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Increasing longitudinal ventilation velocity enhances the heat transfer from hot gases to fuel and then results in an increase of the fire growth rate in a tunnel fire. However, the effect of ventilation on the flame spread and the fire growth rate has not been fully explored. In this paper the relationship between the flame spread and the fire gro...
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... schematic diagram of flame spread over a solid surface is shown in Fig. 1. The temperature in each control volume close to the pyrolysis zone increases gradually due to heat feedback from the flame and the hot gases until it reaches the ignition value where it starts to burn. The energy equations for the control volumes upstream and downstream can be expressed as ...
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Citations
... However, owing to numerical sensitivity, the design fire curve should be predicted by randomly selecting r, k, and n. Ingason analyzed Numajiri and Furukawa's model equation and energy balance relationship and presented a modified exponential equation, in which r and k are dependent on n [14][15][16][17][18][19]. According to their findings, if the maximum heat release rate and time required to reach this maximum heat release rate are given, then the design fire curve can be relatively accurately predicted over the entire duration of the fire by using n. ...
... where Q ig is the calorific value of the ignition heat source. Ingason presented a modified exponential equation (Equation (4)) to represent the phenomenon of the varying heat release rate during the combustion period using Numajiri and Furukawa's exponential model equation, Q max , and the total energy generated (E tot ) [14][15][16][17]. (4) where n, r, and k are the retard index, amplitude coefficient, and wave width coefficient, respectively. When t = t max , Q f (t max ) = Q max ; hence, r and k must satisfy Equations (5) and (6). ...
This study analyzed a design fire curve in accordance with of an ignition heat source in a compartment. For this purpose, a structure with a 1:3 reduced scale of the ISO 9705 room corner tester was fabricated using fireboard, and the time variant heat release rate was calculated according to the volume of a polyethylene foam combustible. To predict the design fire curve, the exponential equation proposed in a previous study was compared with the heat release rate measured in a fire experiment. The retard index, which is the main factor used to predicting the time required to reach the maximum heat release rate, decreased proportion to the ignition heat source. This relationship was presented in an empirical equation. Especially, the retard index decreased according to the size of the ignition heat source regardless of the volume of the polyethylene foam combustible. By establishing experimental data considering the type and change in the volume of combustibles, the findings of this study can be used to create improved design fire curve prediction models.
... [15,16]. Our experience of tunnel fire tests shows there is a good agreement between model scale and large scale test results on many focused issues [17][18][19]. Despite the radiation terms cannot be simply preserved, some previous researches, e.g. ...
A series of model scale tunnel fire tests was carried out to investigate effects of the fire suppression system on production of key combustion products including CO and soot. The key parameters accounted for in the tests include fuel type, ventilation velocity and activation time. The results show that fire suppression indeed has influence on production of combustion products especially for cellulose fuels. In case that the fire is not effectively suppressed, e.g. when the water density is too low or activation is too late, the CO concentration and visibility could be worse than in the free-burn test. From the point of view of production of combustion products, only fire suppression systems with sufficient capability and early activation are recommended to be used in tunnels.
... In most cases, the transient heat release rate curves are of interest. Li and Ingason [38] showed that the fire growth rate for solid fuels exposed to wind is proportional to the wet perimeter of the fuel. The scenarios are similar to fires mainly with vertical fire spread, as the hot gases flowing through the surfaces could also be considered as forced air flows assuming the buoyancy is well scaled. ...
... The scenarios are similar to fires mainly with vertical fire spread, as the hot gases flowing through the surfaces could also be considered as forced air flows assuming the buoyancy is well scaled. According to Li and Ingason's work [38], to preserve the fire growth rate the total wet perimeter should scale as 3/2 power of the length scale. Note that the total average wet perimeter in one direction (either of the three directions), w p , can approximately be expressed as: ...
A method for scaling time-resolved burning behaviors of wood pallet fires has been developed. A series of validation tests was carried out in two different scales and the time-resolved heat release rates were obtained and compared. The results show that the scaling method proposed works very well. The scaling method proposed could be applied to general wood pallets.
... However, tunnel fire is a complex phenomenon involving many aspects such as turbulence, combustion radiations and geometry layout [7]. Some other aspects have also been investigated, such as burning rate [8,9], radiation heat transfer [10,11] and produce of toxic gases [12]. Other fire characteristics, including flame length and tilt angle, are also critical to address the risk of tunnel fire. ...
