Lower Explosion Limit Research Articles

Assessment of explosion risk for wood dust in a ventilation-dust separation installation, by determining the concentration of total dust in suspension inside of the installation

Most of combustible dusts present both fire and explosion hazard. Explosion may occur at certain concentrations of dust mixed with air and in the presence of an ignition source. The threat posed by this real danger was confirmed by the events that took place in economic units such as: feed factories, wood products, textile industry, steel, etc. Among the parameters of explosiveness of combustible dust, which can cause an explosion, we mention: maximum explosion pressure, lower explosion limit, explosive index, minimum ignition energy, electrical resistivity of dust, minimum ignition temperature of dust layer and cloud, particle size and concentration of dust in suspension. The current paper presents the results of determinations of combustible wood dust concentrations, performed at an important economic unit, manufacturing veneer and wood panels, at a dusting ventilation installation composed of fan, cyclone and textile filter. These determinations were made in the pipe connecting the fan and the bag filter, to assess possible danger of explosion in the pipe, by relating the measured concentration to the lower explosion limit (concentration of wood dust).

Research on the effect of thermal runaway gas components and explosion limits of lithium-ion batteries under different charge states

The combustion and explosion of thermal runaway gases from lithium-ion batteries may accelerate the propagation of thermal runaway from lithium-ion batteries and pose a serious threat to surrounding people and property. Therefore, the research of thermal runaway gas composition and explosion limits of lithium-ion batteries is of great significance for the prevention and control of thermal runaway of lithium-ion batteries. In this paper, we use experiments combined with empirical formulas to investigate the composition of gases generated by the thermal runaway and the explosion limit of 18,650 lithium-ion batteries. The analysis of the thermal runaway gas components of lithium-ion batteries by using gas chromatography-mass spectrometry (GC-MS) shows that as the SOC increases, the number of thermal runaway gases increases. With the increase of SOC, the change of lower explosion limit (LEL) shows the same trend as that in alkanes content, which increases and then decreases; while the change of upper explosion limit (UEL) shows the same trend as that in unsaturated hydrocarbons content, which decreases and then increases. In addition, 50% SOC battery shows the lowest exhausted gas combustion explosion danger.

Modeling the environmental, health, and safety aspects of xylene isomer emission from storage tanks in petrochemical industries, Iran.

The release of xylene isomers from storage tanks poses a significant threat to petrochemical industries, and their safe transportation and storage is a widely researched topic. This paper focused on modeling the environmental, health, and safety effects of P-xylene and O-xylene leakage from storage tanks via Areal Locations of Hazardous Atmospheres (ALOHA) and Wireless Information System for Emergency Responders (WISER). The meteorological data of the area, characteristics of the tanks, and the roughness of the land surrounding the tanks were used to run the ALOHA model. The dispersion distances of P-xylene and O-xylene toxic and flammable vapor clouds were estimated according to the Immediately Dangerous to Life or Health (IDLH) and lower explosive limit (LEL) criteria. Also, the levels of thermal radiation due to the burning of P-xylene and O-xylene were estimated. The results showed that in the cold seasons, the IDLH was a maximum distance of 62m and 45m for P-xylene and O-xylene, respectively. The LEL criteria were 10% with a magnitude of 1100ppm for a maximum distance of 54m and 35m for P-xylene and O-xylene, respectively. The maximum distance of 20m for O-xylene based on the results of the LEL criteria of 60% (6600ppm) was attained in the warm seasons. They are potentially lethal within 60s at 21m (10.0kW/m2) when burned. The WISER software predicted the protective distance for xylene isomers to be about 300m. The results show that creating a protective zone around the P-xylene and O-xylene tanks with a radius of 54m is necessary to reduce hazards.

