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Quantitative Analysis of the Influence of Air Entrainment Restriction Degree on Burning Characteristics of Two Parallel Rectangular Pool Fires in Still Air

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Abstract

Flame merging is deemed to enhance the burning intensity and make the fire more destructive. This paper presents an experimental study on merging behaviors of two same rectangular heptane pool fires with long sides parallel. The pan aspect ratio was set 2–4 and the spacing was changed. The burning rate and flame height were measured. As the spacing decreases, the flame shape was divided into five regions, i.e., (I) no interaction, (II) tilt but non-merging, (III) intermittent merging, (IV) upper flames fully merging but lower flames separated and (V) flames merging from the pan base. The results showed that both the burning rate and flame height increase within the stages I–IV and then decrease in stage V. A normalized parameter ψ is introduced to characterize the air entrainment restriction. A unified correlation between burning rate and ψ is then developed. Connecting with the theoretical force analysis, the criteria of merging from the base and beginning merging are determined as ψ = 0.33 and ψ = 0.61. Then a piecewise correlation of the merging flame height is established. The proposed correlations for burning rate and flame height are verified using present and literature data and their scope of application is further expanded into square pool fires.

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Abbreviations

B :

Buoyancy force (N)

c :

Introduced parameter in Eq. (11)

H f :

Mean flame height above the pan surface (m)

ΔH c :

Heat of combustion (MJ/kg)

k :

Proportion coefficient in Eq. (15)

K :

Introduced parameter in Eq. (16)

L :

Pan length (m)

L′:

Pan length of the assumed single fire under S = 0 (m)

\(\dot{m}^{\prime \prime }\) :

Burning rate per unit area of each pan (g/(m2 s))

\(\dot{m}_{a,S = 0}\) :

Air entrainment mass of S = 0 (kg/s)

\(\dot{m}_{a,S > 0}\) :

Air entrainment mass of S > 0 (kg/s)

p :

Pressure (Pa)

P :

Pressure thrust (N)

\(\dot{Q}\) :

Heat release rate of each pan (kW)

\(\dot{Q}_{WL}^{*}\) :

Normalized heat release rate in Eq. (19)

\(\dot{Q}_{{W^{\prime}L^{\prime}}}^{*}\) :

Normalized heat release rate in Eq. (20)

S :

Pan edge spacing (m)

T ∞ :

Ambient temperature (K)

T f :

Flame temperature (K)

ΔT re :

Temperature rise in the restriction region (K)

u :

Horizontal gas inflow velocity (m/s)

\(\bar{U}_{\infty - f}^{{}}\) :

Velocity flow from ambient region to the flame zone (m/s)

\(U_{re - f}^{{}}\) :

Velocity flow from restriction region to the flame zone (m/s)

\(V_{\infty - re}^{{}}\) :

Velocity flow from ambient region to the restriction zone (m/s)

W :

Pan width (m)

W′:

Pan width of the assumed single fire under S = 0 (m)

α :

Entrainment constant

α S :

Characteristic entrainment constant for a given S

γ :

Constant in Eq. (19)

η :

Constant in Eq. (19)

θ :

Flame tilt angle (°)

ρ :

Density (kg/m3)

χ :

Combustion efficiency

ψ :

Normalized parameter in Eq. (1)

∞:

Ambient zone

f :

Flame zone

re :

Restriction zone

SF :

Single fire

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (NSFC, Grant Nos. 51722605 and 51906239), and Natural Science Foundation of Anhui Province (Grant No. 2008085QE251).

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Authors and Affiliations

  1. State Key Laboratory of Fire Science, University of Science and Technology of China, JinZhai Road 96, Hefei, 230026, Anhui, China

    Huaxian Wan, Longxing Yu & Jie Ji

  2. Department of Fire Protection Engineering, Southwest Jiaotong University, Chengdu, 610031, China

    Huaxian Wan

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Correspondence to Jie Ji.

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Wan, H., Yu, L. & Ji, J. Quantitative Analysis of the Influence of Air Entrainment Restriction Degree on Burning Characteristics of Two Parallel Rectangular Pool Fires in Still Air. Fire Technol 57, 1149–1165 (2021). https://doi.org/10.1007/s10694-020-01043-4

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