... Under the longitudinal ventilation, flame can be pushed downstream, resulting in the spread of more smoke and radiation heat to the downstream [20]. These are totally different from those without longitudinal ventilation, because the fire spread rate can be largely increased under the rising radiation heat from the tilted flame [8] . In addition , the flame can cause serious structure damage if they impinge on the tunnel ceiling [21,22]. ...
Curved flame is one of the determining aspects in evaluating the risk of tunnel fire. In this study, a series of experiments are carried out to investigate the characteristics of fires in a reduced-scale tunnel model, including the center-line trajectory, length and tilt angle of curved flame. It can be known from the experiments that the total flame length in the tunnel without longitudinal ventilation is almost equal to that in open space. For the flame in the tunnel with longitudinal ventilation, a third-power relationship is shown in the center-line trajectory equation of the curved flame. Meanwhile the length of curved flame can be obtained by the method of calculus. Based on the experimental data from this study, an empirical model is developed to predict the tilt angle of the curved flame, which is based on Oka’s model but with much improved accuracy for the curved flames in the tunnel.
... From the point of view of design fire, there are two key parameters that attract special attention, i.e. the maximum heat release rate (HRR) and the fire growth rate. Important findings of the fire growth rate in ventilated tunnel fires were reported by Li and Ingason (2011). They proposed a theoretical model of fire growth rate in tunnel fires, explored the relationship between the flame spread rate and the fire growth rate in a ventilated flow, and used a large amount of data relevant to the fire growth rate from model scale and full scale tunnel fire tests for validation. ...
... Ingason 13 also carried out a series of 1:10 model scale railcar tunnel fire tests to investigate the effect of openings on the fire sizes. Li et al. [14][15][16][17][18][19][20] carried out several series of model scale tunnel fire tests to investigate the critical velocity, backlayering length, maximum ceiling gas temperature, smoke control in cross-passages, and smoke control in rescue stations in long railway tunnels. Lo¨nnermark et al. 21,22 carried out a 1:3 model scale metrocar fire tests for the fullscale fire tests in Brunsberg tunnel. ...
... 2,5 A large amount of model scale fire tests show that there is good agreement between model scale and large-scale test results on many focused issues. [11][12][13][14][15][16][17][18][19][20]28 However, in most of the model scale tests that have been carried out worldwide, the thermal properties of the involved materials were not taken into account. One reason could be that for those studies, the internal wall temperatures were not the focus; however, the wall materials are expected to have strong influence on the scaling of the fires, especially in small scale. ...
Physical scaling is an efficient and cost-effective modelling tool to be used in fire safety engineering. Scaling of internal wall temperatures were investigated in room fire tests in three different scales, i.e. full scale (1:1), medium scale (1:2) and small scale (1:3.5). The fire sources were either placed at the center or in the corner of the enclosures. The measured time-dependent internal wall temperatures, incident heat fluxes and gas temperatures in different scales are compared and analyzed. Test results show that the proposed scaling method is able to scale the internal wall temperatures (temperatures inside the walls) and incident heat fluxes well, especially in medium scale.
... Li and Ingason [26] proposed a theoretical approach to model the fire growth rate in a ventilated tunnel fire. The relationship between the flame spread and the fire growth rate in a ventilated flow with fuels exposed to wind was analyzed theoretically. ...
Five large-scale fire tests, including one pool fire test and four HGV mock-up fire tests, were carried out in the Runehamar tunnel in Norway in year 2003. New data and new analyses are presented in this paper, together with a short summary of previous work on these tests. Heat release rate (HRR), radiation, fire spread, gas production, backside wall temperature, visibility, backlayering, fire growth rate, gas temperature, flame length, ventilation and pulsation are investigated. Simple theoretical models are developed to estimate and predict these parameters. The correlations developed can be used by engineers working on fire safety in tunnels.
... The Reynolds number is not conserved in the different scales. Previous studies by the authors have, however, proved that model-scale studies can give interesting results and give important information on fire behaviours under different conditions [7][8][9][10][11][12][13][14][15]. Table 1. ...
