Smoldering and spontaneous transition to flaming over horizontal cellulosic insulation

Yang, Jiuling; Liu, Naian; Gao, Wei

doi:10.1016/j.proci.2018.05.054

Cited by 23 publications

(13 citation statements)

References 14 publications

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“…The results by Dodd et al (2012) for temperature and transition time agreed well with the experimental results by Putzeys et al (2007). Putzeys et al (2007), Dodd et al (2012), Yang et al (2018), and dotted blue line indicates heat feedback from char oxidation that ignite flaming reaction as concluded by Torero and Fernandez-Pello (1995), Tse et al (1996), Putzeys et al (2007), Dodd et al (2012), Yang et al (2018). In the kinetic model by Dodd et al (2012), secondary char oxidation (SCO) is important in providing gaseous fuel and heat required to ignite flaming combustion.…”

Section: Figure 8 | (A)supporting

confidence: 74%

“…This finding is related to the mechanism proposed by Torero and Fernandez-Pello (1995). To computationally reproduce the experimental work of smouldering cellulosic insulation by Ohlemiller (1990), Yang et al (2018) found that char oxidation and pyrolysis of cellulose provide gaseous fuel, while the ignitor is the hot char at the surface of the cellulosic insulation (Figure 9). There is no SCO in this model.…”

Section: Figure 8 | (A)mentioning

confidence: 53%

“…¶ No transition to flaming in samples with particle diameters <0.1 cm. I Computationally predicted by Yang et al (2018).…”

Section: The Chimney Effectmentioning

confidence: 99%

“…Most wildland fuels fall in this category, except wood, which is a consolidated fuel with low permeability. In the smouldering of this fuel category, the transition tends to occur at the surface of the fuel bed (Palmer, 1957;Ohlemiller, 1990;Manzello et al, 2006a,b;Valdivieso and Rivera, 2014;Wang et al, 2017;Yang et al, 2018).…”

Section: Permeability and Consolidationmentioning

confidence: 99%

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Review of the Transition From Smouldering to Flaming Combustion in Wildfires

et al. 2019

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Wildfires are uncontrolled combustion events occurring in the natural environment (forest, grassland, or peatland). The frequency and size of these fires are expected to increase globally due to changes in climate, land use, and population movements, posing a significant threat to people, property, resources, and the environment. Wildfires can be broadly divided into two types: smouldering (heterogeneous combustion) and flaming (homogeneous combustion). Both are important in wildfires, and despite being fundamentally different, one can lead to the other. The smouldering-to-flaming (StF) transition is a quick initiation of homogeneous gas-phase ignition preceded by smouldering combustion, and is considered a threat because the following sudden increase in spread rate, power, and hazard. StF transition needs sufficient oxygen supply, heat generation, and pyrolysis gases. The unpredictable nature of the StF transition, both temporally and spatially, poses a challenge in wildfire prevention and mitigation. For example, a flaming fire may rekindle through the StF transition of an undetected smouldering fire or glowing embers. The current understanding of the mechanisms leading to the transition is poor and mostly limited to experiments with samples smaller than 1.2 m. Broadly, the literature has identified the two variables that govern this transition, i.e., oxygen supply and heat flux. Wind has competing effects by increasing the oxygen supply, but simultaneously increasing cooling. The permeability of a fuel and its ability to remain consolidated during burning has also been found to influence the transition. Permeability controls oxygen penetration into the fuel, and consolidation allows the formation of internal pores where StF can take place. Considering the high complexity of the StF transition problem, more studies are needed on different types of fuel, especially on wildland fuels because most studied materials are synthetic polymers. This paper synthesises the research, presents the various StF transition characteristics already in the literature, and identifies specific topics in need of further research.

