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Hydrogen energy stands at the forefront of low carbon energy development owing to its environmentally friendly attributes. The storage and transportation of hydrogen have emerged as pivotal components in constructing the hydrogen value chain. Although liquid hydrogen represents a primary method for storing and transporting hydrogen across remote areas, the liquefaction process entails significant energy conversion and harsh operating conditions. In addition, hydrogen is characterized by its wide flammability limit, low minimum ignition energy, and susceptibility to hydrogen embrittlement with metals, leading to high leakage probabilities. These factors raise safety concerns for hydrogen liquefaction. However, the system safety of the hydrogen liquefaction system remains a notable gap in hydrogen safety research. In this study, we apply system-theoretic process analysis (STPA) to identify system hazards and improve the STPA by integrating a best-worst method (BWM) to quantify the risk of hazards in the hydrogen liquefaction system. The STPA-BWM method effectively ranks identified hazards, showing that hydrogen leakage due to equipment damage is the most severe hazard in the hydrogen liquefaction system. This is followed by system pressures above normal due to leaks and rupture of equipment and pipelines. As a result, 14 control actions (CAs) and 24 unsafe control actions (UCAs) are identified. Possible causal factors for UCAs are analyzed, and corresponding low-level safety constraints are proposed. The qualitative and quantitative hazard assessment of hydrogen liquefaction systems can provide a basis for enhancing the safety and reliability of such systems. • Proposing an integrated STPA-BWM for risk analysis. • Assessing risks in hydrogen liquefaction system using the proposed methodology. • Developing a risk control strategy for hydrogen liquefaction system. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to study the detonation re-initiation through multiple reflections upon its entry into a confined space containing liquid fuel within a flow system, which holds significant implications for two-phase pulse detonation engines (PDE) and rotating detonation engines (RDE). Utilizing the Eulerian-Lagrangian method, this study investigates the disparities in the diffraction, quenching, and re-initiation processes of liquid n-heptane/air detonation upstream and downstream. Additionally, it explores the interaction between shock waves and droplets as well as determines the lean flammability limit for re-initiation within a flow system. The findings suggest that the incoming flow significantly contributes to the upstream decoupled detonation re-initiation, as it intensifies the leading shock, thereby expediting droplet fragmentation and evaporation. However, the compressive effect of the incoming flow is insufficient to initiate upstream detonation independently. To achieve re-initiation, it is still necessary for the detonation wave to be reflected by the wall. Moreover, the incoming flow expands the re-initiation boundaries, thereby facilitating the re-initiation of upstream detonation. As the equivalence ratio decreases, a higher inflow Mach number is required to achieve upstream re-initiation. • Upstream and downstream detonation re-initiation are compared. • Interaction between droplets and leading shock upstream and downstream are illustrated. • The detonation re-initiation boundaries beneath an incoming flow are found. [ABSTRACT FROM AUTHOR]

Date palm fiber (DPF) holds great potential for composite materials, but its flammability limits its practical applications. In this study, DPF was modified using a pad-drying method to impregnate it with a 5 wt.% solution of ammonium dihydrogen phosphate (ADP). These treated fibers were then utilized to fabricate poly(β-hydroxybutyrate)- (PHB-) based composites. The resulting thermal insulators were comprehensively evaluated for their flammability, physical, mechanical, and thermophysical properties, as well as morphological and thermal stability characteristics. The findings revealed a significant reduction in flame spread and smoke suppression; however, the concentration used is not sufficient to achieve the desired rating grades. The thermal insulation capacity of the modified fiber composites was substantially enhanced, particularly with the 40% PHB/DPF-ADP composite displaying the lowest thermal conductivity at 0.0564 W/m.K. Moreover, the presence of gaps and voids at the interface led to a reduction in tensile strength to 4-7 MPa. Additionally, the modified fiber composites exhibited significantly reduced water absorption (~0.76%), attributed to the formation of a highly water-resistant substance containing a furan compound. This work provides a simple and effective approach for achieving durable flame retardancy and long-term thermal insulation performance, offering promising opportunities for the practical application of biobased PHB composites. [ABSTRACT FROM AUTHOR]

Based on computational fluid dynamics technology, the effect of hydrogen blending ratio (HBR) on the concentration distribution of leaked gas diffusion in utility tunnels was investigated, and based on this, the explosion characteristics of hydrogen-blended natural gas (HBNG) were studied in an inhomogeneous concentration field. The results showed that the concentration field of HBNG gradually stabilized in the downstream of the leak site, and the peak concentration increased linearly with HBR. When HBR≤5%, a high concentration region above the upper explosive limit is formed inside the gas cloud. This characteristic of the distribution induces secondary combustion in utility tunnels. The maximum flame velocity and steady acceleration distance increase with the increase of HBR. The flame shape is significantly affected by the concentration field distribution. The explosion overpressure induced by the real concentration field created multiple peak structures that exacerbated the explosion disaster complexity. The first overpressure peak at the ends was formed by the superposition of the precursor shock wave and its reflected wave, and those at other locations are caused by the shock waves. However, all maximum overpressure peaks are formed by the superposition of multiple reflections of the explosion wave. The maximum peak overpressure at both ends of the tunnel is higher than that in the middle. The explosion overpressure induced by the inhomogeneous gas cloud is lower than that caused by homogeneous gas cloud under the same volume. The research results can provide an effective reference for the anti-explosion design and risk assessment of utility tunnel. • Characteristics of HBNG leakage and diffusion in utility tunnels were investigated. • Effects of hydrogen blending ratios on leakage and explosion were investigated. • Flame evolution process under real concentration field of HBNG leakage is revealed. • Distribution law of explosion overpressure loads in utility tunnels is revealed. [ABSTRACT FROM AUTHOR]

This study examines the influence of polyurethane porous materials and carbon dioxide on hydrogen/air explosions within an enclosed vessel. Through analysis of peak overpressure, maximum rate of pressure rise, and shock wave propagation velocity, the suppression effects on explosions in hydrogen-air mixtures with different equivalence ratios at room temperature and atmospheric pressure are investigated. Findings indicate that porous materials with a PPI (pores per inch) of 60 significantly mitigate hydrogen/air explosions across all equivalence ratios. Conversely, a PPI below 60 exacerbates the explosions. Simultaneous presentation of PPI60 porous material and a CO 2 addition level of x = 2 (carbon dioxide to oxygen ratio) reduces hydrogen explosion pressure to only 13.7 kPa at "Φ = " 1.2, representing an attenuation rate of 84% and falling well below the human safety threshold of 28 kPa. Independent effects of carbon dioxide and porous materials on hydrogen explosions across various equivalence ratios are also explored. The experimental design encompasses a broad range of equivalence ratios, covering hydrogen's explosive limits. These results contribute to the design of flame arrestors and enhance understanding of explosion suppression in hydrogen systems. • Aterials ≥60 PPI prevent hydrogen explosions; ≤50 PPI promotes explosions. • Higher CO 2 levels enhance hydrogen explosion inhibition. • Further suppression of hydrogen explosions is achieved when they act together. • Compared to porous materials, CO 2 more effectively inhibits pressure rise. • Porous materials more effectively inhibit overpressure compared to CO 2. [ABSTRACT FROM AUTHOR]

To investigate the suppression effect of fluorine-containing explosion suppressants (FESs) on methane (CH4) explosions and the corresponding suppression mechanism, a 20-L spherical explosion testing device was used to analyze and compare the effects of perfluorohexanone (C6F12O) and heptafluoropropane (C3F7H) on CH4 explosion parameters. The explosion limit and pressure were obtained before and after adding these FESs. CH4 explosion triangles under the action of the FESs were drawn, and the explosion hazard degree (F) was determined. The results reveal that the addition of C6F12O and C3F7H reduces the upper explosion limit (UEL) and lower explosion limit (LEL) of CH4, with increased concentrations of C6F12O and C3F7H causing faster decreases in the UEL than in the LEL. The explosion limit range of CH4 with C6F12O is smaller than that with C3F7H. When the concentration of CH4 is low, increases in the C6F12O and C3F7H concentrations first cause an increase and then a decrease in the explosion pressure, and the rise rate of explosion pressure increases. After adding the aforementioned FESs, F first increases and then decreases. When the concentration of CH4 is high, the two FESs only inhibit the explosion pressure. Compared with C3F7H, C6F12O has a stronger inhibitory effect; C6F12O has a smaller CH4 explosion triangle area, higher critical oxygen concentration (18.27% vs. 17.70%), and lower F value. Both FESs have promotion and inhibition effects on CH4 explosion because of the comprehensive physical and chemical effects on CH4 explosions; however, the performance of C6F12O is superior to C3F7H. [ABSTRACT FROM AUTHOR]