... In our case, 35 % was assumed given that a large amount of heat was lost through the doors and openings. Therefore, we obtain the possible maximum HRR inside the carriage, i.e. excluding the energy release outside the openings using: max,in 1.85 a Qm (14) If the influence of the fuel mass rate is accounted for, the increase of the fuel mass flow rate results in a slight decrease of the mass flow rate into the carriage. The influence of the fuel mass on the total outgoing mass flow rate is limited and has been neglected. ...
A fire development analysis of three series of train carriage fire tests in different scales was carried out. These train carriage fire tests included 1:10 model scale tests, 1:3 model scale tests and 1:1 full scale tunnel tests. The heat release rate (HRR) correlations between different scales of carriage fire tests were carefully investigated. The mechanism of fire development is very similar in different scales of tests involving fully developed fires. After the critical fire spread, the fire travelled along the carriage at an approximately constant speed. The maximum heat release rate obtained for a fully developed fire is dependent on the ventilation conditions and also the type and configuration of the fuels, and a simple equation has been proposed to estimate the maximum heat release rate. A global correction factor of the maximum heat release rate is presented and examined. A f fuel surface area (m 2) t time (s) A i ith exposed surface area (m 2) T Gas temperature (K) A o area of opening (m 2) u velocity (m/s) A t total exposed surface area (m 2) Greek c p heat capacity (kJ/kg K) density (kg/m 3) E energy content (kJ) ξ i correction factor for ith surface Fr Froude number ξ tot global correction factor H carriage height (m) χ r fraction of heat absorbed by surfaces H o height of opening (m) subscripts H c effective heat of combustion (kJ/kg) c convection heat transfer l length scale (m) cal calculated L p heat of pyrolysis (kJ/kg) f fuel m fuel mass (kg) F full scale a m mass flow rate of the fresh air (kg/s) g gas f m fuel mass burning rate (kg/s) i ith opening or ith surface m mass burning rate per unit area (kg/m 2 s) M model scale Q heat release rate (MW) max maximum Q max maximum heat release rate (MW) meas measured Q in maximum heat release rate in carriage (MW) o opening or initial value e q absorbed external heat flux (kW/m 2) stoi stoichiometric loss q heat loss from the surface (kW/m 2) tot total
... The Reynolds number is not conserved in the different scales. Previous studies have, however, proved that model-scale studies can give interesting results and give important information on fire behaviours under different conditions [7][8][9][10][11][12][13][14][15]. ...
An analysis of four series of metro carriage fire tests in different scales was carried out. These metro carriage fire tests including 1:10 model scale tests, 1:3 model scale tests, 1/3 carriage section carriage tests and full scale tunnel tests. The correlation between different scales of carriage fire tests is carefully investigated. The mechanism of fire development is very similar in different scales of tests involving fully developed. A critical fire spread is identified as the key parameter to a fully developed carriage fire and is related to a minimum heat release rate. After the critical fire spread, the fire travels along the carriage at an approximately constant speed. The maximum heat release rate obtained for a fully developed fire is dependent on the ventilation conditions and also the type and configuration of the fuels, and a simple equation has been proposed to estimate the maximum heat release rate. Good agreement has also been found between different scales of maximum gas temperature, gas concentration and extinction coefficient. The heat fluxes from the flames could be slightly overestimated in model scales.
... In the authors' opinion, the scaling ratio should not be smaller than about 1:20. Experience with model tunnel fire tests at this scale shows there is a good agreement between model scale and large scale on many focused issues [14,15,[17][18][19]. This type of scaling is widely used in model tunnel fire tests all over the world. ...
... A correction coefficient of 0.971 was found for equation (20). Comparing equations (17) and equation (20) shows that the critical smoke depth ...
Rescue stations are usually provided in very long railway tunnels. Those stations already constructed or under construction worldwide are reviewed and the basic pattern of smoke control during a rescue station fire is identified. A total of 54 model scale tests were carried out to investigate smoke control issues in rescue station fires. The effects of heat release rate, train obstruction, fire source location and ventilation condition on smoke control in the cross-passages of a rescue station were tested and analyzed. A critical smoke layer temperature near the fireproof door protecting the rescue station was investigated theoretically and experimentally and a simple equation for this temperature is obtained. A height of 2.2 m is proposed for the fireproof doors in cross-passages of rescue stations.