Evaluation on explosion characteristics and parameters of pulverized coal for low-quality coal: experimental study and analysis

Fully utilizing the energy generated by the explosion of pulverized coal will contribute to realize the clean and efficient exploitation of coal resources. The pulverized coal explosion characteristics will be a far-reaching and important task to explore. In this paper, ten kinds of low-quality coals such as high sulfur, high ash, and low metamorphic degree coals were investigated and the minimum ignition energy (MIE), lower explosion limit (LEL), and explosion intensity (EI) parameters under different particle sizes and coal powder concentration conditions were also analyzed combined with a 1.2-L Hartmann tube and a 20-L explosion sphere experimental system. Finally, the morphological characteristics of the exploded coal powder surface were evaluated by scanning electron microscopy (SEM). The results show that the particle size is positively correlated with MIE. LEL shows an inverted "U"-shaped trend with the increasing degree of coal deterioration. The low-rank coal is more flammable and explosive. The maximum pressure PMax at the LEL concentration and maximum pressure rise rate (dP/dt)Max overall value is small. Here, optimum pulverized coal particle size (75μm) for explosive utilization of low-quality coal was determined. Within 50-225 g/m3 of pulverized coal concentration range, the explosion intensity increases with increasing concentration. The smaller the particle size of pulverized coal, the greater the possibility of agglomeration of pulverized coal particles. The surface of the exploded coal particles produces more developed pores. They are irregularly shaped and have more rounded edges than the original coal.

The Fire and Explosion Hazard of Coloured Powders Used during the Holi Festival.

During the world-famous Holi festival, people throw and smear each other with a colored powder (Holi color, Holi powder, Gulal powder). Until now, adverse health and environmental effects (skin and eye irritation, air pollution, and respiratory problems) have been described in the available literature. However, the literature lacks data on the flammable and explosive properties of these powders during mass events, despite the fact that burns, fires, and explosions during the Holi festival have taken place many times. The aim of the article is to present the fire and explosion parameters of three currently used Holi dust and cornflour dust types as reference dust. The minimum ignition temperature of the dust layer and dust cloud, the maximum explosion pressure and its maximum rate of growth over time, the lower explosion limit, the limit of oxygen concentration, and the minimum ignition energy were determined. Tests confirmed that the currently available Holi powders should be classified as flammable dusts and low-explosive dusts. The likelihood of a fire or explosion during mass incidents involving a Holi dust-air mixture is high.

Ideal Positioning of a Pt-Interlayer for H2-O2-Recombination in Polymer Electrolyte Membrane Water Electrolysis