During the process of coal spontaneous combustion (CSC), a plethora of combustible gases alongside inert gases, such as CO2, are copiously generated. However, prior investigations have regrettably overlooked the pivotal influence of inert gas production on the propensity for methane explosions during CSC. To investigate the impact of the flue gas environment generated by CSC, containing both combustible and inert gases, on the risk of methane explosion, a high-temperature programmed heating test system for CSC was employed to analyze the generation pattern of flue gas. It was found that CO, CO2, and CH4 were continuously generated in large quantities during the process of CSC, which are the main components of CSC flue gas. The effect of the concentration and component ratio (CCO2/CCO) of the flue gas on the methane explosion limit was tested. It was found that the CSC flue gas led to a decrease in the methane explosion limit, and that the explosion limit range was facilitated at 0 < CCO2/CCO < 0.543 and suppressed at CCO2/CCO > 0.543. As the temperature of CSC increases, the risk of methane explosion is initially suppressed. When the coal temperature exceeds 330~410 °C, the explosion risk rapidly expands. [ABSTRACT FROM AUTHOR]

This study examines air quality conditions in and around a classroom located in the Sarıçam/Adana region of Türkiye, near the campus of Adana Alparslan Türkeş Science and Technology University and the Sofulu municipal solid waste (MSW) facility. This academic setting was strategically chosen due to its proximity to the waste facility. The study aims to provide a comprehensive view of the environmental and social impacts of solid waste management through a methodological approach that combines quantitative on-site measurements and qualitative survey studies. Findings from measurements and surveys underline the significant and measurable impacts of MSW facilities on the ambient air quality of university residents. The analysis revealed a marked increase in concentrations of key pollutants, including carbon monoxide (CO), hydrogen sulfide (H2S), dust, and methane (CH4). At sampling point N1, H2S levels rose from 0 ppm in July to 13 ppm in November. Methane increased from 0.2% to 2.5% of the Lower Explosive Limit (LEL) at the same point, although it remained within safety limits. Additionally, CO levels showed a 40% increase, and dust concentration levels rose from 0.21 mg/m3 to 2.36 mg/m3 from summer to winter, indicating a seasonal variation likely influenced by the landfill's operational dynamics, as well as changes in temperature and relative humidity. In particular, the results indicate high concentrations of CO, H2S and dust, which are directly related to air quality degradation. The study also sheds light on the impacts of these waste disposal facilities on the general well-being and health of the university community, particularly on students and staff. In addition to these findings, the study highlights a general lack of awareness in the university community about the impacts of MSW facilities on air quality. This highlights the need for increased education and information dissemination. The results support the development of comprehensive and effective strategies, including technical solutions and public awareness initiatives, to mitigate the impacts of these facilities on residential areas. In conclusion, the impacts of MSW facilities on air quality should be seen as a multidimensional issue that requires a holistic approach addressing environmental, health, social, and educational dimensions. [ABSTRACT FROM AUTHOR]

Unlike the explosion limit of liquid fuel vapour, the explosion limit of aerosol is a function of the aerosol state. In this study, a prediction model of the lower explosion limit (LEL) of liquid fuel aerosol was established through theoretical analysis, and typical liquid fuels of n-heptane and n-hexane were used to observe the aerosol state and the lower explosion concentration limits in the experiments to verify the reliability of the established model for predicting the LEL of aerosol. The predicted LELs of the two n-heptane aerosols (D32 = 12.16 µm) and (D32 = 21.23 µm) are 3.59 and 3.62 times of that of n-heptane vapour, respectively. The relative errors for the predictive results are 5.4% and 8.8%, respectively, compared with the experimental results. The predicted LEL of n-hexane aerosol (D32 = 18.51 µm) is 3.5 times that of n-hexane vapour, and the relative error is 3.99% compared with the experimental results. [ABSTRACT FROM AUTHOR]

• The flammability limits of R13I1 + R152a/R600a/R1270 binary mixtures were measured. • The critical flammable volumetric ratios of R13I1 + R152a/R600a/R1270 were obtained. • A generalized equation for the LFL of R13I1 mixtures was provided. • F -number and HOC were calculated and the inhibitory effects of R13I1 were analyzed. Trifluoroiodomethane (R13I1) is a flame retardant with an extremely low global warming potential (GWP) and can be used as a component to improve the flammable characteristics of most promising low-GWP refrigerants. In this paper, the flammability limits of R13I1 + 1,1-Difluoroethane (R152a), R13I1 + isobutane (R600a) and R13I1 + propylene (R1270) binary mixtures were measured at 60 °C and atmospheric pressure with a 12 L flask according to ASHRAE standards. The critical suppression ratios of R13I1 + R152a, R13I1 + R600a and R13I1 + R1270 are 0.45, 2.24 and 0.99, respectively. A generalized equation for the lower flammability limit (LFL) of R13I1 mixtures was provided. With the LFL of the fuel gas in air and the ratio of R13I1 to the fuel gas, the developed generalized equation can calculated the LFL of R13I1 mixtures with a reasonable accuracy. The influence of R13I1 on the flammability of R152a, R600a and R1270 were studied. The LFL increases and heat of combustion (HOC) decreases significantly with the increase of the R13I1 concentration. The flammability inhibition effects of R13I1 decrease in the order: R152a > R1270 > R600a. [ABSTRACT FROM AUTHOR]

• Accurate semi-empirical model for variable speed multi-chiller systems. • Determination of the optimum number of operating chiller units, and their compressor speed. • Energy efficiency as a function of compressor speed and cooling water temperature. • Comparison of energy savings for different operation strategies. Environmental protection drives the replacement of environmentally harmful refrigerants with potentially flammable alternatives, necessitating efficient cooling strategies for varying loads. Legislation limits flammable refrigerant charge, leading to the adoption of multi-chiller systems with smaller charges and therefore also smaller loads per chiller. However, operating such systems requires complex strategies, addressable through fast and reliable models. This study presents a semi-empirical model predicting the behaviour of variable-speed multi-chiller systems. The model focuses on predicting cooling capacity and coefficient of performance (COP) for cooling, with input parameters of evaporation and condensation temperatures, and compressor speed. Experimental validation of the parameterized model shows COP predictions within 3 % for a two-module system using R-290 (propane) under different conditions and compressor speeds. The model assesses various operation strategies, including the conventional mode with fewer chiller modules running at high speed, compared to modes where all chillers run but at reduced speeds. Comparing COP values in these modes reveals energy-saving potentials of up to 14.57 % for constant condensation temperatures. Moreover, strategies involving condensation temperature reduction, or a combination with compressor speed reduction are analysed for energy-saving potentials. Reducing the condensation temperature by 3 K results in savings of up to 13.25 % and combined with the compressor speed reduction savings of up to 23.54 % are feasible. These findings emphasize the importance of considering compressor speed when operating multi-chiller systems to maximize energy savings. The presented model effectively evaluates various strategies and implements variable-load control in multi-chiller systems, serving as a valuable tool for optimising energy efficiency and promoting environmentally friendly cooling practices. [ABSTRACT FROM AUTHOR]

