Search Results (103)

Cable fires pose significant risks to electrical infrastructures, and cable spacing plays a crucial role in influencing fire propagation behaviors. In this study, the combustion characteristics of two parallel thermoplastic cables under varying spacing conditions were systematically investigated through controlled experiments. Key parameters, including flame merging behavior, flame morphology, mass loss rate, flame spread rate, flame temperature, and radiant heat flux, were analyzed. The results revealed that cable spacing critically affects flame interaction, with three distinct flame merging modes—continuous merging, intermittent merging, and non-merging—identified as spacing increases. A critical spacing of 2.5 mm was found, at which the flame spread rate and mass loss rate reached their maximum, approximately 1.7 times higher than that of a single cable. At intermediate spacings (2.5–12.5 mm), enhanced flame interaction and radiative feedback significantly intensified combustion, leading to higher flame temperatures and radiant heat peaks. Conversely, insufficient oxygen supply at zero spacing and reduced flame interaction at large spacings (15 mm) resulted in diminished combustion efficiency. These findings highlight the importance of cable spacing as a key design parameter for mitigating fire hazards in electrical installations, providing valuable insights for fire safety engineering and risk assessment. Full article

This paper investigates the dual effects of slope variation and flame interaction on counter-directional flame propagation through numerical simulations of polymethylmethacrylate (PMMA) plates. Critical flame propagation parameters, including flame morphology, flame spread speed, mass loss rate, and radiative heat flux density, were analyzed using the Fire Dynamics Simulator (FDS v6.7.5) software. By comparing counter-directional flames and unilateral flames under varying slope conditions, we evaluated how flame interactions influence flame spread speed and mass loss rate, as well as the role of the view factor in radiative heat flux distribution. Numerical results revealed that the counter-directional fire propagation process on slopes could be divided into four distinct stages based on variations in flame spread rate and mass loss rate. Moreover, we propose a novel method to quantify flame interaction intensity on slopes using flame spread time. These findings enhance the mechanistic understanding of slope-dependent counter-directional flame propagation. Full article

In recent years, there has been increasing interest in new materials such as ceramic matrix composites (CMCs) for power generation and aerospace propulsion applications through hydrogen combustion. This study employed a deep artificial neural network (DANN) model to predict the ablation performance of CMCs in the hydrogen torch test (HTT). The study was conducted in three phases to increase the accuracy of the model’s predictions. Initially, to predict the thermal behavior of ceramic composites, two linear machine learning models were used known as Lasso and Ridge regression. In the second step, four decision tree-based ensemble machine learning models, namely random forest, gradient boosting regression, extreme gradient boosting regression, and extra tree regression, were used to improve the prediction accuracy metrics, including root mean square error (RMSE), mean absolute error (MAE), correlation coefficient (R² score), and mean absolute percentage error (MAPE), relative to the previously introduced linear models. Finally, to forecast the thermal stability of CMCs with time, an optimized DANN model with two hidden layers having rectified linear unit activation function was developed. The data collection procedure involved preparing CMCs with continuous Yttria-Stabilized Zirconia (YSZ) fibers and silicon carbide (SiC) matrix using a polymer infiltration and pyrolysis (PIP) technique. The samples were exposed to a hydrogen flame at a high heat flux of 183 W/cm² for a duration of 10 min. A good agreement between the DANN model’s predictions and experimental data with an R² score of 0.9671, RMSE of 16.45, an MAE of 14.07, and an MAPE of 3.92% confirmed the acceptability of the developed neural network model in this study. Full article

Enhancing the thermal resistance of carbon fiber-reinforced polymers (CFRPs) with flame retardants or coatings often leads to increased weight and reduced mechanical integrity. To address these challenges, this study introduces an innovative approach for developing nanocomposites using carbon-based nanoparticles, while preserving the structural lightweight properties. For this, carbon black particles (CBPs) up to 10% and carbon nanotubes (CNTs) up to 1.5% were incorporated into the RTM6/G939 composite material. The obtained samples were then analyzed for their properties and heat resistance under one-sided thermal loading at a heat flux of 50 kW/m². Results demonstrate that integrating these particles improves heat conduction without compromising the material’s inherent advantages. As a result, thermo-induced damage and the resulting loss of mechanical strength are delayed by 17% with CBPs and 7% with CNTs compared to the unmodified material. Thereby, the thermal behavior can be accurately modeled by a straightforward approach, using calibrated, effective measurements of the nanoparticles in the polymer matrix rather than relying on theoretical assumptions. This approach thus provides a promising methode to characterize and improve thermal resistance without significant trade-offs. Full article

