Suppression of a nonpremixed flame stabilized by a backward-facing step

Takahashi, Fumiaki; Schmoll, W. J.; Strader, Edward A.; Belovich, Vincent

doi:10.1016/s0010-2180(00)00106-1

Cited by 11 publications

(12 citation statements)

References 9 publications

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“…Corresponding propane flows of 33 mL/s ± 2 mL/s and 85 mL/s ± 2 mL/s, respectively, were utilized. The low flow condition corresponds to what Takahashi et al [10] describe as regime I suppression (rim-stabilized flame), and the high flow is transitional between regimes I and II (intermittent turbulent flame).…”

Section: Flow Characterizationmentioning

confidence: 72%

“…Takahashi et al [10] measured the characteristic mixing time in a similar facility and found γ to be around 40. Evaluating Eq.…”

Section: Data Correlationmentioning

confidence: 99%

“…Experiments by Hamins et al [9], in cooperation with Walter-Kidde Aerospace, were conducted in a wind tunnel scaled down from the earlier work by Hirst to examine the performance of HFC-125 and HFC-227ea. Investigations at the Air Force Research Laboratory [10] as part of the Next Generation Program (NGP) sought to determine the detailed structure during suppression of a nonpremixed methane/air flame stabilized behind a step. The changing character of the flame with step height and air velocity was examined, along with the amount of halon 1301 required to suppress the flame as a function of the flow parameters and injection interval.…”

Section: Previous Studiesmentioning

confidence: 99%

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Transient application, recirculating pool fire, agent effectiveness screen:

Grosshandler¹,

Hamins²,

McGrattan³

et al. 2001

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NISTIR 6733ii EXECUTIVE SUMMARY * Because of its many positive attributes, halon 1301, or trifluorobromomethane (CF 3 Br), has been used as a fire extinguishing agent in many applications including aircraft, ships, and specialized structures. Due to its high ozone depletion potential, however, world-wide production was halted in 1994. In the search for a long-range replacement, novel types of extinguishing agents and delivery mechanisms are under development. To gauge the suitability of a replacement agent, methods are needed to evaluate the material's suppression effectiveness under conditions that relate to field applications.In this study, a laboratory-scale facility has been developed to screen the suppression effectiveness of agents that are delivered in a transient fashion such as solid propellant gas generators. The transient application, recirculating pool fire (TARPF) agent effectiveness screen features a propane fire stabilized behind an obstruction, which is known to be a highly challenging suppression configuration. The character of the flame and the impact of the air flow, fuel flow, obstruction geometry, and rate of agent addition on the amount of material needed for suppression are evaluated for N 2 , CF 3 Br, and a solid propellant gas generator (SPGG). The importance of the injection process on the flow field and the transport of the agent downstream is examined, and a simple mixing model is used to explain the observed trend of decreasing suppressant mole fraction with increasing injection duration, even for agents as different as CF 3 Br and N 2 . Direct numerical simulation of the suppression event is shown to successfully predict the quantity and rate of N 2 required to extinguish the flame based upon a published global reaction rate for premixed propane/air flame propagation. Important Findings:• The minimum mole fraction of agent for suppression, normalized by the cup burner value, correlates with [1 -exp(-∆ t/ τ )] -1 , where ∆ t is the injection time interval and τ characterizes the mixing time behind the obstacle in the flow.• The general character of the flame and its extinction by a thermal gaseous agent is captured by a direct numerical simulation of the flow based upon single -step chemistry, and numerical experiments have corroborated the simple correlation of the experimental data for N 2 .• The measured difference between the decrease in agent storage bottle pressure and the arrival of the agent at the fire highlight the importance of determining the agent concentration locally and the difficulty in relating changes in bottle pressure to actual mixing conditions. • For the first time, both compressed and solid-propellant generated gases can be compared side by side, and the effect on performance of different formulations, particle loadings and burning rates for various SPGG designs can be unambiguously discriminated.• When the temperature of a hot surface downstream of the pool is above 800 o C, the flame, following suppression, will reignite and stabilize on the hot surface. At ...

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Section: Flow Characterizationmentioning

confidence: 72%

“…Takahashi et al [10] measured the characteristic mixing time in a similar facility and found γ to be around 40. Evaluating Eq.…”

Section: Data Correlationmentioning

confidence: 99%

Section: Previous Studiesmentioning

confidence: 99%

See 1 more Smart Citation

Transient application, recirculating pool fire, agent effectiveness screen:

Grosshandler¹,

Hamins²,

McGrattan³

et al. 2001

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“…The transient agent supply system (Takahashi et a!., 2000) for halogenated suppressants, which is similar in principle to that of Hamins et a!. (I 994a, 1995, 1996), has been used for halon l301 or HFC-125 (pentafluoroethane, C 2HFs) to extinguish JP-8 pool flames and modified for nitrogen, which requires an order-of-magnitude greater concentration to extinguish flames than halogenated Downloaded by [Nanyang Technological University] at 05:38 16 June 2016 suppressants.…”

Section: Figure I the Experimental Apparatusmentioning

confidence: 99%

“…For the suppression of baffle-stabilized JP-8 spray flames, Hamins et al (1996) identified two crucial parameters; i.e., a characteristic mixing time in the recirculation zone and the critical agent concentration at suppression for long agent injection durations and derived a theoretical expression for the critical agent mole fraction as a function of the injection duration. In a previous paper (Takahashi et al, 2000), the authors reported for the first time the results of characteristic mixing time measurements using obstruction-stabilized methane flames and incorporated the results into the correlation between the critical mole fraction at suppression and the agent injection period.…”

Section: Introductionmentioning

confidence: 99%

Suppression Behavior of Obstruction-Stabilized Pool Flames

Takahashi

Schmoll

Strader

et al. 2001

Combustion Science and Technology

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The suppression phenomena of a nonpremixed flame stabilized by a recirculation zone behind an obstruction in a combustion tunnel have been studied because of their relation to fires in aircraft engine nacelles, dry bays, and sbipboard and ground-vehicle compartments. The JP-8 fuel was supplied as a liquid fuel pool, or a gaseous (methane or ethane) fuel issued from a flat porous plate, downstream of a backward-facing step or J-shape flange. The OH planar laser-induced fluorescence revealed a narrow, wrinkled diffusion flame zone that was deeply folded into the recirculation zone in response to the dynamic air entrainment and back-tlow. Both transient and steady-state fire suppression limits were determined; by impulsively injecting a gaseous fire-extinguishing agent (nitrogen, CF 3Br, or CzHF S)' or by continuously adding nitrogen, into the approaching airflow in the combustion tunnel. For high air velocities. the normalized critical agent mole fraction at suppression was a unique function of the agent injection period normalized by the effective mixing time in the recirculation zone, independent of types of fuels, agents, and obstacles. The extinction of the relatively low-strain-rate diffusion flame zone in the recirculation zone appears to determine the suppression limits of obstruction-stabilized flames.

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