Lower Flammability Research Articles

A CFD based methodology to design an explosion prevention system for Li-ion based battery energy storage system

This work developed a performance-based methodology to design a mechanical exhaust ventilation system for explosion prevention in Li-Ion-based stationary battery energy storage systems (BESS). The design methodology consists of identifying the hazard, developing failure scenarios, and providing mitigation measures to detect the battery gas and maintain its global concentration lower than 25% of the lower flammability limit (LFL) to meet the prescriptive performance criterion of NFPA 69 – Standard on Explosion Prevention Systems. Representative UL 9540A test data is used to define the battery gas composition, release rate, and release duration to describe the failure scenario involving thermal runaway propagation. In addition, an exemplar BESS enclosure geometry is defined to model the failure scenarios using a computational fluid dynamics (CFD) solver. A grid convergence study is performed to estimate the grid resolution required to perform the CFD analysis. In addition, sensitivity studies for different input parameters are performed to understand the impact of inputs on the detection times and ventilation performance. The approach used in this work provides a systematic procedure for the fire protection engineering community to understand the explosion prevention requirement for a BESS installation. The explosion prevention system functionality presented in this work is limited to removing flammable battery gas generated due to the non-flaring decomposition of batteries.

Thermal Runaway Characteristics and Gas Composition Analysis of Lithium-Ion Batteries with Different LFP and NCM Cathode Materials under Inert Atmosphere

During thermal runaway (TR), lithium-ion batteries (LIBs) produce a large amount of gas, which can cause unimaginable disasters in electric vehicles and electrochemical energy storage systems when the batteries fail and subsequently combust or explode. Therefore, to systematically analyze the post-thermal runaway characteristics of commonly used LIBs with LiFePO4 (LFP) and LiNixCoyMnzO2 (NCM) cathode materials and to maximize the in situ gas generation during battery thermal runaway, we designed experiments using an adiabatic explosion chamber (AEC) under an inert atmosphere to test LIBs. Additionally, we conducted in situ analysis of the gas components produced during thermal runaway. Our research findings indicate that after thermal runaway, NCM batteries produce more gas than LFP batteries. Based on battery gas production, the degree of harm caused by TR can be ranked as follows: NCM9 0.5 0.5 > NCM811 > NCM622 > NCM523 > LFP. The primary gas components during thermal runaway for both NCM and LFP batteries include H2,CO,CO2,C2H4, and CH4. The gas produced by LFP batteries contains a high proportion of H2. The high concentration of H2 results in a lower flammability limit (LFL) for the gas generated by LFP batteries during TR compared to the mixed gas produced by NCM batteries. Therefore, in terms of battery TR gas composition, the order of hazard level is LFP > NCM811 > NCM622 > NCM523 > NCM9 0.5 0.5 0.5. Although experimental results show that LFP batteries have superior thermal stability and lower gas production during large-scale battery thermal runaway events, considering gas generation composition and thermal runaway products, the thermal runaway risk of LFP batteries may be higher than that of NCM batteries. Although LFP batteries are considered very safe, our research results have once again drawn researchers’ attention to LFP batteries. These gases can also serve as detection signals for battery thermal runaway warnings, providing a cautionary note for the future development of electrochemical energy storage and the renewable energy sector.

Lower flammability limit of hydrogen/air mixture under different electrode parameters, initial pressure and diluent gas

The investigation of the lower flammability limit (LFL) is essential to the security application of hydrogen. In the present work, the LFL of hydrogen under a variety of conditions is systematically measured. The effect of electrode gap length (2–4 mm), electrode shape (30°, 90°, and spherical) and initial pressure (40–200 kPa) on the LFL of hydrogen/air mixture are analyzed. It shows that the LFL of hydrogen/air mixture increases with the increase of initial pressure and decreases with the increase of electrode gap length. The LFL of 30° electrodes is higher than that of 90° and spherical electrodes at the initial pressure higher than 80 kPa. Besides, the LFL of hydrogen/air mixture diluted with inert gas (CO2 and N2) at different initial pressure (50 kPa, 100 kPa, and 150 kPa) is investigated. The LFL of H2/air/CO2 mixture increases with increasing CO2 concentration, while the LFL of H2/air/N2 mixture is almost unchanged under different N2 concentration.