The hydrogen tube skid container is designed to protect the hydrogen gas cylinder group from insolation, rain, and other environmental factors. However, in the event of a leakage accident, the container becomes a confined space. Therefore, it is essential to assess the risks associated with high-pressure hydrogen leakage in this confined space and determine the effectiveness of various risk mitigation methods under conditions of natural ventilation and forced ventilation, taking into consideration factors such as inlet velocity and vent position. The results showed forced ventilation was more effective than natural ventilation in reducing potential risks associated with hydrogen leakage. Furthermore, the magnitude of inlet velocity and the positioning of the vent were found to play crucial roles in reducing hydrogen concentration within the confined space. The vents on the horizontally symmetrical top (R–UP cases) were the most effective for ventilation. With the inlet air velocity set to 15 m/s, forced ventilation could reduce the average hydrogen molar fraction to the theoretical lower flammability limit (LFL) in approximately 17 s. [Display omitted] • The inlet air velocity and vent positions affect the discharge capability of leaked hydrogen. • Multi-perspective analysis of the distribution of leaked hydrogen at different time periods. • Placing vents on both sides at the top proves to be the most effective ventilation method. [ABSTRACT FROM AUTHOR]

This work presents a state-of-the-art review of micro-combustion flame dynamics and micro propulsion systems. In the initial section, we focus in on the different challenges of micro-combustion, investigating the typical length and time scales involved in micro-combustion and some critical phenomena such as flammability limits and the quenching diameter.We present an extensive collection of studies on the principal types of micro-flame dynamics, including flashback, blow-off, steady versus non-steady flames, mild combustion, stable flames, flames with repetitive extinction, and ignition and pulsatory flame burst. In the final part of this review, we focus on micropropulsion systems, their performance metrics, conventional manufacturing methods, and the advancements in Micro-Electro-Mechanical Systems manufacturing. [ABSTRACT FROM AUTHOR]

Currently, mixing hydrogen into natural gas networks is the most cost-effective method for transporting significant quantities of hydrogen over long distances. However, after mixing natural gas with hydrogen, the properties of the mixed gas will change significantly, manifested as faster diffusion rate, increased combustion rate, and wider flammability limit. In this paper, a CFD numerical simulation method is used to establish a numerical model for the leakage and diffusion of buried hydrogen-blended natural gas (HBNG) pipelines, and the concentration diffusion trend and velocity flow field distribution of HBNG in soil under different leakage conditions are studied, as well as the alarm time when HBNG diffusion reaches the lower flammability limit (LFL) at the ground surface. At the same time, the effects of hydrogen blending ratio (HBR), pipeline operating pressure, soil porosity and leakage diameter on HBNG leakage and diffusion are investigated. The simulation results indicate that increasing the HBR will increase the diffusion rate of the mixed gas and reduce the LFL, resulting in a decrease of the alarm time. The increase of pipeline operating pressure and leakage diameter will increase the mass flow rate, and the increase of soil porosity will reduce the resistance when HBNG spreads in the soil. All three cases will significantly reduce the alarm time. The results of this study will provide some references for the emergency response work of buried pipeline leakage and the risk assessment of HBNG leakage and explosion. • A numerical model of leakage and diffusion in a buried hydrogen-blended natural gas pipeline is established. • The concentration diffusion trend of hydrogen-blended natural gas in soil under different leakage conditions are studied. • The effects of hydrogen blending ratio, pipeline operating pressure, soil porosity and leakage hole diameter on HBNG leakage and diffusion are investigated. [ABSTRACT FROM AUTHOR]

The application of hydrogen for fuel enrichment and blending has recently gained importance. The sustainability and performance enhancement through hydrogen addition in flameless combustion mode for liquid fuels needs further investigation to enhance our understanding. Therefore, the present study reports the effect of hydrogen addition on the flameless combustion of a kerosene-fired 30 kW swirl combustor with hydrogen addition. A divergence-shaped conical combustor with tangential air injection and asymmetric fuel injection scheme is adopted. The liquid fuel was injected using a solid-cone swirl nozzle with 34 μm Sauter Mean Diameter. The hydrogen addition was varied from 0 to 20% on a thermal input basis, and the thermal input of liquid fuel was maintained at a 30 kW level. Computational studies helped understand the flow physics behavior within the combustor volume. The hydrogen addition was observed to improve the reactant dilution ratio (R dil). The maximum values of the R dil increased from 4.47 to 5.44 with hydrogen addition. Hydrogen addition further helped extend the flameless combustion regime to φ = 0.3 without any air preheating. A uniformly distributed reaction with a reduced-temperature gradient is observed with extended combustion stability limits. A marginal increase in NO x emissions was observed with hydrogen addition, albeit within permissible limits, accompanied by ∼8–20 dB reduction in acoustic emissions. [Display omitted] • Effect of H 2 addition in flameless combustion is studied with kerosene. • H 2 in flameless combustion, enhancing sustainability via wider flammability limits. • H 2 improves temperature uniformity, minimizing temperature gradients. • H 2 addition reduced the CO emissions. [ABSTRACT FROM AUTHOR]

Hydrogen generated in severe accidental conditions poses a threat to nuclear containment once it exceeds the flammability limit in the air. A passive Autocatalytic Recombiner (PAR) device is one of the best options to tackle this scenario. In view of this, we have developed a novel breed of bimetallic Pt–Pd nano-catalysts supported over cordierite by a chemical reduction route. Pt–Pd particles with dimensions ∼4.5–11.5 nm were found to be in a metallic state and amorphous in nature. They were assessed for H 2 and O 2 recombination reactions and found to be catalytically active for the same. Their activity was also established in the presence of various probable contaminants viz. CO, CO 2 , CH 4 , relative humidity, and catalyst wetness. • Pt + Pd bimetallic catalyst was developed for hydrogen mitigation under severe accident conditions. • Ceramic support was used for enhanced properties of the catalyst. • Catalyst exhibits unaltered catalytic activity in presence of various poisons. • Catalyst retains its activity in presence of CO for wider range of concentrations. • Activation energy calculated and compared to earlier reported catalyst. [ABSTRACT FROM AUTHOR]

With the rapid development of the world's natural gas industry, LNG (Liquefied Natural Gas) has received widespread attention as a clean energy source. However, the leakage accidents of LNG are usually accompanied by safety hazards such as explosions, low temperatures, and phase transitions. In this study, the field experiment is carried out to cover LNG leakage pool with HEF (High-Expansion Foam). In the process of LNG leakage, when the ambient temperature at the bottom of the reservoir drops to about − 82.3 °C (the critical temperature of LNG), the ambient temperature would rise briefly due to the effect of phase transition. Meanwhile, the temperature distribution of different vertical and horizontal positions in the reservoir during the process of leakage is analyzed. Besides, it is also found that the density of the spilled vapor is much lower than that of the air, but the water in the surrounding air encounters the cryogenic vapor to condense into small droplets, the small droplets entrap part of the flammable gas during the process of settling to the ground, therefore, the flammable vapor still shows a heavy gas effect. During the initial period of HEF coverage, evaporation from the liquid pools accelerates, resulting in a 386% increase in peak concentration of methane above the reservoir. Nevertheless, when HEF application is maintained an effective thickness, it can effectively reduce the methane vapor concentration downstream of the reservoir near the surface to less than 1/2 LFL (1/2 of the Lower Flammability Limit). In general, the large-scale field experiments have far-reaching engineering significance and reference value for the occurrence and emergency treatment of LNG leakage accidents under actual working conditions. [ABSTRACT FROM AUTHOR]

• Flammability limits of azeotropic mixtures consist of R1243zf are tested for the first time. • A brief mechanism for flame-retardant effect of R13I1, R227ea and R134a is analyzed. • CSCs of R1243zf mixtures are tested and compared with calculation results by 3 methods. 3,3,3-trifluoropropene (R1243zf) is a low climate change effect refrigerant that has great development potential. However, R1243zf is flammable and its safety classification is A2 as per ISO standard 817. To reduce its risk of flammability, the method of using mixed refrigerants in practical applications is an effective approach. In this paper, an experimental system was established according to the ASHRAE standard 34 to measure the flammability limits of four azeotropic mixtures containing R1243zf. First, the critical suppression ratio (CSR) of R13I1/R1243zf was tested out that is 0.353. Further measurements were made to determine the lower flammability limits (LFLs) and critical suppression concentrations (CSCs) of three ternary mixtures consisted of R1243zf, thermodynamic performance enhancer (RE170) and flame retardants (R13I1, R134a or R227ea), at various compositions. The experimental non-flammable proportions of R1243zf/RE170/R13I1, R1243zf/RE170/R134a, and R1243zf/RE170/R227ea were 31.81 %, 5.49 %, and 22.42 %, respectively. Besides, a comparison was made between the experimental data and the predicted results by means of three different theoretical methods (the equal effect method, thermal balance method, and group contribution method). The fresh experimental results will provide practical guidance for the applications that utilize the R1243zf blends in low flammability risk. [ABSTRACT FROM AUTHOR]

