Smoke Temperature Distribution Research Articles

The Impact of Initial Fuel Depth on the Combustion Efficiency of Pool Fire in an Enclosed Compartment: A Study Based on Zone Model Theory

In this paper, the effect of initial fuel depth on the combustion efficiency of pool fires in an enclosed compartment was experimentally studied. Three different sizes of pool fires were conducted in the experiments. Several combustion parameters including burning rate, smoke temperature distribution, and oxygen concentration of pool fires under the different initial fuel depths in closed compartments were obtained. Results showed that the pool fire with the different initial fuel depths would appear in two typical extinction modes: fuel burning out and self-extinction due to lack of oxygen. The whole burning process of the pool fire in the enclosed compartment can be divided into the following five stages: rapid rise stage, transition stage, stable combustion stage, boiling combustion stage, and extinguishing decay stage. The maximum and average values of the burning rate presented the power function of the initial fuel depth. The consumption of oxygen concentration in the compartment was mainly affected by the initial fuel depth, the pool size, and the compartment volume. Dimensionless characterization of the oxygen concentration was adopted to characterize the fire extinction behavior in the enclosed compartment. In addition, based on the combustion process and the extinction behavior, a global combustion efficiency of pool fire was proposed to predict the combustion characteristic while considering the initial fuel depth in the enclosed compartment.

Predicting smoke temperature distribution beneath ceiling for a large subway station fire

Fire accident seriously threatens the stable operation and personnel security in the subway station, and clarifying the smoke temperature distribution is conducive to arranging reasonably fire alarm. In this study, model experiments and numerical simulations are conducted to investigate the ceiling temperature profiles, mainly altering the heat release rate (HRR) and fire locations in a large subway station. The repeatability of the experimental data is confirmed, and the numerical model is validated by the measurement data. During a fire happening in a large-wide space, the smoke movement beneath the ceiling can be divided into radial and one-dimensional flow, whose prediction models are proposed under fire source located at the center. On this basis, it can be found that the radial temperature profile is independent of fire source location. While, the one-dimensional temperature distribution model is modified by introducing the effects of transvers and longitudinal fire locations respectively. This work could provide data support and theoretical reference for clarifying the smoke movement for large subway station fire.

Numerical study on smoke temperature distribution in naturally ventilated inclined tunnels: Effects of tunnel width and tunnel slope

Inclined tunnel fires exhibit unique characteristics compared to horizontal tunnel fires as a result of the stack effect. Nevertheless, there is still a lack of consensus among previous scholars regarding the smoke temperature distribution in inclined tunnel fires. This work conducts a numerical investigation on the smoke back-layering length upstream of the fire source and the temperature decay downstream of the fire source in naturally ventilated inclined tunnels with varying widths and slopes. Results indicate that as the tunnel slope increases from 0° to 8°, the smoke back-layering length first decreases and then continues at a constant value of 1.47H4/3/W1/3, while the effect of tunnel width is negligible. The decay factor in the one-dimensional flow stage (x/H≥4) exhibits two distinct patterns related to tunnel width: it initially remains constant and then drops when the tunnel is wide, whereas it monotonically drops when the tunnel is narrow. Two empirical models are developed to identify the segmented characteristics and verified through the relevant data from existing literature with similar fire scenarios. This work offers a method for estimating the smoke temperature distribution in inclined tunnels, providing crucial insights for fire prevention, smoke detection, and safety strategies in tunnel engineering.

Full-field temperature prediction in tunnel fires using limited monitored ceiling flow temperature data with transformer-based deep learning models

In practical tunnel scenarios, full-field coverage of sensors is impractical and costly. During a tunnel fire, the available information is constrained and localized, making the prediction of full-field smoke temperature distribution becoming a noteworthy challenge. This study proposes a transformer-based deep learning model to predict full-field smoke temperature distributions during fire incidents in real-time using limited temporal data from the sensors installed in localized regions below the ceiling, considering heat release rate of the fire source is unknown. The results indicate that proposed approach can predict the longitudinal temperature distribution throughout the tunnel with a length of 750 m by leveraging temperature data from limited sensors within a monitoring length of 210 m. It can further predict the vertical temperature profiles, and eventually estimate the full-field temperature distribution within the tunnel. The transformer model achieved R2 of 0.95 and 0.87 for longitudinal and vertical temperature distribution predictions, respectively. Under the influence of the self-attention mechanism, the transformer model has an advantage over the long short-term memory model in capturing global information, enhancing the accuracy of longitudinal temperature distribution predictions by 18.8 %. This study significantly contributes to effective emergency response and rescue strategies during tunnel fire incidents.