Polymer electrolyte membrane water electrolysis (PEMWE) is a promising technology for the production of hydrogen in future energy scenarios.[1] The main electric voltage loss in PEM electrolysers is caused by the ohmic losses of the polymer electrolyte membrane. However, the reduction of the membrane thickness not only reduces the cell voltage, but also leads to lower faradaic efficiencies, which can be accompanied by severe safety issues. The crossover of the produced hydrogen gas through the membrane into the anodic compartment can lead to explosive gas mixtures (lower explosion limit (LEL) of H2 in O2 is ~ 4 % [2]).[3, 4] Typically, PEM electrolysers operate only up to 2 % H2 in O2 (50 % of LEL). An elevation of the hydrogen pressure during electrolysis enhances the crossover of hydrogen even more.[5] For realizing high market penetrations of PEMWE, a safe operation is essential.In order to meet the safety requirements, mitigation strategies for the reduction of the hydrogen in oxygen content are necessary. When increasing the membrane thickness and reducing the operation temperature are not desired, other mitigation strategies need to be evaluated. The integration of a Pt-interlayer in the polymer electrolyte membrane is one possibility.[6] When hydrogen and oxygen permeate through the membrane, they recombine to water at the platinum particles.Klose et al. proposed that the method of incorporating a recombination layer can be optimized further by evaluating its position.[7] The concentration of oxygen at the interlayer must be high enough to let a sufficient amount of hydrogen recombine. However, the oxygen concentration towards the cathode is much lower than a full recombination of hydrogen requires, which is mainly due to the lower oxygen permeation rate (lower diffusivity, lower gradient). Therefore, it is assumed that a Pt-interlayer close to the anode catalyst layer yields higher recombination rates than an interlayer close to the cathode.In this contribution, the influence of the Pt-interlayer position on the H2 in O2 content was investigated. Catalyst coated membranes (CCMs) based on spray-coated Nafion with Pt-interlayers with a loading of 0.01 mg/cm² at three positions (close to anode, centred, close to cathode, see Figure 1a)) and a reference type (without interlayer) were fabricated. The CCMs were examined with regard to their polarisation behaviour and hydrogen crossover characteristics in a 4 cm² cell. The hydrogen crossover was investigated during electrolysis operation at ambient pressure and at elevated cathode pressures (p c = 10 bar).The resulting membrane thicknesses of the CCMs were ~ 100 µm (in dry state). Since commercial Nafion membranes for water electrolysis applications are available in thicknesses between 25 and 183 µm (N211 and N117, respectively), the present membranes correspond to the state of the art. The electrochemical polarisation behaviour of the CCMs shows that the integration of a Pt-interlayer does not lead to additional voltage losses. At current densities as high as 3.5 A/cm², cell voltages below 2 V were achieved.With regards to H2 crossover, each CCM with interlayer reduced the measurable anodic H2 content in comparison to the reference CCM (Figure 1b)). Additionally, the position of the interlayer affected the resulting H2 content. The H2 content decreased with positioning the interlayer closer to the anode. Thus, a higher recombination rate of hydrogen and oxygen is observed when placing the interlayer close to the anode. Since the available oxygen amount in the membrane has obviously to decrease towards the cathode catalyst layer, the experimental findings reflect the aforementioned theoretical situation.In summary, the results of this study confirm that Pt-interlayers are a suitable mitigation strategy to reduce the H2 in O2 content in PEMWE. Further, it was shown that the positioning of the interlayer affects the results. Since the available amounts of hydrogen and oxygen in the membrane depend on the location in the membrane and on the experimental conditions (e. g. operating pressure), the integration of a recombination interlayer at an optimized position within the membrane offers an effective means to safe PEMWE operation with reduced membrane thickness. This improvement will help to consolidate PEMWE as a key technology for hydrogen generation.Literature:[1] K. Ayers, Annu. Rev. Chem. Biomol. Eng., 2019, 10.[2] H. Janssen, Int. J. Hydorgen Energ., 2004, 29.[3] H. Ito, Int. J. Hydorgen Energ., 2016, 41.[4] S.A. Grigoriev, Int. J. Hydorgen Energ., 2009, 34.[5] P. Trinke, Int. J. Hydorgen Energ., 2017, 42.[6] P. Trinke, Int. J. Hydorgen Energ., 2018, 165.[7] C. Klose, J. Elec. Soc., 2018, 165. Figure 1

A step toward lifting the fog off mist explosions: Comparative study of three fuels

