Experimental investigations on two-sided upward flame spreading over thin flax fabric under the influence of restricted distance

2021 ◽  
pp. 004051752110510
Author(s):  
Yunji Gao ◽  
Xiaolong Yang ◽  
Yueyang Luo ◽  
Zhisheng Li ◽  
Liang Gong
Keyword(s):  
Heat Flux ◽  
Flame Spread ◽  
Ignition Time ◽  
Flame Length ◽  
Solid Fuels ◽  
Spread Rate ◽  
Upward Flame Spread ◽  
Opposite Trend ◽  
Distance Effects ◽  
Flame Spread Rate

Up to 2021, most previous work focused on upward flame spread over thin solid fuel completely attached to objects or with both sides freely exposed to the air, but did not take the restricted distance (distance between fuel and objects) effects into account. In this paper, the restricted distance effects on upward flame spread over thin solid fuels were investigated using 0.65 mm thick, 120 cm tall and 6.0 cm wide flax fabric sheets under various restricted distances of 1.0–3.5 cm. The essential parameters were monitored and analyzed simultaneously, including flame length, pyrolysis spread rate, surface temperature and ignition time. The main conclusions drawn are as follows: when the restricted distance is no more than 1.5 cm, the flame length on the unrestricted side is larger than that on the restricted side, whereas the variation exhibits the opposite trend when the restricted distance is beyond 1.5 cm. As the restricted distance increases from 1.0 to 3.5 cm, the flame length and flame spread rate first increase and then decrease, reaching a maximum value at 3.0 cm restricted distance, whereas the ignition time shows the opposite trend. The decrease rate of the surface temperature with the distance from the pyrolysis front first drops and then rises as the restricted distance increases, which qualitatively characterizes that the heat flux received by the virgin surface first increases and then decreases with restricted distance. The non-monotonic trends of heat flux received by the virgin surface and consequently the flame spread rate as a function of restricted distance are due to the combined restricted distance effects of the chimney effect, wall radiation and restricting oxygen supply. The results of this paper are not only helpful in better understanding the upward flame spread over a thin flax fabric under restricted distance, but also provide some basic data for fire prevention of thin solid fuels.

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

2020 ◽  
pp. 004051752094774
Author(s):  
Yunji Gao ◽  
Hui Zhu ◽  
Yuchun Zhang ◽  
Guoqing Zhu ◽  
Guoqiang Chai
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Flame Spread ◽  
Ignition Time ◽  
Flame Length ◽  
Standoff Distance ◽  
Spread Rate ◽  
Area Density ◽  
Upward Flame Spread ◽  
Flame Spread Rate

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.

Experimental study of welding region effects on upward flame spread over textile membranes

2018 ◽  
Vol 89 (10) ◽  
pp. 2041-2053 ◽  
Author(s):  
Yunji Gao ◽  
Guoqing Zhu ◽  
Mengwei Yu ◽  
Feng Guo ◽  
Yu Xia ◽  
...  
Keyword(s):  
Flame Spread ◽  
Ignition Time ◽  
Flame Temperature ◽  
Air Entrainment ◽  
Flame Length ◽  
Flame Height ◽  
Spread Rate ◽  
Pyrolysis Gas ◽  
Upward Flame Spread ◽  
Pyrolysis Spread Rate

Textile membranes are used widely as a main architectural material in membrane structure buildings. However, very few studies have been conducted to investigate the flame spread characteristics of textile membranes, especially in the case of upward flame spread. In this paper, the effects of welding region on upward flame spread were investigated experimentally using sample sheets of textile membranes 60 cm tall and 6 cm wide with and without welding region. The corresponding observations are as follows: the width of flame with welding region is narrower than that without welding region; flame height, pyrolysis height, preheating length, flame length, and pyrolysis spread rate decrease significantly in the presence of a welding region, while ignition time increases; flame temperature decreases in the presence of a welding region, and temperature along the welding region is higher than that near the edge. The welding region effects are as follows: in presence of a welding region, the thickness of welding region increases and, accordingly, ignition time shows an increase, leading to relatively low pyrolysis gas generated per unit time and relatively less heat released; in addition, a relatively larger pyrolysis gas concentration gradient over the width for welding membranes results in a relatively stronger air entrainment occurring at the sample sides, taking away part of the heat flux and narrowing the flame width. Thus, the presence of a welding region has negative effects of increasing ignition time and reducing preheating length on upward flame spread over textile membranes, eventually decreasing the pyrolysis spread rate.

Experimental study of moisture content effects on horizontal flame spread over thin cotton fabric

2018 ◽  
Vol 89 (15) ◽  
pp. 3189-3200 ◽  
Author(s):  
Yunji Gao ◽  
Guoqing Zhu ◽  
Hui Zhu ◽  
Weiguang An ◽  
Yu Xia
Keyword(s):  
Moisture Content ◽  
Cotton Fabric ◽  
Flame Spread ◽  
Extreme Values ◽  
Ignition Time ◽  
Convective Heat Transfer Coefficient ◽  
Flame Height ◽  
Spread Rate ◽  
Untreated Cotton ◽  
Flame Spread Rate

In this paper, moisture content effects on horizontal flame spread were experimentally investigated using 0.245 mm thick, 28 cm tall and 28 cm wide untreated cotton fabric sheets with various moisture contents varying from 0 to 34%. The pyrolysis spread rates, flame heights and ignition times were obtained and analyzed. The corresponding results are as follows: as moisture content increases, the flame height and spread rate first increase and then decrease. In contrast, the ignition time shows an opposite trend with moisture content. The extreme values are observed in cases of 2% moisture content samples. Moreover, the flame spread rate in the warp direction is larger than that in the weft direction. For horizontal flame spread, the moisture content has the effect of consuming part of the heat feedback, which can play a role in reducing the flame spread rate; simultaneously, the moisture content can enlarge flame size and increase the convective heat transfer coefficient, thereby resulting in an increase in flame spread rate. The non-monotonous trend in pyrolysis spread rate is the result of competition between these effects.