The Effect of Slope on Smoke Characteristics of Natural Ventilation Tunnel with Shafts

Tunnels with natural ventilation and extraction have become the focus of ventilation research in recent years. It is significant to study the characteristics of smoke in tunnel fires to ensure the safety of people and the tunnel structure. Previous research has mainly focused on natural ventilation in horizontal tunnels, and there are few studies on sloped tunnels. In this paper, we studied the smoke characteristics of natural ventilation extraction in slope tunnel fires both experimentally and theoretically. The small-scale experimental results showed that the position of the fire source, heat release rate (HRR), and the size of the shaft had little effect on the deflection angle of the fire plume. The deflection angle of fire plume was only related to the tunnel slope and increased with the tunnel slope. The slope had no effect on the smoke temperature distribution on the downside of the tunnel, while the smoke temperature on the upside decreased with the increase in the slope. The calculation models of the maximum smoke temperature rise and the smoke temperature distribution were obtained based on the experimental results and theoretical analysis. Compared with the experimental data, the developed semi-empirical models could provide a reliable prediction of smoke temperature.

Enhancing resilience in urban utility tunnels power transmission systems: Analysing temperature distribution in near-wall cable fires for risk mitigation

Urban utility tunnels are integral to the underground power transmission systems of cities. Enhancing the understanding of cable fire hazards within these tunnels is pivotal for fostering risk-resilient underground environments. This study delves into the temperature distribution characteristics of near-wall cable fires in urban utility tunnels. Employing a reduced-scale utility tunnel model, a series of fire experiments were conducted, focusing on the safety monitoring of horizontally arranged cables. Cone calorimeter tests were initially performed to ascertain the heat release rate of cable fires. The study meticulously considered cable spatial position parameters, such as cable height and near-wall distance, as dependent variables, and monitored real-time temperature changes within the utility tunnel under various fire scenarios.The findings reveal that the cable’s proximity to the wall significantly influences the fire temperature field. For instance, when a fire near the sidewall (at 1 cm) is compared to one in the middle of the tunnel (at 20 cm), the ceiling maximum temperature is reduced by 38.9 %. The sidewall’s limiting effect diminishes fire energy release, moderates vertical temperature decay, and enhances longitudinal temperature attenuation. The study introduces dimensionless mathematical models that account for the sidewall effect, quantifying the characteristics of fire-induced smoke temperature distribution in utility tunnels, such as ceiling maximum temperature rise, vertical smoke temperature profile, and longitudinal smoke temperature decay. The models’ predicted values closely align with the experimental results.These insights are pivotal for integrating cable numbers and spatial positioning in scenario-based fire prevention and mitigation strategies. The study’s implications extend to the design and operation of urban utility tunnels, emphasizing the need for strategic cable placement and the potential for mathematical models to inform risk mitigation measures. The research contributes to the advancement of sustainable urban development by providing a framework for enhancing the safety and resilience of critical infrastructure against fire hazards.

Numerical study on the smoke temperature distribution beneath the ceiling of a single-ended sealing tunnel under the condition of double fire sources

As a special tunnel structure, the single-ended sealing tunnel has only one evacuation port, which increases greatly the risk of fire. Numerical modeling of a double source fire in a single-ended sealed tunnel was developed based on FDS 6.7. The effects of double-source spacing and end walls on ceiling smoke temperature were analyzed and discussed. The results show that when the double fire sources are considered as a whole, there are varying degrees of smoke backflow throughout the tunnel, with the upstream smoke backflow phenomenon being more pronounced under the influence of the end wall. In this study, the dimensionless separation distance φ is introduced and divided into two regions to quantify the effect of the spacing of the double fires. When 0 ≤ φ < 0.625, the maximum smoke temperature beneath the ceiling falls exponentially with increasing separation distance. On the other hand, when 0.625 < φ ≤ 1, the maximum smoke temperature under the ceiling rises exponentially. Furthermore, we suggest empirical formulas for forecasting the longitudinal distribution of downstream temperatures as well as the maximum smoke temperature of the ceiling. The predictive equations’ dependability was further confirmed by contrasting the predicted equations with simulated and historical experimental data. The study results serve as a reference for fire prevention and rescue in similar special tunnel structures, such as single-end sealing.