Gases, vapors, and dusts are all potential explosion threats; however, mists should also be taken into account. Indeed, dozens of accidents involving hydrocarbon mists were identified in incident surveys. Mist explosions continue to occur, highlighting the need to evaluate and assess the validity of present approaches for assessing mist ATEX risks and to establish reliable standardized safety parameters for fuel mists.In a modified apparatus based on the 20 L explosion sphere, three fluids of industrial interest were investigated. A new siphon injection system comprising a Venturi junction was installed, offering a wide range of dispersion performances. This system was controlled by a specifically developed program, ensuring the apparatus's versatility and adaptability to various tested liquids. It enables precise control of the gas carrier flow, liquid flow, and injection and ignition durations, allowing modification of the dilution rate of a particular droplet size distribution (DSD). The mist cloud dispersed in the 20 L sphere was characterized by determining its DSD using an in-situ laser diffraction sensor and by performing Particle Image Velocimetry (PIV). Mists of kerosene, diesel and ethanol were then subjected to tests to assess their lower explosive limit (LELmist), minimum ignition energy (MIE), maximum explosion pressure (Pmax), and rate of pressure rise (dP/dtmax). For instance, it was found that the LELmist of ethanol, kerosene Jet A1, and diesel fuel for a DSD averaged at 8–10 μm reach 77, 94, and 93 g/m3 respectively. This LELmist was also shown to increase with increasing DSD in the case of Jet A1 mists. A sensitivity study was also performed to emphasize the impact of parameters such as the fuel type, the DSD, and the mist temperature. Findings showed that the explosion severity is strongly influenced by the chemical nature and the volatility of the dispersed fuel. Moreover, controlling the sphere temperature was proven to be a crucial step when using such apparatus for the evaluation of the explosibility of mists. An evaporation model based on the d2 law was also developed to visualize the vapor-liquid ratio before ignition. These findings have already led to the development of a new procedure for determining safety standards for hydrocarbon mists, as well as tools to assess mist explosion risks. They have proven that it is possible to evaluate the ignition sensitivity and explosion severity of fuel mists using a single well-known apparatus.

The research into the propagation law of the shock wave of a gas explosion inside a building

Based on the dissipation rate conservation equations of turbulent kinetic energy in the k-ε turbulence model, a complicated three-dimensional finite element model of a kitchen filled with gas mixture is developed by using the open source field operation and manipulation (OpenFOAM). Two representative kitchens were used to investigate the propagation law of the shock wave of a gas explosion inside a building by considering the key characteristics of the blast shock wave. The influence of some crucial parameters, such as initial conditions and kitchen parameters, on the properties of the blast shock wave is investigated. The basic steps to predict the peak pressure of the blast shock wave are given in consideration of the initial condition and the kitchen whilst the injury effect of the blast shock wave on the humans and animals is evaluated. The research results indicate that the pressure time history and the peak pressure space distribution are greatly influenced by the kitchen design layout. The coupled interaction between the initial temperature and gas volume concentration, especially at the upper and lower explosion limits of the gas, significantly affects the peak pressure. The peak pressure varies significantly with the opening and the buffer; however, it has little relation with the width, length, and height of the kitchen. The proposed method can accurately and effectively predict the peak pressure of the blast shock wave inside buildings. In terms of the peak pressure space distribution of the explosion shock wave, the peak pressure is much higher than the threshold of the killing pressure, which is unsafe for the humans and animals in the building.

Analysis of natural gas leakage diffusion characteristics and prediction of invasion distance in utility tunnels

With the continuous development of urbanization, the number of underground supplies and demanded pipelines is increasing. In order to reasonably plan the construction of urban underground space, underground utility tunnels emerge, and show potential to reduce the difficulty of pipeline maintenance and repair. For natural gas pipelines laying in utility tunnels, however leakage accident can result in serious consequences. In this study, the numerical simulation method was used to analyze the leakage and diffusion characteristics of natural gas in utility tunnels under various working conditions, and the single-factor change and multi-factor change of different pressures, leakage diameters, ventilation conditions and leakage locations were investigated. The results showed that: the increase of pipeline operating pressure and leakage diameter could accelerate the diffusion velocity of methane in the utility tunnel. According to the prediction equation of methane invasion distance (MID) under natural ventilation condition, the average error was 8.29%. The mechanical ventilation condition accelerated the methane discharge and greatly reduced the distribution range and concentration of methane in the utility tunnel. In the single-factor change analysis, when the mechanical ventilation frequency was above 15times/h, the methane concentration at each monitoring point was below the lower explosion limit. No matter where the leakage occurs, the mechanical ventilation will prevent methane from diffusing upstream direction, and the downstream was at higher risk for methane distribution. The larger the coordinate value x of leakage location was, the smaller the distribution area of methane in utility tunnel was. When x = 90 m, the methane concentration at each monitoring point was 0. The prediction equation of MID under natural ventilation condition can provide reference for the installation distance of methane leakage alarm device. The research on methane diffusion characteristics under mechanical ventilation conditions provides suggestions for daily maintenance and accident prevention of gas pipelines in the utility tunnel.

