygen or air.•Critical concentrations of helium increase with H2/O2 ratio from 0.5 to 2 for mixture at 21 °C.•Critical concentrations of helium increase with initial pressure from 0.1 to 0.4 MPa for mixture at 21 °C.•Critical concentrations of helium tend to its limit of 95% at 2:1 H2/O2 ratio and 60 °C and 0.3 MPa.The objective of this study is to determine the critical concentrations of helium making hydrogen–oxygen nonflammable under various volume fraction ratios of hydrogen and oxygen. Tests were conducted for three volume fraction ratios of hydrogen and oxygen 2:1, 1:1 and 1:2, at the initial pressures of 0.1, 0.2, 0.3 and 0.4 MPa and the initial temperatures of 21, 40, 60, 75 and 90 °C. The flammability limits of mixtures with the lower volume fraction ratios between hydrogen and oxygen are much different from the lower flammability limits of hydrogen in oxygen or air. Compared with the lower flammability limits of hydrogen in oxygen or air, the critical concentrations of helium determined in this study are significant for process safety of the mixtures with various volume fraction ratios between hydrogen and oxygen. For the mixtures at 21 °C, the critical concentrations of helium making hydrogen–oxygen nonflammable increase with the volume fraction ratios of hydrogen and oxygen in the range from 0.5 to 2. The variation of the critical concentrations of helium with the initial pressure depends on the initial temperature. For the mixtures at the initial temperature of 60 °C and the initial pressure of 0.3 MPa, the critical concentration of helium reaches to its limit of 95% in the case of volume fraction ratio of hydrogen and oxygen 2:1. The limit values of the critical concentration of helium are 93% for 1:1 volume fraction ratio of hydrogen and oxygen and 89% for 1:2 volume fraction ratio of hydrogen and oxygen ratio, respectively.

The critical oxygen concentration (COC) in this study is defined as the maximum oxygen concentration at which a mixture of methanol vapor in nitrogen does not explode, regardless of the nitrogen concentration in the mixture. This paper presents data on the critical oxygen concentration (COC), in the presence of added N2, of methanol (CH4O) saturated vapor mixtures at elevated temperature and pressure. We have used a COC measurement system consisting of a 4-L explosion vessel, an ignition subsystem, and a transient pressure measurement subsystem. Through a series of experiments carried out in this system, the COCs of methanol-saturated vapor/O2/N2 mixtures at different initial pressures and an elevated temperature of 80 °C have been studied, and the influence of concentration of nitrogen on the COC has been analyzed and discussed. Variation of the initial pressure within the studied range was found to have significant effect on the COCs of the methanol saturated vapor/O2/N2 mixtures. There is a very large difference between the COCs (or CNCs) of the methanol-saturated vapor/O2/N2 mixtures at the elevated temperature and pressure and those of methanol vapor in air at atmospheric pressure and room temperature. The COCs of the methanol-saturated vapor/O2/N2 mixtures with the initial temperature of 80 °C at the initial pressure of 0.5, 0.4, and 0.3 MPa are 36, 28, and 21 vol %, respectively. The corresponding CNCs at initial pressures of 0.5, 0.4, and 0.3 MPa are 54, 59.5, and 62 vol %, respectively.

After a methane-in-air explosion in a coal mine tunnel, a secondary explosion of coal dust is prone to happen. The shockwave in the gas explosion produces a coal dust suspension, and the peak temperature band may detonate that suspension. This secondary detonation depends on the space-time relation between the shockwave and the peak temperature band. This paper presents a methodology to estimate the coupling relation between the air shockwave and high-temperature flow from the explosion of methane in air. The commercial software package AutoReaGas was used to carry out the numerical simulation for the explosion processes of methane in air in the tunnel. Based on the numerical simulation and its analysis, the coupling relation between the leading shock wave and high-temperature flow was demonstrated for a methane-in-air explosion in a tunnel. In the near field of the ignition point, the deflagration wave transmits energy by heat, and the temperature load is in the front of the pressure wave. With development of deflagration and deflagration-to-detonation transition, the corresponding mechanism of energy transmission is changed from heat conduction to shock compression, and a precursor pressure wave is formed gradually. The time interval between the precursor pressure wave and high-temperature flow behind the wave increases with distance. Attenuation of the precursor shock wave and high-temperature flow depends on the length of the methane-in-air space in a tunnel. Beyond the methane-in-air space, the quantitative relation of the time interval between the precursor shock wave and high-temperature flow with axial distance from ignition and the length of methane-in-air space was proposed.