Influence of external wind on fire characteristics and smoke dynamics in a stairwell adjacent to a room

A range of fire experiments were conducted to explore fire characteristics and smoke dynamics in a 1/6-scale stairwell adjacent to a room at different external wind velocities. The results indicated that the flame volume during the initial stage and the time taken for combustion to enter the steady stage both decrease with the increasing wind velocity. There are two opposite effects of the external wind on the fire combustion in a burning room adjacent to a stairwell. The inhibition effect plays an important role at lower wind velocities, leading to a decrease in the mass loss rate (MLR) of the pool fire. Conversely, the promotion effect dominates at higher wind velocities, resulting in an increase in the MLR. Stack effect and external wind demonstrate a synergistic relationship during experiments, and a correlation of the airflow velocity, wind velocity and heat release rate (HRR) is established. There are intersections in temperature curves at different wind velocities due to the smaller temperature decay rate in the stairwell and the lower smoke temperature near the pool fire at a higher velocity. Furthermore, a prediction model is also proposed for the smoke temperature distribution inside the stairwell, taking into account the wind velocity and HRR.

Effect of width and slope of large cross-section tunnel on ceiling smoke temperature under natural ventilation

ABSTRACT When a fire occurs in a large cross-section tunnel with slope, the distribution characteristic of ceiling smoke temperature illustrates special laws under the effect of chimney effect, the thermal radiation feedback, and the air entrance limit from walls. A series of numerical simulations are conducted through FDS simulation software based on the actual size of highway tunnel. The influence of large cross-section tunnel width and slope on ceiling smoke temperature when fire occurs are discussed. The research results show that (1) as the tunnel slope increases from 5° to 20°, the distance between the maximum ceiling smoke temperature point and the fire source is 0.5 m, 1 m, 1.7 m, 2.4 m, respectively, and the distance between the ceiling impact point and the fire source is 1 m, 1.8 m, 2.3 m, 3 m, respectively. As the tunnel width increases from 10 m to 20 m, the distance between maximum ceiling smoke temperature point and fire source increases 0.9 m, 1.1 m, 1.3 m, 1.8 m, 2.5 m, and 2.6 m. (2) The prediction formula of maximum ceiling smoke temperature is modified, and a dimensionless relationship among the maximum ceiling smoke temperature and tunnel slope and tunnel width is established. (3) The formula of longitudinal ceiling smoke temperature distribution is modified, and the relationship among tunnel slope, tunnel width, tunnel height, and longitudinal ceiling smoke temperature distribution is established. The research conclusions can provide a theoretical basis for fire prevention design, smoke control and evacuation of this kind of large cross-section tunnel fire.

Study of spatial temperature features of road tunnel fires under multiple factors

AbstractAfter a highway tunnel fire, the rapid change of the internal ambient temperature directly affects the personal safety of pedestrians. Based mainly on the lateral possibility of fire location and considering the coupling effect of multiple factors in a two‐lane highway tunnel, this study systematically carried out 63 full‐size tunnel fire simulation studies relying on Fluent software. The smoke temperature distribution patterns in the transverse and longitudinal spaces of the tunnel after the fire were revealed. This study shows that the smoke temperature below the tunnel vault is susceptible to the effect of sidewall restraint, making the maximum temperature of the tunnel vault of the offset fire source large; considering the lateral location of the fire source, the maximum temperature prediction formula of the tunnel vault is modified to expose the change law of the longitudinal temperature decay of the vault. This paper reveals for the first time the law of temperature distribution changes at the characteristic height of the human eye on the evacuation platform in the tunnel; the systematic study of the fire source cross‐sectional temperature distribution changes at the key lining structure points, and it is found that a low‐temperature space conducive to personnel escape exists in the lower part of the tunnel away from the fire source side. The results of the study are beneficial to the design of safe evacuation paths in the tunnel and the active emergency evacuation of personnel in the near‐fire source area.

