Experimental investigation on the temperature profile of large scale RP – 5 aviation kerosene pool fire in an open space

Fuel 264 (2020) 116852

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Full Length Article

Experimental investigation on the temperature profile of large scale RP – 5 aviation kerosene pool fire in an open space ⁎

T

⁎

Yang Taoa, Kaihua Lua, , Xiangfeng Chenb,c, Shaohua Maoa,d, , Yanming Dinga, Yunsheng Zhaoa a

Faculty of Engineering, China University of Geosciences, Wuhan, Hubei 430074, China School of Safety Science and Emergency Management, Wuhan University of Technology, Wuhan 430070, China c School of Chemical Machinery and Safety Engineering, Dalian University of Technology, Dalian 116024, China d China Ship Development and Design Center, Wuhan 430064, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Large scale pool fire Temperature profile Open space Ambient wind RP – 5 aviation kerosene

This paper investigates the temperature profile of large scale RP – 5 aviation kerosene pool fire in an open space through a series of large scale experiments of 1 m2, 5 m2, 10 m2, 25 m2 pool sizes. The temperature profile is acquired by thermocouple trees positioned in various distances to the pool centerline, while the ambient wind velocity is captured by four transducers in the experimental field. Results show that the large scale pool fire behaves different to the used small to medium scale experiments. The mass loss rate is in good agreement with Blinov and Khudyakov’s results, but the vertical temperature is much lower than the McCaffery’s results due to the reduced global combustion efficiency as more sooty smoke produced. The three regimes in McCaffery’s model is redefined, correlating well with the vertical temperature profile upon the pool centerline. Gaussian Fit is well proposed for the lateral temperature profile at the pool base level, however as the ambient wind inevitable, the fire plume would be tilted to the downstream direction. Finally, the isothermal diagrams of fire plume for various pool sizes are plotted showing the temperature field of plumes, and also the tilt angle of plumes is presented.

1. Introduction In the petrochemical industry or transportation process, fire disasters caused by fuel leakage occur frequently, which would lead to disastrous consequences. The combustion behavior of liquid pool fire is a classical and basic problem in fire research, on which a large amount of theoretical, experimental and numerical research are focused for decades [1], including all aspects such as the burning rate [2–8], the flame shape [9–16], the temperature profile as well as radiation intensity [17 –22] etc. In 1961, Blinov and Khudyakov [2] conducted various hydrocarbon liquids pool fire with diameters ranging from 0.0037 m to 22.9 m under a still air condition, indicating the scale effects on the mass loss rate per unit area of pool fire (MLRPUA) is determined by the dominant heat transfer process of fire flame to fuel, namely a) conduction-controlled for equivalence pool diameter D < 0.1 m, b) convection-controlled for 0.1 m < D < 0.2 m, and c) radiation-controlled for D > 0.2 m. Then the radiation-controlled part has been divided into two categories, i.e. 0.2 m < D < 1 m for optically-thin stage while D > 1 m for optically-thick stage. Noting that the MLRPUA represents the heat release

⁎

rate (HRR) which is a key index to describe the fire power, it becomes independent for diameter in the optically-thick stage. More recently, be aware of the importance of fire hazard to on human lives, properties and surroundings, lots of scientists have paid more attention to the pool fire characteristics including the flame shape, the vertical and longitudinal temperature profile as well as the soot formation mechanisms which are all fundamental to the radiation models. The most representative models on the fire plume temperature characteristics are from Zukoski [18], Heskestad [9] and McCaffrey’s [10] experimental results. Using a small scale fire source under a gascollecting hood, Zukoski [18] found the fire plume can be regarded as an ideal plume, showing that the lateral temperature profile should be abided to Gaussian distribution, while the vertical temperature profile is related to 2/3 power of the heat release rate Q̇ and −5/3 power of the local height Z: 1/3

⎛ T ⎞ ΔTz = Tz − T∞ = 5.0·⎜ 2∞ 2 ⎟ ⎝ gρ∞ Cp ⎠

· Q̇

2/3

·Z −5/3 (1)

Later on, Heskestad [9] discovered the shortcoming of Zukoski’s model, then the concept of virtual origin height Z0 was brought up

Corresponding authors at: Lumo Road 388, China University of Geosciences, Wuhan, Hubei 430074, China. E-mail addresses: [email protected] (K. Lu), [email protected] (S. Mao).

https://doi.org/10.1016/j.fuel.2019.116852 Received 2 October 2019; Received in revised form 23 November 2019; Accepted 9 December 2019 Available online 14 December 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.

