Experimental investigation of the lower flammability limit of volatile liquid fuel-aluminum powder mixtures in air

Aluminum powder was always chosen as an additive to improve the explosive performance. In this work, experiments were performed to investigate the lower flammability limit (LFL) of volatile liquid fuel-aluminum powder mixtures using a 20 L closed spherical stainless steel vessel at a temperature of 20 °C (293 K) and 40 °C (313 K). The volatile liquid fuels tested in the work were diethyl ether (DEE), epoxypropane (PO), n-pentane and n-hexane. DEE, PO and n-pentane are in the liquid phase at room temperature and can easily transition to the gas phase at 40 °C (313 K). Through a series of experiments carried out, it was found that the change in phase would affect the interaction between the components. Aluminum powder always has an inhibitory effect on the flammability of the mixtures when it is mixed with gas-phase fuels. The inhibition effect was most obvious when the aluminum powder concentration reached 200 g/m³. While the interaction between aluminum powder and liquid-phase volatile fuels was promotion and was influenced by the component proportion and the type of the volatile fuels.     

Experimental measurement and numerical analysis of binary hydrocarbon mixture flammability limits

The flammability limits of binary hydrocarbon mixtures in air were measured in a combustion apparatus using an innovative method developed for this apparatus. The experimental results were obtained at standard conditions (room temperature and ambient atmospheric pressure) with upward flame propagation. The experimentally determined flammability limits for pure hydrocarbons (methane and ethylene) were compared with existing data reported in the literature. Le Chatelier's Law was fit to all experimental data to obtain LFLs and UFLs for various two-component combinations of saturated and unsaturated hydrocarbons (methane, ethylene, acetylene, propane, propylene, and n-butane). A modification of this law was used if experimental observations showed large deviations from Le Chatelier's predictions. Also, experimentally measured flammability limit data of the binary hydrocarbon mixtures were analytically related to the stoichiometric concentrations.     

A correlation of the lower flammability limit for hybrid mixtures

Hybrid mixtures are widely encountered in industries such as coal mines, paint factories, pharmaceutical industries, or grain elevators. Hybrid mixtures explosions involving dust and gas can cause great loss of lives and properties. The lower flammability limit (LFL) is a critical parameter when conducting a hazard assessment or developing mitigation methods for processes involving hybrid mixtures. Unlike unitary dust or gas explosions, which have been widely studied in past decades, only minimal research focuses on hybrid mixtures, and data concerning hybrid mixtures can rarely be found. Although methods to predict the LFL have been developed by using either Le Chatelier's Law, which was initially proposed for homogeneous gas mixtures, or the Bartknecht curve, which was adopted for only certain hybrid mixtures, significant deviations still remain. A more accurate correlation to predict an LFL for a hybrid mixtures explosion is necessary for risk assessment. This work focuses on the study of hybrid mixtures explosions in a 36 L dust explosion apparatus including mixtures of methane/niacin, methane/cornstarch, ethane/niacin and ethylene/niacin in air. By utilizing basic characteristics of unitary dust or gas explosions, a new formula is proposed to improve the prediction of the LFL of the mixture. The new formula is consistent with Le Chatelier's Law.     

Flammability limits of binary mixtures of dimethyl ether with five diluent gases

Flammability limits of binary mixtures of dimethyl ether with five kinds of diluent gases were measured by ASHRAE method at room temperature. The five diluent gases are nitrogen, carbon dioxide, chlorodifluoromethane (HCFC-22), 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). The experimental results were correlated with the extended Le Chatelier's formula. It was found that the experimental results were well reproduced by the formula. In addition, flammability limits of binary mixtures of dimethyl ether with nitrogen and carbon dioxide were compared with the estimated values based on the adiabatic flame temperature method. The experimental results were found to be in satisfactory agreement with the estimated values.     

Flash point of biodiesel/glycerol/alcohol mixtures for safe processing and storage

Mixtures of biodiesel, glycerol, and ethanol/methanol are commonly processed and stored in biodiesel production. In this work, non-ideal models are used to calculate the Flash Points (FPs) of binary and ternary mixtures, using data available from different feedstocks. Despite the fact that biodiesel is considered safer than common diesel fuels, results show a synergistic effect of biodiesel/methanol and biodiesel/ethanol mixtures, resulting in a reduction of the flash point of mixtures to values lower than the ones of pure compounds. Most soluble ternary mixtures were found flammable, the only exception being mixtures with a relatively lower alcohol content (45% mol. ethanol or 42% methanol) at temperature lower than 303 K. Accidental increase in temperature can cause domino effect, due to the higher solubility and the formation of new flammable ternary mixtures.     

