Limiting Length, Steady Spread, and Nongrowing Flames in Concurrent Flow Over Solids

Tseng, Ya-Ting; T’ien, James S.

doi:10.1115/1.4001645

Cited by 31 publications

(17 citation statements)

References 17 publications

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“…With the exception of the pyrolysis relation, the flame spread formulation is the same as a previous model [13]. Consequently, we will only mention briefly the model details except the portion on the formulation of the pyrolysis reaction which will be dealt with more thoroughly.…”

Section: Model Descriptionmentioning

confidence: 99%

“…The inert matrix density is 10% of the virgin solid density. The solid fuel properties (except A I and E I ) can be found in [13]. The kinetics parameters for the first-order pyrolysis are A I = 1×10 10 1/sec, and E I = 3×10 4 cal/mole.…”

Section: Solid-phase and Pyrolysis Modelsmentioning

confidence: 99%

“…The flame structure and comparisons will be presented when the flame base is located at an x-location after the steady spread is achieved. Details of the transient processes can be found in [13].…”

Section: Numerical Schemementioning

confidence: 99%

“…Computations in [13] states. For a thick solid, the steady state is a nongrowing stationary flame with a limiting length.…”

Section: Model Descriptionmentioning

confidence: 99%

“…Reference [13] is a transient two-dimensional model for laminar flame spread over solids in a low-speed forced concurrent flow with zero gravity. It uses an unsteady solid phase and a quasisteady gas-phase.…”

Section: Model Descriptionmentioning

confidence: 99%

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A Comparison of Flame Spread Characteristics over Solids in Concurrent Flow Using Two Different Pyrolysis Models

Tseng

T’ien

2011

Journal of Combustion

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Two solid pyrolysis models are employed in a concurrent-flow flame spread model to compare the flame structure and spreading characteristics. The first is a zeroth-order surface pyrolysis, and the second is a first-order in-depth pyrolysis. Comparisons are made for samples when the spread rate reaches a steady value and the flame reaches a constant length. The computed results show (1) the mass burning rate distributions at the solid surface are qualitatively different near the flame (pyrolysis base region), (2) the first-order pyrolysis model shows that the propagating flame leaves unburnt solid fuel, and (3) the flame length and spread rate dependence on sample thickness are different for the two cases.

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Section: Model Descriptionmentioning

confidence: 99%

Section: Solid-phase and Pyrolysis Modelsmentioning

confidence: 99%

Section: Numerical Schemementioning

confidence: 99%

“…Computations in [13] states. For a thick solid, the steady state is a nongrowing stationary flame with a limiting length.…”

Section: Model Descriptionmentioning

confidence: 99%

Section: Model Descriptionmentioning

confidence: 99%

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A Comparison of Flame Spread Characteristics over Solids in Concurrent Flow Using Two Different Pyrolysis Models

Tseng

T’ien

2011

Journal of Combustion

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Experimental Studies on the Effects of Spacing on Upward Flame Spread over Thin PMMA

et al. 2016

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Experiments were carried out to study the effect of spacing between wall and thin fuels on upward flame spread. The front flame height, back flame height, pyrolysis height, burnout length, and pyrolysis spread rate were measured by video image analysis with spacings of 2 mm, 7 mm, 13 mm, 19 mm, and 25 mm. Experiments were performed on uniform PMMA (polymethyl-methacrylate) samples with 200 mm height, 50 mm width, and 1 mm thickness. The results are as follows: (1) As the spacing increased, the front flame height, back flame height, pyrolysis height, and burnout length showed the same trajectory, first increased and then decreased. The maximum trajectory was observed at a spacing of 6.5% of the wall height. (2) At an infinite length of PMMA, the pyrolysis zone and pyrolysis spread rate would reach an asymptotic steady state, and the pyrolysis and burnout spread rates will be asymptotically equal. (3) Of particular interest is the maximum mass-loss rate for a wall spacing/sample height ratio (0.065) due to enhanced the radiation fluxes. In this study, the effects of spacing between wall and fuels on upward flame spread was investigated for the first time using 1 mm thick PMMA sheets, including two-face burning case.

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Concurrent Flame Spread Over Two-Sided Thick PMMA Slabs in Microgravity

et al. 2019

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Concurrent flame spread over two-sided thick PMMA slabs in microgravity Spacecraft fire safety is an important consideration when designing future exploration spacecraft. Concurrent flow flame spread experiments were carried out aboard the Cygnus spacecraft while in orbit to address current knowledge gaps related to solid fuel combustion in microgravity. The experiments used PMMA (polymethylmethacrylate) samples that were 50 mm wide and 290 mm long with two variationsone sample was a 10 mm thick flat slab, while the other was a 10 mm thick flat sample that had a 4 mm thick grooved center section. The thickness variation had a major impact on the flame shape, and the grooved sample developed a deep inverted-V shaped notch as the thin center section burned through. This notch enhanced heat transfer from the flame to the solid through an effectively wider flame base, which is the part of the flame with the highest temperature. Unlike in normal gravity (and also likely in partial gravity), where buoyant flow promotes acceleratory upward flame growth, the microgravity flames reached a steady size (limiting length) for a fixed forced convective flow in agreement with theory (i.e. there is a zero net heat flux at the flame tip). The limiting length implies that the spread rate of the flame will be controlled by the regression rate (burnout rate) of the material because the flames remains anchored to the upstream end of the fuel samples. This is a significant finding for spacecraft fire safety, and makes the probability of flashover in a spacecraft unlikely as the flame size will be small for low convective ventilation flow environments typical in spacecraft. On the other hand, long-burning flames in small vehicles will generate significant quantities of fuel vapor that may reach the lean flammability limit and cause a backdraft. The rapid extinction of the flame when the flow was turned off also supports the existing fire mitigation strategy on the ISS to deactivate the ventilation system in the event of fire alarm. These findings can be applied to improve the safety of future space exploration missions.

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Limiting Length, Steady Spread, and Nongrowing Flames in Concurrent Flow Over Solids

Cited by 31 publications

References 17 publications

A Comparison of Flame Spread Characteristics over Solids in Concurrent Flow Using Two Different Pyrolysis Models

A Comparison of Flame Spread Characteristics over Solids in Concurrent Flow Using Two Different Pyrolysis Models

Experimental Studies on the Effects of Spacing on Upward Flame Spread over Thin PMMA

Concurrent Flame Spread Over Two-Sided Thick PMMA Slabs in Microgravity

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