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This paper presents measurements of combustion species of low pressure laminar premixed flat methane-oxygen flames inhibited by trifluoromethane (CF3H) using synchrotron radiation-molecular beam mass spectrometry (SR-MBMS). Fire suppression chemistry of CF3H is investigated by selective detection of combustion radicals and intermediates. Results show that SR-MBMS offers a powerful tool for studying fire suppression chemistry of halon replacements, which may extensively detect combustion species in the inhibited flames, especially radicals and inter- mediates. The suppressant CF3H is completely consumed in the preheat zone of premixed flames and produces fluorinated radicals such as CF3 and CF2, CF3 is the main radical participating in flame inhibition cycles in the reactive zone. Unlike HBr, HF produced by CF3H is very stable and will not act as a radical scavenger because the bond energy of H-F is much higher than that of H-Br, which is responsible for less effectiveness than conventional bromine-based suppressants. [ABSTRACT FROM AUTHOR]

Electric vehicle (EV) fire accidents induced by the thermal runaway of li-ion batteries are increasingly frequent, and the fire dynamics of EVs parked in rows are still unclear. Hence the fire evolution process and characteristics of two parallel placed EVs were studied by analyzing the burning behaviors and thermal fields. The fire source was the battery pack of a battery electric vehicle (BEV). Results showed that the precursor to the BEV fire was the emission of white smoke from the chassis. Flames did not appear until the accumulated smoke exploded, and they engulfed both the EVs. The flame switched between momentum and buoyancy control on the vehicle scale. The maximums of the length and duration of the jet fires were determined. The maximum temperature of the EV fire was consistent with that of internal combustion engine vehicle (ICEV) fires, but the flame spread faster between the EVs compared to ICEVs. Pragmatic methods were proposed to quantify the fire evolution rate. The heat effect of the EV fire on humans was also quantitatively evaluated. These results provide a fundamental understanding of fire rules in a high EV concentration scenario. [ABSTRACT FROM AUTHOR]

The convective heat transfer coefficient h c characterizes the heat transfer capacity between the fluid-solid interface in a thermal convection phenomenon. At present, values adopted from specifications are mostly used to define the h c coefficients in localized fire researches. In this paper, the specific scenario of the steel column surrounded by fire plume is selected as a typical case to explore the surface h c change rules of the steel column under the action of the fire source at the bottom. Different from the application of the concept of adiabatic surface temperature (AST) to achieve fluid-solid thermal coupling, this paper takes the scenario with the fire source heat release rate (HRR) being 81 kW as an example and conducts a two-way coupling simulation analysis of the fire and the thermal models by means of CFD codes. First, the validity of this simulation methodology is verified by comparing the results of the numerical model and the experiment. Following this, the distribution laws of the spatial velocity and temperature fields are analyzed, and the h c coefficient of the steel column surface is explored in detail using theoretical formula and traditional empirical formula respectively. It is noted that the h c results obtained based on theoretical formula can comprehensively consider the velocity boundary layer and temperature boundary layer situations above the column surface, which is a direct result of the definition of the convective heat transfer coefficient. It is found that the h c ‾ is lower at the bottom of the column and increases with height, with relative maximum value in the lower and middle parts of the column, reaching around 40 W/m2 K. The h c ‾ results decrease along the axial direction, with the value of upper part of the column being about 20 W/m2 K. In contrast, the h c ‾ distributions along the height obtained by the empirical formulas are similar to the distribution of fire plume velocity along the height. In other words, it considers only the effect of the velocity boundary layer, while the effect of significant changes in fluid temperature on convective heat transfer behavior is less considered. Compared to the results based on the theoretical definition, the h c ‾ results obtained by empirical formulas are significantly smaller in the lower and middle parts of the column, and higher at the top of the column. Finally, a new h c ‾ practical formula for the column surfaces surrounded by fire plume is proposed, which agrees well with the results based on the theoretical definition in several cases. • h c based on theoretical definition comprehensively considers velocity and temperature boundary layers, and shows large differences from that based on empirical formulas. • A new practical formula for the column surface h c coefficient surrounded by fire source is proposed. [ABSTRACT FROM AUTHOR]