Excessive hydrofluorocarbons (HFCs) usage significantly contributes to the global warming. Therefore, there is a widespread shift toward natural refrigerants with low global warming potential (GWP). Among these alternative refrigerants, R290, R600a, and their mixtures have gained considerable attention. However, their flammability limits the charge. To decrease the equipment volume and reduce the refrigerant charge, internally threaded tubes have been introduced to enhance the heat transfer. Therefore, in this study, flow boiling experiments were conducted on R290, R600a, and mixtures inside an internally threaded tube, obtaining heat transfer data under a pressure of 0.216–0.416 MPa, heat flux of 10.5–73.0 kW m−2, mass flux of 70–190 kg m−2 s−1. To quantitatively discern the dominant heat transfer mechanism, a dimensionless number Nz was introduced. In the nucleate boiling dominant region, an increase in the heat flux markedly enhances the heat transfer, with pressure and mass flux playing minor roles. Furthermore, the heat transfer deterioration trend of the mixtures aligns with the variation trends of concentration slip and boiling range. In the convective heat transfer dominant region, a rise in the mass flux significantly increases the heat transfer coefficient, while the pressure and heat flux have minor effects. Additionally, at high R290 mole fraction and vapor quality, high surface tension maintains a continuous liquid film, enhancing the heat transfer. Furthermore, new heat transfer correlations for flow boiling inside the internally threaded tubes were established, which exhibit a mean relative deviation of −2.30 % and 8.80 % for the obtained experimental results and collected data, respectively. [ABSTRACT FROM AUTHOR]

As fossil fuels currently account for approximately 85 % of the world's energy demands, the rapid growth of the global population and the economy is projected to increase greenhouse gas emissions. Consequently, there is a growing interest in the concept of ultra-lean combustion. This advanced combustion technology has the potential to effectively reduce both fuel consumption and emissions, offering a more environmentally sustainable approach. This comprehensive review delves into hydrogen ultra-lean combustion, specifically exploring the flame ball phenomenon by specifically investigating computational solutions in uniform and non-uniform mixtures. Noteworthy is the attention given to the emergence of stable flame balls within quiescent premixtures, especially in microgravity conditions. The review elucidates how these flame balls achieve stability through thermal radiation loss. A thorough examination of the role of the Lewis number (Le) in flame instability is conducted, considering its integral connection with diffusive-thermal instability across various experimental setups. Beyond the theoretical aspects, this review encompasses the practical domain of stable spherical flames originating from ultra-lean premixed reactants based on hydrogen. The exploration extends to comprehending the intricate mechanisms governing lean flammability limits, particularly the interplay between low-speed counterflow premixed flames and flame balls. It sheds light on how the concept of flame balls contributes to a more profound understanding of emission characteristics in ultra-lean combustion. Lastly, the review provides valuable insights into potential avenues for further research. It outlines the challenges that lie ahead, which encapsulates experimental observations and in-depth investigations into flame balls and the propagation of hydrogen ultra-lean flames. • Focusing on the phenomenon and characteristics of hydrogen in ultra-lean combustions. • Exploration of the stability mechanisms of ultra-lean combustion flame ball. • Elucidating the role of the Lewis number in flame instability and emission characteristics. • Emphasizing the further investigations into hydrogen based ultra-lean flame propagation. [ABSTRACT FROM AUTHOR]

The combustion of rich mixtures of methanol and hydrogen with air has been studied by experimental and numerical methods. It has been shown that the deviation from Le Chatelier's principle for the rich flammability limits is due to two factors: flame inhibition by methanol in rich mixtures of hydrogen and the presence of superadiabatic temperatures in rich mixtures of methanol. It has been found that the effect of adding small amounts of hydrogen to rich methanol mixtures is the same as the effect of adding inert nitrogen and carbon dioxide. Numerical simulation has shown that the addition of small amounts of hydrogen to rich methanol mixtures has only a physical effect on the normal flame speed. The addition of H2 affects the occurrence of superadiabatic temperatures in methanol flames in the same way as the addition of inert CO2 and N2. [ABSTRACT FROM AUTHOR]

Induction and reaction times of hydrogen–air mixtures (ϕ = 0.5–2) have been measured behind reflected shock waves at temperatures of 1000–1600 K, pressures of 0.1, 0.3, 0.6 MPa in the domain of the extended second explosion limit. The measurements were performed in the shock tube with a completely transparent test section of 0.5 m long, which provides pressure, ion current, OH and high-speed chemiluminescence observations. The experimental induction time plots demonstrate a clear increasing of the global activation energy from high- to low temperature post-shock conditions. This trend is strongly pronounced at higher post-shock pressures. For a high-temperature range of T > 1200 K, induction time measurements show an activation energy for the global reaction rate of hydrogen oxidation of 64–83 kJ/mole. Detected reaction times exhibit a big scatter and a weak temperature dependence. The minimum reaction time value was nearly 2 µs. Obtained induction time data were compared with calculations carried out in accordance with the known kinetic mechanisms. For current and former shock-tube experiments within a pressure range of 0.1–2 MPa, critical temperatures required for strong (1000–1100 K), transient and weak auto-ignition modes behind reflected shock waves were identified by means of the pressure and ion-probe measurements in stoichiometric hydrogen-air mixture. The transfer from the strong volumetric self-ignition near the reflecting wall to the hot spot ignition (transient) was established and visualized below <1200 K with a post-shock temperature decreasing. [ABSTRACT FROM AUTHOR]

The diffusion of oil vapor after oil spill from tank caused serious consequences. It is studied by combining wind tunnel experiment and numerical simulation. Results show that the higher the fire dike, the more oil vapor accumulates at the inner corner of fire dike; the explosion limit area is the largest when the oil spills in front of single tank on the windward side; concentration of multi-spills will superimpose to induce the presenting of multi-explosion limit areas. It can provide a reference for the research and development of the oil vapor traceability system and prevent explosion accidents in oil depots. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of the hydrogen-enrichment strategy on a Wankel engine for unmanned aerial vehicles (UAVs). The primary motivation behind this study is to contribute to the Wankel-type rotary engine designs by revealing the influences of the hydrogen enrichment method on the Wankel engine performance at various altitudes. To achieve these objectives, CFD simulations were conducted by applying a hydrogen enrichment method to a neat gasoline Wankel engine model at sea level, 5000 ft and 15,000 ft altitudes. The hydrogen energy fraction at the intake was gradually increased from 0% to 10%. The decrease in ambient air temperature, pressure, density, and insufficient fresh charge with the increase in altitude leads to the reduced reference chamber temperature and pressure of the Wankel engine. Thus, the combustion worsens, the heat release rate (HRR) and performance decrease, also emissions deteriorate in these colder operating conditions. On the other hand, the unique physicochemical properties of hydrogen such as wide flammability limits, high homogeneity, relatively small quenching distance and high flame speed allow hydrogen-enriched mixture flames to propagate toward the narrower gaps in the combustion chamber and make up for some drawbacks of Wankel engines. As a result, flame propagation is accelerated and fuel burning rate, peak pressure and temperature values in the reference chamber are increased by hydrogen addition. For the cases at sea level with 5% and 10% hydrogen energy fraction, IMEP is increased by 6.59%, 8.50%, and the indicated power is increased by 35.51% and 52.47%. In the cases with the same energy fraction at 15,000 ft, IMEP is increased by 26.61% and 48.75%, and the indicated power is reduced by 26.61% and 48.75%, respectively. It has been proven that a small amount of hydrogen by energy fraction improves combustion efficiency and performance. The findings show that hydrogen has excellent compatibility with Wankel engines and hydrogen enrichment is a very practical concept for the improvement of the performance of these engines for UAVs. Thus, Wankel engines, which are already a very favorable power source for UAVs, become even more favorable by the hydrogen-blending strategy. • A hydrogen-enriched Wankel engine for UAVs was simulated at various altitudes. • The effectiveness of the hydrogen-enrichment on a Wankel engine was investigated. • Performance parameters reduce with altitude yet enhance with hydrogen addition. • Despite emissions worsening with altitude, they improve with hydrogen addition. [ABSTRACT FROM AUTHOR]

