Experimental Analysis of Critical Acceleration Condition for Two-Sided Upward Flame Spread Over Inclined Thin Fuel Surfaces

Gao, Yunji; Zhu, Guoqing; Hui, Zhu; An, Weiguang; Yu, Meng-wei; Huang, Jinlei; Xia, Yu

doi:10.1007/s10694-018-0803-2

Cited by 17 publications

(35 citation statements)

References 31 publications

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“…18,27 The previous works proved that the true surface temperature profile could be successfully obtained by the means of the IR thermography technique. 4,11,27 Flax fabric, as a widely used material in building decoration, is selected for the test samples, which are composed of 100% flax. The test sample fabrics are 8.0 cm in width and 160.0 cm in length.…”

Section: Methodsmentioning

confidence: 99%

“…Although the upward flame spread is a typical acceleration process, the change in spread rate over a relatively small distance is not great. 9,11 Therefore, the average Figure 8. Notably, the values of the flame spread rate are larger than those of the corresponding pyrolysis spread rate for all test samples, which clearly shows that upward flame spreading does not reach a completely steady state.…”

Section: Spread Ratementioning

confidence: 99%

“…Pizzo et al 8 established a transient pyrolysis model based on the modified mass transfer number to predict the flame spread rate over inclined PMMA. Gollner et al, 9 Huang and Gollner 10 and Gao et al 11 investigated the upward flame spread characteristics over inclined solid fuel surfaces and proposed that the flame tilt angle and flame standoff distance could qualitatively describe the heat flux profiles in the preheating region. Moreover, the effects of ambient pressure, [12][13][14] oxygen concentration, [15][16][17] moisture content, [18][19][20] external flow velocity [21][22][23][24] and different configurations [25][26][27][28] on flame spread over solid fuel surfaces have been widely investigated by experimental measures and theoretical analyses.…”

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confidence: 99%

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Effects of porosity and area density on upward flame spread characteristics over thin flax fabric

Gao

Hui

Zhang

et al. 2020

Textile Research Journal

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Few investigations have systematically addressed the porosity effects of upward flame spread over fabric fuels, although the porosity is a special property for fabric fuels. The present paper studies the porosity and area density effects on upward flame spreading using 160.0 cm tall and 8.0 cm wide flax fabric samples with various porosities and area densities. The flame shape, flame length, flame spread rate, ignition time, standoff distance and surface temperature distribution are obtained and analyzed. The major findings are summarized as follows: as the porosity increases and corresponding area density declines, the flame spread rate and flame length increase, whereas the ignition time decreases, which is because the oxygen can reach the fuel surface in the pyrolysis region more easily and, subsequently, the heat flux received by the virgin fuels increases. The two parameters of flame standoff distance and surface temperature in the preheating region can be applied to characterize the heat flux received by the virgin fuels. Generally, when the porosity increases and the corresponding area density decreases, the flame standoff distance and the surface temperature at the same distance from pyrolysis front increase, which reveals that the heat flux received by the virgin surface increases.

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Section: Methodsmentioning

confidence: 99%

Section: Spread Ratementioning

confidence: 99%

mentioning

confidence: 99%

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Effects of porosity and area density on upward flame spread characteristics over thin flax fabric

Gao

Hui

Zhang

et al. 2020

Textile Research Journal

Self Cite

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“…1 At the beginning, all samples experienced an approximately 2.0 cm pyrolysis zone, where the pyrolysis gases are released to participate in the flame. 33 Each test at the same condition was repeated at least four times to reduce experimental uncertainty. All the experiments were performed under controlled conditions at 25 AE 2 C and 42 AE 3% relative humidity within a combustion chamber.…”

Section: Methodsmentioning

confidence: 99%

“…To the best of our knowledge, the upward flame spread behaviors at different widths are dominated by two different heat transfer regimes: the convection regime and the radiation regime. 33,37 When the sample is narrow, convective effects are dominant and the flame spread rate should drop. In contrast, when the sample width is large, radiative effects are dominant and the flame spread rate should rise.…”

Section: Flame Spread Ratementioning

confidence: 99%

Experimental study of the width effects on self-induced buoyant blow off in upward flame spread over thin fabric fuels

Zhu

Gao

Chai

et al. 2019

Textile Research Journal

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In this paper, a series of upward flame spreading experiments were conducted on thin flax fabric with various widths ranging from 3.0 to 8.0 cm and length of 1.6 m. Symmetric ignition at the entire bottom edge of samples led to two-sided upward flame growth initially. A very interesting behavior of flame blown off was observed in upward flame spreading and an explanation was provided based on the increased buoyancy-induced velocity at the flame base. When the sample width is 6 cm or less, the flame length increases to a critical value and, correspondingly, the buoyancy-induced velocity reaches the blow off velocity, which results in a flame being blown off on one side. The remaining flame on the other side would shrink in length and propagate to the end of the sample with an asymptotically constant length and steady spread rate. For samples wider than 6 cm, the two-sided flame continues to spread to the end of samples and the self-induced blow off phenomenon is not observed. Moreover, the width effects on the flame height, flame thickness and flame spread rate are analyzed and explained in this paper. The results of this study may help advance better understanding of flame blow off behaviors over solid surfaces and have implications concerning fire control of flame spread over solid fuels.

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Upward flame spread and self‐induced buoyant blow‐off over two‐sided thin fabric at different inclination angles

et al. 2021

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Summary A series of upward flame spread experiments over two‐sided long thin flax fabric sheets were conducted at different inclination angles from horizontal (0°) to vertical (90°). With the inclination increased to a critical angle, the flame on the lower side of the 4 and 6 cm wide samples can be blown off spontaneously. After the lower‐side blow‐off, the remained flame on the upper side spread steadily to the end of the sample. To clarify the controlling mechanism, the flame spread rates and flame geometry characteristics were investigated and compared in different inclination angles. The maximum flame spread rate and flame length monotonically increased with the inclination angle under the assistance of self‐induced buoyancy. However, the steady flame spread rate and flame length on the remained side dropped significantly after one‐side extinction. The lower side flame was blown off by the large buoyant flow velocity induced from the critical flame length, which is controlled by the small Damköhler number. Flame thickness and flame tilt angle were analyzed at varied inclinations to help understand the heat transfer from the flame to the unburnt fuel surface. Two opposite effects of self‐induced buoyancy were proposed at different ranges of inclination: the thermal assistance regime at the lower inclination angle and the kinetical extinguishing regime at a higher inclination angle. They are dominated by the heat transfer from the flame and local fluid dynamic around the flame base, respectively.

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Experimental Analysis of Critical Acceleration Condition for Two-Sided Upward Flame Spread Over Inclined Thin Fuel Surfaces

Cited by 17 publications

References 31 publications

Effects of porosity and area density on upward flame spread characteristics over thin flax fabric

Effects of porosity and area density on upward flame spread characteristics over thin flax fabric

Experimental study of the width effects on self-induced buoyant blow off in upward flame spread over thin fabric fuels

Upward flame spread and self‐induced buoyant blow‐off over two‐sided thin fabric at different inclination angles

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