The research approach of multi-physical field coupling can be used to analyze the structural fire resistance problem. In the process of numerical simulation, multiple coupling interfaces are involved. Regarding fluid-thermal-solid coupling, most of the previous numerical studies on structural fire resistance have used the adiabatic surface temperature (AST) parameters in order to accurately describe complex boundary conditions in fire analysis. This approach belongs to the iterative coupling form, and the other type of direct coupling form is rarely used. In this paper, the specific scenario of a steel column surrounded by fire source is selected as a typical case to explore the thermodynamic phenomena of the steel column. Based on the computational fluid dynamics (CFD) method, the fire model analysis in the fluid domain was first implemented to investigate the distribution laws of the spatial velocity and temperature fields. Then the fluid-thermal-solid coupling was realized via iterative coupling (Adiabatic Surface Temperature method, AST method) and direct coupling (Full Conjugate Heat Transfer method, FCHT method) respectively to obtain the steel column temperatures. The accuracy of these two coupling methodologies was verified by comparing their results with the experimental data, and the accuracy of AST method depends on the reasonable sampling of fire analysis results. Following this, structural model analysis was completed using the solid temperature as the boundary condition to achieve the solid thermal-mechanical coupling. The yield strength degradation of the steel column after heating was explored. Finally, the non-necessity of fluid-mechanical-solid coupling in structural fire resistance was discussed. • The fluid-thermal-solid coupling can be realized via iterative coupling and direct coupling respectively. • The accuracy of AST method depends on the reasonable sampling of fire analysis result. [ABSTRACT FROM AUTHOR]

LNG is stored in cryogenic conditions, where the temperature is under 111K. In case of an accidental leakage into a normal atmosphere, LNG will vaporize and form cold methane gas cloud, namely LNG vapor cloud. In the existing researches, few have studied the effect of the inevitable water vapor phase change on the dilution of LNG vapor cloud under different relative humidity conditions. In this paper, a two-phase multi-species model is used in combination with three common water phase change treatments to simulate the dispersion of LNG vapor cloud and analyze the effect of relative humidity on it. The three approaches to deal with water phase transfer are: the one neglecting water phase change, and the other two considering water phase change by using the Lee model and the Sun model respectively. It is found that the results obtained by the Lee model and the Sun model show a similar response to humidity. In addition, although the density of LNG vapor clouds is usually higher than that of the surrounding air, there is a chance for the ambient air to overweigh the LNG vapor cloud in a hot and rather wet setting (RH>80%) if water phase transfer is considered. • The water vapor phase change was integrated into the LNG vapor cloud dispersion. • Three types of phase change treatments were applied to simulate the water droplets generation and dissipation. • The effect of relative humidity on LNG vapor dispersion was examined in detail. • The relationship was discussed between the visible cloud and the flammable cloud. [ABSTRACT FROM AUTHOR]

Syngas is a promising alternative energy carrier with low carbon and pollutants emissions, which has huge application potential in internal combustion engines and gas turbines. The combustion characteristics of stoichiometric syngas/air mixtures with varied initial pressure (0.5–2.5 atm) and hydrogen content (10%–90% v/v) were examined through experiments in a rectangular closed channel. The flame images and overpressure dynamics were captured by high-speed schlieren photography and pressure sensors. The flame instabilities and the flame-acoustic wave interaction were explored. The results showed that the flame morphology and dynamics were enhanced with increasing hydrogen content and initial pressure. The Darrius-Landau instability has an impact on flame deformation, which was strengthened with growing initial pressure, while the thermo-diffusive instability could be neglected during combustion. At later stages after tulip inversion, the flame-acoustic wave interaction was relatively outstanding inducing wrinkled flame front and cellular structures on the flame surface. • Resonance made the flame evolution different at varied initial pressures. • The hydrogen content had greater impact on flame deformation than initial pressure. • Acoustic effects were outstanding in later stages of flame propagation. • Flame-acoustic wave interaction caused cellular structure on the flame surface. [ABSTRACT FROM AUTHOR]

