Characterization of thermal radiation spectra in 2 m pool fires

Abstract

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.