Search Results (474)

Port-area hydrogen refueling stations face low-frequency but high-consequence events when high-pressure leaks ignite as jet fires in wind-exposed, constrained environments. This study develops a consequence-based framework coupling theoretical screening, CFD combustion analysis, and hazard zoning to support separation-distance setting and emergency planning. A jet-fire model estimates flame-impingement distances for multiple leak diameters, and a weighted multi-point radiation model predicts heat-flux fields, from which lethal and irreversible-injury zones are delineated using thresholds of 7 and 5 kW/m², respectively. To move beyond wind-free screening, steady reacting-flow CFD is conducted for a representative release under four ambient conditions, with 4.34 m/s adopted as the representative wind speed for the windy cases based on Ningbo Port conditions. Validation against a visible-flame correlation defined by T ≥ 1573 K shows a deviation of 6.99%. Results show that radiation footprints expand markedly with diameter, with lethal and injury distances scaling approximately linearly within the studied range. Under wind, near-ground hot-plume extents defined by T ≥ 388 K and T ≥ 582 K depend strongly on wind direction and station geometry, whereas visible flame length is less sensitive. Additional sensitivity analyses indicate that the quasi-steady results are weakly affected by the selected ignition snapshot, while inclined releases modify projected plume/flame extents without altering the main engineering interpretation of the baseline case. The results support theory-based preliminary screening, but wind direction should be explicitly considered in exclusion-zone definition. Full article

To address the limitations of existing NH₃/H₂ combustion mechanisms, laminar flame speeds of NH₃/H₂/air mixtures were measured using the heat flux method over a range of equivalence ratios from 0.7 to 1.6 at different blending ratios. The results indicate that current mechanisms exhibit large prediction errors under fuel-rich conditions. Subsequently, based on the original mechanism, the pre-exponential factors of 13 key reactions were optimized using a particle swarm optimization algorithm, leading to the development of a new NH₃/H₂ chemical kinetic mechanism. The optimized mechanism not only improves the prediction of laminar flame speeds for NH₃/H₂/air mixtures but also significantly enhances accuracy in the fuel-rich region. In addition, it accurately predicts the ignition delay times of NH₃/H₂ and reliably reproduces the concentrations of H₂O, NH₃, NO, and N₂O under low-equivalence-ratio conditions. Although the optimized mechanism was not specifically developed for pure NH₃ or pure H₂ fuels, it still performs well in describing their combustion characteristics. Overall, the optimized mechanism provides reliable predictions for both the laminar flame speeds and ignition delay times of NH₃/H₂ mixtures. Full article

Recently, numerous countries have experienced devastating wildfires, leading to significant destruction and loss of life. These catastrophic events highlight the shortcomings in current building regulations and testing methods. There is a pressing need for a more profound understanding of the characteristics and behaviour of large outdoor fires to address these inadequacies effectively. Wildfires can spread to structures located at the wildland–urban interface, leading to further fire propagation from one building to another. In this study, the Fire Dynamics Simulator (FDS) model was validated using experimental data from the National Institute of Standards and Technology (NIST). The experiment consisted of a target wall and a small wooden shed containing six wooden cribs as fuel, with a separation distance of 3 m. Both FDS and the experiment proved that 3 m is the safe separation distance. Different shed materials, such as steel, were used, which reduced the total heat release rate by 40% and the flame height by 20%. The effects of wind speed and direction were investigated using two wooden sheds in FDS to observe fire spread between them. The safe separation distance was 3 m for both wind speeds (2 and 5 m/s) in all directions, where the critical temperature was not reached to cause self-ignition of the second shed, except in the north direction (inward) at a speed of 5 m/s. When the separation distance increased to 3.5 m, the average heat flux at the other shed reduced to 3.18 kW/m², which did not cause self-ignition. Therefore, the safe separation distance between two structures for a wind speed of 5 m/s should be 3.5 m to mitigate the spread of fire based on the shed dimensions and the fire source load. Full article

