Lower Flammability Limit Research Articles

Development of Proton Exchange Membrane Water Electrolyzers with Low Catalyst Loadings and Recombination Layers By Reactive Spray Deposition Technology

Hydrogen is an important material for many different applications including materials processing, oil refining, ammonia production, energy storage, among many others. In commercial development since the 1950s, proton exchange membrane water electrolyzers (PEMWEs) have been identified as a green source of high-purity hydrogen which can be utilized for many applications [1]. While hydrogen produced by PEMWEs has shown significant promise as a clean hydrogen source for fuels or energy storage, there are a few technical challenges that need to be addressed to allow for its widespread use. One such challenge involves hydrogen crossover. In operation, hydrogen that is formed in the highly pressurized (~400 psi) cathode can diffuse back through the proton exchange membrane and into the anode chamber where oxygen is being formed as a result of the water splitting reaction [2]. This can lead to both performance and safety concerns. With the lower flammability limit (LFL) of hydrogen in oxygen around 4 vol%, typical operating conditions of a PEMWE are set such that the hydrogen concentration in the anodic stream does not approach 50% of the LFL. In order to ensure operation of the PEMWE at the desired operating conditions, mitigation strategies have been implemented to reduce the hydrogen crossover. One such mitigation strategy recently published by Klose, Trinke et al. has shown that introducing a platinum recombination layer within the membrane can significantly reduce the hydrogen crossover [3]. This work will examine PEMWEs with recombination layers developed entirely by Reactive Spray Deposition Technology (RSDT). The RSDT process provides significant advantages for recombination layer development as the small platinum nanoparticles (~2nm diameter) produced by RSDT allows for a significant reduction of hydrogen crossover with low loadings while also being able to optimize the thickness of the Nafion® insulating layer for the recombination layer to optimize the reduction of gas crossover while minimizing Ohmic losses. Platinum recombination layers will be able to reduce the hydrogen crossover to less than 10% of the lower flammability limit. In addition, the RSDT will be able to deposit low-loaded Pt/C cathodes and IrOx anodes which will assist in the cost reduction of the PEMWE without negatively effecting the performance of the electrolyzer. These low-loaded PEMWE samples developed by RSDT will allow for a cost-effective PEMWE with reduced gas crossover which will allow for more flexible operating conditions.

A lower flammability limit prediction model of alkane-CO2 mixtures based on flame phenomenon simulation

In the present study, a novel model is proposed to evaluate the lower flammability limit (LFL) of alkane diluted with CO2. The LFL model is based on flame phenomenon simulation (FS-LFL). The model consists of combustion, turbulence, and igniter models, which are used to characterise the combustion based on the chemical kinetics and CFD, which is not feasible with traditional methods. The flame simulation phenomenon was validated by contrast with experiment and same criterion of flammability limit in the experiment was adopted. The FS-LFL model was used to predict the LFLs of a propane-CO2 mixture and propane at various temperatures. The model performance was analysed by comparing the results with experimental data and predictions obtained from existing methods. The AARDs between the predicted and experimentally determined LFLs of the propane-CO2 mixture are 0.34%, 1.19%, and 1.35% at 30°C, 50°C, and 70°C, respectively. The model also has a good predictive power with respect to the LFLs of propane at initial temperatures ranging from 30°C-300°C, with an AARD of 2.10%. When the dilution of CO2 is 90%, the model yields a better result due to the utilisation of the chemical kinetics mechanism. This result is instructive for the use of this method in the prediction of upper flammability limits.

Effect of Carbon Dioxide on the Lower Flammability Limit of Propane in O2/CO2 Atmosphere

The paper presents the results of the lower flammability limit (LFL) of C3H8/O2/CO2 at normal temperature and pressure. The LFL of C3H8/O2/CO2 mixture was measured with an explosion vessel. The mea...