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Nomenclature

Z0

Specific heat capacity (J·kg−1·K−1) Equivalence diameter (m) Acceleration of gravity (m/s2) Distance to the centerline (m) Mass loss rate (kg/s) Combustion heat of fuel (kJ/kg) Heat release rate (kW) Convective heat release rate (kW) Temperature at location Z (K) Local temperature rise (K) Ambient temperature (K) Vertical height (m)

Cp D G L ṁ ΔH Q̇ Qċ Tz ΔTz T∞ Z

Greek symbols

Subscripts c ∞

2/3

(2)

The virtual origin height Z0 can be deduced as: 2/5

Z0 = 0.083Qċ

− 1.02D

(3)

The above expressions indicate that for a larger pool size D, the virtual origin would be lower and therefore the temperature rise would be also decreased. It should be also clarified that the above Zukoski and Heskestad’s models are basically a single function limited to the buoyant plumes above the level where the mean flame height can achieve. Differed from the one-zone relationship of the above Zukoski and Heskestad’s model, McCaffrey [10] summarized the centerline temperature distribution of fire plume through a series of methane diffusion flame experiments. It was concluded that the fire plume zone should be distinguished into three regimes which could reflect the flame variation effect to the temperature. The three zones are the continuous flame regime, the intermittent flame regime as well as the buoyant plume regime respectively. The relations of temperature, vertical height Z and heat release rate Q̇ can be expressed as a piecewise function listed below: 2

2. Experimental setup Large scale experiments of 1 m2, 5 m2, 10 m2 and 25 m2 pool fire are carried out applying in a variable-size oil tray as shown in Fig. 1, along with the wind speed measuring system collecting the ambient flow speed, as well as the temperature measurement system capture the thermal field during experiments. The oil tray is square and made of stainless steel of 5 mm thickness. When conducting the oil pool fire experiment, the bottom of oil tray is submerged by a 30 cm thickness water level for fire protection, and then, 2 cm thickness aviation kerosene is injected by an oil pump into oil tray center by an oil supply system (with fuel volume accuracy of ± 1%). We select the RP – 5 aviation kerosene as fuel. The top surface of the RP – 5 aviation kerosene is maintained even throughout the experiments and then the fuel is ignited by a handheld igniter. Being an essential parameter in a fire scenario, the total HRR (Q̇ ) could be calculated by mass loss rate ṁ times the combustion heat of fuel ΔH (for RP – 5 aviation kerosene ΔH = 43100 kJ/kg) as:

2η − 1

κ ⎞ ⎛ Z ⎞ ΔTz = ⎜⎛ ⎟ · ⎜ 2/5 ⎟ ⎝ 0.9· 2g ⎠ ⎝ Q̇ ⎠

·T∞

(4)

or in a dimensionless form: 2

2η − 1

ΔTz κ ⎞ ⎛ Z ⎞ = ⎜⎛ ⎟ · ⎜ 2/5 ⎟ T∞ 0.9· 2 g ⎝ ⎠ ⎝ Q̇ ⎠

convective ambient condition

and inevitable ambient wind. For example, a typical fire disaster caused by an air crash induced-fuel leakage could be a large scale liquid pool fire in an open space under ambient wind conditions. As a result of its extensive consumption on large scale pool fire experiments, such data is still very scant but particularly valuable. For the large scale pool fire in an open space, we all know that the pool fire behaves completely different under wind conditions. Hu and Tang et al [14,20,22]. investigated the pool fire characteristics with stable ambient winds, bringing up some physical models on the flame length, flame tilt angle and base drag, but still because the wind is no longer stable in an open space, such models would become invalid. Therefore, this paper is focused on the combustion behavior of four large scale pool fires in an open space with ambient winds to simulate a real fire caused by air crashes. The fuel load is selected as RP – 5 aviation kerosene since it has been widely used fuel in airplanes. The study on temperature profile in an open space of large size RP – 5 aviation kerosene pool fire is beneficial for better mastering to what extent of these kind of fire disasters could be, which has a great realistic significance on the fire prevention.