Burning characteristic and ceiling temperature of moving fires in a tunnel: A comparative study

Moving fire is a very important fire scenario in highway tunnel and subway tunnel. Compared to fixed fire sources, there is still limited research on moving fires in tunnels. In order to reveal the burning characteristics and evolutionary mechanisms of moving fires in tunnels, this study conducted reduced scale tunnel fire experiments on moving fires under natural ventilation conditions (Movefire) at travelling speeds ranging from 0.5 m/s to 2.0 m/s, as well as fixed fires under longitudinal ventilation (Ventfire) velocities ranging from 0.5 m/s to 2.0 m/s. The results demonstrate that it is unreasonable to solely use Ventfire experiments as a substitute for Movefire experiments to study fire development and ceiling smoke temperature distributions. When the travelling speed of fire and the ventilation velocity were equal, the HRRs of Movefires were less than those of Ventfires. At the same relative moving velocity of 0.5 m/s, Ventfire received more fresh air to increase burning intensity, while Movefire experienced decreases in thermal feedback and burning intensity. The Movefire smoke temperature rise was small and short in duration, while the Ventfire smoke temperature rise was large and long in duration. Furthermore, the dimensionless maximum ceiling temperature rise of the Movefire experiment was lower than that of the Ventfire experiment. And then a modified ceiling temperature model applicable to the Movefire experiment was proposed by introducing a speed correction factor.

Study on Smoke Temperature Distribution Characteristics of Coal Mine Inclined Roadway Fire

ABSTRACT Mine roadway fire is a major natural disaster that threatens the safety of mine production for a long time. 65% of the total casualties of coal mines are caused by mine roadway fire. In order to study the smoke temperature distribution characteristics of inclined roadway fire in coal mine and reduce personnel injury and equipment loss. In this paper, the calculation formula of the maximum air flow temperature and the expression of the maximum temperature on the downwind side of the fire area are presented. Based on the actual roadway of Wusu Coal mine in Hohhot, Inner Mongolia, a “Mine inclined roadway fire simulation experimental system” with similarity ratio of 1:20 is established. The fire smoke temperature under different roadway inclination (5°, 10°, 15°) and different inlet wind speed (0.5 m/s, 1.0 m/s, 1.5 m/s) was tested and analyzed, and the temperature field of inclined roadway during fire was simulated and analyzed by Ansys numerical simulation software. The research shows that when the inlet wind speed is larger or the roadway inclination is larger, the heat diffusion is faster, the temperature field is longer and narrower, and the temperature is lower, but the temperature variation trend of the overall combustion process remains unchanged. By studying the temperature distribution of smoke in inclined roadway fire, it is convenient to take corresponding measures in time to minimize the impact of fire.

Water spray effects on fire smoke temperature distribution beneath a symmetrical V-shaped tunnel ceiling

The coupling effects of the double-slope stack effect, the thermal buoyancy induced by the V-shaped tunnel fire and the drag force generated by the water spray system alter fire smoke flow regulation compared to fire smoke flow in a horizontal tunnel. By numerical simulation, this work investigates the effect of water spray flow rate (0 L/min – 600 L/min), atomization angle (0–150°) and the length within fire source and the grade change point (0–120 m) on smoke temperature distribution beneath a symmetrical V-shaped ceiling. The findings indicate that the cooling effect on smoke temperature can be significantly improved by increasing the rate of water spray flow, while water spray increasing angle and tunnel slope have little contribution to the cooling smoke temperature. Thus an improved ceiling smoke temperature distribution model is proposed by importing the flow rate, angle coefficients and tunnel slope. As the fire source distance from the grade change point increases, stack effect on fire smoke flow could be categorized into three zones, which are the double-slope control zone, the transition zone and the single-slope control zone, which causes that downstream smoke temperature become higher gradually than the upstream one, while the smoke temperature difference tends to stabilize at the single-slope control stage. Finally, a global ceiling smoke temperature distribution in the symmetrical V-shaped tunnel installed a water spray system is established by introducing fire source distance coefficients.