Effects of a carbon monoxide-dominant gas mixture on the explosion and flame propagation behaviors of methane in air

This work aimed to experimentally evaluate the effects of a carbon monoxide-dominant gas mixture on the explosion characteristics of methane in air and report the results of an experimental study on explosion pressure measurement in closed vessel deflagration for a carbon monoxide-dominant gas mixture over its entire flammable range. Experiments were performed in a 20-L spherical explosion tank with a quartz glass window 110 mm in diameter using an electric spark (1 J) as the ignition source. All experiments were conducted at room temperature and at ambient pressure, with a relative humidity ranging from 52 to 73%. The peak explosion pressure (P_max), maximum pressure rise rate ((dp/dt)_max), and gas deflagration index (K_G) were observed and analyzed. The flame propagation behavior in the initial stage was recorded using a high-speed camera. The spherical outward flame front was determined on the basis of a canny method, from which the maximum flame propagation speed (S_n) was calculated. The results indicated that the existence of the mixture had a significant effect on the flame propagation of CH₄-air and increased its explosion risk. As the volume fraction of the mixed gas increases, the P_max, (dp/dt)_max, K_G and S_n of the fuel-lean CH₄-air mixture (7% CH₄-air mixture) increase nonlinearly. In contrast, addition of the mixed gas negatively affected the fuel-rich mixture (11% CH₄-air mixture), exhibiting a decreasing trend. Under stoichiometric conditions (9.5% CH₄-air mixture), the mixed gas slightly lowered P_max, (dp/dt)_max, K_G, and S_n. The P_max of CH₄-air mixtures at volume fractions of 7%, 9.5%, and 11% were 5.4, 6.9, and 6.8 bar, respectively. The S_n of CH₄-air mixtures at volume fractions of 7%, 9.5%, and 11% were 1.2 m/s, 2.0 m/s, and 1.8 m/s, respectively. The outcome of the study is comprehensive data that quantify the dependency of explosion severity parameters on the gas concentration. In the storage and transportation of flammable gases, the information is required to quantify the potential severity of an explosion, design vessels able to withstand an explosion and design explosion safety measures for installations handling this gas.     

Study of the explosion parameters of vapor–liquid diethyl ether/air mixtures

The knowledge of the vapor–liquid two-phase diethyl ether (DEE)/air mixtures (mist) on the explosion parameters was an important basis of accident prevention. Two sets of vapor–liquid two-phase DEE/air mixtures of various concentrations were obtained with Sauter mean diameters of 12.89 and 22.90 μm. Experiments were conducted on vapor–liquid two-phase DEE/air mixtures of various concentrations at an ignition energy of 40.32 J and at an initial room temperature and pressure of 21 °C and 0.10 MPa, respectively. The effects of the concentration and particle size of DEE on the explosion pressure, the explosion temperature, and the lower and upper flammability limits were analyzed. Finally, a series of experiments was conducted on vapor–liquid two-phase DEE/air mixtures of various concentrations at various ignition energies. The minimum ignition energies were determined, and the results were discussed. The results were also compared against our previous work on the explosion characteristics of vapor–liquid two-phase n-hexane/air mixtures.     

Lower flammability limits of flammable ternary organic mixtures: Synergistic behavior

Organic flammable liquids and their mixtures, which possess high risk of combustion and explosion, are widely used as raw materials and solvents in chemical and pharmaceutical industries. Lower flammability limits (LFL) is one of the most important parameters to characterize the combustion and explosion hazards of combustible gases and liquid vapors. The LFL of various ternary organic mixtures consist of ketone (acetone and butanone), ester (ethyl acetate) and alcohol (ethanol and isopropanol) were tested at 25 °C and atmospheric pressure. The results showed that resulted LFL values of the experiment were always lower than those calculated by volume fraction weighting method when the volume fraction of alcohol was less than 20 vol% but more than 10 vol%. The co-existence of alcohol and ethyl acetate had synergistic effect on reducing the LFL values of ternary organic mixtures and thus increased their explosive risk. The mechanism of synergistic effect was analyzed, and the results showed that the OH· and H· radicals produced by the oxidation decomposition of alcohols and esters accelerated the oxidation process of ternary organic mixtures, which led to the decrease of experimental LFL values and thus corresponding increased of their explosive risk. This study would be expected to provide some guidance for designing or choosing safer and more suitable ternary organic mixtures prior to their applications for engineering.     

