Effects of fuel absorption on radiative heat transfer in methanol pool fires

Abstract

Spectrally resolved infrared absorption coefficients of methanol were measured using high temperature Fourier transform infrared (FTIR) spectroscopy for a range of temperatures (up to 1000 K) expected to be within the fuel rich core of pool fires. Principal absorption band peaks decreased with increasing temperature. The spectral region of the dominant C–O stretching peak causes the integrated Planck mean absorption coefficient to decrease above 350 K. Unidirectional radiation intensity along the fire centerline for a 0.3 m diameter methanol pool was calculated using the 1-D radiative transport equation with the highly resolved absorption coefficient database of methanol and combustion products, and gas-phase temperature and species profiles calculated by NIST’s Fire Dynamics Simulator. The spectrally integrated intensity at the methanol pool surface was calculated at 12,400 W/m 2 sr, which agreed to within 2% of previously reported unidirectional radiation intensity measurements. Intensity calculations with oft-used simplifications for modeling fuel vapor absorption were compared with the spectrally resolved, temperature-dependent absorption calculations, and errors with the simplified approaches for integrated radiation intensity to the pool surface were as high as 20%. This study suggests that even for small methanol pool fires, gas-phase fuel absorption coefficients should have accurate assessments for calculating radiation heat transfer to the pool surface.