Explosion Regions Research Articles

Experimental study on the explosion characteristic and flame propagation of methanol spray at different injection pressures

The risk of methanol spray explosion increased under negative pressure. And the explosion characteristics and flame propagation of methanol spray at different injection pressures under negative pressure have been further investigated in this paper. Experiments were carried out by varying the injection pressure (13–21 bar) to study effects of different turbulence intensities on spray explosion. The effect of different concentrations (198–514.8 g/m3) and initial temperatures (303.15–323.15 K) on the explosion of methanol sprays (308.15 K) was also explored. At different injection pressures, decreasing concentrations and increasing initial temperatures promoted a reduction of particle size linearly. The effect of initial turbulence on the combustion and explosion regions was not remarkable. However, the increasing injection pressures facilitated the pmax, (dp/dt)max, and Tmax of methanol spray. The excessive methanol concentration inhibited the explosion characteristics. The increase of initial temperature significantly increased the risk of spray explosion. However, when the initial temperature was above 313.15 K, the particle size of methanol spray was less than 10 μm. The expansion rate of the combustion region remained stable. And the spray explosion was close to the vapor-phase methanol explosion.

Explosion regions of 1,3-dioxolane/nitrous oxide and 1,3-dioxolane/air with different inert gases - Experimental data and numerical modelling

In this study, experimental determination and modelling investigations for the explosion regions of 1,3-dioxolane/inert gas/N2O and 1,3-dioxolane/inert gas/air mixtures were carried out and compared. The experimental measurements were carried out at 338 K and atmospheric pressure according to EN1839 method T using the inert gases N2, CO2, He and Ar. The results showed that the ratio of the lower explosion limit in N2O (LELN2O) to the lower explosion limit in air (LELair) is 0.52 and the ratio of the maximum oxygen content in air (MOCair) to the limiting oxidizer fraction in nitrous oxide (LOFN2O) is 0.36 ± 0.02 independent of the inert gas. When comparing the inert gas amount at the apex based on the pure oxidizing component, which is O2 in case of air, N2O-containing mixtures need less inert gas to reach the limiting oxidizer quantity whereas the efficiency of inert gases is in the same order. The coefficients of nitrogen equivalency however were found to differ to some extent. The explosion regions of 1,3-dioxolane/inert gas/oxidizer mixtures were modelled using the calculated adiabatic flame temperature profile (CAFTP) method as well as corrected adiabatic flame temperatures. The results indicate good agreement with experimental data for CO2, N2 and Ar- containing mixtures. The noticeable deviations that occur when He is the inert gas are due to the lacking transport data of that mixture.

Explosion regions and limiting oxygen concentrations of methyl propionate, methyl acetate, dimethyl carbonate with air and inert gas mixtures

New data about explosion regions with special focus on limiting oxygen concentrations for methyl propionate, methyl acetate, dimethyl carbonate with air in the presence of nitrogen, helium and carbon dioxide were determined at ambient initial pressure and 423 K. The measurements were executed according to EN 1839 method T. The changes of the explosion regions with temperature and type of inert gas were also modeled mathematically using an extended calculated adiabatic flame temperature profile (CAFTP) method. The shift of the explosion region boundaries with temperature when switching from nitrogen to carbon dioxide were reproduced well. For a switch to helium a good agreement could be reached only if the very high thermal conductivity of helium had been considered properly by using the Lewis number. This requires the knowledge of the respective Lennard-Jones parameters. The LOC of helium-containing mixtures can, however, be calculated with acceptable accuracy even if the Lennard-Jones parameters of the flammable substance are not known exactly by using reasonable estimations.

Numerical study on the evolution of methane explosion regions in the process of coal mine fire zone sealing

To explore the distribution rules of methane explosion regions after the beginning of coal mine fire zone sealing, this paper analyzes the change law of methane explosion limits under the influence of CO2 and CO by using a thermal balance methodology. The distribution rules of methane, smoke and oxygen in the fire zone are obtained for different fire source locations. On this basis, the temporal and spatial distributions of the methane explosion regions at the working face are determined. The modeling results show that during the sealing process, the methane explosion limits are greatly affected by fire smoke. In the early stage of sealing, the methane explosion limit range in the fire zone is reduced due to the dilution of CO2, but later, due to the production of CO, the risk of methane explosion increases. A methane explosion region will appear in the working face tunnel within 1 h after the beginning of sealing, and the timing is closely related to the location of the fire source. When the fire source is located on the intake side of the working face, the methane explosion region first appears on the return side and has the longest duration among all the cases studied; the methane explosion region appears the earliest when the fire source is located on the return side of the working face, and the possibility of methane explosion is the largest in this case.