Quasi-static dispersion of dusts for the determination of lower explosion limits of hybrid mixtures

Knowledge of the explosion limiting concentration of explosible materials is necessary for the design of explosion protection measures. Currently employed methods of testing the minimum explosible concentration (MEC) of a dust cloud or the lower explosion limit (LEL) of a hybrid mixture are based on arbitrary assumptions and possess technical limitations that often lead to values of MEC/LEL, which are unrealistically low or poorly reproducible.This contribution presents an improved method for the experimental determination of the MEC of a combustible dust cloud or the LEL of a flammable gas or a hybrid mixture. The new set-up operates under laminar conditions and allows a uniform suspension of dust particles in an open top acrylic glass tube. Dust concentration is measured with the help of infrared sensors installed a few centimeters above and below the ignition source.In order to evaluate the dependence of MEC on flow front velocity, MEC of lycopodium was determined at four flow velocities. The results show that the flow field intensity does not significantly influence the MEC of lycopodium for the flow ranges tested in this work. Moreover, LEL of hybrid mixtures of lycopodium and methane was also tested at flow velocities of 4.7 cm/s, 5.8 cm/s, 7 cm/s and 11 cm/s and compared with the values obtained from other sources. The results suggest that the requirement of high energy pyrotechnical igniter may be relinquished, provided that a truly homogeneous suspension of dust particles could be achieved.Moreover, the effect of relative amount of dust and gas, on the course of ignition and flame propagation in hybrid mixtures at their LEL, was studied by the help of high speed videos. For hybrid mixtures of carbonaceous dusts (like lycopodium) at their LEL, ignition occurs in the gas phase, however, flame propagation is only possible through a two-way interaction of dust and gas during the course of combustion.

Evaluation of propane explosion with applied water mist

This article discusses the overpressure of a gas explosion and the performance of applying water mist for explosion suppression. According to the experimental results, the larger the opening area, the more difficult it is for pressure to accumulate, resulting in lower overpressure of a gas explosion. When the opening was opened under a high air speed environment, the amount of entrained air was greater. Consequently, the occurrence time of the explosion was shorter than at a low air speed. Despite the water mist nozzle being installed outside the enclosure, a propane gas explosion still occurred regardless of the amount of water mist used, failing to suppress the explosion. However, the water mist nozzle installed inside the enclosure supplied an adequate amount of water mist that could wash a part of the propane, resulting in the fuel concentration dropping below the lower explosion limit, hindering the occurrence of an explosion.

Visible light-induced, highly responsive, below lower explosive limit (LEL) LPG sensor based on hydrothermally synthesized barium hexaferrite nanorods

Here, the photo-enhanced behavior in LPG sensing of hydrothermally synthesized BaFe12O19 nanorods at room temperature under visible light radiation has been thoroughly inspected and reported. The sensing element is observed to be poorly responsive towards LPG in dark conditions at room temperature, while it reveals a good photo response in presence of visible light of 30 mW/cm2, and the visible light aids in improving the LPG sensing response up to a great extent at room temperature. Under the irradiation, the nanorods are found to detect the presence of LPG molecules of concentration as small as 0.5 vol% at the response and recovery times ~5.02 s and ~10.10 s respectively. The sensitivity of the visible-light induced material was evaluated ~41.27 sensor response/vol% with the maximum sensor response as high as 108, whereas, in dark, the same material showed a maximum response of ~6.64 with a sensitivity of merely 1.94 sensor response/vol%. The photo-generated carriers are suggested to be responsible for achieving a significant, stable, fast response in presence of LPG. This is the first ferrite based visible light-induced LPG sensor.

