Experimental study of transitional behavior of fully developed under-ventilated compartment fire and associated facade flame height evolution

Fei Ren, Longhua Hu, Xiaolei Zhang, Xiepeng Sun, Jianping Zhang, Michael Delichatsios

Research output: Contribution to journalArticle

Abstract

For compartment fires with an opening, two distinct states are widely recognized: well-ventilated (oxygen is sufficient for combustion inside the compartment) and under-ventilated (oxygen is completely used inside the compartment). And as a consequence, the flame ejects out through the opening with excess fuel burning outside when reaching under-ventilated condition. However, in this work, a further transitional behavior of under-ventilated compartment fires with increasing fuel supply is revealed and quantified. Experiments were carried out using an under-ventilated fire compartment (0.4 m cubic) with a fixed opening width (0.25 m) and various opening heights (0.0125 m to 0.15 m) (corresponding ventilation factors, AH, 3.49 × 10 −4 to 1.45 × 10 −2 m 2.5). The temperature inside the compartment and the facade flame ejected through the opening were recorded with increasing fuel supply (or namely total heat release rate) for under-ventilated conditions. The results showed that when the under-ventilated compartment fire reached a transitional state, the temperature inside the compartment experienced a sudden drop associated with a sudden increase of facade flame height outside the opening, posing a more severe impact on the building facade. The critical fuel supply rate for reaching the transitional state could be divided into two different mechanisms by a critical value of the opening ventilation factor ([0.5AH]=0.0033kg/s), based on the mass balance and flame stoichiometric extinction analysis inside the compartment. The formula for describing the critical fuel supply rate by considering the evolution of the critical air-fuel equivalence ratio (χ) for both mechanisms was proposed. The classic model on the facade flame height for common under-ventilated compartment fires was found to be not applicable when the transitional state of under-ventilated condition had been reached. A new model was proposed to correlate the facade flame height for the transitional state of under-ventilated condition, which was shown to have a 2/3 power dependence on the total heat release rate taking the opening width as the characteristic length.

LanguageEnglish
Pages235-245
Number of pages11
JournalCombustion and Flame
Volume208
Early online date13 Jul 2019
DOIs
Publication statusE-pub ahead of print - 13 Jul 2019

Fingerprint

Facades
compartments
flames
Fires
Ventilation
Enthalpy
Oxygen
ventilation
heat
mass balance
oxygen
Temperature
equivalence
Air
extinction
Experiments
temperature

Keywords

  • Facade flame height
  • Opening ventilation factor
  • Temperature
  • Transitional state
  • Under-ventilated compartment fire

Cite this

Ren, Fei ; Hu, Longhua ; Zhang, Xiaolei ; Sun, Xiepeng ; Zhang, Jianping ; Delichatsios, Michael. / Experimental study of transitional behavior of fully developed under-ventilated compartment fire and associated facade flame height evolution. 2019 ; Vol. 208. pp. 235-245.
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abstract = "For compartment fires with an opening, two distinct states are widely recognized: well-ventilated (oxygen is sufficient for combustion inside the compartment) and under-ventilated (oxygen is completely used inside the compartment). And as a consequence, the flame ejects out through the opening with excess fuel burning outside when reaching under-ventilated condition. However, in this work, a further transitional behavior of under-ventilated compartment fires with increasing fuel supply is revealed and quantified. Experiments were carried out using an under-ventilated fire compartment (0.4 m cubic) with a fixed opening width (0.25 m) and various opening heights (0.0125 m to 0.15 m) (corresponding ventilation factors, AH, 3.49 × 10 −4 to 1.45 × 10 −2 m 2.5). The temperature inside the compartment and the facade flame ejected through the opening were recorded with increasing fuel supply (or namely total heat release rate) for under-ventilated conditions. The results showed that when the under-ventilated compartment fire reached a transitional state, the temperature inside the compartment experienced a sudden drop associated with a sudden increase of facade flame height outside the opening, posing a more severe impact on the building facade. The critical fuel supply rate for reaching the transitional state could be divided into two different mechanisms by a critical value of the opening ventilation factor ([0.5AH]=0.0033kg/s), based on the mass balance and flame stoichiometric extinction analysis inside the compartment. The formula for describing the critical fuel supply rate by considering the evolution of the critical air-fuel equivalence ratio (χ) for both mechanisms was proposed. The classic model on the facade flame height for common under-ventilated compartment fires was found to be not applicable when the transitional state of under-ventilated condition had been reached. A new model was proposed to correlate the facade flame height for the transitional state of under-ventilated condition, which was shown to have a 2/3 power dependence on the total heat release rate taking the opening width as the characteristic length.",
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Experimental study of transitional behavior of fully developed under-ventilated compartment fire and associated facade flame height evolution. / Ren, Fei ; Hu, Longhua; Zhang, Xiaolei ; Sun, Xiepeng ; Zhang, Jianping; Delichatsios, Michael.

Vol. 208, 01.10.2019, p. 235-245.

Research output: Contribution to journalArticle

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AU - Hu, Longhua

AU - Zhang, Xiaolei

AU - Sun, Xiepeng

AU - Zhang, Jianping

AU - Delichatsios, Michael

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AB - For compartment fires with an opening, two distinct states are widely recognized: well-ventilated (oxygen is sufficient for combustion inside the compartment) and under-ventilated (oxygen is completely used inside the compartment). And as a consequence, the flame ejects out through the opening with excess fuel burning outside when reaching under-ventilated condition. However, in this work, a further transitional behavior of under-ventilated compartment fires with increasing fuel supply is revealed and quantified. Experiments were carried out using an under-ventilated fire compartment (0.4 m cubic) with a fixed opening width (0.25 m) and various opening heights (0.0125 m to 0.15 m) (corresponding ventilation factors, AH, 3.49 × 10 −4 to 1.45 × 10 −2 m 2.5). The temperature inside the compartment and the facade flame ejected through the opening were recorded with increasing fuel supply (or namely total heat release rate) for under-ventilated conditions. The results showed that when the under-ventilated compartment fire reached a transitional state, the temperature inside the compartment experienced a sudden drop associated with a sudden increase of facade flame height outside the opening, posing a more severe impact on the building facade. The critical fuel supply rate for reaching the transitional state could be divided into two different mechanisms by a critical value of the opening ventilation factor ([0.5AH]=0.0033kg/s), based on the mass balance and flame stoichiometric extinction analysis inside the compartment. The formula for describing the critical fuel supply rate by considering the evolution of the critical air-fuel equivalence ratio (χ) for both mechanisms was proposed. The classic model on the facade flame height for common under-ventilated compartment fires was found to be not applicable when the transitional state of under-ventilated condition had been reached. A new model was proposed to correlate the facade flame height for the transitional state of under-ventilated condition, which was shown to have a 2/3 power dependence on the total heat release rate taking the opening width as the characteristic length.

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