Measurement of instantaneous flame spread rate over solid fuels using image analysis

2017 ◽  
Vol 91 ◽  
pp. 123-129 ◽  
Author(s):  
Subrata Bhattacharjee ◽  
Luca Carmignani ◽  
Gregory Celniker ◽  
Blake Rhoades
Keyword(s):  
Image Analysis ◽  
Flame Spread ◽  
Solid Fuels ◽  
Spread Rate ◽  
Flame Spread Rate

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

2019 ◽  
Vol 90 (11-12) ◽  
pp. 1404-1413 ◽  
Author(s):  
Guoqing Zhu ◽  
Yunji Gao ◽  
Guoqiang Chai ◽  
Jinju Zhou ◽  
Shuai Gao
Keyword(s):  
Flame Spread ◽  
Flame Length ◽  
Flame Height ◽  
Spread Rate ◽  
Fire Control ◽  
Constant Length ◽  
Flame Spreading ◽  
Upward Flame Spread ◽  
Flame Thickness ◽  
Induced Velocity

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.

Large-Scale Experimental Investigation of the Fire Characteristics Parameters of Methanol in Coal Chemical Industry

2015 ◽  
Vol 713-715 ◽  
pp. 2745-2749
Author(s):  
Lu Wang ◽  
Yi Xing Bi ◽  
Wei Wu ◽  
Da Jun Xu
Keyword(s):  
Heat Flux ◽  
Flame Spread ◽  
Large Scale ◽  
Flame Height ◽  
Characteristic Parameters ◽  
Spread Rate ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Flame Spread Rate ◽  
Fire Characteristics

A steel channel with the size of 30×2×1.2 m was made to simulate the full surface fire of 50000 m3methanol tank in coal-to-olefins industry. Some fire characteristic parameters of methanol were investigated, including flame spread rate, flame height, temperature distribution and radiation heat flux distribution. It is found that the flame spread rate of methanol is 1.98 m/s and the flame height could reach to 3.2 m. The temperature of methanol flame is first up and then down with the increase of height, while the highest temperature is 768oC. It is also found that the radiation heat flux of methanol flame is in the changes between 4.4 kW/m2and 12.2 kW/m2. The feature of methanol fire is different from the normal oil fire, which is worth for us to pay more attention.

Steady flame spread rate measurement at discrete levels of external radiant heat flux

1991 ◽  
Vol 23 (1) ◽  
pp. 1693-1699
Author(s):  
Subodh Kumar Bhatnagar ◽  
B.S. Varshney ◽  
B. Mohanty ◽  
C.P. Agarwal
Keyword(s):  
Heat Flux ◽  
Flame Spread ◽  
Radiant Heat ◽  
Rate Measurement ◽  
Radiant Heat Flux ◽  
Spread Rate ◽  
Flame Spread Rate

scholarly journals Thermodynamic and Kinetic Characteristics of Combustion of Discrete Polymethyl Methacrylate Plates with Different Spacings in Concave Building Facades

Polymers ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 167
Author(s):  
Weiguang An ◽  
Lujun Peng ◽  
Minglun Cai ◽  
Kaiyang Hu ◽  
Song Li ◽  
...  
Keyword(s):  
Polymethyl Methacrylate ◽  
Flame Spread ◽  
Structure Factor ◽  
Turning Point ◽  
Fire Risk ◽  
Flame Height ◽  
Hazard Evaluation ◽  
Spread Rate ◽  
Building Facades ◽  
Flame Spread Rate

Polymethyl methacrylate plates are widely applied to buildings, producing significant fire hazards. It lacks a theoretical basis for the fire risk assessment of polymethyl methacrylate in concave building facades. Therefore, experimental methods are used to investigate combustion characteristics of discrete polymethyl methacrylate plates in a concave building facade. Influences of fuel coverage and structure factor are investigated, which is scant in previous works. When structure factor is invariable, average flame height increases first and then decreases as fuel coverage increases, and the turning point is between 0.64 and 0.76. In total, three different patterns of pyrolysis front propagation are first observed for different fuel coverages. Flame spread rate first increases and then decreases as fuel coverage rises, and the turning point is also between 0.64 and 0.76. When fuel coverage is invariable, the flame spread rate first increases and then decreases with increasing structure factor, and the turning point is 1.2. A model for predicting the flame spread rate of discrete polymethyl methacrylate is also developed. The predicted values are consistent with experimental results. Fuel spread rate of discrete polymethyl methacrylate rises as the fuel coverage increases. The above results are beneficial for thermal hazard evaluation and fire safety design of polymethyl methacrylate used in buildings.

Sign in / Sign up

Export Citation Format

Share Document