1/3

·Qċ ·(Z − Z0)−5/3

Ambient density of the hot gases current (kg/m3) coefficient coefficient global combustion efficiency

ρ∞ κ η φ

taking the pool size effect into consideration. The used local height Z in Zukoski’s model was replaced to the net height from the local position to the virtual origin Z - Z0. On the other hand the convective heat release rate Qċ was also introduced for correction (Qċ is about 60% – 80% of the total heat release rate Q̇ so that normally we use Qċ ≈ 0.7Q̇ ):

T ΔTz = Tz − T∞ = 9.1·⎜⎛ 2∞ 2 ⎟⎞ gρ ⎝ ∞ Cp ⎠

Virtual origin height (m)

(5)

where ΔTz is the local temperature rise; T∞ is the ambient temperature; g is the acceleration of gravity; κ and η are the coefficients as displayed in Table 1: More recently, Shen [20] analyzed the temperature profile within the continuous flame regime, indicating that the temperature within the developing area could be different and then the McCaffrey’s model is verified and corrected. But still, we have to point out that most of above observations and conclusions are basically from small or medium scale pool fire experiments, by which the fire scenario and the ambient conditions are controllable [20,22–28]. However, the ultimate object of pool fire tests is to make the general findings more applicable to a real fire, but normally, to apply the results from small or medium scale experiments in the large scale one is still impossible, especially under the presence of random

Q̇ = φ ·ṁ ·ΔH

(6)

Table 1 The three different zones and coefficients in McCaffrey’s model. κ

Different zones continuous flame regime(

Z 2/5 Q̇

< 0.08 m·kW−2/5)

intermittent flame regime(0.08 m·kW−2/5≤

2

6.8 m1/2·s−1 1.9 m·kW

Z 2/5 Q̇

≤ 0.2 m·kW−2/5)

η 1/2

−1/5 −1

·s

0

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Y. Tao, et al.

Series No. 1 (16 thermocouples)

for about 1.81 m/s for pool size 5 m2 condition, but drops down to about 0.88 m/s for pool size 1 m2 condition. 3. Results and discussion

Ambient wind direction (no larger than 2.5 m/s)

Series No. 9-15 (9 thermocouples)

3.1. General combustion process of large scale No. RP – 5 aviation kerosene pool fire The combustion process of RP – 5 aviation kerosene pool fire can be divided into 3 stages. Stage 1 is the initiative rapid growth stage; Stage 2 is the stable combustion stage and Stage 3 is the fire decay and extinguished stage, which can be simply obtained by a typical time–temperature curves as shown in Fig. 3. Generally, the Stage 1 lasts about 50 s, whereas the Stage 2 is the longest for about 200–250 s. The average combustion duration time is 290–308 s for each series as listed in Table 2. Focused on the Stage 2, it can been seen that the temperature captured by the thermocouple almost stable but still some small fluctuation exists due to flame turbulence. Meanwhile, Fig. 4 presents a typical frame of the large scale pool fire experiments. It is seen that most of the fuel reacts in the continuous flame area next to the flame base, then the flame pulsation entrains fresh air into reaction in the intermittent flame area and eventually large amount of unburnt fuel and produced smoke forms the buoyant plume area where no reaction takes place. The presence of ambient wind velocity, even though weak enough (averaged velocity less than 2.0 m/s), would definitely have an effect on the pool fire, leading the flame to be tilted. This is completely different to those results from the small to medium scale pool fire experiments as the wind speed is much easier to be controlled and close to 0. As a result of the flame tilted behavior, the temperature profile would be also different which could also change the radiation feedback of flame on the fuel surface.

Series No. 2-8 (9 thermocouples)

Thermocouple Trees

Oil tray (30 cm water and 2 cm fuel) Fig. 1. Schematic of experimental setup.