On the explosion and flammability behavior of mixtures of combustible dusts

In the work presented in this paper, the explosion and flammability behavior of combustible dust mixtures was studied. Lycopodium, Nicotinic acid and Ascorbic acid were used as sample dusts.In the case of mixtures of two dusts, the minimum explosive concentration is reproduced well by a Le Chatelier's rule-like formula, whereas the minimum ignition energy is a linear combination of the ignition energies of the pure dusts.An unexpected behavior has been found in relation to the explosion behavior and the reactivity. When mixing Lycopodium and Nicotinic acid or Ascorbic acid, the rate of pressure rise of the mixture is much higher than the rate of pressure rise obtained by linearly averaging the values of the pure dusts (according to their weight proportions), thus suggesting that strong synergistic effects arise; but it is comparable to that of the most reactive dust in the mixture.The observed behavior seems to be linked to the presence of minerals in the Lycopodium particles which catalyze oxidation reactions of Nicotinic acid and Ascorbic acid, as suggested by TG analysis.In the case of mixtures of three dusts, a similar behavior is observed when the concentration of Lycopodium is twice that of the other two dusts.     

Validation of a new formula for predicting the lower flammability limit of hybrid mixtures

A correlation of the lower flammability limit for hybrid mixtures was recently proposed by us. The experimental conditions including ignition energy and turbulence which play a primary role in a gas or dust explosion were at fixed values. The sensitivity of such experimental conditions to the accuracy of the proposed formula was not thoroughly discussed in the previous work. Therefore, this work studied the effect of varying the ignition energy and turbulence intensity to the formula proposed in our previous paper. For ignition energy effect, results from methane/niacin mixture demonstrated that the MEC and LFL will not be affected by changing ignition energy. There is no distinguishable difference among gas explosion index (K_G) and dust explosion index (K_St) derived from tests with every ignition energy (2.5 kJ, 5 kJ and 10 kJ) in a 36 L vessel. The proposed formula is independent of ignition energy. For turbulence effect, the proposed formula can have a good prediction of the explosion and non-explosion zone if the ignition delay time is within a certain range. The formula prediction is good as the ignition delay time increases up to 100 ms in this work. Propane/niacin and propane/cornstarch mixtures are also tested to validate the proposed formula. It has been confirmed that the proposed formula predicts the explosion and non-explosion zone boundary of such mixtures.     

Gas flame acceleration in long ducts

In many practical situations, a flame may propagate along a pipe, accelerate and perhaps transform into a devastating detonation. This phenomenology has been known, more or less qualitatively, for a long time and mitigation techniques were proposed to try and avoid this occurrence (flame arresters, vents,...). A number of parameters need to be known and in particular the “distance to detonation” and more generally the flame acceleration characteristic scales. Very often, the ratio between the detonation run-up distance and the pipe diameter is used without any strong justification other that using a non-dimensional parameter (L/D). In this paper, novel experimental evidence is presented on the basis of relatively large scale experiments using 10 cm and 25 cm inner diameter duct with a length between 7 and 40 m. Homogeneous C₂H₄-air, CH₄-air, C₃H₈-air and H₂-air mixtures were used and different ignition sources. The interpretation suggests that the self-acceleration mechanism of the flame may be much better represented by flame instabilities than by turbulence build-up. One consequence would be that the maximum flame velocity and, following, the maximum explosion overpressure, would be rather linked with the run-up distance than with the L/D ratio.     