This study numerically investigates the conversion of a Heavy-Duty (HD) Spark-Ignition (SI) Compressed Natural Gas (CNG) engine to operate with hydrogen-rich syngas produced from waste plastic pyrolysis. The engine was modeled with a one-dimensional simulation tool. Fuel-specific properties were included through a tabulated Laminar Flame Speed (LFS) approach, and knock occurrence was predicted with a Tabulated Kinetic of Ignition (TKI) model. Full-load simulations revealed that direct substitution of CNG with syngas leads to abnormal combustion. With adjusted values of Spark Advance (SA) to avoid knock, syngas operation resulted in average reductions of approximately 15% in brake torque and 6% in total efficiency compared to the CNG baseline. Parametric analyses showed that Late Intake Valve Closing (LIVC) provides no benefits, whereas increasing the Compression Ratio (CR) partially recovers performance and efficiency, with knock being a limiting factor. Lastly, a complete engine map of the converted configuration was generated, reporting Brake-Specific Fuel Consumption (BSFC) and emissions. Overall, the study demonstrates that HD SI engines can be operated on hydrogen-rich syngas at the cost of moderate performance penalties. Moreover, it provides a robust modeling framework to support system-level and well-to-wheel assessments of syngas-based powertrains. Full article

To quantitatively elucidate the effects of overload current on the ignition and burning hazards of polyethylene-insulated wires, 2.5 mm² polyethylene-insulated copper wires used commercially were tested in an electrical fire fault simulation system. Experiments were conducted to study the evolution of overloads, ignition, and burning. The entire process, from insulation smoking and ignition to sustained burning and final extinction driven by wire fusing, was recorded using synchronized digital and high-speed imaging. Video-based measurements were used to extract the following: smoking emission duration, ignition time, burning duration, maximum flame height, and segmented flame width. The results show that stable ignition and sustained burning occur when the overload current is greater than or equal to 180 A. As the current increases, ignition occurs earlier, while the smoking stage becomes shorter but exhibits nonmonotonic fluctuations. The burning duration shows a staged response. It first increases, then decreases toward a relatively stable level. This reflects the competition between enhanced Joule heating and accelerated wire melting and fusing. Maximum flame height and segmented flame width vary nonmonotonically with current, and the segmented flame width peaks at 200 A. A multi-indicator fire hazard evaluation framework was established and an entropy-weight TOPSIS method was applied to integrate the quantification and ranking. The overall fire hazard is greatest at 200 A. These findings provide experimental insight into overload-induced ignition and combustion behavior and contribute to a quantitative understanding of fire hazard evolution in overloaded electrical wires. Full article

As a multiple-energy carrier, hydrogen can facilitate the transition to a low-carbon future, and coupling renewable energy sources with hydrogen-power generation systems (e.g., gas turbines) can markedly enhance gas turbine combined cycles (GTCCs) power generation regarding cleanliness and flexibility. Conventional gas turbines fuel the natural gas–hydrogen mixture and encounter issues like unstable combustion and elevated nitrogen oxide (NO_x) emissions. Initially, the alterations in combustion characteristics resulting from the fuel transition are analyzed, and the principal technical challenges of hydrogen-mixed combustion are summarized. It is found that hydrogen exhibits a laminar flame speed approximately 7–10 times higher than that of methane, and a hydrogen blending ratio beyond 30% significantly increases the risk of flashback and thermoacoustic oscillations. The existing technical proficiencies of advanced hydrogen combustion strategies are delineated to offer decision-making assistance for the industry. For instance, micromix combustors can achieve NOx emissions below 20 ppm even with 100% hydrogen, while axial staging technology expands the stable operating range to 25–106% load. Additionally, current research on hydrogen-fueled gas turbines primarily focuses on enhancing traditional combustor designs. Conversely, the focus on the overall alteration of gas turbines has been relatively restricted. It further examines component failure issues arising from elevated temperatures and material hydrogen embrittlement, highlighting that X80 pipeline steel experiences a 17-fold increase in hydrogen embrittlement index when the hydrogen blending ratio rises from 1% to 20%, as well as safety concerns related to fuel transitions from conventional gas turbines to hydrogen gas turbines, offering technical references for the comprehensive optimization of hydrogen-fueled gas turbines. Full article