We note that the RP – 5 aviation kerosene has a large ratio of carbon-hydrogen, and a great amount of unburnt black smokes are generated when combustion, so the global combustion efficiency φ is selected as 0.6 in the experiments. However, unfortunately, it is not a simple thing to acquire the mass loss rate ṁ very precisely especially in the large scale experiments. Hence, we decide to employ a timer (accuracy ± 1 s) to record the combustion duration time, and thus the mass loss rate could be approximated by the fuel load versus the combustion duration time as listed in Table 2 (with integral uncertainty of ± 1.05%). The drop rate of fuel surface due to combustion would be at about 3.9–4.1 mm/min, showing a good agreement to the kerosene experimental results by Blinov and Khudyakov [2]. K-type thermocouples (diameter: 1 mm, accuracy ± 1 °C) are installed above the center of oil pool, as well as in the upstream and downstream direction, divided into 15 series longitudinally as shown in Fig. 1. Series No. 1 contains 16 thermocouples located from 0 to 6 m at an interval of 0.4 m for pool area of 1 m2 and 5 m2, while from 0 to 18 m at an interval of 1.2 m for pool area of 10 m2 and 25 m2 above the pool center. Series No. 2–8 consisting of 9 thermocouples are set longitudinally with different horizontal distances L to the pool centerline, while the series No. 9–15 locates symmetrically to the series No. 2–8 along the pool centerline. The detailed distances to the pool centerline are listed in Table 3, in which the dimensionless distance L/D maintains almost constant ranging from 0 to 1.5 for the different pool sizes. The vertical intervals of the thermocouples of series No. 2–15 are the same with the Series No. 1. We repeat the experiments 5 times for each pool size. Since the large scale pool fire experiment system is in an open space, the ambient wind velocity is inevitably but affecting the combustion process. To utmost eliminate the ambient wind effect on combustion process, only when the average wind velocity no larger than 2.5 m/s the experiments could be carried on. The wind measuring system located at the experimental field, consisting four wind velocity transducers (accuracy ± 0.1 m/s) with sampling time 20 s is introduced to record and monitor the wind effect certainly and objectively at the same time. The average ambient wind velocity recorded by the transducers are plotted in Fig. 2, revealing that the ambient wind velocity is not the same for different pool size conditions. The ambient wind velocity is the greatest

3.2. The vertical temperature profile upon the pool centerline The vertical temperature profile upon the pool centerline for the stable combustion stage (Stage 2) will be discussed hereinafter. Fig. 5 lists the temperature versus the vertical height for all the four pool sizes. Coincide to the first two regimes of McCaffrey’s theory, it can be seen that the temperature remains almost constant with a slight increment for the core area next to fire base, but then declines sharply with the increasing vertical height. The increment of the temperature near the flame base because the fire has not well developed as less fresh air entrained, which agree well with the results by McCaffrey [10], Ishida [29] and Fischer [30]. The maximum temperature is about 750 °C for pool sizes 1 m2, 5 m2 and 10 m2, whereas it reaches 800 °C for pool size 25 m2 within the core area of combustion, indicating that the maximum temperature is almost independent with the pool size. However, except for the core area, the temperature is higher at a given height level with a larger pool size. The comparison of the experimental results with the McCaffrey’s model is shown in Fig. 6, in relation to the normalized temperature rise 2/5 ΔTz/T∞ with the factor of Z / Q̇ based on Eq. (1). We can see that the Table 2 Experimental conditions. Pool size (m2)

1

5

10

25

Fuel load (L) Fuel mass (kg) Average combustion duration time (s) Mass loss rate ṁ (kg/s−1)

20 16.32 308 0.0529 0.0529

100 81.6 292 0.2795 0.0559

200 163.2 290 0.5622 0.0562

500 408.0 290 1.408 0.0563

1368 23 34

7228 27 36

14,533 20 31

36,398 25 30

1

MLRPUA ṁ ′ ′ (kg·m−2·s−1) HRR (kW) 2 Average ambient Temperature (°C) 3 Average Ambient Humidity (%) 1,2, 3

3

The average value are from the five groups for each pool size.

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Table 3 The detailed locations of thermocouples. Pool size (m2) Equivalence diameter D (m) Distance to the centerline L (m)

Series Series Series Series Series Series Series Series Series Series Series Series Series Series Series

No. No. No. No. No. No. No. No. No. No. No. No. No. No. No.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 1.13

5 2.52

10 3.57

25 5.64

Average L/D

0 0.2 0.5 0.7 0.9 1.1 1.4 1.7 −0.2 −0.5 −0.7 −0.9 −1.1 −1.4 −1.7

0 0.5 1 1.5 2 2.5 3 3.8 −0.5 −1 −1.5 −2 −2.5 −3 −3.8

0 0.7 1.4 2.1 2.9 3.6 4.3 5.4 −0.7 −1.4 −2.1 −2.9 −3.6 −4.3 −5.4

0 1.1 2.3 3.4 4.5 5.6 6.8 8.5 −1.1 −2.3 −3.4 −4.5 −5.6 −6.8 −8.5

0 0.2 0.4 0.6 0.8 1.0 1.2 1.5 −0.2 −0.4 −0.6 −0.8 −1.0 −1.2 −1.5

Ambient wind velocity (m/s)

4.0 Buoyancy plume regime

Pool size

3.5

2

1m 2 5m 2 10 m 2 25 m

3.0 2.5 2.0

1.0 0.5 0.0

Continuous flame regime

0

100

200 Time (s)

300

400 Fig. 4. The fire plume regimes for large scale pool fire (with area 25 m2).

Fig. 2. The averaged ambient wind velocity in the experimental field.