Effect of temperature and humidity on the flammability limits of hydrocarbons

In this study, the flammability limits of R290 and R600a were measured in different environmental conditions. All the experiments were performed on a self-made experimental rig at temperature ranging from 5 to 55 °C and relative humidity of air ranging from 0 to 100%. The results showed that the temperature dependences for the flammability limits of both R290 and R600a can be predicted by linear model precisely. The humidity dependences for the flammability limits of R290 and R600a were distinctive, which was increased slowly for lower flammability limits (LFLs) but changeable for the upper flammability limits (UFLs). Meanwhile, it was found that the flammability limits of both R290 and R600a became sensitive with the relative humidity changing. A special case for the water vapor influencing on the flammability limits of hydrocarbons was found, especially for UFLs. It has maximum and minimum values in the experimental curve of UFLs when the relative humidity increased from 0 to 100%, which revealed that water vapor does not inhibit the combustion of hydrocarbons simply.

Use of explosibility diagrams in potentially explosive atmospheres

Although the first research in the field was carried out by Davy in 1816, the first discovery emerged in 1891 when Le Chatellier defined the law for determining the explosive limits. Lower Explosive Limit (LEL) represents the lowest concentration of gas or vapours in air which is able to generate the explosion in the presence of an efficient ignition source. It is considered to be the same as the Lower Flammability Limit (LFL). Upper Explosive Limit (UEL) represents the highest concentration of gas or vapours in air which is able to generate the explosion in the presence of an efficient ignition source. It is considered to be similar with the Upper Flammability Limit (UFL) [1]. For the optimal management of underground or surface industrial environments, confined, obstructed or open environments, is required to know the point which defines the monitored atmosphere in relation with the explosion triangle. For confined underground environments, monitoring the atmosphere and using the explosibility diagrams are required during the closure process and also for re-opening the area. For underground environments specific to active mine workings and for industrial environments located on the surface, monitoring the atmosphere and using explosibility diagrams are required permanently.

Dilution of flammable vapor cloud formed by liquid hydrogen spill

The flammable vapor cloud formed by liquid hydrogen spill can severely threaten the safety of life and property, which is one of the primary concerns during handling liquid hydrogen. Mixture model and Realizable k-ε model are adopted in ANSYS Fluent to predict the two-phase flow of liquid hydrogen spill. Dilution of the hydrogen vapor cloud formed by liquid hydrogen spill is analyzed, including the turbulent disturbance during cloud dispersion, and the cloud dilution characteristics especially its behavior under different wind speeds. The results show that the turbulent disturbance in the upper part of flammable vapor cloud can be 7.21 times of that in the background atmosphere, due to the mixing of the vapor cloud with the incoming wind and the upper air. The dilution time, needed for the vapor cloud to be diluted below the lower flammable limit since the end of the spill, increases firstly and then turns to decrease with the increasing wind speed. The atmospheric turbulence, the turbulent disturbance induced by the upward movement of vapor cloud, and the cloud frontal area all affect the dilution behavior.

Analysis of Hazard Area of Dispersion Caused by Leakage from Underground Gas‐Storage Caverns in Salt Rock

To provide information concerning quantitative risk analysis of gas‐storage caverns, it is vital to estimate the hazard area of dispersion caused by accidental leakage. The Gaussian plume model is selected to calculate the hazard area caused by continuous leakage; the method of analysis is validated using wind‐tunnel experiments of acetylene. Fluent is used to simulate the hazard area of dispersion caused by instantaneous leakage; the method of numerical simulation is verified by Burro/Coyote trials. Furthermore, a sample underground gas‐storage cavern in salt rock is examined with respect to the toxic threshold limit value and the upper and lower flammability limits. In doing so, the factors that influence the hazard range of dispersion from salt cavern are discussed. The results indicate that the hazard area decreases with an increase in wind speed and a decrease in atmospheric stability when the leakage is continuous. However, the hazard area decreases with a decrease in wind speed when leakage is instantaneous.

