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Fire dynamics simulator technical reference guide volume 1 :: mathematical model

Flame radiation feedback to fuel surface in medium ethanol and heptane pool fires with cross air flow

A wind tunnel experimental study on burning rate enhancement behavior of gasoline pool fires by cross air flow

Pool fires – An empirical correlation

This paper quantifies experimentally the evolution of heat feedbacks through conduction, convection and radiation in medium square pool fires (10–25 cm) with horizontal cross air flows ranged in 0–3.0 m/s. Ethanol and heptane are used as representative fuels producing typically less-sooty and sooty flames. Results show that the overall conduction heat feedback flux through the four sides increases with cross air flow speed, being more prominent for smaller pools than for larger ones. And the rate of overall conduction heat feedback increment is more prominent for heptane, of which the rate of increase with flow speed nearly 2 times that of ethanol. Meanwhile, the radiation heat feedback declines with cross air flow speed, with its contribution fraction nearly negligible at larger flow speeds for both fuels. The convection feedback fraction increases with cross air flow speed. Its increment is more prominent (a) for heptane (increasing fast with flow speed to be even the dominate one among the three heat feedbacks) than ethanol (increasing slowly with flow speed; being nearly constant and maintaining to be the dominant one); and (b) for larger pools than for smaller ones. The changing of dominant heat feedback mechanism with cross air flows, results in the change of the scaling behavior of the mass burning flux with pool size. A stagnant layer solution theory is then proposed, by including fuel mass transfer Spalding number B , to describe the change of mass burning flux of different size pool fires with cross air flow speed for different fuels in relative strong cross air flows [as indicated by Froude number (Fr =  u /[ gd ] 1/2 ) larger than about unity]. Experimental data are shown to be well correlated by the proposed theory.

Evolution of heat feedback in medium pool fires with cross air flow and scaling of mass burning flux by a stagnant layer theory solution

A mid-infrared spectrometer was used to measure the thermal radiation spectra within the turbulent flame brush and vapor dome of a 2 m diameter well-controlled pool fire. Fuels used include ethanol, an ethanol/toluene blend, JP-8, and heptane. These unique data provide insight into the relative contributions of soot and gas species emissions to the overall emission. They further assess the impact of absorption of thermal radiation from within the flame zone and the fuel rich region on the incident flux to the fuel pool. In addition, laboratory-scale experiments investigated the spectrally-resolved absorption of thermal radiation by the liquid fuel in the wavelength range of 1.3–4.8 μm, corresponding to the majority of the expected emitted radiation from the fire. The dominant emission in the ethanol fires was from water and carbon dioxide, the products of combustion; while, emission from soot dominated the thermal radiation spectra from the other three fuels. The overall intensity of the thermal radiation reaching the fuel surface for the three soot producing fuels was reduced due to absorption by cold water, carbon dioxide, fuel vapor (due to the C–H bond stretching), and soot. The transmission of thermal radiation through liquid fuel revealed that a significant fraction (>75% for JP-8 and >90% for ethanol) of the thermal radiation that reaches the fuel surface is absorbed within the first 3 mm. All fuels were particularly opaque in the 3.2–3.6 μm range and some fuels (heptane and JP-8) were relatively transparent at wavelengths less than 1.6 μm and from 1.85 to 2.1 μm, where a significant amount of thermal energy exists. These data sets provide a sound basis for assessing the thermal radiation incident upon the fuel surface and suggest the penetration depth of the incident flux through the liquid pool.

Alexander L. Brown

Papers

Characterization of thermal radiation spectra in 2m pool fires