Study on moving fire smoke characteristics and mechanical ventilation system of tunnel

Limited by the narrow space of the tunnel, fire has become one of the important factors threatening the safe operation of subway especially the fire on a moving vehicle. Researches on moving fire through the large length-width ratio of tunnels are extremely lacking at present. This study investigates the characteristics of moving fire and the influence of mechanical ventilation under different conditions. First, a three-dimensional model of the tunnel with the moving train is established, and the dynamic mesh simulation is conducted and validated by the experiments. Then, the variation of smoke temperature distribution under different fire source intensities, train speeds, and blocking ratios are studied. Based on the smoke flow characteristics, the mechanical ventilation with different layouts of draught fans is investigated. It is found that the maximum growth rate of smoke spread is 70.90% with an increase of two fans. Finally, the influence of the tunnel shaft on the smoke characteristics under different fire source locations is discussed. When the fire source is under the shaft, the smoke discharge efficiency reaches the highest, almost 5.89% and 21.91% higher than other conditions. This study provides the basis and reference for the research and control of the tunnel moving fire.

Simulation Research on Effects of Ambient Pressure on Plug-Holing Phenomenon in Tunnel Fires with a Shaft

This paper studied the effects of ambient pressure on the plug-holing phenomenon in tunnel fires with a shaft by a Fire Dynamics Simulator. The influence of ambient pressures on the smoke movement, temperature distribution, critical Richard number (Ric) and critical shaft height for plug-holing were analyzed in detail. A new prediction formula of smoke flow velocity considering different pressures was modified. A prediction formula of smoke temperature distribution beneath the ceiling under different pressures was developed. As a result, a prediction model of Richard numbers to determine whether the plug-holing occurs was proposed by combining smoke flow velocity and smoke temperature distribution. The critical Richard numbers (Ric) and critical shaft height (hc) increases as the pressure decreases. Outcomes in this study can provide references for the design of a natural ventilation system in tunnel fires at a higher altitude.

Experimental Study on the Smoke Temperature Decrease near Natural Vents Induced by Air Entrainment in a Tunnel Fire

Previous studies have shown that there is a large difference in the temperature of smoke in the upstream and downstream of a vertical shaft, but no quantitative study on the subject has been conducted. In this paper, a model experimental test was conducted to study the effect of a natural vertical shaft on the distribution of smoke temperature in tunnel fires. A laser sheet was used as an assisting tool to show the smoke flow field. A series of tests were conducted with shaft heights varying from 0.2 m to 1.2 m and a heat release rate (HRR) of 9 kW, 17 kW, 29 kW, and 65 kW. The entrainment phenomenon around the vertical shaft was analyzed, and the results showed that the amount of fresh air entrainment is the main reason for the temperature decrease in upstream and downstream smoke temperatures. Based on the experimental results, an empirical model for predicting the amount of fresh air entrainment and a prediction model of the downstream smoke temperature were proposed, and the predicted values are in good agreement with the experimental values.

Smoke movement and control in longitudinal ventilated tunnel fires with cross-passages

This paper studies the characteristics of smoke movement and control in longitudinal ventilated tunnel fires with cross-passages through numerical modeling. Previous reports mainly focused on fires in single-hole tunnel, however, tunnels with cross-passages have been widely applied in real life, the cross-passages between main tunnels provide additional path for air and fire smoke, and significantly affect smoke temperature and back-layering length, which has not been studied in the past. Hence, full-scale simulations were conducted considering different heat release rates, fire locations, longitudinal ventilation velocities, and cross-passage intervals in this study. It shows that the smoke temperature distribution with or without cross-passages is almost the same under natural ventilation condition, while the temperature gradually increases with the decrease of interval of cross-passages under longitudinal ventilation condition. Due to the more air leakage, the smoke back-layering length increases with decreasing interval of cross-passage. The air leakage mass through the cross-passage was then characterized by the interval of cross-passages and fire location. Considering fire position and interval of cross-passages, the actual ventilation velocity is used to establish a new smoke back-layering length model. A basic understanding was provided by new findings in this study for smoke movement and control in tunnel fires with cross-passages.