General estimation method for lower flammability limits of organic compounds: The simpler the better

Due to the lack of well-established procedures to estimate the lower flammability limit (LFL) of arbitrary fuel-air mixtures, we report therein a simple method derived from a relationship introduced over 80 years ago for C–H–O molecules and presently extended to molecules containing C–H–N–O–F–Cl–Br–I–Si–P–S elements. The LFL was usually found to represent a constant fraction α≃1/2 of the stoichiometric concentration of fuel, except for halogen compounds for which α increases with the fraction of halogen atoms in the fuel molecules. Interestingly, this extremely simple scheme, which could be then easily integrated into any molecule design workflow, indicates that LFL values are mainly determined by the element count on the fuel structure, in sharp contrast with the premises underlying quantitative structure–property relationship (QSPR) and group contribution (GC) approaches.

Performance-based assessment of an explosion prevention system for lithium-ion based energy storage system

This work developed and analyzed a design methodology for Powin Stack™ 360 enclosures to satisfy the requirements for explosion prevention per NFPA 855. Powin Stack™ 360 enclosures are lithium-ion-based stationary energy storage systems (ESS). The design methodology consists of identifying the hazard, developing failure scenarios, and providing mitigation measures to detect the battery gas and maintain its global concentration lower than 25% of the lower flammability limit (LFL) to meet the prescriptive performance criterion of NFPA 69 – Standard on Explosion Prevention Systems. The UL 9540A test data is used to define the battery gas composition, release rate, and release duration to describe the failure scenario involving thermal runaway propagation. The ESS enclosure consists of individual stacks (compartments) with targeted airflow to ensure the cooling of batteries during normal operational conditions. This arrangement makes it difficult to use a standard exhaust ventilation methodology to design an explosion prevention system. An innovative approach is used to purge the battery gas from individual Powin Stacks™ and from the main enclosure during a thermal runaway event. The designed method is analyzed using a computational fluid dynamics (CFD) model to ensure it meets the intent of NFPA 69. The explosion prevention system functionality presented in this work is limited to removing flammable battery gas generated due to the non-flaring decomposition of batteries and does not consider its interactions with other fire protection features.

Lower flammability limits of H2/NH3/CH3OH mixtures under elevated pressures, temperatures and different blending ratios

The lower flammability limits (LFLs) of H2/NH3/CH3OH mixtures and related flame morphologies are experimentally investigated under elevated pressures, elevated temperatures, and blending ratios. The results show that the flame morphologies of LFLs are mushroom-like, darkening with an increase in initial pressures and remaining unchanged with an increase in initial temperatures. Except for the flame wrinkles at 10:0:0 and 5:5:0, there is little difference in the flame morphologies with blending ratios. When NH3:CH3OH = 1:1, the LFLs of 0 % H2 decrease with elevated pressures while the rest increase, and the LFLs steadily decrease as H2 increases. When H2:CH3OH = 1:1, the LFLs of 100 % NH3 decrease with elevated pressures while the rest increase, and the LFLs increase as the NH3 increases. The LFLs of 0–40 % CH3OH rise with the increasing pressure when H2:NH3 = 1:1, while the LFLs of 60 % CH3OH are almost unchanged and the LFLs of 80–100 % CH3OH decrease. Additionally, the LFLs increase at 50–100 kPa and decrease at 150–250 kPa as CH3OH increases. The LFLs of the mixtures decrease with elevated temperatures. The prediction formula of H2/NH3/CH3OH mixtures’ LFLs under elevated pressures, elevated temperatures, and blending ratios is established. The average absolute error (AAE) and average relative error (ARE) are 0.11 % and 1.54 %.

Flammability of Polymer Compositions Filled with Wheat Bran.