Liquefied natural gas (LNG) serves as a crucial alternative fuel for ships, yet the potential for jet fires arises when compressed natural gas (CNG) is accidently released in a ship engine room. Taking the pipe as the typical cylindrical obstacle, this study conducted a numerical investigation on flame shape characteristics resulting from a vertical jet fire impinging on a horizontal pipe. It is found that both the vertical flame length above the pipe and the horizontal extension flame length underneath it increases with a higher gas leakage velocity. Additionally, a larger pipe diameter was found to suppress the vertical flame length above the pipe while contributing to the horizontal extension length underneath it. Moreover, as increase in the nozzle-pipe distance led to a decrease in both the vertical flame length above the pipe and the horizontal extension flame length. With smaller pipe-nozzle distances and higher gas leakage velocities, more flame spikes were observed above the pipe. To quantify these phenomena, new dimensionless models were developed for the vertical flame length above pipe and the horizontal extension flame length. These models were validated against experimental results, demonstrating deviations within 12.5%. The outcomes of this research can offer an essential reference for fire prevention design, fire risk assessment and fire science research in the engine room of LNG-powered ships. • Shape characteristics of jet fire impinging on a pipe are numerically studied. • Pipe diameter and nozzle-pipe distance have great effect on the jet fire shape. • Prediction model about vertical flame length above pipe is developed. • Prediction model about horizontal extension flame length under pipe is developed. • Model predictions of jet fire impinging on pipe agree well with experimental data. [ABSTRACT FROM AUTHOR]

To predict pedestrian movement is of vital importance in a wide range of applications. Recently, data-driven models are receiving increasing attention in pedestrian dynamics studies, demonstrating a great potential in enhancing simulation performance. This paper presents a pedestrian movement simulation model based on the artificial neural network, in which two submodels are, respectively, used to predict velocity displacement and velocity direction angle at each time step. Destination information, the pedestrian's historical movement information, neighboring pedestrians, and environmental obstacles within a semicircular-shaped perception area are used as inputs to learn pedestrian movement behavioral rules. In the velocity direction angle submodel, a novel division method on pedestrian's perception area is adopted. Specifically, perception radius is divided into several bands, and perception angle range is divided into a number of sectors, establishing a weighted spatial matrix to represent varied influences of neighboring pedestrians and obstacles. Experiments on two typical scenarios, the unidirectional flow and bidirectional flow in a long straight corridor, were conducted to obtain pedestrian movement datasets. Then, a series of simulation cases were conducted to investigate the proper values for critical parameters, including perception radius, perception angle division, weights of the spatial matrix, and historical movement adoption. In comparison of pedestrian trajectory between simulation results and real data, the mean trajectory error (MTE) and mean destination error (MDE) are, respectively, 0.114 m and 0.171 m in the unidirectional flow scenario, which are, respectively, 0.204 m and 0.362 m in the bidirectional flow scenario. In addition, the fundamental diagram representing density-velocity and density-flow relationships in simulation results agree well with that in real data. The results demonstrate great capacity and credibility of the presented model in simulating pedestrian movement in real applications. [ABSTRACT FROM AUTHOR]

Nowadays, the famous tourist attractions are becoming more and more popular for people from all over the world. Thus, to ensure the safety of tourists is a tough task in such crowded area. The study of pedestrian's characteristics in crowd movement is essential for safety management. In this article, both uni- and bidirectional observational experiments were conducted to quantitatively analyze the movement properties of pedestrians in a zigzag corridor which is located in a tourism area named Yuyuan business district in Shanghai. Several phenomena have been found during the tourists' movement process: congestion at boundary, competing and bypassing behavior, and flow gap. As indicated by the transit time of pedestrians in both uni- and bidirectional scenarios, pedestrians in bidirectional pattern (>10 s) spend more time on going through the corridor than that in unidirectional one (<10 s). Besides, the fundamental diagrams in both uni- and bidirectional scenarios are significantly different from data in a controlled experiment, and obvious differences are observed within the density regime from 1.5 to 2.5 ped/m2 between the uni- and bidirectional scenarios. In addition, spatial distributions of density and velocity demonstrate that pedestrians would like to cluster at the boundary of straight corridors in both uni- and bidirectional scenarios. The results could enrich the database of fundamental diagrams, and then be used for model calibration by taking the actual situation into consideration in similar scenarios. [ABSTRACT FROM AUTHOR]