In night-time construction scenarios of under-construction nuclear power plants, some yellow lights and open flames exhibit highly similar visual characteristics, resulting in frequent false alarms of fire sources. Such false alarm information tends to drown out real fire alarm signals, which not only severely disrupts construction operations but also endangers fire safety. To address this problem, this paper proposes an intelligent fire risk identification method based on an enhanced YOLOv8n (named YOLO-Fire). Specifically, shallow convolutional layers embedded with a coordinate attention mechanism are integrated into the Backbone of YOLOv8n; the Neck is optimised to improve the efficiency of multi-scale feature fusion; and the Head is enhanced to strengthen the localization and classification branches. Additionally, a composite loss function combining classification loss, regression loss, and similarity loss is designed, coupled with night-scene-specific data augmentation techniques and a two-stage progressive training strategy. Experimental results show that YOLO-Fire reduces the false alarm rate by 14.3%, increases the mean average precision (mAP@0.5) for open flames by 11.3% to 75.2%, and maintains an inference speed of over 85 frames per second (FPS). This study achieves an optimal balance between false alarm control, small object detection accuracy, and real-time processing efficiency, effectively resolving the misclassification issue between open flames and lights in night-time construction scenarios, and providing precise and efficient intelligent technical support for fire risk prevention and control during the construction phase of nuclear power plants. Full article

Unmanned aerial vehicle (UAV) forest fire detection is vital for forest safety. However, early-stage UAV fire scenarios often involve small targets, weak smoke signals, and strict onboard resource constraints, which pose significant challenges to existing detectors. To improve the speed and accuracy of UAV forest fire detection, this paper proposes a lightweight fire detection algorithm, AHE-YOLO, specifically designed for UAVs. The proposed method adopts a coordinated lightweight design to improve feature preservation and cross-scale representation under limited computational budgets. Specifically, the Adaptive Downsampling (ADown) module preserves shallow fire-related cues during spatial reduction, improving sensitivity to small flame and smoke targets. The high-level screening-feature fusion pyramid network (HS-FPN) introduces cross-scale attention to promote more discriminative multi-level feature interaction while reducing redundant computation. Furthermore, the Efficient Mobile Inverted Bottleneck Convolution (EMBC) module is employed to improve receptive-field efficiency and feature selectivity under lightweight constraints, further enhancing detection accuracy and inference speed. Finally, the performance of AHE-YOLO is comprehensively evaluated through ablation and comparative experiments on the same dataset. The final experimental results show that YOLO-AHE achieves a mean average precision (mAP) of 94.8% while reducing model parameters by 39.7%, decreasing FLOPs by 27.0%, and shrinking the model size by 36.4%. In addition, its inference speed improves by 16.5%. Beyond detection performance, the proposed framework supports sustainable forest monitoring by enabling early fire warning with reduced computational and energy demands, showing strong potential for real-time deployment on resource-constrained UAV and edge platforms. Full article

Explosion venting is an important measure for mitigating gas explosion hazards in confined spaces; however, conventional venting processes often generate high speed, high temperature jet flames, leading to severe secondary hazards. To achieve flameless venting, an experimental study on methane explosions under the coupled effects of dual explosion vents and porous materials was conducted in a confined pipe. Porous silicon carbide foam ceramics with different pore densities (10, 20, and 25 PPI) were installed at the vent openings under various vent layout conditions. Combined with high-speed imaging and dynamic pressure measurements, the flame evolution, jet flame suppression, and explosion overpressure characteristics were systematically analyzed. The results indicate that porous materials effectively attenuate jet flame intensity without compromising venting efficiency and increasing pore density significantly enhances flame-quenching performance. In addition, explosion vents located closer to the ignition source facilitate earlier energy release, thereby improving the reliability of flameless venting. Full article