Simple Program for Step-by-Step Time Integration in Chemical Kinetics, Applied to Simple Model for Hydrogen Combustion

A simple algorithm is proposed for step-by-step time integration of stiff ODEs in Chemical Kinetics. No predictor-corrector technique is used within each step of the algorithm. It is assumed that species concentrations less than 10-6 mol·L-1 do not activate any chemical reaction. So, within each step, the time steplength Δt of the algorithm is determined from the fastest reaction rate maxR by the formula Δt = 10-6mol·L-1/max R. All the reversible elementary reactions occur simultaneously; however, by a simple book-keeping technique, the updating of species concentrations, within each step of the algorithm, is performed within each elementary reaction separately. The above proposed simple algorithm for Chemical Kinetics is applied to a simple model for hydrogen combustion with only five reversible elementary reactions (Initiation, Propagation, First and Second Branching, Termination by wall destruction) with six species (H2, O2, H, O, HO, H2O). These five reversible reactions are recommended in the literature as the most significant elementary reactions of hydrogen combustion [1] [2]. Based on the proposed here simple algorithm for Chemical Kinetics, applied to the global mechanism of proposed five reversible elementary reactions for hydrogen combustion, a simple and short computer program has been developed with only about 120 Fortran instructions. By this proposed program, the following are obtained: 1) The total species concentration of hydrogen combustion, starting from the sum of initial reactants concentrations [H2] + [O2], gradually diminishes, due to termination reaction by wall destruction, and tends to the final concentration of the product [H2O], that is to the 2/3 of its initial value, in accordance to the established overall stoichiometric reaction of hydrogen combustion 2H2 + O2 → 2H2O. 2) Time-histories for concentrations of main species H2, O2, H, H2O of hydrogen combustion, in explosion and equilibrium regions, obtained by the proposed program, are compared to corresponding ones obtained by accurate computational studies of [3]. 3) In the first step of the algorithm, the only nonzero species concentrations are those of reactants [H2], [O2]. So, the maximum reaction rate is that of the forward initiation reaction max R = Rif = kif[H2] [O2], where the rate constant kif is very slow. Thus, the first time steplength Δt1 = 10-6mol·L-1/max R results long in sec. After the first step, the sequences of all the following Δt’s are very short, in μsec. So, the first time steplength Δt1 can be considered as ignition delay time. 4) It is assumed that explosion corresponds to ignition delay time Δt1 < 10 sec. So, the curve on T-P plane, obtained by proposed program for Δt1 = 10 sec., can be considered as explosion limit curve. This curve is compared to the corresponding one obtained by the accurate computational studies of [2].

Explosion regions of acetone and alcohol/inert gas/air mixtures at high temperatures and atmospheric pressure

The explosion regions of 1-propanol, 2-propanol, acetone and 1-butanol in air were measured in the presence of CO2, He, N2 and Ar in accordance with EN1839 method T at high temperatures and at atmospheric pressure. The experimental results show that 1-propanol, 2-propanol and acetone have very similar lower explosion limits (LELs). 1-Butanol shows a slightly wider explosion area near the LEL line. In addition, the explosion regions of all combustible/inert gas/air mixtures were calculated with the method of constant adiabatic flame temperature profiles (CAFTP), using the flame temperature profile along the explosion region boundary curve of each combustible/N2/air mixture as a reference to determine the explosion regions of combustible/inert gas/air mixtures with inert gases other than N2 at different initial temperatures. To calculate the explosion regions for systems containing He, the calculation method was modified to include the very different physical transport properties of He. Moreover, the procedure for calculating the apexes in the ternary explosion diagrams was modified. The calculation results show good agreement with the experimental results.

Study on the methane explosion regions induced by spontaneous combustion of coal in longwall gobs using a scaled-down experiment set-up

In order to effectively control and prevent the disasters of methane explosions induced by spontaneous combustion of coal in longwall gobs, the formation condition of methane explosions induced by spontaneous combustion of coal was proposed. Furthermore, the effect of the area of spontaneous combustion of coal on the distribution of oxygen and methane concentration was studied using a scaled-down experiment set-up of mine gob. The results indicated that the area of spontaneous combustion of coal had little effect on the oxygen distribution, but played a key role in the methane distribution. With a ventilation velocity of 0.2 m/s, 0.6 m/s and 1.0 m/s, the methane concentration showed a conspicuous accumulation distribution near the area of spontaneous combustion of coal. In addition, based on the formation condition of methane explosions proposed, the explosion range induced by spontaneous combustion of coal was determined quantitatively. The results showed that compared with the experimental conditions of no spontaneous combustion of coal in the gob, the range of methane explosions with the occurrence of spontaneous combustion of coal increased by 16.45%, 13.36%, 11.87% and 9.30% with a ventilation velocity of 0.2 m/s, 0.6 m/s, 1.0 m/s and 1.4 m/s, respectively. The results revealed that the entrainment effect created by hot gases in the spontaneous combustion area had expanded the explosion region. Finally, the relationship between the area of methane explosion and the ventilation velocity was developed. The experimental results may provide some instructions on how to control and prevent the disaster of methane explosions induced by spontaneous combustion of coal in longwall mining gobs.