The wind and slope are deemed to be the determinant factors driving the extreme or erratic spread behavior of wildfire, which, however, has not been fully investigated, especially to elaborate the mechanism of fire spread associated with heat transfer and fluid dynamics. A systematic study is therefore carried out based on a physical-based simulation and proper orthogonal decomposition (POD) analysis. Results show that compared to the wind, the slope plays a more profound effect on the fire structure; with the increase in slope, the fire line undergoes a transition from a W-shape to the U- and pointed V-shape, accompanied by stripe burning zones, indicating a faster spread but incomplete combustion. The wind effect is distinguished by mainly inducing a turbulent backflow ahead of the fire front, while the slope effect promotes convective heating via the enhanced slant fire plume. Different mechanisms are also identified for the heat transfer ahead of the fire line, i.e., the radiative heat is affected by the combined effects of the flame length and view angle, and in contrast, the convective part of the heating flux is dominated by the action of the flame attachment, which is demonstrated to play a crucial role for the fire spread acceleration at higher slopes (>20°). The POD analysis shows the distinct pattern of flame pulsating for the respective wind and slope effects, which sheds light on modeling the unsteady features of fire spreading and reconfirms the necessity of considering the different effects of these two environmental factors. Full article

The growing intensity and frequency of bushfires across the globe pose serious threats to building safety when it comes to the vulnerability of glass windows. During bushfires, extreme heat can cause significant damage to these windows, creating openings that allow embers, radiant heat, and flames to enter buildings. This study investigated the effectiveness of various construction materials, including thin steel sheets, glass fibre blankets, aluminium foil layers, and intumescent layers on glass fibre blankets, as bushfire-resistant shutters for protecting windows in bushfire-prone areas. The shutters were tested under two scenarios of radiant heat exposure: rapid and prolonged exposures of 11 and 47 min, respectively. Heat transfer models of the tested shutters were developed and validated using fire test results, and then comparisons of the performance of materials were made through parametric studies for bushfire radiant heat exposure. The results show that a 0.4 mm glass fibre blanket with aluminium foil performed best, with very low glass temperatures and ambient heat fluxes due to the reflective properties of the foil. Similarly, a thin steel sheet (1.2 mm) also effectively maintained low glass temperatures and ambient heat fluxes. Additionally, graphite-based intumescent coating on a glass fibre blanket reduced the ambient heat flux. These results highlight the importance of bushfire-resistant shutters and provide valuable insights for improving their design and performance. Full article

This study presents an experimental investigation into the effects of fire size on burning characteristics within well-confined military vehicle engine compartments. The research evaluates burning duration, self-extinguishing phenomena, heat release rates, pressure dynamics, and flame morphology using heptane pool fires of varying pan diameters (8 cm, 16 cm, and 24 cm). Key findings include the proportional relationship between fire size and heat release rate, with larger pans causing higher oxygen consumption, elevated pressure differences, and increased total heat flux. Self-extinguishment was observed for larger pans due to oxygen depletion, with extinction time linked to the ratio of compartment volume to heat release rate. Temperature measurements revealed significantly higher ceiling temperatures and heat flux levels for larger fires, emphasizing the structural and thermal risks. These results contribute to understanding fire behavior in confined spaces, offering practical implications for designing fire protection systems tailored to military vehicles. Full article

In the H₂O₂/Kerosene bipropellant thruster, a liquid fuel jet is transversely injected into a crossflow of hot oxygen and water vapor, catalytically decomposed from a liquid oxidizer. Due to the high temperature and oxygen-rich environment, kerosene is auto-ignited without the need for an additional ignition source. Hence, fuel trajectory and breakup processes play a significant role in determining the performance of the rocket engine. However, little effort has been made to analyze these characteristics during actual rocket engine operation, mainly due to its harsh operating conditions of high temperature and pressure. In this study, an optically accessible combustion chamber was prepared to visualize the trajectory and breakup processes of the liquid jet during rocket engine operation. Physical and chemical processes inside the chamber were recorded using a high-speed camera utilizing a shadowgraph technique along with chemiluminescence suppression. Hot-fire tests were performed using 90 wt.% hydrogen peroxide and Jet A-1 in various jet-to-crossflow momentum flux ratios. Test cases with water injection replacing fuel were conducted with varying momentum flux ratios to identify the effect of the combustion process on the liquid jet. The study revealed that the existing correlations for the liquid jet trajectory commonly used for designing the H₂O₂/Kerosene bipropellant thruster in the past induced significant errors and suggested that the radiation heat transfer from the combustion flame downstream could affect the breakup processes upstream. A new correlation was suggested that accurately predicts the liquid fuel jet trajectory of the H₂O₂/Kerosene bipropellant thruster. Full article