Explosion hazards from lithium-ion battery vent gas

Lithium-ion battery technology is rapidly being adopted in transportation applications and energy storage industries. Safety concerns, in particular, fire and explosion hazards, are threatening widespread adoption. In some failure events, lithium-ion cells can undergo thermal runaway, which can result in the release of flammable gases that pose fire and explosion hazards for the compartment housing the cells. However, there is little available information characterizing the flammability properties of the gases released after cell thermal runaway. In this paper, analytical and modeling methods to estimate explosion characteristics, such as lower flammability limit, laminar flame speed, and maximum over-pressure are evaluated for use in quantifying the effect of cell chemistry, state-of-charge and other parameters on the overall explosion hazard potential for confined cells.

Highly accurate prediction of flammability limits of chemical compounds using novel integrated hybrid models.

Two novel and highly accurate hybrid models were developed for the prediction of the flammability limits (lower flammability limit (LFL) and upper flammability limit (UFL)) of pure compounds using a quantitative structure–property relationship approach. The two models were developed using a dataset obtained from the DIPPR Project 801 database, which comprises 1057 and 515 literature data for the LFL and UFL, respectively. Multiple linear regression (MLR), logarithmic, and polynomial models were used to develop the models according to an algorithm and code written using the MATLAB software. The results indicated that the proposed models were capable of predicting LFL and UFL values with accuracies that were among the best (i.e. most optimised) reported in the literature (LFL: R2 = 99.72%, with an average absolute relative deviation (AARD) of 0.8%; UFL: R2 = 99.64%, with an AARD of 1.41%). These hybrid models are unique in that they were developed using a modified mathematical technique combined three conventional methods. These models afford good practicability and can be used as cost-effective alternatives to experimental measurements of LFL and UFL values for a wide range of pure compounds.

Leakage analysis and concentration distribution of flammable refrigerant R290 in the automobile air conditioner system

The natural refrigerant R290 has been gradually investigated as an alternative refrigerant of R134a in the automobile air conditioning (MAC) systems at present. As an A3 class refrigerant, the application of R290 is associated with the greatest challenge of its flammable and explosive characteristics. This paper aimed to describe the distribution of R290 gas under different leakage conditions through experiments in the engine compartment and the passenger compartment. Our results showed that, evaporator leakage was the most risky situation of the system. In this case, R290 gas leaked to the passenger compartment, as a result, the R290 concentration in the environment was above the lower flammable limit (LFL). In the case of leakage in the engine compartment, the leak pressure, leak hole size, and wind speed were recognized as the three main parameters affecting R290 distribution. Moreover, increasing the hole size and decreasing the wind speed would raise the maximum R290 concentration as well as the duration in which the R290 gas concentration was above the LFL level. Additionally, a lower pressure suggested that the R290 concentration rose slower but it was maintained for a longer time above the LFL than that under high pressure situation.

Obstacle Influence on High-Pressure Jets based on Computational Fluid Dynamics Simulations

In the industrial safety framework, high-pressure jets involving toxic or flammable substances represent one of the major risks. The presence of one or more obstacles affects the extent of the plume, normally to higher dimensions, which means that an open field modeling would not be conservative and that it is necessary to explicitly consider the obstacles effects. Thus, to study this kind of scenario, only a computational fluid dynamic model allows a complete and proper description of the obstacles influence on the jet behavior.In this work, we deal with a realistic case-study of industrial interest which involves a high-pressure methane jet impinging a nearby cylindrical tank positioned in front of the jet release.The aims of this work are to define the geometrical parameters of the scenario, to quantify their influence on the jet-obstacle interaction, with respect to the free jet case, and then to find which of them are the most relevant. Therefore, the effect of the cylindrical tank on the lower flammability limit area extent is systematically studied using computational fluid dynamics simulations, performed with ANSYS FLUENT.