Response modulation of silicon nanowires-based sensor to carbon number in petroleum vapor detection

To ensure high safety level in crude oil and its distillates storage tanks, petrochemical industry needs responsive and reliable hydrocarbon vapor sensing devices. We propose here a cost-effective petroleum vapor sensor that could be used effectively in oil tanks. The fabricated device is based on silicon nanowires (SiNWs) and has a good response to petroleum vapor concentration fluctuations. The chemiresistive sensitive device is a layer of SiNWs elaborated on a Cz-Si wafer with top planar Ag-Al electrical contacts. Petroleum vapors are obtained by heating crude oil. Detection measurements are performed at temperatures ranging from the ambient (18 °C) to 70 °C and for vapor concentrations varying between the Lower Explosion Limit (LEL) ~ 10000 ppmv and the Upper Explosion Limit (UEL) ~ 60000 ppmv.By measuring the time-dependent electrical resistance of the device at a fixed temperature, multiple cycles of response-recovery are obtained. As a main finding, we report on how the response of SiNWs to carbon number (nC) of petroleum vapor could be modulated by varying the device temperature.Therefore, at room temperature, when the petroleum vapor is rich of light hydrocarbon molecules (nC ≤ 7), adsorption–desorption cycles are quasi-reversible. However, at higher temperature, when vapors substantially contain heavier hydrocarbon molecules (nC > 7), we obtain a time dependent pronounced increasing drift in the chemiresistance of the device. Interestingly we found that the carbon number of molecules in the petroleum vapor plays a key-role in the response of the sensor.

Influence of acetylene on methane\u2013air explosion characteristics in a confined chamber

To study the impact of acetylene on methane explosions, the safe operation of coal mines should be ensured. In this paper, a 20 L spherical tank was used to study the explosive characteristics of acetylene–methane–air mixture. In addition, the GRI-Mech3.0 mechanism was used to study the chemical kinetic mechanism for the mixed gas, and the effect of adding acetylene on the sensitivity of methane and the yield of free radicals was analysed. The results show that acetylene can expand the scope for methane explosion, lower the lower explosion limit, and increase the risk of explosion. Acetylene increases the maximum explosion pressure, laminar combustion rate and maximum pressure rise rate for the methane–air mixture while shortening the combustion time. Three combustion modes for the acetylene–methane–air mixture were determined: methane-dominated, transitional and acetylene-dominated combustion modes. Chemical kinetic analysis for the mixed gas shows that as the volume fraction of acetylene increases, the generation rate for key free radicals (H*, O* and OH*) gradually increases, thereby increasing the intensity of the explosive reaction. The results from this research will help formulate measures to prevent coal mine explosion accidents.

Effects of initial temperature and pressure on explosion characteristics of propane–diluent–air mixtures

The explosion characteristics of propane–diluent–air mixtures under various temperatures and pressures were investigated using a 20-L apparatus. The explosion limits of propane diluted with nitrogen or carbon dioxide were measured at high temperatures from 25 to 120 °C. The results showed that the upper explosion limit (UEL) increased, and the lower explosion limit (LEL) decreased with the rising temperature. The explosion limits of propane diluted with nitrogen or carbon dioxide were also measured at high pressures from 0.10 to 0.16 MPa. The results showed that the UEL increased, and the LEL almost remainedunchanged along with increased pressure. Under the same initial operating conditions, the concentration of nitrogen required to reach the minimum inerting concentration (MIC) point was higher than the concentration of carbon dioxide. Finally, the study investigated the limiting oxygen concentration (LOC) of propane under various initial temperatures, initial pressures, and inert gases. The LOC of propane decreased approximately linearly with increased temperature or pressure, and the LOC of propane dilution with carbon dioxide was greater than dilution with nitrogen from 25 to 120 °C or from 0.10 to 0.16 MPa, which indicated that the dilution effect of carbon dioxide was better than that of nitrogen.