Experimental study on the minimum explosion concentration of anthracite dust: The roles of O2 mole fraction,inert gas and CH4 addition

The explosion characteristics of anthracite coal dust with/without small amount of CH₄ (1.14 vol %) were investigated by using a 20 L spherical explosion apparatus with an emphasis on the roles of oxygen mole fraction and inert gas. Two methods based on overpressure and combustion duration time were used to determine the minimum explosion concentration (MEC) or the lower explosion limit (LEL) of the pure anthracite coal dust and the hybrid coal-methane mixtures, respectively. The experiment results showed that increasing oxygen mole fraction increases the explosion risk of coal dust: with increasing oxygen mole fraction, the explosion pressure (P_ex) and the rate of explosion pressure rise ((dp/dt)_ex)) increase, while MEC decreases. The explosion risk of anthracite dust was found to be lower after replacing N₂ with CO₂, suggesting that CO₂ has a better inhibition effect on explosion mainly due to its higher specific heat. However, the addition of 1.14% CH₄ moderates the inhibition effect of CO₂ and the promotion effect of O₂ on anthracite dust explosion for some extent, increasing explosion severity and reducing the MEC of anthracite dust. For hybrid anthracite/CH₄ mixture explosions, Barknecht's curve was found to be more accurate and conservative than Chatelier's line, but neither are sufficient from the safety considerations. The experimental results provide a certain help for the explosion prevention and suppression in carbonaceous dust industries.     

Internal short circuit and accelerated rate calorimetry tests of lithium-ion cells: Considerations for methane-air intrinsic safety and explosion proof/flameproof protection methods

Researchers with the National Institute for Occupational Safety and Health (NIOSH) studied the potential for lithium-ion cell thermal runaway from an internal short circuit in equipment for use in underground coal mines. In this third phase of the study, researchers compared plastic wedge crush-induced internal short circuit tests of selected lithium-ion cells within methane (CH₄)-air mixtures with accelerated rate calorimetry tests of similar cells. Plastic wedge crush test results with metal oxide lithium-ion cells extracted from intrinsically safe evaluated equipment were mixed, with one cell model igniting the chamber atmosphere while another cell model did not. The two cells models exhibited different internal short circuit behaviors. A lithium iron phosphate (LiFePO₄) cell model was tolerant to crush-induced internal short circuits within CH₄-air, tested under manufacturer recommended charging conditions. Accelerating rate calorimetry tests with similar cells within a nitrogen purged 353-mL chamber produced ignitions that exceeded explosion proof and flameproof enclosure minimum internal pressure design criteria. Ignition pressures within a 20-L chamber with 6.5% CH₄-air were relatively low, with much larger head space volume and less adiabatic test conditions. The literature indicates that sizeable lithium thionyl chloride (LiSOCl₂) primary (non rechargeable) cell ignitions can be especially violent and toxic. Because ignition of an explosive atmosphere is expected within explosion proof or flameproof enclosures, there is a need to consider the potential for an internal explosive atmosphere ignition in combination with a lithium or lithium-ion battery thermal runaway process, and the resulting effects on the enclosure.     

Numerical studies on minimum ignition energies in methane/air and iso-octane/air mixtures

In this study, the dependence of minimum ignition energies (MIE) on ignition geometry, ignition source radius and mixture composition is investigated numerically for methane/air and iso-octane/air mixtures. Methane and iso-octane are both important hydrocarbon fuels, but differ strongly with respect to their Lewis numbers. Lean iso-octane air mixtures have particularly large Lewis numbers. The results show that within the flammability limits, the MIE for both mixtures stays almost constant, and increases rapidly at the limits. The MIEs for both fuels are also similar within the flammability limits. Furthermore, the MIEs of iso-octane/air mixtures with a small spherical ignition source increase rapidly for lean mixtures. Here the Lewis number is above unity, and thus, the flame may quench because of flame curvature effects. The observations show a distinct difference between ignition and flame propagation for iso-octane. The minimum energy required for initiating a successful flame propagation can be considerably higher than that required for initiating an ignition in the ignition volume. For iso-octane with a small spherical ignition source, this effect was observed at all equivalence ratios. For iso-octane with cylindrical ignition sources, the phenomenon appeared at lower equivalence ratios only, where the mixture's Lewis number is large. For methane fuel, the effect was negligible. The results highlight the significance of molecular transport properties on the decision whether or not an ignitable mixture can evolve into a propagating flame.     