Simulation of blast lung injury induced by shock waves of five distances based on finite element modeling of a three-dimensional rat

Blast lung injury (BLI) caused by both military and civilian explosions has become the main cause of death for blast injury patients. By building three-dimensional (3D) models of rat explosion regions, we simulated the surface pressure of the skin and lung. The pressure distributions were performed at 5 distances from the detonation center to the center of the rat. When the distances were 40 cm, 50 cm, 60 cm, 70 cm and 80 cm, the maximum pressure of the body surface were 634.77kPa, 362.46kPa, 248.11kPa, 182.13kPa and 109.29kPa and the surfaces lung pressure ranges were 928–2916 Pa, 733–2254 Pa, 488–1236 Pa, 357–1189 Pa and 314–992 Pa. After setting 6 virtual points placed on the surface of each lung lobe model, simulated pressure measurement and corresponding pathological autopsies were then conducted to validate the accuracy of the modeling. For the both sides of the lung, when the distance were 40 cm, 50 cm and 60 cm, the Pearson’s values showed strong correlations. When the distances were 70 cm and 80 cm, the Pearson’s values showed weak linear correlations. This computational simulation provided dynamic anatomy as well as functional and biomechanical information.

A SPH-Lagrangian-Eulerian Approach for the Simulation of Concrete Gravity Dams under Combined Effects of Penetration and Explosion

The damage prediction of high dams under the attacks of earth-penetrating weapons has gained significant importance in recent years. For this purpose, a SPH-Lagrangian-Eulerian coupled approach is proposed to describe the damage processes of concrete gravity dams subjected to the combined action of the penetration and explosion. The SPH method is used to model the concrete material with the large deformation near the penetration and explosion regions. The Lagrangian algorithm is adopted to simulate the high-velocity projectile and dam body with the small distortion. And the Eulerian algorithm is employed to describe the dynamic behavior of the water and air media. The validity of the penetration model is calibrated against a previous penetration test. Meanwhile, the SPH-Lagrangian-Eulerian coupled method is verified by implementing an underwater explosion test in a concrete cube. The computed distribution of cracking damage is consistent with the result of the experimental test, which validates the validity of the proposed SPH-Lagrangian-Eulerian coupling method. Subsequently, the penetration processes of a concrete gravity dam under the high-velocity projectile are presented. After the rapid penetration, the explosives are detonated in the dam with the initial penetration damage. The shock wave propagation characteristics in the dam and reservoir water are discussed. The failure processes and dynamic responses of the dam subjected to the combined action of the penetration and explosion are investigated. The influence of the initial penetration damage and the reservoir water on the failure processes of the dam subjected to the internal blast loading is also discussed. The results show that the penetration of the high-velocity projectile only causes a local damage to the concrete gravity dam. However, the combined effects of the penetration and explosion cause significantly more damage to the upper region of the dam.

Explosion regions of propane, isopropanol, acetone, and methyl acetate/inert gas/air mixtures

The explosion regions for propane, isopropanol, acetone, and methyl acetate with air in the presence of nitrogen, argon, helium, and carbon dioxide were determined experimentally according to EN 14756/EN1839, method T. Except for propane, all the measurements were executed at 323 K and 1 bar. Propane experiments were carried out at 293 K and 1 bar. The results show that for the same type of inert gas, propane, isopropanol, and acetone have great closeness concerning the concentration of the inert gas at the apex of the explosion envelope in a ternary diagram with air as oxidizer. This leads to consistency in the limiting oxygen concentration (LOC) and minimum required amount of inert gas (MAI) values. Concerning methyl acetate, the apex was always reached at higher percentages of inert gases compared with the other fuels. This can be attributed to the presence of two oxygen atoms inside the chemical structure. Calculation of the explosion regions was carried out based on calculated adiabatic flame temperature (CAFT) method. The flame temperatures for the experimentally determined fuel/air/N2 mixtures were calculated. Then, these temperatures were used to predict the explosion limits of similar mixtures with other inert gases than nitrogen. The modeling results show reasonable agreement with the experimental results.