This article presents the simulation methodology and results of dual-fuel combustion for internal combustion engines (ICE). Simulations were performed in ANSYS Forte^®, which modeled flame propagation using the G-equation model, and results were validated against experimental data. The article also presents results from simulations performed in Converge CFD^®, which used the SAGE combustion model, presented in previous work. Typical combustion modelling challenges in such ICE simulations are discussed, and the applied methodology is described. The range of methane-air equivalence ratio was 0.47 ≤ ϕ ≤ 0.57 across four load conditions with a rotational velocity range of 1228 ≤ RPM ≤ 1800. The methane-air combustion at these low equivalence ratios led to the required tuning of the stretch factor coefficient used in the flame speed model in ANSYS Forte^® due to methane’s thermo-diffusive effects at lean equivalence ratios. As a result, the flame stretch factor coefficient was found to increase with decreasing equivalence ratio. The study thus demonstrates the importance of flame stretch sensitivity and thermo-diffusive instabilities in ICE combustion through CFD combustion simulations. Full article

In this paper, experimental and numerical analyses are performed with a Rapid Compression and Expansion Machine (RCEM) equipped with a passive pre-chamber (PC) and fueled with premixed stoichiometric air/methane mixture to replicate engine-like conditions. The main objective of this work is to study the effects of PC geometry, initial charge conditions and hydrogen addition to methane on combustion and flame extinction. From the experiments at different PC geometries, the combustion images acquired with a high-speed camera show the existence of a critical PC configuration (Long φ4) exhibiting the highest flame extinction probability (~54% under baseline conditions). The increase in the initial charge pressure and/or the enrichment of the methane with hydrogen (up to 30% H₂ by volume) help to mitigate the flame extinction by reducing its probability to about 10%. Subsequently, a 0D RCEM model is developed (GT-Power^TM) and enhanced with user sub-models of turbulent combustion and flame quenching. Once tuned, the model reproduces the impact of PC design, higher initial gas pressure and hydrogen enrichment on the combustion evolution. The quenching sub-model, calibrated for the side wall quenching configuration, is able to forecast the experimental flame extinction tendency for the critical PC by modifying the hydrogen enrichment or initial gas pressure. The proposed methodology, describing the flame extinction tendency in PC combustion systems through 0D quenching modeling, represents the novel aspect for PC-equipped devices aiming to support their study and supplement engine investigations during the development phase. Full article

Modern high-speed train compartments contain intricate internal configurations. In the event of a fire emergency, the propagation velocity of flames through the passenger cabin is determined by multiple factors, including compartment design, ignition source characteristics, and airflow conditions. This study employed computational fluid dynamics (CFD) and large eddy simulation (LES) to investigate the effects of fire source power, fire source location, and longitudinal ventilation velocity on the rate of flame progression. Unlike simplified homogeneous fuel models, this study incorporates the specific heterogeneous material layout of the CR400AF to capture realistic flame spread dynamics. The simulation results reveal that, under forward ventilation conditions, the magnitude of fire power has a minimal influence on flame propagation speed. However, stronger fire sources lead to earlier initiation of flame spread along the carriage. Central positioning of the ignition source results in bidirectional flame movement toward both ends of the carriage, with faster propagation rates than those of fires originating at the extremities. Longitudinal airflow patterns significantly influence the fire dynamics. When the airflow speed within the tunnel remains below 3 m/s, the impact of longitudinal ventilation on fire propagation speed in the train is minimal under forward ventilation conditions. Conversely, in reverse-ventilation scenarios, the rate of flame advancement shows a positive correlation with increasing ventilation speed. Nevertheless, once tunnel ventilation velocities exceed 3 m/s, combustion propagation within high-speed rail carriages becomes impossible due to intact windows, which create oxygen-deficient conditions that prevent the development of fire. This paper investigates the heat release rate and spread process of vehicle fires. It comprehensively considers the effects of fire source power, fire source location, and longitudinal ventilation rate on the rate of spread. The research results provide data support for the fire-resistant design of rail transit vehicles and for the formulation of emergency evacuation strategies for different fire scenarios, which are vital for enhancing rail vehicle fire safety and ensuring personnel evacuation safety. Full article