The article presents the results of flammability tests on polymer compositions with wheat bran (WB) as the applied filler, and polyethylene (PE) or poly(butylene succinate) (PBS) as the matrix material. Tests were conducted using samples of compositions containing 10, 30 and 50%wt wheat bran. The test samples were manufactured by injection moulding from compositions previously produced by extrusion pelleting. For comparative purposes, samples made only of the plastics used for the composition matrix were also examined. Flammability tests were carried out in accordance with the recommendations of EN 60695-11-10 Part 11-10 with horizontal and vertical positioning of the sample, using a universal flammability-test-stand. During the flammability tests, changes in the temperature field in the area of the burning sample were also recorded, using a thermal imaging camera. Sample residues after flammability tests were also examined with infrared spectroscopy (FTIR) to assess their thermal destruction. The results of the study showed a significant increase in flammability with bran content for both PE and PBS matrix compositions. Clear differences were also found in the combustion behaviour of the matrix materials alone. Both the burning rate and maximum flame temperature were lower in favour of PBS. PBS compositions with wheat bran also showed lower flammability, compared with their PE matrix counterparts.

Effect of ignition energy on combustion characteristics of flammable working fluids

Working fluids with low global warming potential (GWP) will play an important role in the research and development of alternative working fluids for organic Rankine cycles and refrigeration cycles. However, the flammability of low GWP working fluid limits their development, and the energy of typical fire sources has a significant impact on their safe application. At present, there is a lack of relevant research on the effect of ignition energy on their flammability. In this paper, the effect of ignition energy on the combustion characteristics for propane (R290), fluoroethane (R161), 1,1-Difluoroethane (R152a), and 3,3,3-Trifluoropropene (R1243zf) was studied using a variable ignition energy system. The initial flame propagation process, flammability limit, and burning velocity were tested and analyzed in the range of 50 mJ to 20 J. The results showed that with the increase of ignition energy, the lower flammability limit (LFL) decreased and the upper flammability limit (UFL) increased, but their rate of change decreased with the increasing ignition energy. The effect of ignition energy on the flammability limit of R1243zf was significantly greater than that of the other three working fluids. In addition, the effect of ignition energy on flame propagation was mainly limited to the initial stage, and the burning velocity was independent of ignition energy. The mechanism of ignition energy on combustion characteristics was obtained. The research results have guiding significance for the safe application of flammable working fluids.

Effect of swirler vane angle on the combustion characteristics of premixed lean hydrogen-air mixture in a swirl micro-combustor

This study analyses the influence of swirler vane angle (β) on the combustion characteristics of premixed lean hydrogen-air flame in a swirl micro-combustor via numerical simulations. The results show that lower flammability limit (LFL) under β = 15° is larger than that of β = 0°; and β = 30°, 45° and 60° have very little difference in the LFL, and their LFL are smaller than that of β = 0° Flame anchoring mainly depends on the corner recirculation zone (CRZ) when β is 0° and 15°, and when β exceeds 30°, flame anchoring is chiefly determined by the inner recirculation zone (IRZ). The flame stabilization ability of IRZ is stronger than that of CRZ, but excessive swirling intensity will increase the length of IRZ, which in turn results in a decrease in stabilization ability. Increasing β improves outer wall temperature when inlet velocity is relatively small. Under a larger inlet velocity, an enormous β reduces combustor thermal performance and combustion efficiency due to the downstream movement of flame root and reaction zone. This work helps us to better understand the swirling flame characteristics in micro-combustor and provides guidance for the design and optimization of swirl micro-combustor.