Minimum ignition energy theoretical model for flammable gas based on flame propagation layer by layer

To achieve the rapid prediction of minimum ignition energy (MIE) for premixed gases with wide-span equivalence ratios, a theoretical model is developed based on the proposed idea of flame propagation layer by layer. The validity and high accuracy of this model in predicting MIE have been corroborated against experimental data (from literature) and traditional models. In comparison, this model is mainly applicable to uniform premixed flammable mixtures, and the ignition source needs to be regarded as a punctiform energy source. Nevertheless, this model can exhibit higher accuracy (up to 90%) than traditional models when applied to premixed gases with wide-span equivalence ratios, such as C₃H₈-air mixtures with 0.7–1.5 equivalence ratios, CH₄-air mixtures with 0.7–1.25 equivalence ratios, H₂-air mixtures with 0.6–3.15 equivalence ratios et al. Further, the model parameters have been pre-determined using a 20 L spherical closed explosion setup with a high-speed camera, and then the MIE of common flammable gases (CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₂H₄, C₃H₆, C₂H₂, C₃H₄, C₂H₆O, CO and H₂) under stoichiometric or wide-span equivalence ratios has been calculated. Eventually, the influences of model parameters on MIE have been discussed. Results show that MIE is the sum of the energy required for flame propagation during ignition. The increase in exothermic and heat transfer efficiency for fuel molecules can reduce MIE, whereas prolonging the flame induction period can increase MIE.     

Effect of inert species on the laminar burning velocity of hydrogen and ethylene

The maximum laminar burning velocity (LBV) of a fuel-air mixture is an important input parameter to vapor cloud explosion (VCE) blast load prediction methods. In particular, the LBV value has a significant impact on the predicted blast loads for high reactivity fuels with the propensity to undergo a deflagration-to-detonation transition (DDT). Published data are available for the maximum LBV of many pure fuel-air mixtures. However, little test data are available for mixtures of fuels, particularly for mixtures of fuels and inert species. Such mixtures are common in the petroleum refining and chemical processing industries. It is therefore of interest to be able to calculate the maximum LBV of a fuel/inert mixture based on the mixture composition and maximum LBV of each component.This paper presents measured test data for the maximum LBV of H₂/inert and C₂H₄/inert mixtures, with both nitrogen and carbon dioxide as the inert species. The LBV values were determined using a constant-volume vessel and the pressure rise method. This paper also provides a comparison of the measured LBV values with simplified LBV prediction methods.     

Venting of deflagrations: hydrocarbon–air and hydrogen–air systems

A set of 34 experiments on vented hydrocarbon–air and hydrogen–air deflagrations in unobstructed enclosures of volume up to 4000 m³ was processed with use of the advanced lumped parameter approach. Reasonable compliance between calculated pressure–time curves and experimental pressure traces is demonstrated for different explosion conditions, including high, moderate, low and extremely low reduced overpressures in enclosures of different shape (L_max:L_min up to 6:1) with different type and position of the ignition source relative to the vent, for near-stoichiometric air mixtures of acetone, methane, natural gas and propane, as well as for lean and stoichiometric hydrogen–air mixtures. New data were obtained on flame stretch for vented deflagrations.The fundamental Le Chatelier–Brown principle analog for vented deflagrations has been considered in detail and its universality has been confirmed. The importance of this principle for explosion safety engineering has been emphasized and proved by examples.A correlation for prediction of the deflagration–outflow interaction number, χ/μ, on enclosure scale, Bradley number and vent release pressure is suggested for unobstructed enclosures and a wide range of explosion conditions. Fractal theory has been employed to verify the universality of the dependence revealed of the deflagration–outflow interaction number on enclosure scale.In spite of differences between the thermodynamic and kinetic parameters of hydrocarbon–air and hydrogen–air systems, they both obey the same general regularities for vented deflagrations, including the Le Chatelier–Brown principle analog and the correlation for deflagration–outflow interaction number.     

Propagation of ethylene–air flames in closed cylindrical vessels with asymmetrical ignition

A study of explosions in several elongated cylindrical vessels with length to diameter L/D = 2.4–20.7 and ignition at vessel's bottom is reported. Ethylene–air mixtures with variable concentration between 3.0 and 10.0 vol% and pressures between 0.30 and 1.80 bara were experimentally investigated at ambient initial temperature. For the whole range of ethylene concentration, several characteristic stages of flame propagation were observed. The height and rate of pressure rise in these stages were found to depend on ethylene concentration, on volume and asymmetry ratio L/D of each vessel. High rates of pressure rise were found in the early stage; in later stages lower rates of pressure rise were observed due to the increase of heat losses. The peak explosion pressures and the maximum rates of pressure rise differ strongly from those measured in centrally ignited explosions, in all examined vessels. In elongated vessels, smooth p(t) records have been obtained for the explosions of lean C₂H₄–air mixtures. In stoichiometric and rich mixtures, pressure oscillations appear even at initial pressures below ambient, resulting in significant overpressures as compared to compact vessels. In the stoichiometric mixture, the frequency of the oscillations was close to the fundamental characteristic frequency of the tube.     