1000

Stage 1

900

Stage 2

Stage 3

)

800

Temperature (

Flame tilt

Intermittent flame regime

1.5

Vertical Height 9.6 m 10.8 m 12.0 m 13.2 m 14.4 m 15.6 m 16.8 m 18.0 m

0.0 m 1.2 m 2.4 m 3.6 m 4.8 m 6.0 m 7.2 m 8.4 m

700 600 500 400 300

entrainment intensity is strongly enhanced. Meanwhile, the radiation to surroundings would be also under-estimated since the flames and produced smokes are much sooty, due to a lower overall combustion efficiency as it is presented and hence the convection heat may have been over-estimated. Secondly, the presence of ambient wind should certainly result in the heat transfer entrainment process between fire plume and fuel, making the fire plumes to be tilted so that the temperature cannot be higher than the well-verified small to medium scale pool fires under a relatively quiescent or controllable ambient wind. In order to have a better prediction on the temperature profile for large scale pool fires, modification should be applied in the used McCaffrey’s model. The proposed new model would persist the three regimes as the same with McCaffrey’s and furthermore the power index for each section are also followed as they are deduced by carefully dimensionless analysis. Now, the bounds of three regimes needs to be reconsidered again as: 2/5 a) the continuous flame regime forZ / Q̇ < 0.015, b) the intermittent 2/5 flame regime for 0.015≤Z / Q̇ ≤ 0.1 and c) the buoyancy plume re2/5 > 0.1. The updated correlation for the vertical temgime for Z / Q̇ perature profile upon the pool centerline in the Fig. 6 is expressed as a piecewise function of Eq. (7):

200 100 0 -100

0

100

200

300 Time (s)

400

500

Fig. 3. Typical temperature-time curves for large scale pool fire (25 m2).

McCaffrey’s model is still capable for the prediction of normalized 2/5 < 0.02 (m·kW−2/5) area, with about temperature rise withinZ / Q̇ 10%–20% over-estimation, however it is no longer suitable as the 2/5 > 0.02 (m·kW−2/5) area where large vertical height elevates toZ / Q̇ discrepancy is observed. We consider two aspects do effect on the vertical temperature to be much lower to the theoretical models as follows. Firstly, a much larger amount of air is required for the large scale pool fire, making the pool fire to be highly turbulent because the

Z

for < 0.015 ⎧ 2.48 Q̇2/5 ⎪ −1 ⎪ Z Z ΔTz for 0.015 ≤ 2/5 ≤ 0.1 = 0.0372 ⎛ Q̇2/5 ⎞ Q̇ ⎝ ⎠ ⎨ T∞ −5/3 ⎪ Z Z ⎪ 0.008 ⎛ 2/5 ⎞ for > 0.1 Q̇ Q̇2/5 ⎝ ⎠ ⎩

(7)

The new coefficients for each section should be selected to make a 4

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Y. Tao, et al.

900

900

800 600

Pool size 10 m2 25 m2

700

Temperature ( )

Temperature ( )

800

Pool size 1 m2 5 m2

700 500 400 300 200 100

600 500 400 300 200 100

0

0 0

1

2

3

4

5

6

0

Vertical height upon centerline of pool (m)

2

4

6

8

10

12

14

16

18

Vertical height upon centerline of pool (m)

(a)pool size 1 m2 and 5 m2

(b) pool size 10 m2 and 25 m2

Fig. 5. The vertical temperature upon the centerline of various pool sizes.