Unstable thermal stratification, quantified by the Richardson number (Ri) herein, has important effects on pollutant dispersion. In this study, the impacts of unstable thermal stratification on airflow and pollutant dispersion around a rectangular building are investigated through large eddy simulation (LES), in which a wide range of Richardson numbers (−1.5–0) is considered. Increasing instability enhances the removal of pollutant near the ground with strengthened advection and turbulence, and thus results in lower normalized pollutant concentration near the ground and higher concentration around the building height. Meanwhile, the streamwise length of the recirculation region behind the building decreases by 32% when Ri decreases from 0 to −1.5, which further enhances pollutant dispersion behind the building. In terms of pollutant dispersion behind the building where the recirculation region emerges, the advection flux of concentration plays a crucial role, which is nearly four times the turbulent diffusion flux in magnitude when Ri ​= ​−1.5. On the other hand, near the boundaries of the recirculation region, turbulent diffusion flux is non-negligible in transporting the pollutant along the concentration gradient. With lower stability, the proportions of fluctuation energy of velocity and concentration in the low-frequency range decrease behind the building compared to those in the high-frequency range. • The effects of unstable conditions on airflow and gas dispersion are studied in a wide range of Richardson numbers (−1.5–0). • Increasing instability enhances pollutant transport from ground to higher region with strengthened advection and turbulence. • Behind the building, proportions of fluctuation energy of airflow in low-frequency range decrease with higher instability. [ABSTRACT FROM AUTHOR]

A numerical study of oil pool fire with different cylindrical obstacles in a ship engine room was carried out. The characteristics of flame height, maximal temperature rise, and centerline axial velocity of fire plume were investigated and analyzed. The results showed that the flame height of the merged flame decreases with the increased radius ratio and obstacle height, while the plume maximal temperature rise and axial velocity decreases with a larger radius ratio. Under the broken flames, the flame height only decreases with a larger radius ratio, while the plume temperature rise and axial velocity decreases with the increase of both radius ratio and obstacle height. When the obstacle is smaller, the annular flames merge above the obstacle, while the annular broken flames surround the cylindrical obstacle when the obstacle is larger. And there is a competition between flame height enhancement effect and weakening impact when the flame could merge above obstacle. The empirical models of flame height, centerline temperature rise and axial velocity of annular pool fire with different cylindrical obstacles are obtained and validated by experimental test data. These results can offer an essential reference for fire prevention design and fire science research in the ship engine room. • Fire plume features of annular pool fire with obstacles are numerically studied. • Flame height declines with larger r/R and obstacle height under merged flame. • Temperature declines with larger r/R and obstacle height under broken flame. • Influence of cylinder obstacle on fire plume is determined by its size and height. • Empirical models of annular pool fire plume with cylinder obstacles are obtained. [ABSTRACT FROM AUTHOR]

Syngas is a promising renewable energy carrier, and its combustion can result in a significant reduction of pollutant emissions. However, syngas has various production sources, its compositions are diverse accordingly. That brings some challenges in its practical application. Therefore, in order to deeply investigate the premixed stoichiometric syngas/air combustion in confined spaces, experiments were conducted in a closed duct with varied aspect ratios (12, 26 and 40) and initial pressures from 0.5 atm to 1.5 atm. Flame shape evolutions in varied cases were captured through high-speed photography, and four flame speed oscillation regimes were distinguished qualitatively. The pressure buildup was recorded by sensors and scrutinized by dimensionless method. The results denoted the propagation dynamics became more violent with higher initial pressure or aspect ratio. Further, the combustion instability was examined, and it indicated the acoustic effect and the Rayleigh-Taylor/Richtmyer-Meshkov instability would be stronger in cases with large aspect ratio, resulting in the deformation of elongated tulip flame. Besides, the Bychkov's theory considering gas compression effect was validated by the experimental data. The discrepancy between them was interpreted with a comprehensive view of enlarged laminar burning speed, non-adiabatic sidewall and finite flame front thickness. [Display omitted] • The aspect ratios (12, 26 and 40) were examined for syngas combustion in ducts. • Flame regimes varied with aspect ratio and initial pressure. • The RT and RM instability has combined effect at later stages. • Bychkov's theory gave better predictions considering gas compression effect. [ABSTRACT FROM AUTHOR]