CFD modelling of hydrogen and hydrogen-methane explosions – Analysis of varying concentration and reduced oxygen atmospheres

This paper evaluates the predictive capabilities of the advanced consequence model FLACS-CFD for deflagrations involving hydrogen. Two modelling approaches are presented: the extensively validated model system originally developed for hydrocarbons included in FLACS-CFD 22.1 and a Markstein number dependent model implemented in the in-house version FLACS-CFD 22.1 IH. The ability of the models to predict the overpressure and the flame arrival time for scenarios with different concentrations of hydrogen, and thus different Lewis and Markstein numbers, is assessed. Furthermore, the effect of adding methane or nitrogen on overpressure for different regimes of premixed combustion are investigated. The validation dataset includes deflagrations in the open or in congested open areas and vented deflagrations in empty or congested enclosures. The overpressure predictions by FLACS-CFD 22.1 IH are found to be more accurate than those obtained with FLACS-CFD 22.1 for scenarios with varying hydrogen concentrations and/or added nitrogen or methane in the mixture. The predictions by FLACS-CFD 22.1 IH for lean hydrogen mixtures are within a factor of 2 of the values observed in the experiments. Further development of the model is needed for more accurate prediction of deflagrations involving rich hydrogen mixtures as well as scenarios with other fuels and/or conditions where the initial pressure or temperature deviate significantly from ambient conditions.     

Inhibiting effects of gas–particle mixtures containing CO2, Mg(OH)2 particles,and NH4H2PO4 particles on methane explosion in a 20-L closed vessel

The main risk factors from methane explosion are the associated shock waves, flames, and harmful gases. Inert gases and inhibiting powders are commonly used to prevent and mitigate the damage caused by an explosion. In this study, three inhibitors (inert gas with 8.0 vol% CO₂, 0.25 g/L Mg(OH)₂ particles, and 0.25 g/L NH₄H₂PO₄ particles) were prepared. Their inhibiting effects on methane explosions with various concentrations of methane were tested in a nearly spherical 20-L explosion vessel. Both single-component inhibitors and gas–particle mixtures can substantially suppress methane explosions with varying degrees of success. However, various inhibitors exhibited distinct reaction mechanisms for methane gas, which indicated that their inhibiting effects for methane explosion varied. To alleviate amplitude, the ranking of single-component inhibitors for both explosion pressure (P_ex) and the rate of explosion pressure rise [(dP/dt)_ex] was as follows: CO₂, NH₄H₂PO₄ particles, and Mg(OH)₂ particles. In order of decreasing amplitude, the ranking of gas‒particle mixtures for both P_ex and (dP/dt)_ex was as follows: CO₂–NH₄H₂PO₄ mixture, CO₂‒Mg(OH)₂ mixture, and pure CO₂. Overall, the optimal suppression effect was observed in the system with the CO₂–NH₄H₂PO₄ mixture, which exhibited an eminent synergistic effect on methane explosions. The amplitudes of P_ex with methane concentrations of 7.0, 9.5, and 11.0 vol% decreased by 37.1%, 42.5%, and 98.6%, respectively, when using the CO₂–NH₄H₂PO₄ mixture. In addition, an antagonistic effect was observed with CO₂‒Mg(OH)₂ mixtures because MgO, which was generated by the thermal decomposition of Mg(OH)₂, can chemically react with water vapor and CO₂ to produce basic magnesium carbonate (xMgCO₃·yMg(OH)₂·zH₂O), thereby reducing the CO₂ concentration in a reaction system. This research revealed the inhibiting effects of gas‒particle mixtures (including CO₂, Mg(OH)₂ particles, and NH₄H₂PO₄ particles) on methane explosions and provided primary experimental data.