The role of secondary char oxidation in the transition from smoldering to flaming

Putzeys, Olivier; Bar-Ilan, Amnon; Rein, Guillermo; Fernandez‐Pello, A. C.; Urban, David L.

doi:10.1016/j.proci.2006.08.006

Cited by 37 publications

(38 citation statements)

References 15 publications

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“…The experimental setup is a modification of that previously used to study the spontaneous transition from smoldering to flaming [9,10,12]. It consists of a vertically oriented foam sample heated on three of its surfaces with guard heaters and with the fourth, free surface, exposed to a parallel forced oxidizer flow and radiant heat flux.…”

Section: Experimental Conceptmentioning

confidence: 99%

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The piloted transition to flaming in smoldering fire retarded and non‐fire retarded polyurethane foam

et al. 2008

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The piloted transition from smoldering to flaming, though a significant fire safety concern, has not been previously extensively studied. Experimental results are presented on the piloted transition from smoldering to flaming in non-fire retarded (NFR) polyurethane foam and the fire retarded polyurethane foam Pyrell ® . The samples are small blocks, vertically placed in the wall of an upward wind tunnel. The free surface is exposed to an oxidizer flow and a radiant heat flux. The smolder product gases pass upwards through a pilot. The experiments on NFR foam show that the smolder velocity and peak smolder temperature, which increase with the oxygen concentration and heat flux, are strongly correlated to the transition to flaming event, in that there are minimum values of these parameters for transition to occur. The existence of a minimum smolder velocity for ignition supports the concept of a gaseous mixture reaching a lean flammability limit as the criterion for the transition to flaming. To compensate for the solid-and gas-phase effects of the fire retardants on the piloted transition in Pyrell, it was necessary to increase the oxygen concentration and the power supplied to the smolder igniter and the pilot. The piloted transition is observed in oxygen concentrations above 17% in NFR foam, and above 23% in Pyrell. The results show that although Pyrell is less flammable than NFR foam, it is still susceptible to smoldering and the piloted transition to flaming in oxygen-enriched environments, which is of interest for special applications such as future space missions.

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Section: Experimental Conceptmentioning

confidence: 99%

“…Several works have studied the spontaneous transition from smoldering to flaming, whereby the smolder reaction supplies the gaseous fuel and the heat to trigger a gas-phase ignition [8][9][10][11][12]. However, very little fundamental work has been done on the piloted ignition of the gaseous products of smoldering [13].…”

Section: Introductionmentioning

confidence: 99%

The piloted transition to flaming in smoldering fire retarded and non‐fire retarded polyurethane foam

et al. 2008

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“…Putzeys et al [17] found that the smoulder velocity and peak temperature are strongly correlated to the occurrence of transition from smouldering to flaming. The transition has also been observed to occur when pores are formed in the region behind the smouldering front [18]. This implies that the smouldering front acts as the source of combustible vapours and heat for the flaming ignition.…”

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confidence: 99%

Radiant Ignition of Polyurethane Foam: The Effect of Sample Size

et al. 2012

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Abstract. Although smouldering ignition of upholstery items remains a leading cause of residential fire deaths, relatively little research is conducted on the topic. An experimental investigation of the effect of sample size on the ignition and spread of smouldering and flaming in polyurethane foam under natural flow conditions is reported here. Polyurethane foam samples are used because this is a common material in modern, residential environments and one for which there exists significant quantities of previous experimental data in the literature. Samples of different square cross-section size and a fixed height of 150 mm are insulated on all sides except the top which is exposed to a radiant heat flux and is open to the air. Samples with side lengths of 50 mm, 100 mm, and 140 mm are studied. Ignition and spread dynamics are diagnosed using thirteen thermocouples located along the vertical centre line. The onset of smouldering ignition (13 kW m À2 , 8 kW m À2 and 7 kW m À2 for 50 mm, 100 mm and 140 mm sample sizes respectively) is observed at significantly lower heat fluxes that flaming (45 kW m À2 , 32 kWm À2 and 30 kW m À2 respectively). Critical heat fluxes for smouldering and flaming ignition increase with decreasing sample size, with smouldering ignition being significantly more sensitive to sample size than flaming ignition under the size range studied. Smouldering spread rates are measured in the range from 3 mm min À1 to 25 mm min À1 and found to be a strong function of the heat flux and depth of the smoulder front. The effect of sample size on smouldering has been theoretically proposed before but this is the first time that this effect has been demonstrated experimentally for ignition. The fact that large samples result in the lowest critical heat flux could have implications for testing procedures and translation of results from small-scale testing to real-scale in the built environment.

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“…Smolder combustion has received considerable attention in the literature both experimentally [1]- [12] and computationally [13]- [30]. Experimental focus has ranged from studying smolder propagation to examining transition to flaming for various fuels.…”

Section: Introductionmentioning

confidence: 99%

“…The reaction mechanism includes three pyrolysis reactions and four oxidation reactions. One of the oxidation reactions included is what has been referred to as "secondary char oxidation", which has been identified as the key step leading to transition to flaming [10], [12]. While the current focus is not to examine the transition from smoldering to flaming, the work establishes the framework to potentially do so in the future.…”

Section: Introductionmentioning

confidence: 99%