Study on the Air Inlet Velocity and Temperature Distribution in an Inclined Tunnel with Single Shaft under Natural Ventilation

The emergence of inclined tunnels under natural ventilation has brought many new fire safety issues. The smoke movement in the tunnel is affected by the chimney effect induced by the shaft and the downstream tunnel. The characteristics of temperature distribution in inclined tunnels are different from horizontal tunnels, which is worthy of further study. A series of conditions were carried out in an inclined model tunnel with a single shaft to investigate the temperature distribution characteristics. In this study, the longitudinal air inlet velocity is used to replace the longitudinal ventilation wind velocity. Results showed that the variation of fire source location Lf,, shaft height Ls, and the tunnel slope φ have obvious effect on the air inlet velocity. Based on the previous theories and the non-dimension analysis, the formulas of the dimensionless longitudinal inlet air velocity and the distribution of the maximum smoke temperature under the ceiling are proposed, which show good consistency with the simulation results. The reduced-scale experiments were conducted to validate the results of numerical simulation. The error range between the theoretical results and the simulation results is less than 20%.

Numerical Simulation on Smoke Temperature Distribution in a Large Indoor Pedestrian Street Fire

In order to study the characteristics of fire smoke spread and temperature distribution of a large indoor pedestrian street under different heat release rates and smoke exhaust modes, this paper focuses on the analysis of fire smoke spread, visibility, smoke temperature distribution and variation curves in an atrium. This paper uses a numerical simulation method to conduct research. PyroSim fire simulation software is used to calculate this project, which is based on a full-scale experimental design scheme. The numerical simulation results show that under the conditions of higher heat release rate, the smoke spread rate is greater than that under the conditions of lower heat release rate. Furthermore, the average temperature of smoke in the atrium is also greater, up to about 400 °C. The conditions of a higher heat release rate also show the characteristics of faster generation, faster spread and a larger volume of smoke. When the smoke exhaust system is turned on, the thickness of the smoke layer and the smoke temperature decrease. There then comes a situation where the stabile section of the fire ends in advance. The simulation results of vertical temperature distribution in an atrium can fit the modified McCaffrey plume model in any case. Under all cases, the smoke temperature reaches the maximum directly above the fire source. The horizontal dimensionless smoke temperature rises under the atrium roof, and decreases exponentially with the dimensionless distance from the fire source. The greater the heat release rate of fire source is, the smaller the attenuation coefficient is, with a more than 50% change. When the smoke exhaust system is turned on, the smoke flow accelerates and the smoke is cooled rapidly. Thus, the attenuation coefficient increases. Additionally, the effect of mechanical smoke exhaust is better than natural smoke exhaust, because mechanical smoke exhaust makes air flow and heat exchange more intense. The variation amplitudes of the attenuation coefficient under natural smoke exhaust and mechanical smoke exhaust are 13% and 22%, respectively.

Numerical Study on Smoke Diffusion and Smoke Control in Urban Underground Curved Tunnel

Effects of the radius and fire heat release rate on the smoke propagation and smoke control in curved tunnel are studied by the numerical methods. Six radiuses as 70 m, 150 m, 200 m, 250 m, 300 m and 400 m and two different fire sizes as 5 MW and 30 MW are involved. Numerical results show that comparing with the smoke flow in the straight tunnel, smoke temperature distributions across the cross-section is not symmetry with the centerline in the curved tunnel, and the smoke diffusion close to the outside boundary appears to be fast. At the higher level of the curved tunnel, such as 3 m above the tunnel floor, the smoke temperature would decrease with the distance from the fire increasing. However, at the lower level of the tunnel, the temperature would increase firstly and then decrease, maximum temperature would occur in the bend region of the curved tunnel. When the fire heat release rate is big, this temperature might be high enough to injure the people. Smoke ventilation system would run in time under this condition. Critical velocity in curved tunnel is larger than that in the straight tunnel.