3.5 3.0

Continous flame

2.5

Pool size 2 1m 2 5m 2 10 m 2 25 m

2.0

Tz / T

temperature profile for different vertical height levels is not the same with the Z = 0 level. The major difference should be attributed to the presence of ambient wind bringing in new effects on the lateral temperature distribution. The flame is shown to be tilted to the downstream area with wind conditions. Regarding the temperature drops sharply as the vertical height is increased and thus the uprising buoyancy becomes much weaker, the effect of ambient wind is more important in higher levels. On the other hand, the tilted flame would enhance the radiative heat transfer from flame to fuel, giving that the heat generation to be much greater in the downstream area. The above two facts indicate the highest temperature location is derivate from the pool centerline but move to the downstream area, so that the original central symmetric Gaussian Fit have become invalid for the Z > 0 levels. The above lateral temperature profile for different vertical height levels can be transformed to isothermal diagrams. The peak of the temperature at each vertical height level is not at the pool centerline, but leaning towards the downstream side as the same to the flame shape presented in Fig. 9. The tilt angle of plumes can be proposed by using a straight line subjected to the pool center.

McCaffrey's model Proposed new correlation

1.5 1.0 0.5 0.0

Intermittent flame

Buoyant plume

-0.5 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 .

Z / Q 2/5 Fig. 6. A new proposed model for the normalized temperature rise upon the centerline of various pool sizes.

continuity function for correlation. We should also point out that since we can hardly acquire the flame height in our experiments as it mostly obstructed by the large amount of produced sooty smokes, the piecewise function of temperature profile seems not that precise, but still it could somewhat reflect the different combustion behavior for the large scale pool fires rather than the small to medium ones.

4. Conclusion The RP – 5 aviation kerosene pool fire in an open space is investigated in this paper through a series of large scale experiments with pool sizes of 1 m2, 5 m2, 10 m2, 25 m2. The mass loss rate is presented in comparison to the Blinov and Khudyakov’s results and hence the heat release rate acquired. The temperature profile from the vertical and lateral directions are captured by the thermocouples and well discussed while the ambient wind effect is also depicted and discussed. The major findings in this work are:

3.3. The lateral temperature profile The lateral temperature recorded by different series of thermocouple trees are plotted in Fig. 7 for various height levels Z. Picking up the temperature from Z = 0 level in our large scale experiments, it can be observed that the highest temperature is reached at the vicinity of pool centerline, as a result of the strong buoyancy overwhelming the inertia force from the ambient wind. In the classical Zukoski’s and Heskestad’s models, an ideal and symmetrical distribution, namely a Gaussian Fitting, is employed for the description of the lateral temperature rise of pool fires, as they came from small to medium scale experiments under no ambient winds. Here,

(1) The three classical temperature profile models upon the pool centerline are no longer suitable; they over predict the temperature for the large scale pool fire as a result of a relatively low global combustion efficiency. The three regimes in McCaffery’s model is redefined and a new correlation is well proposed on the vertical temperature profile for the large scale pool fires (Fig. 6, Eq. (7)). (2) The Gaussian Fit is still available in the modeling of the lateral temperature profile for the vertical height level Z = 0 positions next to the pool base. However, with the increasing vertical height level, the temperature field is strongly influenced by the ambient wind, even though the inevitable ambient wind velocity is less than 2 m/s. The flame would be tilted due to the competition of the inertia force of ambient wind versus the uprising buoyancy due to combustion heat (Fig. 4, Fig. 8). (3) The Isothermal diagrams of fire plume for various pool sizes are

2 − x

a central symmetric Gaussian Fit of y = e 2w2 is still available for the ΔT T−T normalized temperature rise ΔT = T −∞T versus the distance to the max max ∞ pool centerline L/D, except for the L/D > 0.4 area in the downstream direction of pool size 5 m2 where the highest ambient wind velocity occurred during experiments, as can be seen in Fig. 8. Nonetheless, it should be also pointed out that the lateral 5

Fuel 264 (2020) 116852

Y. Tao, et al.

-1.5 800

-0.5

L/D 0.0

0.5

1.0

Vertical height 0m 0.4 m 0.8 m 1.2 m 1.6 m 2.0 m 2.4 m 2.8 m 3.2 m

600 500 400 300

1m

-1.5 900

1.5

800

2

700

Temperature ( )

700

Temperature ( )

-1.0

200 100

600 500 400 300

-1.0

0.5

1.0

Vertical height 0m 0.4 m 0.8 m 1.2 m 1.6 m 2.0 m 2.4 m 2.8 m 3.2 m

1.5

5m

2

200 100

0

0

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

-5

Distance to pool center L (m)