Comparison of Flammability of Low-GWP Refrigerants Using 1.76-m3 Combustion Chamber

ABSTRACT The transition to low global-warming potential (GWP) refrigerants is ongoing. Since a large part of Low-GWP refrigerants is combustible, fundamental flammability parameters have been studied. However, the combustion behavior of accidentally released refrigerants is not fully understood. In this study, we studied the relationship between the flammability parameters such as lower flammability limit (LFL), the fundamental burning velocity (FBV) and the combustion behaviors of Low-GWP refrigerants including R290 (C3H8), R152a (CH3CHF2), R143a (CH3CF3), R142b (CH3CClF2), R41 (CH3F), and R32 (CH2F2). We conducted tests using three experimental configurations: static configuration, laminar and turbulent flow configuration simulating realistic refrigerant leak. Under static conditions, the burning velocities for R290, R152a (CH3CHF2), and R32 were measured in a 1.76 m3 combustion chamber. The measured values of burning velocities were in a good agreement with available literature data. Laminar refrigerant leak was studied for R290, R152a, R41(CH3F), R142b (CH3CClF2), and R32 in a 1.76 m3 combustion chamber. Flammability of turbulent flow leak of R290, R152a, R143a (CH3CF3), and R32 was analyzed using a 237 L plastic container. Experiments simulating laminar and turbulent flow refrigerant leak demonstrated a positive correlation between LFL and the time before ignition. The refrigerant concentration at ignition agreed with LFL. It was found that the combustion behavior of refrigerants under leak conditions corresponds two types of flame propagation. The first type corresponds to a flame which rapidly spreads horizontally on the floor surface from the ignition source. The second type corresponds to flame kernel irregularly appearing around the continuous spark source. The approximate boundary between two types of combustion behavior corresponds to R152a (FBV = 23.6 cm/s, unsupported flame propagation) and R143a（FBV = 7.1cm/s, combustion supported by the continuous ignition source). This result is consistent with ASHRAE 34, ISO 817 and the GHS classification revised in 2017 adopting the burning velocity of 10 cm/s as a boundary between “highly flammable” and “lower flammable” refrigerants.

Experimental study on the flame stability and color characterization of cylindrical premixed perforated burner of condensing boiler by image processing method

In this paper, a cylindrical premixed perforated burner which is mostly used in condensing boilers is investigated by image processing methods. The burner is experimentally analyzed in its operating heating capacities (11.7–17.1 kW) and equivalence ratios (0.4–1.2). Flame properties were studied using digital images by CCD camera and color processing techniques. The method devised a procedure for finding a reliable relation between a digital image color and flame characteristics in the visible wavelength domain. It is observed that by decreasing the equivalence ratio from 1.2 to 0.4, the flame color changed from green with yellow and then blue. Besides, flame lift-off and blow off were also observed. Lower flammability limit is in the equivalence ratio of 0.44. The optimum conditions of the burner, which is defined by the stable blue flame, are found in the equivalence ratio of 0.7–0.73. Moreover, RGB analysis is used to find the stable operation of the burner. This stable optimum condition can be defined as the intersection of two intensities’ component of Red and Blue in image processing of the flame.

Influence of heat tightness of an enclosure fire on ignition risk of unburnt gases in a connected exhaust system – An experimental study

An experimental study was performed from a reduced scale enclosure with a length/height and width of 2 m. A dodecane pan of 40 cm in diameter is placed at the center of the enclosure floor. An external ventilation system provides an air supply rate with an Air Change Per Hour (ACPH) ranging from 3 to 5. Influence of the intermediate levels of thermal insulation of enclosure on ignition risk in a connected exhaust system is experimentally evaluated. The results show that thermal insulation of an enclosure leads to faster fire growth, implying more important peak in heat release rate, and thus more dangerous fire in regards to the ignition risk. Heat tightness of enclosure enhances the mass loss rate of liquid fuel, but reduces the air supply rate from the admission duct due to decrease of the depression level in the compartment. As a consequence, the fire becomes quickly very-under-ventilated, and a large vaporized fuel is converted into the unburnt gases such as hydrocarbons, CO and H2. In the early stages of a fire, a hotter unburnt fuel layer with a concentration above the Lower Flammability Limit (LFL) is formed in the extraction duct connected to a mechanically ventilated enclosure fire. With a long time delay in a range of 16–21 min in the current study, the energy released per mass of oxygen consumed allows to raise the smoke temperature above 350 °C. Occurrence of flame extinction in vitiated air enclosure makes a sudden increase of the depression level inside enclosure due to cooling effects. This results in a sudden supply of fresh air from dilution duct, providing a sufficient amount of oxygen to trigger ignition of a fuel rich mixture near the extraction duct. It is found that ignition of unburnt volatiles at entrance of the extraction duct occurs more easily when the compartment is more heat-tight with a reduction by about 30% in the ignition delay.