Elucidation of Enhanced Lithium Conductivity in Nanoporous Ionogel Using Solid State NMR

AbstractNanostructured solid composite electrolyte or nano‐SCE, which is composed of an ionic liquid, nanoporous silica, and residuals of immobilized precursor components, shows promising synergistic properties. The ionic conductivity of nano‐SCE is in the range of 2–5 mS cm−1, which exceeds the bulk ionic liquid conductivity at ambient temperature, while maintaining characteristics of a solid electrolyte such as having no leakage issues as the ionic liquid is confined, and lower flammability compared to conventional liquid electrolytes. In this study, the underlying mechanism of enhanced conductivity is investigated by using magic angle spinning NMR and NMR relaxometry analysis. Water, one of the volatile precursor molecules has shown to play a key role in the final conductivity and stability at the solid‐electrolyte interface, as it enhances the temperature range in which the ionic liquid remains mobile. In line with previous studies, water with lowered mobility is found in the silicon matrix. The activation energies of lithium ion transfer probed by NMR relaxometry, however, do not change as function of water content. The increase in bulk mobility of lithium ions under ambient conditions compared to water‐less nano‐SCE is found to be the origin of the altered conductivity of this material.

Thermodynamic analysis and turbine design of a 100 kW OTEC-ORC with binary non-azeotropic working fluid

The present paper deals with the performance analysis of an ocean thermal energy conversion (OTEC) plant based on the organic Rankine cycle (ORC) with a theoretical outpower of 100 kW where a non-azeotropic mixture has been used as the working fluid. Hydrofluoroolefins (HFOs) are selected as the components of the binary non-azeotropic working fluid due to their desired thermodynamic properties, higher safety and stability, lower cost and environmental friendliness i.e., zero ODP (Ozone Depletion Potential) and low GWP (Global Warming Potential). In this study, R1224yd(Z) is adopted as the first component due to its lower flammability and toxicity comparing with other HFOs. Through comparisons between several refrigerants, R1243zf was selected as the second component of the binary non-azeotropic working fluid by considering temperature glide and the system efficiency. The performance of OTEC-ORC is also evaluated for two different working fluids i.e., R1224yd(Z)/R1243zf mixture, and pure NH3 (common working fluid in the OTEC-ORC). The optimal composition of the mixed working fluid R1224yd(Z)/R1243zf is obtained of 16:84 with the maximum system efficiency. Next, a gas turbine is designed one-dimensionally and simulated three-dimensionally. The one-dimensional calculation results fit well with the three-dimensional results. At the design point, the turbine output power is 88.63 kW and the efficiency is 87.10%. The thermodynamic findings prove that organic Rankine cycle with binary mixture of R1224yd(Z)/R1243zf is a promising alternative for pure NH3.

Proposal and validation of a new innovative solution for green hydrogen storage, via clathrate hydrates.

According to the European Green Deal, the production of green hydrogen is gaining the growing interest of scientists and industrialists. The European Strategy for Hydrogen denotes it as one of the main contributors to achieve the carbon neutrality of Europe within 2050. In this context, the whole chain of hydrogen must be defined with accuracy: from the raw energy needed for its production, to the following crucial phases, like storage and transportation. This article aims to propose an innovative solution to store hydrogen at competitive conditions. According to it, H2 molecules are enclathrated in solid crystalline water structures and form gas hydrates. Prior than this phase, it is mixed with carbon dioxide and/or small chain hydrocarbons, in order to lower the pressures required for the process. The final product will show high energy density, safety for humans (non-toxicity and lower flammability and explosivity, compared to the known techniques), easy of transportation. Moreover, it will assume a highly competitive energy stored/energy spent ratio. Finally, being the gas molecules only physically trapped into water cages, the following separation of hydrogen from the aid gases, also due to the different sizes between them, can be easily obtained at competitive costs.

Tracer Gas Test and CFD Analysis of Semiconductor Gas Box for Flammable Gas Leakage