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Section: Figure 8 | (A)supporting

confidence: 74%

Section: Figure 8 | (A)mentioning

confidence: 53%

“…¶ No transition to flaming in samples with particle diameters <0.1 cm. I Computationally predicted by Yang et al (2018).…”

Section: The Chimney Effectmentioning

confidence: 99%

Section: Permeability and Consolidationmentioning

confidence: 99%

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Review of the Transition From Smouldering to Flaming Combustion in Wildfires

et al. 2019

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“…Porous flow is described by extending Darcy's law to consider the dissipation of the kinetic energy by viscous shear [23]. The mass fraction of solid-phase species (yi) and gas-phase species (yj), are normalized by the initial total mass.…”

Section: Foammentioning

confidence: 99%

Smoldering propensity in upholstered furniture:

Yang¹,

Rein²,

Chen³

et al. 2020

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Reduced-scale mock-ups had been developed to assess and regulate smoldering ignition resistance of residential upholstered furniture (RUF). However, there are limited data available on the effect of the mock-up test configuration on smoldering propensity and how it affects the degree of correlation with full-scale performance. In this work, the smoldering propensity for standard mock-ups (SMs, where the foam is in contact with a support frame) and modified mock-ups (MMs, where an air gap is introduced between the foam and the frame), were computationally simulated and compared to experimental results. Experimental data showed an up to a four-fold increase in smoldering mass loss in a MM as compared to a SM for a test time of 35 min with a 51 mm-thick foam. The model results indicated that the buoyant airflow at the bottom of the mock-up was enhanced in the MM, giving rise to a higher foam oxidation rate, a higher peak smoldering temperature and higher mass loss rate as compared to the SM, and; that oxygen supply was dominated by diffusion-driven transport from the boundaries in proximity of the heating source in the SM. Additionally, the effects of foam thickness on smoldering propensity were studied experimentally and numerically with foam thicknesses of 51 mm (2 inch) and 76 mm (3 inch). With an increase in the foam thickness, the smoldering propensity is weakened in the MM but enhanced in the SM. The model was able to predict the ranking of smoldering propensity quantified by the mass loss in experiments: ML(t)SM2 < ML(t)SM3 < ML(t)MM3 < ML(t)MM2, where MLSM2 is the mass loss (ML) with a 51 mm-thick foam in SM, MLSM3 is the ML with a 76 mm-thick foam in SM, MLMM3 is the ML with a 76 mm-thick foam in MM and MLMM2 is the ML with a 51 mm-thick foam in MM. These results indicate that reduced-scale tests based on SM2 tends to underpredict smoldering propensity and that MM2 may offer a near-worst-case scenario, useful to identify the This publication is available free of charge from: https://doi.org/10.6028/NIST.TN.2087 upholstery materials that prevent most smoldering ignitions independent of the construction and geometry of the actual furniture.

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Thermochemical conversion characteristics of a single wood pellet in a convective low‐temperature air environment

2020

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Summary In this study, the thermochemical conversion process of a single wood pellet under low temperature (350°C‐650°C) isothermal heating is investigated to identify the outstanding low‐temperature ignition and combustion characteristics for heat generation, particularly during the preheating stages in the furnace. The thermal behavior of wood powder was analyzed using thermogravimetric/Fourier transform infrared spectroscopy. The suspended single pellet combustion phenomenon under a convective hot air stream was also explored. The results showed that the wood primarily decomposed in a range from 240°C to 520°C, and low‐temperature ignition was found at 293°C due to heterogeneous oxidation. For pellet combustion, an outstanding heterogeneous‐induced homogeneous combustion phenomenon occurred when the stream temperature was higher than 350°C. In contrast, the ignition mechanism shifted to volatile auto‐ignite mode at 650°C due to the interplay of fuel devolatilization and oxygen diffusion. The pellet temperature evolution was measured, and the results revealed a maximum heating rate of 6.61‐16.95 K/s under a stream temperature ranging from 350°C to 650°C. The weight loss evolution showed three stages during the entire heating process, and the average activation energy (13.12 kJ/mol) was obtained. Char combustion was found favorable to CO production for gaseous emissions, but the burning of volatiles tended to convert fuel into CO2. Finally, a simplified reaction scheme based on different onset temperatures, including pyrolysis, heterogeneous/homogeneous oxidation, and heterogeneous gasification was proposed to illustrate a potential thermochemical conversion route for further utilization.

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Smoldering and spontaneous transition to flaming over horizontal cellulosic insulation

Cited by 23 publications

References 14 publications

Review of the Transition From Smouldering to Flaming Combustion in Wildfires

Review of the Transition From Smouldering to Flaming Combustion in Wildfires

Smoldering propensity in upholstered furniture:

Thermochemical conversion characteristics of a single wood pellet in a convective low‐temperature air environment

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