Effects of ignition energy on fire and explosion characteristics of dilute hybrid fuel in ventilation air methane

Deflagration explosions of coal dust clouds and flammable gases are a major safety concern in coal mining industry. Accidental fire and explosion caused by coal dust cloud can impose substantial losses and damages to people and properties in underground coal mines. Hybrid mixtures of methane and coal dust have the potential to reduce the minimum activation energy of a combustion reaction. In this study the Minimum Explosion Concentration (MEC), Over Pressure Rise (OPR), deflagration index for gas and dust hybrid mixtures (Kst) and explosive region of hybrid fuel mixtures present in Ventilation Air Methane (VAM) were investigated. Experiments were carried out according to the ASTM E1226-12 guideline utilising a 20 L spherical shape apparatus specifically designed for this purpose. Resultsobtained from this study have shown that the presence of methane significantly affects explosion characteristics of coal dust clouds. Dilute concentrations of methane, 0.75–1.25%, resulted in coal dust clouds OPR increasing from 0.3 bar to 2.2 bar and boosting the Kst value from 10 bar m s−1 to 25 bar m s−1. The explosion characteristics were also affected by the ignitors’ energy; for instance, for a coal dust cloud concentration of 50 g m−3 the OPR recorded was 0.09 bar when a 1 kJ chemical ignitor was used, while, 0.75 bar (OPR) was recorded when a 10 kJ chemical ignitor was used.For the first time, new explosion regions were identified for diluted methane-coal dust cloud mixtures when using 1, 5 and 10 kJ ignitors. Finally, the Le-Chatelier mixing rule was modified to predict the lower explosion limit of methane-coal dust cloud hybrid mixtures considering the energy of the ignitors.

Detonation Structure Under Chain Branching Kinetics

Hydrogen–oxygen chemistry is characterized by a chain branching mechanism that yields three explosion limits. While a detailed kinetic scheme appropriate for hydrogen–oxygen should produce correct results, in many circumstances, a simpler yet reasonably realistic model will be warranted. In particular, it is easier to develop a clear understanding of the reaction zone structure using a simpler model, that includes only the key mechanisms. To that effect, we consider a four-step chain branching scheme that exhibits an explosion behavior with three limits, which behaves at least qualitatively like hydrogen chemistry. We focus in particular on the structure of the initiation and chain branching zones, using a combination between numerical simulation and analysis. Numerical simulations using this chemical model show distinctive keystone figures in the flow field, close to observations in hydrogen–oxygen detonation experiments. The structure of the chain branching zone is resolved using a perturbation analysis, which clarifies the differences between explosion and no-explosion regions and allows for an evaluation of the induction length in the steady wave. The analysis assumes both high activation energy and a slow initiation. Three cases are identified, respectively, with pressure and temperature located within the explosion region, close to the explosion limit and within the no-explosion region. The induction length is shorter and the reaction rate is faster by several orders of magnitude in the explosion region.

On the evolution of compression pulses in an exploding atmosphere: initial behaviour

The development in space and time of a plane initial disturbance to a spatially uniform exploding atmosphere is analysed on the assumption that the disturbance amplitude is comparable in magnitude with the inverse (dimensionless) activation energy of the explosion reaction. Particular attention is focused on the shock-fitting problem, which has features that distinguish it from its inert-atmosphere counterpart.Using the positive half of a sine wave to typify an isolated compression perturbation, it is found that the amplifying effect of the ambient reaction leads to very rapid shock wave development, which depends significantly on the spatial extent of the disturbance. The latter also influences the question of whether local explosion (local explosion is recognized here as a logarithmically unbounded growth of the disturbance amplitude; in other words as a local breakdown of the present approximations) occurs at the shock wave or some distance behind it. The subsequent evolution of these two states will no doubt be significantly different, but the answer to this speculation must await extension of the present theory to encompass the rapid events that ensue near the local explosion regions.

Theoretical considerations on the relation between explosion and inflammation regions

AbstractThe author emphatically distinguishes between explosion and inflammation. The shape of the inflammation regions (with pressure and composition of the mixture as variables) is discussed for such gas mixtures as possess a “low pressure inflammation region” in addition to a thermal inflammation region at a higher pressure (e.g. H2‐O2, CO‐O2, CH4‐O2).From experiments on the influence of a spark on the shape of the inflammation region and of the temperature on the position of the explosion limits, the author derives a general shape of the explosion region (as determined at room temperature). It follows from this that indentations in the explosion region may sometimes be expected in the place where thermal and low pressure inflammation regions merge. The “second pressure limits” which then occur were actually found with H2‐O2 and H2 ‐ air mixtures. The “second pressure limit” found by Lavrov and Bestchastny for CH4 ‐ air mixtures must have been due to secondary effects.The inflammation regions cannot be accounted for by one theory, although all the cases are instances of chain reactions. For, these reactions have in the thermal inflammation region a normal relationship between temperature and reaction rate, whereas this relationship is abnormal in the low pressure inflammation region. The various parts of the explosion regions can, therefore, not be accounted for by one theory either.Former attempts to explain the shape of explosion regions by either the thermal or the chain theory were wrong.A simple explanation of the association between explosion and inflammation is given.