Research on the lower explosion limit (LFL) of H 2 /C 2 H 5 OH mixture at elevated pressures and temperatures is essential for the safe production of ethanol to hydrogen process. However, the research on the LFL of mixture at high pressures and temperatures is not sufficient, and no effective model has been established. In this work, the influences of pressure, concentrations and temperature on the LFL of H 2 /C 2 H 5 OH mixture had been investigated experimentally and numerically. The experimental results show that, the content of H 2 in the H 2 /C 2 H 5 OH mixture system is positively correlated with LFL, and initial pressure is more sensitive parameter than initial temperature under this mixture conditions. Computational simulation demonstrates that the difference in sensitivity coefficients is closely related to reaction pathway, representing the sensitivity of elementary reactions. The change in hydrogen concentration will alter the reaction pathway, leading to the sensitivity coefficient transforms in the opposite direction. Moreover, the applicability of Le Chatelier's rule and Bartknecht's prediction model to the LFL of H 2 /C 2 H 5 OH mixture was discussed. And the crucial radical groups affecting the LFL of H 2 /C 2 H 5 OH mixture at elevated pressures and temperatures conditions have also been deeply studied. Finally, an LFL prediction model is established based on the crucial radical by machine learning, enabling a useful experimental and theoretical reference for safety production under related conditions. • A new model based on chemical kinetics has been proposed. • The connection between free radicals and LFL was constructed by machine learning. • A new research perspective was provided to predict the LFL of mixtures under different initial temperatures and pressures. • The H, O, OH, HO 2 and H 2 O 2 radicals have a strong linear relationship with the LFL of the H 2 /C 2 H 5 OH mixture. [ABSTRACT FROM AUTHOR]

Recently, ammonia is getting more attractive as a potential alternative fuel for future power generation and transportation purposes due to its ability to reduce consumption of fossil fuels, soot, CO 2 emissions, and hydrocarbon pollutants. In the recent past, several studies aimed to the development of ammonia combustion systems have been conducted. However, ammonia combustion systems face several challenges, such as poor ignition timings, lower burning velocity, low energy density, shorter flammability limits than hydrocarbons. These issues are compounded by the significant increase in NOx emissions, which makes practical application of ammonia challenging. Various conventional methods, such as blending ammonia with other hydrocarbons and hydrogen, have been employed to improve combustion performance and reduce NO x emission. Meanwhile, it increased the engine complexities and at the same time, it raised CO 2 and NO x emissions. Recently, plasma-assisted combustion (PAC) has emerged as a promising technology to boost the ammonia combustion process by improving ignition delay timings, increasing flame speed, extending flammability limits, and reducing NO x emissions. In recent years, plasma-assisted combustion (PAC) has emerged as a promising technology to enhance the ammonia combustion process by improving ignition delay timings, increasing flame speed, extending flammability limits, and reducing NOx emissions. Nevertheless, only a few studies on plasma-assisted ammonia combustion (PAAC) are available in the literature. This review paper aims to summarize the latest advancements in the field of PAAC during the last years, including progress in the development of numerical models and experimental studies. The paper highlights the detailed procedure of PAAC numerical modeling and the limitations of numerical models. Finally, the latest numerical and experimental developments of PAAC have been discussed. • Ammonia is getting more attraction as an alternative fuel for future power and transportation sectors. • A comprehensive outlook of non-thermal plasma for ammonia combustion is provided. • The in-depth mechanisms of plasma assisted combustion are highlighted. • The latest numerical and experimental studies of Plasma assisted combustion were analyzed. [ABSTRACT FROM AUTHOR]

Methane gas concentration detection faces the challenges of increasing accuracy and sensitivity, as well as high reliability in harsh environments. The special design of the optical path structure of the sensitive element provides an opportunity to improve methane gas concentration detection. In this study, the optical path structure of the sensitive element was newly designed based on the Pyramidal beam splitter matrix. The infrared light source was modulated by multi-frequency point-signal superimposed modulation technology. At the same time, concentration detection results and confidence levels were calculated using the four-channel methane gas concentration detection algorithm based on spectral refinement. Through the experiment, it was found that the sensor enables the full-range measurement of CH4; at the lower explosive limit (LEL, CH4 LEL of 5%), the reliability level is 0.01 parts-per-million (PPM), and the limit of detection is 0.5 ppm. The sensor is still capable of achieving PPM-level detections under extreme conditions in which the sensor's optical window is covered by two-thirds and humidity is 85% or dust concentration is 100 mg/m3. Those improve the sensitivity, robustness, reliability, and accuracy of the sensor. [ABSTRACT FROM AUTHOR]

As modern aeroengine combustors advance towards high temperatures, afterburners are inevitably affected by diminished oxygen content in incoming flows, thus affecting combustion efficiency, instability, and flammability limits. In this study, the dynamic combustion characteristics of V-shaped bluff body-stabilised diffusion flames were investigated using a large eddy simulation method with an oxygen mass fraction range of 14–23% and temperatures ranging from 900 to 1100 K. The results show the significant effects of oxygen content and inflow temperature on the flame/flow behaviours downstream of the bluff-body flame holder. In a separated shear layer, two distinct modes of flow/flame shedding are observed when varying the oxygen content and inflow temperature. The results show that BVK instability governs the far-field wake flow/flame features, whereas the oxygen concentration and temperature significantly affect their oscillation amplitudes. In addition, variations in the incoming oxygen content and temperature shift the axial position of the transition from KH instability to BVK instability. Finally, a spectral analysis is conducted to investigate the characteristics of pressure and heat release pulsations under different scenarios. This study highlights the importance of oxygen content on the combustion dynamics of bluff body-stabilised diffusion flames at various temperatures, which is essential for optimising combustion efficiency and stability in practical applications. [ABSTRACT FROM AUTHOR]

In the pursue of a carbon-free economy, the utilization of fuels with low or zero carbon footprint account for only 1% of global final energy demand, a share that is predicted to follow a dramatic growth to 20% by 2050. Ammonia (NH 3) has become dominant in the international transportation and storage of low-carbon alternative fuels. NH 3 is regarded as an alternative fuel, as a carbon-free fuel, and renewable hydrogen (H 2) carrier with high energy density, and its production and distribution infrastructure are well established. However, a current challenge is that NH 3 has a lower burning velocity and a narrow flammability limit. Thus, the use of NH 3 has numerous limitations in practical combustion applications. Blending NH 3 with H 2 is considered a solution that has been proposed to enhance NH 3 combustion by improving ignition, flammability, and H 2 safety issue. Using NH 3 blended with H 2 as a fuel in combustion systems is a practical approach to decarbonizing the energy sector. Thus, this review highlights the existing influential studies and ongoing research on NH 3 /H 2 blended fuels. The review covers NH 3 assists the safety behaviour of H 2 use, in-situ NH 3 dissociation, NH 3 and H 2 properties, NH 3 /H 2 combustion characterization, techniques for low NO x NH 3 /H 2 combustion, and challenges for NH 3 /H 2 combustion. Finally, recommendations for future studies are provided for further developing the utilization of NH 3 /H 2 as blended fuel. • Ammonia/hydrogen blends as carbon-free fuels have been reviewed. • H 2 is an ideal promoter for improving NH 3 combustion. • Effects of NO x formation and Low- NO x strategies are discussed. • Combining two-stage combustion and humidified operation could achieve greater NO reduction. • Challenges of NH 3 /H 2 combustion have been discussed. [ABSTRACT FROM AUTHOR]