Computational equation discovery of relationships between container ship fuel consumption and hull and propeller fouling phenomena

Abstract Nowadays, when we try to automatize all activities, there is a growing demand for energy in all forms. Increasingly we reach for new energy sources that can be problematic to store or to transport, owing to their toxicity or explosive propensity. The article examines the issues of determining danger zones occurring as a result of liquefied natural gas (LNG) release. The range of danger zones caused through LNG release depends on a multitude of factors. The basic parameter that needs to be considered is a type of the released substance as well as the manner of its release. The range of a danger zone is determined by, inter alia, the concentration of a released substance and the atmospheric conditions existing at the time when depressurization occurs. The article analyses the problem of the range of danger zones in a function of wind speed and surface roughness with a defined value of Pasquill stability for various LNG types, starting with pure methane, and ending with the so-called LNG-heavy. The difficulty of the task becomes more complicated when the analysed surface over which a depressurization incident takes place involves water. The problem deepens even further when the analysed substance possesses explosive properties. Then, apart from regular substance concentration, upper and lower flammability limit ought to be considered. Calculations were conducted with DNV-Phast software, version 7.11.

Experimental study on the flammability limits of natural gas/air mixtures at elevated pressures and temperatures

While injecting air into an oil reservoir for enhanced oil recovery, there may be explosion risks at reservoir conditions including elevated pressures and temperatures. A high-pressure experimental apparatus was developed to investigate the flammability limits of natural gas/air mixtures at reservoir conditions with pressure ranging from 1 MPa to 15 MPa and temperature ranging from 40 °C to 120 °C. The results showed that an increase in initial pressure or temperature leads to a wider flammability limit range. Specifically, the upper flammability limit (UFL) shows a logarithmic pressure dependence, and the lower flammability limit (LFL) is linearly dependent on pressure. The UFL shows a linear dependence on temperature, whereas the LFL is slightly affected by temperature. Moreover, it was also found that when the pressure is between 1 MPa and 5 MPa, the effect of temperature on the UFL is affected by pressure. Temperature has little influence on the relationship between pressure and UFL. These results improve our understanding of the fire and explosion hazards of natural gas in oil recovery processes.

Numerical simulation studies of the effect of atmospheric stratification on the dispersion of LNG vapor released from the top of a storage tank

In this paper, Computational Fluid Dynamics (CFD) approach was used to study patterns of Liquefied Natural Gas (LNG) vapor dispersion under different atmospheric stabilities. First of all, the Burro 8 field test was used to validate prediction results generated by Fluidyn-PANACHE, a CFD modeling software. The test data confirmed that PANACHE is able to describe the dense gas behavior of LNG vapor dispersion. The CFD predictions regarding lower flammable limit (LFL) distances and downwind maximum concentration were in approximate agreement with the test data. After this, the dispersion of LNG vapor, which results from its accidental release from the top of large-scale storage tank under different atmospheric stabilities, were simulated. The results showed that the influence of atmospheric stability on the vertical and lateral distributions of vapor cloud, the downwind near-ground gas concentrations and the LFL distance is significant. The vertical spread of cloud under unstable condition is slightly larger than that under neutral and stable conditions. The dilution of the LNG cloud is suppressed under stable condition due to weaker turbulent mixing. Also, stable atmospheric condition can increase the near-ground gas concentrations, the lateral distribution of the cloud and the LFL distance. The longitudinal distribution of the cloud near the ground under neutral condition is larger than that under unstable and stable condition.