-4

-3

-2

-1.5 700

-1.0

-0.5

L/D 0.0

0.5

1.0

400 300 200

1.5

10 m

2

Temperature ( )

500

100 0 -6

-4

-2

0

0

1

2

3

4

5

(b) pool size 5 m2

Vertical height 0m 1.2 m 2.4 m 3.6 m 4.8 m 6.0 m 7.2 m 8.4 m 9.6 m

600

-1

Distance to pool center L (m)

(a) pool size 1 m2

Temperature ( )

L/D 0.0

-0.5

2

4

6

Distance to pool center L (m)

-1.5 -1.0 -0.5 1100 Vertical height 1000 0m 900 1.2 m 2.4 m 800 3.6 m 700 4.8 m 600 6.0 m 7.2 m 500 8.4 m 400 9.6 m 300 200 100 0 -100 -10 -8 -6 -4 -2

L/D 0.0

0.5

1.0

1.5

25 m

0

2

4

6

2

8

10

Distance to pool center L (m)

(c) pool size 10 m2

(d) pool size 25 m2

Fig. 7. The lateral temperature profile for various pool sizes at different vertical height levels.

1.0

Groups & Gaussian Fit

T/ Tmax

0.8 0.6 0.4

1 m2 5 m2 10 m2 25 m2

provide significant references on today's large pool fire protection planning and practice.

x2

Z=0m

y

e

2 w2

CRediT authorship contribution statement Yang Tao: Writing - original draft, Investigation, Data curation. Kaihua Lu: Writing - review & editing, Supervision. Xiangfeng Chen: Investigation, Data curation. Shaohua Mao: Conceptualization, Funding acquisition. Yanming Ding: Validation, Project administration. Yunsheng Zhao: Resources.

w=0.23

w=0.60

w=0.37

w=0.40

0.2 0.0 -2.0

Declaration of Competing Interest

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0 The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

L/D Fig. 8. A Gaussian Fit for the lateral temperature profile at Z = 0 m level.

plotted showing the temperature field of plumes. The tilt angle of plumes is proposed by using a straight line subjected to the pool center (Fig. 9).

Acknowledgements This study was supported by the National Natural Science Foundation of China, China under Grant No. 51706216, 51706212, 51806156, and the Natural Science Foundation of Hubei Province, China under Grant No. 2018CFB226.

Lastly, the current study, bringing up fresh and essential data of the large scale pool fire which have been rarely reported, would definitely 6

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Y. Tao, et al.

3.0

2

5 m 5 m2

2

1m 1 m2

Vertical Height (m)

2.5

θ=67.9

67.9

2.0 1.5

θ=21.5

21.5

1.0 0.5 0.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

-3.0

1.5

-1.0

-2.0

(a) pool size 1 m2

Vertical Height (m)

2.0

3.0

(b) pool size 5 m2

2

25 m

10 m 10 m2

8

1.0

Distance to pool centerline (m)

Distance to pool centerline (m)

9

0.0

2

25 m2

θ=59

θ=54

7

820 720 620 520 420 320 220 120 20

54

6 5

59

4 3 2 1 0

-5 -4 -3 -2 -1

0

1

2

3

4

5

-8

-7 -6 -5 -4 -3

-2 -1

0

1

2

3

4

Distance to pool centerline (m)

Distance to pool centerline (m)