This study is dedicated to an in−depth analysis of the combustion characteristics of extruded polystyrene (XPS) as a building insulation material with the aim of accurately assessing its fire risk in the built environment. Innovatively, this research employed a cone calorimeter equipped with a self−designed insulating sample holder to conduct a systematic experimental study. Additionally, it performed a comprehensive analysis of the ignition characteristics, heat release rate, fire hazard, smoke release, and toxic gas emission of XPS materials. The experimental results revealed that the combustion behavior of XPS is influenced by multiple factors, including the content of flame retardants and external heat flux, which significantly affect the fire hazard of XPS. When the thermal radiation intensity escalates from 25 kW/m² to 55 kW/m², the peak heat release rate of XPS−B1 rises from 428 kW/m² to 535 kW/m², marking an increase of 25.00%. Conversely, the peak heat release rate of XPS−B2 surges from 348 kW/m² to 579 kW/m², reflecting a substantial increase of 66.38%. This research not only provides a solid theoretical foundation and detailed experimental data for the fire behavior of XPS materials but also holds significant practical importance for enhancing the fire safety of buildings. Overall, this research contributes to the scientific understanding of XPS insulation materials and supports the development of more effective fire prevention measures in construction. Full article

The main purpose of this article was to determine the smoke-generating and thermal properties of selected types of natural leather. Differences in the amount of smoke generated from the type of finish used in the technological processing of leather were observed. Research has shown that the burnt nubuck (367) sample with exposure at the heat flux intensity of 25 kW/m² without the presence of a pilot burner flame achieved the highest value of the specific optical density D_s,max. Comparable values, 312 and 297, were recorded for grain bovine leather and velour bovine leather, respectively; on the other hand, the lowest value of the tested parameter amounting to 220 was recorded for lacquered bovine leather. Tests executed with the use of thermogravimetric analysis show that except for nubuck leather, the start of thermal decomposition for all types of samples appears to be fairly similar and was found to be within the range of 275–282 °C. The highest value of thermal decomposition onset, i.e., 302 °C, was recorded for nubuck leather. The highest percentile of residues from thermal decomposition, i.e., 9%, was obtained for grain bovine leather. This implies that the least gaseous phase during its thermal decomposition in test conditions was generated by this type of leather. The highest average D_s,max value was obtained for nubuck (367), and decreased as follows: grain bovine leather (312) > velour bovine leather (297) > lacquered bovine leather (220). Full article

A jet flame occurs when the release of flammable gas or liquid ignites, resulting in a long, intense, and highly directional flame. This type of fire is commonly associated with industrial incidents involving pipelines, storage tanks, and other pressurized equipment. Jet fires are a significant concern in the oil and gas industry due to the handling and processing of large volumes of flammable hydrocarbons under pressure. The new computational method presented here includes several aspects of hydrogen jet flame accidents and their mitigation: the CFD simulation of a hydrogen jet flame using the HyRAM code and Fire Dynamics Simulator (FDS) software 5.0 using a large eddy simulation (LES) turbulence model; the calculation of the gaseous mixture’s thermo-physical properties using the GASEQ thermochemical code; the calculation of convective and radiative heat fluxes using empirical correlation; and a heat transfer simulation on the pipe thermal barrier coating (TBC) using COMSOL Multiphysics software 4.2a during the heating phase. This method developed for the ceramic blanket was validated successfully against the previous experimental results obtained by Gravit et al. It was shown that a jet fire’s maximum temperature obtained using FDS software was similar to that obtained using GASEQ thermochemical software 0.79 and HyRAM software. The TBC’s surface temperature reached 1945 °C. The stainless steel’s maximal temperature reached 165.5 °C. There was a slight decrease in UTS at this temperature. Full article

A mixture fraction approach was applied to predict the combustion behavior of polymeric materials. In comparison to the combustion of gaseous mixtures, the presence of solid fuels complicates the description of the combustion. Accurate predictions of burning characteristics can only be achieved through the proper resolution of heat and mass transfer between the gas-phase flame and the solid fuel. We focused on a model case of flame spread over a solid fuel surface. Polymethyl methacrylate (PMMA) was selected as a polymeric material. An approach was proposed to account for heat loss from the gas phase to the solid material through calculations of counterflow diffusion flames with the flame positioned closely to the fuel supply. A combination of these solutions was applied to restore temperature and species mass fractions from tabulated chemistry. An analysis of the numerical results from previous studies on flame spread over PMMA, based on one-step combustion reaction and calculating the chemical source term at each time step, demonstrated a monotonic distribution of the mixture fraction in the flame region between the fuel and oxidizer streams. The shape of the flame tip was satisfactorily resolved using the proposed approach that employs a skeletal chemical mechanism for gas-phase combustion consisting of 29 species and 33 reactions. However, the heat flux from the flame to the solid fuel was overpredicted, resulting in higher flame spread rates compared to experimental data and previous calculations. Preliminary results show a promising opportunity for the mixture fraction approach to describe the combustion behavior of polymers. An analysis showed that oversimplifying the heat transfer process in the flame tip area is a main source of prediction inaccuracies. Multidimensional heat transfer has to be properly incorporated into a tabulated chemistry approach. Several potential directions for future work have been outlined. Full article