Electric vehicle (EV) fires resulting from the thermal instability of high-energy lithium-ion batteries (LIBs) have become a significant hazard to public safety. Effective and prompt fire-fighting methods for dealing with EV fires are required. A fire protection method referred to as electric vehicle fire enclosure (EVFE) was proposed in this paper based on EV fire characteristics. Full-scale fire experiments were employed to evaluate the fire extinguishing efficiency of various types of EVFE. Results showed that EVFE could effectively suppress the thermal runaway (TR) of full-size LIB packs in the EVs under these experimental conditions, and the battery packs did not occur re-thermal runaway after EVFE stopped working. The agent consumption of water EVFE was 0.628 m3/kWh, while that of foam EVFE was 0.743 m3/kWh. Moreover, the overheated battery packs had an interesting TR propagation mechanism that TR discretely spread among the cells. The TR critical temperature of unconnected battery modules was not suitable for illustrating the TR characteristics of circuit-connection battery modules. For the full-size LIB packs, the TR onset temperature ranged from 31.8 °C to 117.3 °C. These results provide an insight into the fire protection methods and TR characteristics of the LIB packs in EVs. • A new fire protection method for dealing with electric vehicle fires is proposed. • The fire extinguishing performance of the method is evaluated by full-scale fire tests. • An interesting thermal runaway propagation mechanism is found in full-size lithium-ion battery packs. • The thermal runaway onset temperature of cells in the battery packs is between 31.8 °C and 117.3 °C. [ABSTRACT FROM AUTHOR]

Interaction of water mist with cooking oil fires is studied experimentally and theoretically. A LDV/APV system is used to measure the velocity and diameter of water mist at different pressures in the experiments, and the effect of water mist velocity and diameter on fire extinguishment efficiency is investigated. The experimental results show that water mist has excellent surface cooling effect; it can control and extinguish cooking oil fires quickly without re-ignition. The critical temperature (Tfo) is calculated by energy balance equation, and the fire plume momentum is calculated and compared with that of water mist in order to determine the critical velocity (νwy) of fire extinguishment. This paper provides references for cooking oil fires extinguishment with water mist. [ABSTRACT FROM AUTHOR]

• A seismic casualty prediction method that considers the rescue process is constructed. • In this method, a seismic network model with a dynamic rescue rate is built. • The optimal rescue plan can be obtained by solving the seismic network model. • The optimal rescue plan can minimize the casualties of earthquake. To predict the impact of the rescue work on the casualties after the earthquake, a seismic casualty prediction method that comprehensively considers the burial situation and the rescue process is constructed. In this method, a seismic network model based on the graph theory method is built, then the burial situation on an area of after an earthquake can be quickly calculated by using the calculation method of casualty rate based on the building damage rate. Finally, the optimal rescue plan can be obtained by solving the objective function of the seismic network model through the genetic algorithm. Taking the 1100 campus of University of Shanghai for Science and Technology as a case, the burial situation and the casualties under the influence of the rescue work are analyzed after assuming a Ⅹ-degree earthquake occurs on this area, based on which an optimal rescue plan is proposed. After that, by comparing with two shortest path methods, the superiority of the proposed method is highlighted. This method can be used as the basis for regional earthquake risk assessment and emergency rescue plans establishment, and it can also be used as a tool for generating optimal rescue routes after the earthquake. [ABSTRACT FROM AUTHOR]