Semiconductor manufacturing is performed through unit processes that use various chemicals and facilities. In particular, flammable gases, such as H2, NH3, and CH4, are used, and there is a risk of explosion when such gases leak. In this study, computational fluid dynamics (CFD) simulation and a “tracer gas test” according to the SEMI (Semiconductor Equipment and Materials International) S6 Environmental, Health, and Safety Guideline for Exhaust Ventilation of Semiconductor Manufacturing Equipment specification were performed during the leakage of hydrogen, a highly flammable gas used in the etching process of a gas box in the semiconductor industry. The CFD simulation was conducted to investigate the safety of semiconductor production facilities in relation to the explosion risk. Flow analysis was performed for the interior of a gas box used in the etching process. A steady-state analysis was performed to predict the concentration range of the explosion limit in the case of continuous hydrogen gas leakage. The interior of the gas box used in the simulation was modeled, and the ventilation flow rate, which has a significant impact on the leakage gas concentration distribution, obtained from experiments was used. The lower flammability limit (LFL) value of the leaked gas was 4% based on H2, and LFL/4 (25% of the LFL) was analyzed as the explosion limit concentration according to the acceptance criteria of the SEMI S6 tracer gas test. To validate the CFD simulation, a tracer gas test was performed according to SEMI S6. A mixture of hydrogen (5%) and nitrogen (95%) was used as the tracer gas. The flow rate was controlled by a gas regulator valve and measured using an Aalborg mass flow meter. The measured concentration of the tracer gas was calculated using the equivalent release concentration, which was calculated when 100% of the hydrogen was released, and the risk was assessed by comparing it with the LFL/4 of H2.

Effects of radiation, curvature, and preferential diffusion on the extinction of laminar non-premixed flames

The combined effects of radiative heat loss, curvature, and preferential diffusion on laminar non-premixed flames (or flamelets) are investigated in this work by using asymptotic analysis. A general theoretical description of flame temperature and extinction is derived for curved flames with non-unity Lewis numbers and radiative heat loss. Special attention is paid to the effects of curvature and radiative heat loss on the flammability limits. The results show that (1) a curved flamelet always has two extinction limits: one is the kinetic extinction limit, and the other is the curvature-induced extinction limit for the adiabatic case or the radiative extinction limit for the radiative case; (2) the curvature exerts a different influence on the adiabatic and radiative flames. Specifically for the adiabatic flame, it is found that both flame temperature and flame position significantly decrease as the curvature increases and that a new extinction limit at a low stretch rate occurs due to the existence of curvature. Furthermore, a higher curvature coupled with the increase in the Lewis number results in a lower flammability limit and narrower flammable zone. Therefore, the presence of curvature has a negative impact on the adiabatic flame. On the contrary, for the radiative flame, the results show that the increase in curvature has a positive effect on the flammability limit and thereby increases the flammable zone. It is expected that curved flamelets hold smaller (larger) flammable zones than planar flamelets under the adiabatic (radiative) condition. All results show that the change in flame curvature has a stronger effect on the flame structure and extinction than the deviation of the Lewis number from unity.

Optimization of gas detectors with the aid of computational fluid dynamics - Imposition of realistic restrictions

Flammable or toxic substances are present during oil extraction, production, and refining. Therefore, control measures, protective barriers, and devices responsible for mitigating consequences are necessary. Flammable or toxic gas detectors play a fundamental role in prevention since they usually have an interface with the emergency shutdown, blowdown, ignition source control, ventilation, alarm system, and firefighting systems. However, technical standards and recommendations do not indicate the exact location or the required number of detectors. Although gas detectors are the most effective devices for gas phase releases, they detect approximately 39% of leaks. Several methodologies have been presented to optimize the position and quantity of the detectors. However, it is not guaranteed that mathematical solutions to the optimization problem can be implemented in practice. The unconstrained optimization result may indicate optimal coordinate sensors in a too high position, requiring cable support and making maintenance and calibration difficult. Also, another possibility is that the detectors are too close to the leak source. This condition could make detection difficult if the leak does not occur precisely in that direction. In order to overcome these difficulties, the present study incorporates distance restrictions from the leak point, distance restrictions from the ground and the equipment side. In other words, the solutions obtained from the optimization are intended to be feasible in the real world for the construction and assembly stage in the field. Furthermore, the present study compared the position of the detectors considering heuristic algorithm and binary integer linear programming, the position of the initial detectors with and without restrictions, spacings between the initial detectors, restrictions of proximity to the leak point, and alarm conditions by 20% and 60% of the lower flammability limit (LFL), which resulted in 60 different optimization scenarios. The main results showed that even with the restrictions imposed, it was possible to reach the minimum number of detectors compared to those without restrictions. All cases were detected when the initial matrix spacing was less than or equal to 1 m, regardless of other restrictions. For comparison, the 5 m spacing, adopted in most studies involving optimization of gas detectors, presented its best result with twice as many devices.