The Explosion Severity of Biogas(CH<sub>4</sub>-CO<sub>2</sub>)/Air Mixtures in a Closed Vessel

Biogas which consists of methane (CH4) and carbon dioxide (CO2) could explode when diluted to a certain degree with air in the presence of ignition source. The maximum explosion overpressure (Pmax), the maximum rate of pressure rise (dP/dt)max, flammability limits, and deflagration index are the most important explosion severities parameters to characterize the risk of explosion. In this research paper, the effect of equivalence ratio (ER) of biogas/air mixtures and the effect of CO2 concentrations presence in biogas were studied in a 20 L spherical vessel. The values of Pmax and (dP/dt)max of biogas/air mixtures were more severe at ER 1.2. At various CO2 content, Pmax and (dP/dt)max of biogas/air mixtures were the least affected at 45% vol/vol of CO2. On the other hand, deflagration index (KG) of biogas/air mixtures trend was the most severe at 35% vol/vol of CO2 content despite the lowest Pmax and (dP/dt)max at 45% vol/vol of CO2 content. The lowest values in Pmax and (dP/dt)max were due to the diffusivity properties of CH4 that had surpassed the CO2 suppression effect. Furthermore, the presence of CO2 in biogas/air mixtures had increased the upper flammability limit and lower flammability limit of biogas.

CMOS-compatible plasmonic hydrogen sensors with a detection limit of 40 ppm

Sensing of leakage at an early stage is crucial for the safe utilization of hydrogen. Optical hydrogen sensors eliminate the potential hazard of ignition caused by electrical sparks but achieve a detection limit far higher than their electrical counterparts so far. To essentially improve the performance of optical hydrogen sensors in terms of detection limit, we demonstrate in this work a plasmonic hydrogen sensor based on aluminum-palladium (Al-Pd) hybrid nanorods. Arranged into high-density regular arrays, the hybrid nanorods are capable of sensing hydrogen at a concentration down to 40 ppm, i.e., one thousandth of the lower flammability limit of hydrogen in air. Different sensing behaviors are found for two sensor configurations, where Pd-Al nanorods provide larger spectral shift and Al-Pd ones exhibit shorter response time. In addition, the plasmonic hydrogen sensors here utilize exclusively CMOS-compatible materials, holding the potential for real-world, large-scale applications.

Effects of Propane on the Flammability Limits and Chemical Kinetics of Methane–Air Explosions

ABSTRACT This work presents a comprehensive account of how adding C3H8 impacts the possibility of explosion for CH4–air mixtures. A series of experiments was carried out to determine the upper and lower flammability limits (UFL and LFL, respectively), and the explosive risk value for different mixtures of CH4 and C3H8. The critical oxygen concentration, the concentrations of CH4 and N2 at the point where the LFL and UFL merge, and the CH4 explosive triangle were obtained for nitrogen-diluted mixtures. In addition, we used a detailed mechanism (GRI-Mech3.0) in the CHEMKIN software package to acquire the impacts of adding C3H8 on the chemical kinetics of the explosion of CH4. The flammable limits of CH4 decrease linearly with the addition of C3H8 while the flammable range increases slightly. The explosive risk value for CH4 in air increases greatly upon adding C3H8 following a parabolic relationship. Nitrogen dilution noticeably decreases the UFL and slightly increases the LFL, ultimately resulting in these points merging. The concentration of CH4 and nitrogen at this merging point varies linearly when the C3H8 concentration is varied between 0% and 2.0%. The addition of C3H8 also expands and shifts leftwards and downwards CH4’s explosive triangle. Numerical analysis reveals that the maximum temperature and pressure during the explosion, and the formation rates of CO and NOx, noticeably increase after adding C3H8. Sensitivity coefficients of key dominant reactions show that overall more •H, •O, and •OH are consumed when C3H8 is added. Furthermore, the time between ignition and maximum pressure (the burning time) is evidently shortened by the addition of C3H8, which also shortens the explosion duration.