High Temperature Radiation Absorption of Fuel Molecules And An Evaluation of Its Influence on Pool Fire Modeling

Abstract

Infrared absorption coefficients of various gas and liquid fuels (propane, n-heptane, methanol, toluene, propylene and methyl methacrylate) were measured using high temperature Fourier transform infrared spectroscopy (FTIR) for a range of temperatures up to 1000 K in order to facilitate calculation of radiative absorption of fuel molecules in large-scale, non-premixed flames. Spectrally resolved fits as a function of temperature (up to 600 K) were calculated using a semi-empirical expression derived from quantum theory. These fits provided a basis for calculating infrared spectra for the fuels from 300 K to 1400 K. Extrapolating the fit to high temperature gave integrated total absorption coefficients with errors  20 % temperature up to 1000 K for measured hydrocarbon fuel specie. Highly resolved infrared absorption coefficient database of fuels and combustion products (H2O, CO2, and CO from HITEMP database, and soot from modeling) were created. Comparison of Planck mean absorption coefficients as a function of temperature indicated unique behavior with respect to molecular structure of fuels. Directional radiation intensity at the fuel surface of 0.3 m methanol, heptane and toluene pool fires were solved using a one dimensional radiative transport equation for line of sight at flame centerline using the new radiation absorption coefficient database. The solution of transport equation predicted radiation intensity at fuel surface within 2 % for non-sooty methanol pool, but under predicted < -100% for sooty pool fires of heptane and toluene. Flame structure impacted importance of absorption and emission. Soot within the flame, which has continuous band absorption at entire infrared region, absorbed much more radiation than other species, which has particular discrete band absorption, and resulted in low radiation intensity at the fuel surface.