Experimental study on the lower flammability limit of N2 and CO2 diluted H2/CO/air mixtures at high initial pressure

The lower flammability limits (LFL) of H2/CO/air mixtures over a wide range of H2 fractions (0–100 vol%) with N2 (0–67 vol%) and CO2 (0–67 vol%) dilutions were systematic experimentally studied at various initial pressures (100 kPa–500 kPa) via an 8L cylindrical vessel and using the metal wire fusing as ignition source. The results showed that LFL decreased with the growth of H2 fractions under all measured initial pressures. Due to the larger heat capacity and chemical kinetic effect, CO2 presented a stronger dilution effect on LFL than N2. LFL of diluted syngas slightly decreased with the increase of initial pressures. Kondo's extended Le Chatelier's Rule presented satisfactorily application on estimating LFL of diluted mixtures based on accurate measurements. Moreover, a simple expression of logarithmic function proposed by Zabetakis provided the better accurate prediction on LFL of syngas at different initial pressures than linear regression.

Understanding Gas Permeation during High Pressure Operation of PEM Water Electrolyzers

Governments and industries across the world have initiated implementation of clean hydrogen (H2) to achieve zero emissions, yet significant challenges remain for large scale adoption. With the decreasing renewable electricity cost PEM water electrolyzers (PEMWEs) show significant potential for at scale deployment due to their high faradaic efficiency and high operating current density. To reduce the per kilogram price of hydrogen and increase the overall energy efficiency, PEMWEs need to be operated at high differential pressures (30 to 50 bar) to eliminate the need for compression during storage and transportation1. To achieve high faradaic efficiency, thinner membranes are required to reduce voltage losses within the cell. However, thinner membranes exhibit a higher gas permeation rate which leads to increased crossover of hydrogen from the cathode through the membrane to the anode. Such increased crossover of H2 not only reduces the efficiency but can also result in flammable gas mixtures (lower flammability limit for H2 in O2 is 4 %) as Iridium/Iridium oxide (anode catalyst) is inefficient in oxidizing H2 1. The addition of a gas recombination catalyst (GRC) to the membrane is an useful strategy to oxidize permeating H2 and minimize the H2:O2 ratio at the anode.In this study, a high pressure (up to 30 bar) electrolyzer setup is coupled with online gas chromatography-mass spectrometry to understand the H2 gas permeation in membranes as a function of H2 partial pressure and operating current density (simulated by varying the flow rates) as shown in Figure 1 . Effect of the GRC, its loading, and its location on the H2 permeation will be elucidated. Differences induced by the addition of anode and cathode catalyst layers on H2 permeation rates will also be presented.Figure 1. Ex-situ H2 permeation rate at different cathode operating pressure at 80 °C. The anode was maintained at 1 bar of O2 partial pressure Acknowledgement This research is supported by the U.S. Department of Energy (DOE) through the Hydrogen and Fuel Cell Technologies Office, program manager Dave Peterson Reference Bernt, M., Schröter, J., Möckl, M. & Gasteiger, H. A. Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 167, 124502 (2020). Figure 1

Effective and Durable Recombination Layers for Hydrogen Crossover Mitigation in Proton Exchange Membrane Water Electrolyzers

