Transient Measurements of Radiative Properties, Soot Volume Fraction and Soot Temperature in a Large Pool Fire

Multi-wavelength absorption/emission measurements of extinction coefficient, temperature, and soot volume fraction in a large (6 m by 6 m) JP8 pool fire using an in situ water-cooled fiberoptic probe are reported. These measurements provide the first in situ information on radiative properties, temperature, soot, and the associated time scales in large pool tires. Soot extinction coefficients on the order of 5 to 30m -1 were measured in the visible regime, indicating paths lengths for radiative transport in the infrared of approximately 0.1 to 0.3 m. Temperature measurements follow an approximately normal distribution with a mean of 1400 K. and a standard deviation of approximately 67 K. Integral length scales of approximately 0.25 m were deduced from the temperature data. This length scale corresponds to the size of the smaller combusting eddies visually observed in large fires. Soot concentration integral length scales of 1.4 m were determined from the absorption measurements. Soot volume fractions ranging from 0 to 6.0 ppm were measured. In comparison to laboratory-scale flames, excellent agreement was observed between the volume fractions determined by extinction and emission measurements, indicating a uniform temperature distribution (and hence uniform flame coverage) within the 2.0 cm long by 1.0 cm diameter cylindrical sampling volume. Soot volume fractions determined by emission show a strong peak in the PDF just above 1.0 ppm. The same peak is observed on the soot volume fraction determined by absorption, but an additional maxima in the PDF is observed near 3.0 ppm, indicating the occasional presence of thick, cold soot. The primary uncertainty in the results is due to uncertainty in the soot indices of refraction. Fortunately, the uniform flame volume observed in the results show that the environment is promising for the study of these refractive indices.