With increasingly stringent greenhouse gas emission regulations, carbon emissions from marine engines have become a major concern, driving the shipping industry to actively explore efficient and clean alternative fuels. Among the various candidates, ammonia has attracted considerable attention in recent years due to its carbon-free nature and potential as a high-quality clean fuel. However, its practical application in marine engines is constrained by several inherent drawbacks, including a high auto-ignition temperature, low flame propagation speed, and low calorific value. Blending ammonia with natural gas has been demonstrated as an effective strategy to enhance its ignition performance. In this study, the ignition characteristics of NH₃/C1–C4 alkane mixed fuels were systematically investigated using numerical simulations. Rate of production (ROP) analysis, reaction pathway analysis, and other kinetic evaluation methods were employed to elucidate the underlying ignition mechanisms. The results reveal that blending NH₃ with C1–C4 alkanes significantly shortens the ignition delay time. When X_CH ≥ 30%, at high initial temperatures, the ignition-promoting effect is most pronounced for NH₃/C₂H₆ mixtures. In contrast, under low temperature conditions, ignition performance progressively improves with increasing carbon chain length of the blended alkane fuel. The ignition delay time across different operating conditions is primarily governed by highly reactive radicals, including O, H, and OH. Elevating the initial temperature, pressure, and blending ratio promotes the earlier formation of these key radicals and increases their production rates. ROP analysis of OH radicals indicates that reaction R10 (O₂ + H ⇌ OH + O) contributes most significantly to OH generation. Furthermore, reaction pathway analysis of NH₃ shows that at lower initial temperatures, NH₃ dehydrogenation is dominated by reactions with OH radicals. At higher temperatures, a greater fraction of NH₃ participates in NO reduction reactions, thereby decreasing the proportion of NH₃ involved in dehydrogenation pathways. Full article

Achieving a green transition in the energy structure and reducing reliance on traditional fossil fuels has become a global imperative for addressing climate change and promoting sustainable development. The search for clean energy alternatives to traditional fossil fuels has emerged as a critical challenge in the energy and power sector. Ammonia (NH₃) shows great potential as a zero-carbon fuel in the energy sector, but issues such as its low flame propagation speed, high ignition energy requirements, and elevated NO_x emissions limit its widespread industrial application. To address these issues and enhance ammonia combustion, plasma-assisted combustion technology has gained widespread attention in recent years as an effective solution. The plasma-assisted technology enhances combustion stability and efficiency of ammonia, and effectively suppresses NO_x emissions. Additionally, the high-energy electrons and intense chemical reactions in plasma help to decompose and crack ammonia fuel, increase flame propagation speed, and thus improve ammonia combustion performance. This paper provides a comprehensive review of the latest research advancements in plasma-assisted technology in ammonia combustion. It covers the fundamental principles of plasma generation, the mechanisms of combustion enhancement, industrial application status, and development trends. The aim is to assess the potential of plasma-assisted combustion technology in achieving efficient, stable, and low-carbon ammonia combustion, and to explore its future prospects for industrial application. Full article

This study examines the influence of ignition position on explosion characteristics in linked vessels with a methane concentration gradient, aiming to support the safety of industrial combustible gas storage systems. A numerical simulation method was adopted, using a vessel-pipe-vessel linked device. Explosion parameters including pressure, pressure rise rate, temperature, and flame propagation speed were analyzed, with mechanism insights drawn from methane consumption rate and Reynolds number. Results indicate that maximum explosion pressure always occurs in the small vessel, decaying exponentially with increased dimensionless length of the ignition position, and ignition in the large vessel results in significantly higher pressure. The maximum pressure rise rate, maximum temperature rise rate, maximum flame speed, and maximum methane consumption rate each follow a quadratic trend, first decreasing and then increasing with the dimensionless length of the ignition position. Flame propagation is dominated by pipe acceleration, peaking at one end of the pipe near the small vessel at velocities up to 600 m/s. Turbulence intensity increases linearly with the dimensionless length of the ignition position and is highest when igniting in the small vessel. This research clarifies the influence mechanism of ignition position and provides theoretical support for the explosion prevention and control of linked vessel systems with concentration gradients. Full article