The Hydrogen Economy (HE) is the economy of the near future and is the only viable alternative to the current fossil fuel-based economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. The HE implementation relies on the development of zero-carbon emission technologies for Hydrogen (H2) production. “Green” hydrogen can be produced in large scale by integration of water electrolyzers (WEs) with renewable energy sources. Currently, the proton exchange membrane water electrolyzers (PEMWEs) are considered as the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for PEMWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers (2-3 mgPGM/cm2 in each electrode) and time consuming and expensive multi-step fabrication processes associated with their manufacturing; (ii) limited durability caused by the instability of the catalysts and the materials, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively mitigate and keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].In this paper, we demonstrate the capabilities of the reactive spray deposition technology (RSDT) to fabricate MEAs with one order of magnitude lower PGM catalyst loadings in their electrodes, and catalytic recombination layers integrated in the volume of the MEAs that effectively suppress the H2 crossover. The RSDT is a flame assisted method that combines the catalysts synthesis and deposition directly on the PEM membrane in one-step, which results in fast and facile fabrication of large scale MEAs [4, 5, 6]. RSDT-fabricated recombination layers (RLs) demonstrated effective reduction of H2 crossover from 30-50% of the LFL to less than 10% of the LFL when operating at current densities between 0.58 A/cm2 and 1.86 A/cm2. These recombination layers are with Pt loading of only 0.02 mgPt/cm2 and are incorporated in the volume of the membrane of the RSDT-fabricated MEAs. The MEAs with an active area of 86 cm2 and low catalyst loadings (0.3 mgIr/cm2 in the anode and 0.2 mgPt/cm2 in the cathode) have been tested for over 5000 hrs, and it was found that the H2 crossover increased to about 20 % of the LFL after 2000 hrs of operation. In order to improve the durability of the RLs, a new design comprised from two RLs separated with thin (10 um) Nafion membrane has been fabricated by the RSDT, and the results from the stability test of 3000 hrs will be presented and discussed in detail at the 242th ECS meeting. https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf Klose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Roller, J., Maric, R., 24(8) December 2015 pp. 1529-1541 (2015).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).

Development of a model for the prediction of the ignition properties of combustible dusts undergoing homogeneous combustion: Application to sulfur dust

The determination of ignition properties such as the minimum explosible concentration (MEC) is critical for the control of the risks associated with handling combustible dust. This work describes a novel approach for the determination of the MEC of combustible dusts undergoing homogeneous combustion, using sulfur dust as a case study. The proposed model is developed based on the heat and mass transfer occurring when a sulfur dust particle in a control volume is exposed to a hot planar surface acting as an ignition source. The model includes radiative and convective heat transfer from the ignition source to the particle and predicts the dust particle’s fusion and vaporization. Ignition criteria of sulfur vapor accumulation in the control volume are based on the material’s lower flammability limit (LFL) and the comparison of accumulated energy in the control volume to the activation energy of the vapor-air combustion initiation reaction. The model also includes a correlation describing a time to ignition which accounts for necessary dynamic changes like the exposure time of the dust to the ignition source. The model is capable of predicting the influence of the dust particle diameter on the MEC of sulfur dust and was validated with experimental data.

Lower flammability limits of NH3/H2 mixtures under different initial temperatures and initial pressures

In this paper, the lower flammability limits (LFLs) of NH3/H2 mixtures under different initial pressures (50–250 kPa) and initial temperatures (20–100 °C) are experimentally and numerically investigated. The LFLs of ammonia and hydrogen are reduced by the increase of the initial temperature, and the reduction of ammonia LFL is greater than that of hydrogen. An increase in initial pressure decreases the LFL of ammonia but increases the LFL of hydrogen. The LFL of the NH3/H2 mixture is reduced by the increase of H2, which is consistent with Le Chatelier’s Law. When H2 reaches 10%, the LFL trend of the mixture with the initial temperature and initial pressure is similar to that of hydrogen. The LFL prediction models of NH3, H2 and NH3/H2 mixtures under different initial temperatures and initial pressures are established. The changes of OH radicals in elementary reactions are crucial to the effect of LFL. Except for H + O2 = O + OH and 2OH = O + H2O, the main OH ROP of NH3 is NO2 + H = NO + OH, NH2 + OH = NH + H2O and NH3 + OH = NH2 + H2O, while the main OH of H2 ROP is OH + H2 = H + H2O, which may be the reason why the LFLs of NH3 and H2 are different.