(c) pool size 10 m2

(d) pool size 25 m2

5

6

7

8

(e) Legend

Fig. 9. Isothermal diagrams of fire plume for various pool sizes and the tilt angles due to the presence of ambient wind. diffusion flame length and tilt. Fuel 2016;186:350–7. [15] Tang F, Hu LH, Zhang XC, Zhang XL, Dong MS. Burning rate and flame tilt characteristics of radiation-controlled rectangular hydrocarbon pool fires with cross air flows in a reduced pressure. Fuel 2015;139:18–25. [16] Tao CF, Ye QP, Wei JJ, Shi Q, Tang F. Experimental Study on Flame-Flame Interaction and Its Merging Features Induced by Double Rectangular Propane Diffusion Burners With Various Aspect Ratios. Combust Sci Technol 2019;191:1416–29. [17] Shi CL, Liu W, Hong WJ, Zhong MH, Zhang XK. A modified thermal radiation model with multiple factors for investigating temperature rise around pool fire. J Hazard Mater 2019;120801. in press. [18] Zukoski EE. Properties of fire plumes. Academic Press; 1995. [19] Steinhaus T, Welch S. Large-scale pool fires. Thermal Science 2007;11:101–18. [20] Shen G, Jiang J. Analysis for Fire Plume Temperature in Developing Area and Radiation Heat Flux Distribution in Small-scale Pool Fire. Procedia Eng 2018;211:606–13. [21] Lam CS, Weckman EJ. Wind-blown pool fire, Part I: experimental characterization of the thermal field. Fire Saf J 2015;75:1–13. [22] Hu LH, Zhang XZ, Zhang XL, Kuang C. Flame base drag of pool fires with different side wall height in cross flows: A laboratory-scale experimental study and a new correlation. Fuel 2016;182:857–63. [23] Li B, Wan HX, Gao ZH. Experimental study on the characteristics of flame merging and tilt angle from twin propane burners under cross wind. Energy 2019;174:1200–9. [24] Zhang XZ, Zhang XL, Hu LH, Tu R, Delichatsios MA. An experimental investigation and scaling analysis on flame sag of pool fire in cross flow. Fuel 2019;241:845–50. [25] Hu LH, Liu S. Flame radiation feedback to fuel surface in medium ethanol and heptane pool fires with cross air flow. Combust Flame 2013;160:295–306. [26] Oka Y, Kurioka H, Satoh H. Modelling of unconfined flame tilt in cross-winds. Fire Safety Science 2000;6:1101–12. [27] Chen J, Zhang XL, Zhao YL, Bi YB, Lu SX. Oxygen concentration effects on the burning behavior of small scale pool fires. Fuel 2019;247:378–85. [28] Shi XC, Sahu AK. Effect of ullage on burning behavior of small-scale pool fires in a cavity. Proc Combust Inst 2017;36:3113–20. [29] Ishida H. Initiation of fire growth on fuel-soaked ground. Fire Saf J 1992;18(92):213–30. [30] Fischer SJ, Hardouin-Duparc B, Grosshandler WL. The structure and radiation of an ethanol pool fire. Combust Flame 1987;70(87):291–306.

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.fuel.2019.116852. References [1] Hu LH. A review of physics and correlations of pool fire behavior in wind and future challenges. Fire Saf J 2017;91:41–55. [2] Blinov VI, Khudyakov GN. Diffusion Burning of Liquids. American: Army Engineer Research and Development Labs Fort Belvoir VA; 1961. [3] Babrauskas V. Estimating large pool fire burning rates. Fire Technol 1983;19:251–61. [4] Chatris JM, Quintela J. Experimental study of burning rate in hydrocarbon pool fires. Combust Flame 2001;126:1373–83. [5] Hamins AP, Yang JC. Global Model for Predicting the Burning Rates of Liquid Pool Fires, Report No. NISTIR 6381; NIST Interagency, USA, 1999. [6] Hu LH, Liu S. A wind tunnel experimental study on burning rate enhancement behavior of gasoline pool fires by cross air flow. Combust Flame 2011;158:586–91. [7] Hu LH, Kuang C. An experimental study on burning rate and flame tilt of opticalthin heptane pool fires in cross flows. Proc Combust Inst 2017;36:3089–96. [8] Wang XH, Chen QP, Zhou TN, Li HH, Wang J. In-depth analysis of burning process of binary blended fuel pool fires based on liquid–vapor equilibria. Fuel 2019. 115918 (in press). [9] Heskestad G. Fire Plumes, Flame Height, and Air Entrainment. New York: Springer; 2016. p. 396–428. [10] McCaffrey BJ. Purely Buoyant Diffusion Flames: Some Experimental Results, NBSI 791910. Washington DC, USA: National Bureau of Standards; 1979. [11] Cetegen BM, Zukoski EE. Entrainment and Flame Geometry of Fire Plumes. California Institute of Technology: Daniel and Florence Guggenheim Jet Propulsion Center, USA; 1982. [12] Thomas PH. The size of flame from natural fires. Proceedings of the Combustion Institute 1963, 497, 1–1. [13] Lam CS, Weckman EJ. Wind-blown pool fire, Part II: Comparison of measured flame geometry with semi-empirical correlations. Fire Saf J 2015;78:130–41. [14] Tang F, Li LJ, Wang Q, Shi Q. Effect of cross-wind on near-wall buoyant turbulent

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