The number of mines using roof cutting and pressure relief technology to extract mine deep coal resources is increasing daily. Most of these mines are facing the risk of high gas emission and residual coal spontaneous combustion disasters, and the composite disasters caused by these two risks also threaten the safety of mine production. On the basis of constructing a model for the evolution of porosity and permeability in a single side roof cutting along the gob, this study studied the occurrence locations of gas explosion risk areas, oxidation and heating risk areas, and composite disaster areas under different air supply and gas emission conditions, and summarized the evolution laws of composite disaster risk areas. The research results show that the roof rock collapse caused by roof cutting and pressure relief technology reduces the permeability of porous medium, which significantly reduces the sensitivity of the width of the oxidation temperature rise zone and the composite disaster area to the air supply. The increase in air supply causes the position of the composite disaster risk zone inside the goaf to shift toward the deep part of the goaf, while the width remains basically unchanged. The increase in gas emissions has suppressed the occurrence of coal spontaneous combustion in the goaf, while also keeping the gas concentration in a large area outside the upper limit of gas explosion. The research content enriches the research system of gas and oxygen flow fields in the goaf cutting face, and has positive significance for the promotion and application of goaf cutting technology and the understanding of secondary disasters caused by it. [ABSTRACT FROM AUTHOR]

Methane (CH4) is a widely used gas for the domestic and industrial application, which makes it a prominent fuel for us in daily life. The lower explosive limit of CH4 is 4.9% which makes this gas dangerous. Working with this gas without knowing its concentration in any confined space is much dangerous, so its sensing and monitoring is necessary. Mostly, n-type materials such as ZnO and SnO2 are frequently reported for CH4 sensing. In this work, we have synthesized p-type nanostructures, i.e., CuO using co-precipitation method. Synthesized CuO nanostructures were characterized through the XRD, Raman scattering, FESEM, EDX, and KEITHLEY semiconductor characterization system. Synthesized nano-powder was compressed as a pallet, and silver conductive paste was pasted on each pallet for electrical measurement. In this work, we have developed a highly responsive and energy-efficient p-type sensor, and sensing capability of this sensor, i.e., CuO toward methane gas, was investigated at different operating temperatures, i.e., 250, 300, and 350 °C. Sensitivity (%) at different working temperatures was 34, 38, and 42%, respectively. Maximum sensitivity (%) was evaluated at 350 °C and was found 42%. CuO sensor worked in the temperature range of 250–350 °C. Beyond this temperature limit, again a decrease in response was noted. These results demonstrated the potential of CuO nanostructures for fabricating low-cost, energy-efficient, and high-performance methane gas sensor. [ABSTRACT FROM AUTHOR]

• The flammability limits of R134a/R1270, R134a/R170 and R170/R1270 were measured. • R134a demonstrates a significant flame-retardant effect at volume ratios above 0.75. • The flame color and propagation speed of refrigerants were compared and analyzed. Hydrocarbons (HCs) are considered promising alternative refrigerants due to their excellent thermodynamics, transport properties, and environmental friendliness. However, hydrocarbons are flammable. Conversely, R134a is a widely used non-flammable refrigerant but was listed in the Montreal Protocol-Kigali Amendment due to its relatively high global warming potential (GWP). Therefore, in order to reduce the GWP of R134a and inhibit the flammability of hydrocarbon refrigerants, this study investigated the flammability characteristics of mixed refrigerants R134a/R1270, R134a/R170, and R170/R1270. The flammability limits of different concentrations of R170/R1270, R134a/R1270, and R134a/R170 were measured under standard conditions, and the inhibition mechanism of R134a was briefly analyzed. Additionally, the flammability limits of R170/R1270, R134a/R1270, and R134a/R170 were predicted using the polynomial fitting method. Subsequently, the flame propagation speed and the flame color of R1270 and R170, with and without R134a, were compared and analyzed. Furthermore, the cycle performance of R134a/HCs was calculated. The research results are expected to provide guidance for the safe and effective utilization of R1270, R170, and their mixtures in refrigeration systems. [ABSTRACT FROM AUTHOR]

CILRT is an important work in the overhaul of nuclear power plants. VOCs from paints and cleaners used in the containment during the overhaul will migrate inside the containment, and the numerous rooms and compartments inside the containment make the air flow impeded, and the VOCs may be enriched to bring combustion risk. The complete fire risk analysis method includes volatilization kinetics of chemicals, mixture explosion limits, and numerical simulation of VOCs diffusion and migration. The volatilization rate at the lowest room temperature of 20°C is used as a conservative input, the complement of CAITA realistic model is used as the flow domain, and the geometry is appropriately simplified, and the steady ventilation process, the internal flow and the laws of diffusion and agglomeration of 12 kinds of VOCs gases in the 9-h pressure-holding process are investigated by Computational Fluid Dynamics. The simulation results of steady ventilation show that the VOCs gases are almost uniformly carried by the air to all spaces inside the containment, and the explosion risk is low. The concentration field of the steady ventilation process was taken as the initial boundary condition and unsteady state simulation of the 9-h holding pressure process was performed. The results show that the gas flow inside the containment basically stops after 3456 s of pressure holding. With the extension of time, the VOCs gases accumulate at the bottoms of the three lower layers of the containment under the effect of laminar diffusion and gravitational settling, where the total concentration of the mixed gases reaches the highest at the bottom of the lowest layer. The total concentration of the VOCs gas mixture was below the lower explosion limit throughout the 9-h pressure-holding process, and the explosion risk was low. [ABSTRACT FROM AUTHOR]

Highly flammable substances such as hydrogen and silane are used in the semiconductor manufacturing process. When gas leaks, it is mixed with outside air and connected to a treatment facility through the duct inside the gas box. This study investigated optimal exhaust design to prevent fire explosions and health problems by optimizing the exhaust volume when hydrogen leaks from the gas box of semiconductor manufacturing equipment. After selecting the leakage rate amount based on the KS C IEC 60079-10-1, SEMI S6-0707E, and SEMI F-15 standards, a gas box was manufactured. Subsequently, the fan speed required to ventilate the gas box more than five times per minute according to the SEMI standard and the opening area and location that can reduce the lower explosive limit (LEL) to less than 25% in the event of hydrogen leakage were determined. When the air intakes were placed on the left and right, the flow rate was measured at 32 L per minute (LPM), and the maximum concentration was measured at 9111 ppm. This is less than 25% of the LEL of hydrogen and is believed to be capable of preventing fire and explosion, even if a similarly flammable gas leaks inside the gas box. [ABSTRACT FROM AUTHOR]

Polymers and their processing by engineering production technologies (injection, molding or additive manufacturing) are increasingly being used. Polymers used in engineering production technologies are constantly being developed and their properties are being improved. Granulometry, X-ray, FTIR and TGA were used to characterize polymer samples. Determination of the fire parameters of powder samples of polyamide (PA) 12, polypropylene, and ultra-high molecular weight (UHMW) polyethylene is the subject of the current article. An explosive atmosphere can be created by the powder form of these polymer materials, and introduction of preventive safeguards to ensure safety is required for their use. Although the fire parameters of these basic types of polymers are available in databases (e.g., GESTIS-DustEx), our results showed that one of the samples used (polypropylene) was not flammable and thus is safe for use in terms of explosiveness. Two samples were flammable and explosive. The lower explosive limit was 30 g·m−3 (PA12) and 60 g·m−3 (UHMW polyethylene). The maximum explosion pressure of the samples was 6.47 (UHMW polyethylene) and 6.76 bar (PA12). The explosion constant, Kst, of the samples was 116.6 bar·m·s−1 (PA12) and 97.1 bar·m·s−1 (UHMW polyethylene). Therefore, when using polymers in production technologies, it is necessary to know their fire parameters, and to design effective explosion prevention (e.g., ventilation, explosive-proof material, etc.) measures for flammable and explosive polymers. [ABSTRACT FROM AUTHOR]