Fire Characteristics of Polyethylene Dust

Abstract Dust is a product or by-product in many industries. To ensure effective measures of explosion prevention, it is necessary to know the fire properties of dispersed and settled dust. These parameters cannot be calculated, but can be determined on the base of measurements in standard equipment. The article deals with the measurement of fire properties of polyethylene. The values of the minimum ignition temperature of settled and dispersed dust (MIT) and the values of explosion characteristics of polyethylene dust cloud lower explosion limit (LEL), maximum pressure Pmax and maximum rate of pressure rise (dp/dt)max were measured. The measurements were performed on the equipment according to the STN EN 80079-20-2: 2016 Standard Explosive atmospheres - Part 20-2: Material characteristics - Combustible dust test methods and according to the STN EN 14034 + A1: 2011 Standard Determination of explosion characteristics of dust clouds. The MIT of the settled dust was not determined (the sample melted), the MIT of the dispersed dust was 435 °C. The maximum explosion pressure Pmax reached 7.0 bar, and the maximum rate of pressure rise dP/dt was 37.5 bar.s−1.

Minimum ignition energy of LDPE dust/ethylene hybrid mixture

An experimental device for evaluating the minimum ignition energy (MIE) of LDPE dust/ethylene hybrid mixture was built with the innovative mixing mode. The MIE of the hybrid mixture that contained ethylene below its lower explosive limit (LEL) was studied. The result indicated that adding a small amount of ethylene significantly reduced the MIE of the original dust cloud. All the MIEs with five different particle sizes were found to show similar trends of exponential attenuation with the increase of ethylene concentration; such attenuating effect grew as the dust particle size rose. When ethylene concentration increased and approached to its LEL, the reaction mechanism dominated by combustible dust turned into one dominated by combustible gas. The MIE decreased first and then increased with the dust mass and increased with the dust particle size. A multifactor mathematical correlation model of the MIE with the dust particle size and ethylene concentration was developed.

Effect of initial temperature and initial pressure on the lower explosion limit of aviation kerosene

The effect of initial temperature and initial pressure on lower explosion limit (LEL) of RP-3 aviation kerosene vapor was investigated experimentally. The experiments were conducted in an explosion limit equipment at initial temperature of 40-160 °C and initial pressure 100-160 kPa. In the temperature-pressure range studied, the LEL decreases with the increase of the initial temperature, while increases as the initial pressure increases. A correlation formula established in the present study can predict the experimental data well. A comparison of the temperature dependence and pressure dependence indicates that the LEL of RP-3 aviation kerosene vapor is mainly affected by the initial temperature. This guides people to pay more attention to the aspect of the heat transfer in the fuel tank of aircrafts avoiding the explosion risk caused by high temperature.

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 (Pex) 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.

Sensitivity Enhancement of Methane Detection Based On Hollow Core Photonic Crystal Fiber

Monitoring methane (CH4) concentration is essential in many industrial and environmental applications. Emission of such gases is indeed important to detect for health, safety and environmental reasons. The major risk in all these areas is an explosion hazard, which may occur if methane reaches its Lower Explosive Limit (LEL) of5% concentration in air. For that reason, it is necessary to develop gas sensors to monitor that methane levels below this value. Due to a weak absorption of methane, this gas is difficult to detect using conventional methods.Hollow core photonic crystal fibers (HC-PBF) have emerged as a promising technology in the field of gas sensing. The strong interaction achievable with these fibers are especially advantageous for the detection of weakly absorbing regions of methane. In this paper, we investigated, by full vectorial finite element method (FV-FEM) in Rsoft CAD environment, the dependency of relative sensitivity on the fiber parameters and wavelength. Consequently, we introduced the optimal structureof an index guiding hollow core photonic crystal fiber capable of measuring methane concentrations down to 0.1%in air. The simulations showed that the sensing sensitivity increased with an increase in the core diameter and a decrease in the distance between centers of two adjacent holes.