Jetting of the combustible gas with high pressure is a prelude to bringing into action of the chemistry explosion of gas cloud. Comparing with the leakage and diffusion of combustible gas and the chemistry explosion effect of gas cloud, the distribution of pressure, temperature and velocity formed by high-pressure gas jetting after the destruction of a pipeline, has been paid less attention to in the related field. There are a few fundamental data on the subject of evaluation of physical explosion parameters. In this paper, a physical explosion case of hydrogen gas transported through a high-pressure pipeline is reported, and a cause analysis of the explosion accident is proposed. Numerical simulation yields the field state parameters and the damage characteristics in the process of high-pressure gas jetting. In front of the leakage gas flow, a shock wave forms due to high-pressure gas jetting. The physical explosion can trigger the combustion of leaked hydrogen gas. Though the pressure rapidly attenuates behind the shock wave, a relatively high velocity is maintained until the control valve in the pipeline system is closed down or the jetting finishes. In the given accident case, the shock wave pressure reaches an order of 1 MPa and the temperature reaches 200–300 °C. This temperatures is obviously less than the igniting temperature of hydrogen gas, 400 °C. But the combustion of leaked gas may be triggered by the spark caused by the impact of instrument plates. Since the instrument plates near the leaking port of pipeline has been damaged already before the leaked gas burns, the electric spark from the line short or the strike spark between metal parts are also completely possible to trigger this combustion.

•A methodology for estimating blast wave of a gas explosion in a closed-ended tunnel is proposed.•A practical approach for analyzing the accident induced by a methane/air mixture explosion in a tunnel is provided.•Overpressure attenuation of a gas explosion in a closed-ended tunnel with distance obeys the exponent law.A methodology for estimating the blast wave overpressure decay in air produced by a gas explosion in a closed-ended tunnel is proposed based on numerical simulations. The influence of the tunnel wall roughness is taken into account in studying a methane/air mixture explosion and the subsequent propagation of the resulting shock wave in air. The pressure time-history is obtained at different axial locations in the tunnel outside the methane/air mixture. If the shock overpressure at two, or more locations, is known, the value at other locations can be determined according to a simple power law. The study demonstrates the accuracy of the proposed methodology to estimate the overpressure change with distance for shock waves in air produced by methane/air mixture explosions. The methodology is applied to experimental data in order to validate the approach.

•An approach for predicting the lower flammability limits of oxygenated fuels in air is presented.•The influence of initial pressures and temperatures on lower flammability limits is studied.•The LFL values decrease with the increasing pressures at high temperatures.•The LFL at high temperature and pressure is much lower than that at ambient temperature and pressure.An approach for predicting the lower flammability limits (LFL) of oxygenated fuel in air is presented. The lower flammability limits of methanol, ethanol, methyl formate and dimethyl ether in air are determined using calculated adiabatic flame temperature method at pressures up to 100 bar and temperatures up to 1000 K and the influence of initial pressure and temperature on lower flammability limit is discussed in the study. The results show that the predicted LFLs of mixtures decrease slightly with increasing pressure at high temperature. The predicted LFLs for a methanol-air mixture decrease by 0.24, 0.25, 0.25 vol% with the initial pressure from one to 100 bar at initial temperature of 800 K, 900 K and 1000 K. The variation in the LFLs is 0.11–0.12 vol% for ethanol-air, 0.18–0.19 vol% for methyl formate-air and 0.13–0.14 vol% for dimethyl ether-air at the same temperature and pressure conditions. Moreover, the LFLs of mixtures at 1000 K and 100 bar are much lower than those at atmospheric pressure and ambient temperature. The LFL values at high temperatures and pressures represent potentially greater danger of fires and explosions for these fuels.

•LPG-air explosion temperature has little variation with obstacle number for given blockage ratio.•Dynamic pressures of an LPG explosion reach their maximum always beyond vent of enclosure.•Explosion overpressure for fuel-rich mixture reaches its maximum beyond and near vent of enclosure.•Explosion overpressure of stoichiometric or fuel-lean mixture reaches its maximum within vent.•LPG explosion in enclosure with obstacles is strong enough to make 370 mm brick and mortar wall damaged.Numerical simulations were performed to study explosion characteristics of liquefied petroleum gas (LPG) explosion in enclosure with a vent. Unlike explosion overpressure and dynamic pressure, explosion temperature of the LPG-air mixture at a given concentration in a vented enclosure has very little variation with obstacle numbers for a given blockage ratio. For an enclosure without obstacle, explosion overpressures for the stoichiometric mixtures and the fuel-lean mixtures reach their maximum within the vent and that for fuel-rich mixture reaches its maximum beyond and near the vent. Dynamic pressures produced by an indoor LPG explosion reach their maximum always beyond the vent no matter obstacles are present or not in the enclosure. A LPG explosion in a vented enclosure with built-in obstacles is strong enough to make the brick and mortar wall with a thickness of 370 mm damaged. If there is no obstacle in the enclosure, the lower explosion pressure of several kPa can not break the brick and mortar wall with a thickness of 370 mm. For a LPG explosion produced in an enclosure with a vent, main hazards, within the vent, are overpressure and high temperature. However main hazards are dynamic pressure, blast wind, and high temperature beyond the vent.