In this work, the explosion limits of three different natural gas mixtures (with various proportions of methane (CH 4), ethane (C 2 H 6), and propane (C 3 H 8)) have been investigated numerically based on detailed chemical kinetics. Furthermore, a comprehensive investigation of the effects of hydrogen (H 2) and inert gas (N 2 , CO 2) addition on the explosive properties of natural gas has been carried out. The results indicate that the C 3 H 8 components have a dominant effect on the explosion limits of natural gas. The addition of high-hydrocarbons in natural gas can significantly reduce the auto-ignition temperature, shorten the ignition delay time, and enhance the explosion risk of the mixture. Furthermore, the negative temperature coefficient (NTC) response of natural gas in the second explosion limit gradually disappears, and changes to the Z-curve response with the addition of H 2. However, the explosion tendency of the mixture is reduced with the addition of H 2 under normal to high-pressure conditions. In addition, with the increase of inert gas (N 2 , CO 2), the explosion limits of the mixtures shift upwards to a higher-pressure region, which significantly reduces the explosion tendency. Nevertheless, the explosion propensity of the mixture increases significantly under low-pressure conditions when the mixture contains hydrogen. To elucidate the critical control reactions and determine their synergistic effects, sensitivity analyses under different conditions are performed. Finally, the interaction of different fuels in natural gas mixtures is further summarized by analyzing the explosion limits of single-component, binary-component, and multi-component mixtures of hydrogen to propane. This paper provides an important guidance for the development of natural gas with high safety, low risk, and low pollution. [ABSTRACT FROM AUTHOR]

Liquefied petroleum gas (LPG), like other hydrocarbon gases, has good thermo-physical and ecological properties, but its high-flammability has limited its direct use in refrigeration applications. Therefore, this paper investigates the thermodynamic performance of low flammable and ecological-save mixtures of LPG and tetrafluoroethane refrigerant in a refrigeration system. The computational results of global warming potential (GWP) and low flammability limit shown that the blends with 50 – 90 % LPG contents have GWP below 750 and fall within the lower flammability safety class of which five were selected for further analysis. The results showed that the thermal conductivity and the refrigerating effects produced by the selected blends are greater than those of the reference refrigerant (R134a). Also, the selected blends exhibited appropriate lower pressure ratio, discharge temperature and specific power than R134a refrigerant. Four of the blends required low power input and exhibited higher coefficient of performance which are clear indication that they are more energy efficient than R134a in the refrigeration systems. [ABSTRACT FROM AUTHOR]

The explosion characteristics of the runaway battery vented gas (BVG) was studied using an 8 L column type device. The effects of ambient temperature, turbulence condition, and graphite dusts-ejected along with the BVG on the explosion process-were investigated. At 25 ℃, the explosion limits of pure BVG, the maximum explosion pressure (P max), and the maximum rate of explosion pressure rise (dP/dt) max is 10.8–45.8% by volume, 0.62 MPa, and 37.6 MPa/s, respectively. At 80 ℃, the three parameters changed to 10.4%− 46.5%, 0.49 MPa and 35.5 MPa/s. Moreover, these three parameters changed to 10.2–47.5%, 0.45 MPa and 33.3 MPa/s at 120 ℃. The increase in temperature reduced P max of BVG. While turbulence had little effect on the explosion pressure of BVG, it has significantly affected the dP/dt value. Adding graphite dusts helps BVG get to P max at a much lower volume concentration. As temperature increased, this effect became greater. Also, the graphite dusts can reduce the time of BVG to attain the P max value after igniting – the maximum reduction is from 325 ms to 158 ms. As ambient temperature increased, the combustible gas molecules were reduced, resulting in a lower P max value. The heat released from the BVG explosion drives the graphite involving dust explosion when oxygen is excessive. The above findings can provide a reference for the prevention of environmental explosions caused by the thermal runaway of lithium-ion batteries in process industry. • The effect of ambient temperatures on the explosion parameters of BVG was investigated experimentally. • The effect of turbulence generated during thermal runaway on the explosion characteristics of BVG was considered. • Graphite dusts were induced to investigate the explosion parameters of the hybrid mixture. [ABSTRACT FROM AUTHOR]

In this work, we investigate the effects of chlorine (Cl) and bromine (Br) containing species additions on the pressure-temperature explosion limits of hydrogen-oxygen (H 2 -O 2) mixtures computationally. It is shown that, with the addition of HCl, Cl 2 , HBr and Br 2 , the explosion limit evolves from being a non-monotonic Z-shaped curve to monotonic or maintains its non-monotonic response depending on the different types of additives. Specifically, with the addition of HCl to the mixtures, the limit always maintains the non-monotonic structure, while with the addition of around 18% of Cl 2 , it loses its Z-shaped structure. Compared with HCl and Cl 2 , more sensitive responses were found for HBr and Br 2. With the addition of around 1% of HBr and 0.7% of Br 2 to the H 2 -O 2 mixtures, the limit's non-monotonic feature disappears rapidly, and becomes a monotonic curve. Further detailed kinetics analysis explains that after the addition of the halogen species, the radical competitions are different at the low- (P = 1.0 × 102 Pa), intermediate- (P = 1.0 × 104 Pa) and high- (P = 1.0 × 106 Pa) pressures respectively, resulting in the change of the dominant reactions. These findings enhance the understanding of Cl and Br containing species sensitization for the explosion limits of the H 2 -O 2 mixtures and help to understand the kinetic interaction between the H 2 -O 2 system and halogen. • The effects of halogen species additions on the H 2 -O 2 explosion limits have been investigated computationally. • With the addition of HCl to the mixtures, the limit always maintains the non-monotonic response. • With the addition of Cl 2 , the explosion limit loses its Z-shaped structure. • Compared with HCl and Cl 2 , more sensitive responses were found for HBr and Br 2. [ABSTRACT FROM AUTHOR]

Hydrogen is a flammable gas that can generate thermal and mechanical loads which could jeopardise the containment integrity upon combustion inside nuclear power plants containment. Hydrogen can be generated from various sources and disperses into the containment atmosphere, mixing with steam and air following a loss of coolant accident and its progression. Therefore, the volumetric hydrogen concentration should be examined within the containment to determine whether a flammable mixture is formed or not. Codes with 3D capabilities could serve this examination by providing detailed contours/maps of the hydrogen distribution inside containment in view of the local stratification phenomenon. In this study, a 3D VVER-1000 as-built containment model was sketched in AutoCAD and then processed into GOTHIC nuclear containment analysis code for hydrogen evaluation. The model was modified to a great extent by installing 80 passive autocatalytic recombiners and locating hydrogen sources to evaluate the performance of the hydrogen removal system inside the containment on maintaining the hydrogen concentration below the flammability limit during a large break loss of coolant accident. 2D profiles and 3D contours of volumetric hydrogen concentration with and without PARs are presented as the simulation outcome of this study. The results were validated against the results of the Final Safety Analysis Report, which also demonstrates the effectiveness of the hydrogen removal system as an engineered safety feature to keep the containment within a safe margin. Detailed 3D contours of hydrogen distribution inside containment can be employed to evaluate the local hot spots of hydrogen, rearranging and optimising the number and location of PARs to avoid the hydrogen explosion inside containment. [ABSTRACT FROM AUTHOR]

Parallel buried gas pipelines in tunnels are located in a confined space environment, where natural gas is vulnerable to accumulating to the minimum explosion limit concentration after a leakage accident. Therefore, to reduce the time for locating the leakage source after an accident and compensate for the loss of emergency response, an experimental model for scaling parallel gas transmission pipelines in tunnels was established and the dispersion characteristics and influencing factors of continuous leakage of natural gas within buried soil and in tunnel space were investigated numerically, and the correlation between the volume of the explosion range of natural gas within the tunnel space and each influencing factor was explored using gray correlation analysis. The research shows that the leakage dispersion process of parallel buried gas pipelines in tunnels includes seepage leakage in the soil region and diffusion transport in the tunnel air region. In the soil region, natural gas from the pipeline leak forms a circular shape and tends to percolate upward due to the combined effect of pressure and concentration gradients.In the tunnel air region, the spatial dispersion of natural gas concentration obeys a multivariate Gaussian distribution, and the temporal dimension is divided into three phases: the initial phase of leakage, the spreading phase and the stable phase of leakage. The diffusion speed of natural gas is positively correlated with the operating pressure of pipeline. The concentration peak value (y max) at the leakage orifice position and the leakage aperture (d x) approximately meet the linear relationship: y max = 7.62 d x. The diffusion path of natural gas is greatly influenced by the orientation of the pipeline perforations, and the tunnel walls have a directional effect on the diffusion of natural gas. The main factors affecting the volume of the explosion range of natural gas within the tunnel space are parallel pipeline leakage pressure, pipeline leakage aperture, parallel pipeline leakage position, pipeline operating pressure, and pipeline leakage direction, with grey correlation coefficients of 0.76, 0.675, 0.662, 0.553, and 0.55. The proposed model was demonstrated be able to simulate and predict the diffusion of natural gas under the accidental leakage of buried gas pipelines in tunnels. And the results of this study can guide the installation of buried gas pipelines crossing mountain tunnels to prevent accidents. [ABSTRACT FROM AUTHOR]