The development of a methodological approach to detecting the presence of flame retardants in building materials and products and finding their concentration is an essential part of the performance evaluation of flame retardants for timber. The above issue is a relevant constituent of supervision over fire safety compliance at construction facilities. Thermal analysis was used in this research project to (1) detect the presence of flame retardants in timber, and (2) identify methods of their application. Comparative experiments were conducted to detect the presence and effectiveness of flame retardants applied to the surface and inner layers of specimens of timber planken (façade board) at a construction facility. Relevant values, characterizing the thermal decomposition of timber specimens, enable predicting the heat flux rate that triggers ignition. A quick test, conducted to check the flammability of specimens, confirmed the authors’ hypothesis. The study revealed principal (relevant) thermo-analytical criteria for the fire resistance of timber impregnated with combustion retardants using different methods of impregnation. A methodological approach to studying relevant thermo-analytical characteristics was developed to evaluate the efficiency of (1) fire resistance of timber products and (2) fireproofing techniques. Flammability and combustibility of timber impregnated with fire retardants was prognosticated. It was revealed that the proposed methodology can monitor the efficiency of fireproofing applied to façade structures made of pine timber. Full article

Cryogenic compressed hydrogen (CcH2) technology combines the advantages of high pressure and low temperature to achieve high hydrogen storage density without liquefying the hydrogen, which has broad application prospects. However, the safety concerns related to cryogenic hydrogen need to be carefully addressed beforehand. In the present work, cryogenic hydrogen jet flames are experimentally investigated for various release pressures and initial temperatures. The flame length and thermal radiation flux were measured for horizontally releasing with nozzle diameters of 0.5–2 mm, temperatures ranging from 93 to 298 K, and initial pressures of 2–10 MPa. The results show that the flame length is dependent on the nozzle diameter, stagnation pressure and temperature. At a given pressure, the flame length, size and total radiant power increase with decreasing temperature, which is attributed to the lower jet flow velocity and higher density of low-temperature hydrogen. The normalized flame length L_f/D is correlated with the pressure ratio and temperature ratio. The correlation can be used to predict the flame length at various hydrogen pressures and temperatures. The normalized flame length of the cryogenic hydrogen jet flame is greater than that of the room-temperature hydrogen jet flame. The radiative heat flux of the flame can be predicted by the mass flow rate of the jet flow. Full article

Prescribed burning is a cost-effective method for reducing hazardous fuels in pine- and oak-dominated forests, but smoke emissions contribute to atmospheric pollutant loads, and the potential exists for exceeding federal air quality standards designed to protect human health. Fire behavior during prescribed burns influences above-canopy sensible heat flux and turbulent kinetic energy (TKE) in buoyant plumes, affecting the lofting and dispersion of smoke. A more comprehensive understanding of how enhanced energy fluxes and turbulence are related during the passage of flame fronts could improve efforts to mitigate the impacts of smoke emissions. Pre- and post-fire fuel loading measurements taken during 48 operational prescribed burns were used to estimate the combustion completeness factors (CC) and emissions of fine particulates (PM_2.5), carbon dioxide (CO₂), and carbon monoxide (CO) in pine- and oak-dominated stands in the Pinelands National Reserve of southern New Jersey. During 11 of the prescribed burns, sensible heat flux and turbulence statistics were measured by tower networks above the forest canopy. Fire behavior when fire fronts passed the towers ranged from low-intensity backing fires to high-intensity head fires with some crown torching. Consumption of forest-floor and understory vegetation was a near-linear function of pre-burn loading, and combustion of fine litter on the forest floor was the predominant source of emissions, even during head fires with some crowning activity. Tower measurements indicated that above-canopy sensible heat flux and TKE calculated at 1 min intervals during the passage of fire fronts were strongly influenced by fire behavior. Low-intensity backing fires, regardless of forest type, had weaker enhancement of above-canopy air temperature, vertical and horizontal wind velocities, sensible heat fluxes, and TKE compared to higher-intensity head and flanking fires. Sensible heat flux and TKE in buoyant plumes were unrelated during low-intensity burns but more tightly coupled during higher-intensity burns. The weak coupling during low-intensity backing fires resulted in reduced rates of smoke transport and dispersion, and likely in more prolonged periods of elevated surface concentrations. This research facilitates more accurate estimates of PM_2.5, CO, and CO₂ emissions from prescribed burns in the Pinelands, and it provides a better understanding of the relationships among fire behavior, sensible heat fluxes and turbulence, and smoke dispersion in pine- and oak-dominated forests. Full article