Second pressure limits in gaseous explosion regions: II. Experimental data on explosions of CO and CH4 with oxygen and air

AbstractThe authors investigated the explosion limit as a function of the pressure (below about 120 cm Hg). With CH4‐O2, CH4‐air, CO‐O2 and CO‐ air mixtures no shapes of explosion regions were found which were reminiscent of the lowpressure‐inflammation regions of these mixtures at higher temperatures. Though at the upper limit of mixtures with CO a “second pressure limit” was found, this was not at all comparable with the shape of the explosion region observed with H2‐O2 mixtures1). The “second pressure limit” of CH4‐air mixtures found by Lavrov and Bestchastny cannot have been an explosion limit, but must be attributed to secondary effects.

Flame ranges and explosion regions

AbstractFour ternary systems were investigated viz CH3ClairCCl2F2, C2H5ClairCCl2F2, C4H10airCCl2F2 and C4H10airC2H5Cl. In each system the lengths were determined over which the flame phenomenon was propagated in the mixtures through the explosion tube in the neighbourhood of the explosion limit.The limit curves were constructed and discussed.

Second pressure limits in gaseous explosion regions. I. Experimental data on H2O2 and H2air explosions

AbstractThe author investigates the explosion limit as a function of the pressure (below about 100 cm Hg). In the system H2‐O2 there are between 8.4 and 9.8% hydrogen always two pressures, between which the mixtures are explosive. This is very much reminiscent of the inflammability regions at higher temperatures. The influence of spark strength, position of the electrodes, etc. on this so‐called “second limit” is described together with the procedure employed.Hydrogen‐air mixtures also give these phenomena.Similar peculiarities were found with carbon monoxide‐air, which will shortly be published.

Ternary and quaternary explosion regions and Le Chatelier's formula

AbstractThe author investigated a number of quaternary and ternary explosion regions of gas (gas and vapour) mixtures in which ethylene and air throughout were two of the components. These gases were combined in the quaternary systems with hydrogen and carbon monoxide, hydrogen and carbon dioxide, nitrogen and carbon dioxide; in the ternary systems with vapours of ethylene chloride, ethylene bromide and n‐butyl bromide. It is considered whether in the limit mixtures of these systems Le Chatelier's law and formula was satisfied; in connection with this consideration the result of the investigations is summarized in graphs and tables. A closed explosion region was found in the system C2H4‐air‐H2‐CO2. Moreover a description is given of an apparatus in which a part of the experiments was carried out.

Explosion regions at reduced pressure. II. The influence of pressure on the explosion limits of binary and ternary systems, containing CH4, CH3Cl, O2 and N2O; the quenching action of CO2 and SO2

AbstractThe following systems were investigated at a pressure of 60 cm Hg as well as at lower pressures: CH4O2CO2, CH4O2SO2, CH4N2OCO2 CH4N2OSO2, CH4CH3ClO2, CH4O2N2O, CH3ClN2O in continuation of an investigation of the explosivity of H2O2N2 mixtures published in this journal.The phenomena which were exhibited therein were described. It was found that at low pressure the wall of the reaction vessel becomes catalytically active, if explosions take place in it repeatedly. The change of pressure resulting from an explosive reaction was investigated in some cases.

Explosion regions at reduced pressure. III. The applicability of some simple formulae to experimental data in binary and ternary systems

AbstractThe literature, especially that since 1930, gives extensive discussions on the nature of a reaction which proceeds explosively. If one wishes to investigate the function which the pressure and change of concentration perform in determining the position of the limits one arrives, after a fairly complicated deduction, at formulae which reproduce these influences fairly simplySee C. N. Hinshelwood and A. T. Robinson, The Reaction between Hydrogen and Oxygen, 1932, p. 59. Frost and Alyea, J. Am. Chem. Soc. 55, 3227 (1933). Storch and Montgomery, J. ibid. 56, 2644 (1934) . It is however possible to describe these limits fairly accurately by functions deduced in a very simple way as is shown à propos of experiments described in a previous article in this journal. That holds also for explosions which undoubtedly exhibit a complicated reaction mechanism.