Lycopodium (L.) clavatum powder, due to its uniform particle size distribution and low equilibrium moisture content, is often used as a reference material and a calibration benchmark for dust combustion and dust explosion studies. The aim of the study was to determine its fire and explosion parameters, compare them to values obtained in the previous literature findings, and assess the appropriateness of using lycopodium powder as a reference material. The research included the determination of minimum ignition temperatures of dust layer and dust clouds, spontaneous ignition behavior, and explosion characteristics of dust clouds including maximum explosion pressure, maximum rate of explosion pressure rise, and the lower explosion limit of the air/dust mixture. The results reveal that the maximum equipment temperature used with lycopodium dust should not exceed 215 °C for dust thickness up to 5 mm. In order to eliminate the risk of lycopodium dust ignition, the temperature of the equipment surfaces that can come into contact with the dust cloud should not exceed 300 °C. In order to prevent explosions, the concentration of lycopodium dust in air should not be greater than 15 g/m3. Based on the obtained results, it can be seen that lycopodium fire and explosion parameters vary slightly, and its usage as a benchmark is considered legitimate. [ABSTRACT FROM AUTHOR]

Urea, a basic chemical compound, holds diverse applications across numerous domains, ranging from agriculture to energy storage. Of particular interest is its role as a hydrogen bond donor (HBD). This specific characteristic has propelled its utilization as an essential component in crafting deep eutectic solvents (DESs) for battery electrolytes. Incorporating urea into DESs presents a promising avenue to address environmental concerns associated with traditional electrolytes, thereby advancing battery technology. Conventional electrolytes, often composed of hazardous and combustible solvents, pose significant environmental risks upon improper disposal potentially contaminating soil and water and threatening both human health and ecosystems. Consequently, there is a pressing need for eco-friendly alternatives capable of upholding high performance and safety standards. DESs, categorized as organic salts resulting from the blending of two or more compounds, have emerged as promising contenders for the next generation of electrolytes. Urea stands out among DES electrolytes by enhancing ion transport, widening the electrochemical window stability (ESW), and prolonging battery cycle life. Further, its non-toxic nature, limited flammability, and elevated thermal stability play pivotal roles in mitigating environmental concerns and safety issues associated with traditional electrolytes. Laboratory testing of urea-based DES electrolytes across various battery systems, including Al-ion, Na-ion, and Zn-ion batteries, has already been demonstrated. This review examines the evolution of urea-based DES electrolytes by elucidating their structure, molecular interaction mechanisms, performance attributes, and preparation methodologies. [ABSTRACT FROM AUTHOR]

Lyocell fiber is a green synthetic fiber widely used in the twenty-first century. However, its flammability and fibrillation limit its further use. In this paper, we used online-treatment of coagulated fibers during spinning to obtain flame-retardant and anti-fibrillation Lyocell fibers with crosslinkers and flame retardants that penetrate the fiber surface easily and react more quickly with the cellulose molecular chains. The results of infrared spectroscopy, X-ray diffraction and birefringence showed that the coagulated filaments had more micropores, lower crystallinity and orientation compared to heat setting fibers. At lower concentrations of flame retardant (200 g/L) and cross-linking agent (60–80 g/L), the limit oxygen index (LOI) of Lyocell fibers treated on-line was about 30.2%, the char residue was increased from 7.1 to 23.0%, and the peak of heat release rate (PHRR) and total heat release were reduced by 86.4% and 49.6%, respectively. This is attributed to the better adsorption ability and accessibility of coagulated filaments and the rapid reaction between cellulose and the crosslinker to capture more flame retardant during the online-treatment. After washing 20 times, the LOI was still maintained at 28.7%, and the degree of fibrillation of the fiber was obviously reduced. Compared with conventional Lyocell fibers post-treatment technology, this work provides an industrially feasible and efficient method to continuous prepare Lyocell fibers with both favorable flame retardant and anti-fibrillation properties. [ABSTRACT FROM AUTHOR]

As the applications of hydrogen as a replacement for fossil fuels and energy storage increase, more concerns have been raised regarding its safe usage. Hydrogen's extreme physical properties—its lower flammability limit (LFL), for instance—represent a challenge to simulating hydrogen leakage and, hence, mitigating accidents that occur due to such leakage. In this work, the OpenFOAM-based CFD simulation package containmentFOAM was validated by different experimental results. As in its original use, to simulate nuclear safety issues, the containmentFOAM package is capable of capturing different phenomena, like buoyant gas clouds and diffusion between gases and air. Despite being widely validated in nuclear safety, this CFD package was assessed with benchmark experiments used to validate hydrogen leakage scenarios. The validation cases were selected to cover different phenomena that occur during the hydrogen leakage—high-speed jet leakage, for example. These validation cases were the hallway with vent, FLAME, and GAMELAN experiments. From the comparison of the experimental and simulation results, we concluded that the containmentFOAM package showed good consistency with the experimental results and, hence, that it can be used to simulate actual leakage cases. [ABSTRACT FROM AUTHOR]

Polymethylsilsesquioxane (PMSQ) aerogels have been developed for diverse applications owing to their excellent flexibility and hydrophobicity. PMSQ aerogels, however, are limited by their flammability and low thermal stability. In this study, transparent and robust PMSQ aerogels were synthesized using an environmentally friendly flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-vinyltrimethoxysilane (DOPO) in a facile one-pot manner and successfully dried under ambient pressure without cracks. Briefly, methyltrimethoxysilane (MTMS) and another synthesized precursor, DOPO-vinyltrimethoxysilane (DOPO-VTMS), where DOPO and VTMS were covalently bonded, were used to prepare a DOPO-VTMS MTMS aerogel via co-hydrolytic condensation. The DOPO-VTMS MTMS aerogel showed excellent flame retardancy with a peak heat release rate of 23.48 W g−1, which is 60% lower than that of the MTMS aerogel. It also exhibited enhanced thermal stability, as confirmed by thermogravimetric analysis, originating from the synergistic effect of P and Si. Furthermore, the compressive strength of the DOPO-VTMS MTMS aerogel was 26 times higher than that of the MTMS aerogel. With superior thermal properties and mechanical robustness, the preparation strategy employed in this study can contribute to the development of PMSQ aerogels for various applications such as thermal insulation for buildings, flame-retardant airspace dust collectors, or fire preventive coatings for fabrics. [ABSTRACT FROM AUTHOR]

When developing methods for standoff detection of explosive traces, an important issue is determination of the limit (minimum) amount of a substance available for detection. This limit depends on the features of the measuring complex realization, on the physicochemical properties of the substance, and on the dynamics of sublimation (evaporation) of the substance from the surface. In this work, we consider the problem of detection limit for a measuring complex based on the method of active spectral imaging. In realization of this method, the distance to the object and the measurement time after the appearance at the surface of a substance imprint are important. How long this trace amount of substance can be detected, taking into account its evaporation? An explosive imprint is a thin layer on a surface (usually considered as a fingerprint with traces of the substance). We theoretically consider the dynamics of the change in the area of this imprint on the basis of a mathematical model of evaporation of a thin layer. Based on mathematical modeling, we can estimate the amount of a specific substance available for detection under the given conditions and the availability time. We identified the main parameters that affect the rate of film evaporation and the range of parameter change and calculated the kinetic parameters of sublimation of thin films of some explosives. The performed calculations allowed us to draw conclusions about the detection limit of substances for the active spectral imaging method depending on the distance to the measurement object and the time after the appearance of a surface trace with an initial surface concentration and area specific to a fingerprint. [ABSTRACT FROM AUTHOR]