Suppression Behavior of Obstruction-Stabilized Pool Flames

Abstract

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.

Suppression of cup-burner flames using carbon dioxide inBmicrogravity

“…Consistent with these temperatures, the limiting volume fraction of CO 2 for the cup burner (14.5% computed) falls between those of the two opposing-jet-flame cases, but nearer the critical volume fraction (16.4%) of the lowstrain opposing-jet flame. This result is indeed consistent with the experimental observations that the extinguishment concentrations for the cup-burner flames are generally comparable to those for opposing-jet flames at low strain rates (∼ 50 s −1 ) [35,36]. Interestingly, both opposing-jet flames extinguished at ∼ 1580 K, which indicates that the suppression of opposing-jet diffusion flames is controlled primarily by kinetics, as was observed experimentally [37].…”

Suppression of pool fires with HRC-125 in a simulated engine nacelle.

“…Obstructions such as structural ribs provide a region of recirculating flow where hot products help stabilize the flame that suppressant is relatively slow to penetrate. In certain scenarios, such as those described in [9,13,28], the suppressant concentration must be maintained at an elevated level in the flow past the stabilization region for a substantial period of time to ensure that suppressant penetrates the stabilization region. In the current simulator the mixing times in the flame stabilization regions are estimated to be short compared to the suppressant injection times (see Sec.…”

“…Because of their high ozonedepleting potential, production of these fire-fighting agents has largely ceased, and research programs have identified a number of other promising agents [10]. Takahashi et al [28] and Hamins et al [10] have compiled data on the critical suppressant mole fraction required to suppress fires in various configurations for Halon 1301 and other potential fire suppressants. It is reported that non-ozone depleting agents identified with the most desirable toxicity, corrosion, stability, etc., characteristics generally require a greater agent mass and/or volume, relative to Halon 1301, to suppress a fire.…”

Advanced Integrated Fuel/Combustion Systems

“…Methane issued from a porous plate downstream of the step to simulate a pool fire in the aircraft engine nacelle. As the mean air velocity was increased, Takahashi et al (2001) observed two distinct flame stabilization and suppression regimes: rim-attached wrinkled laminar flame and wake-stabilized turbulent flame. In both regimes, as the agent injection period was increased at a fixed mean air velocity, the critical agent mole fraction at suppression decreased.…”