Fireball during combustion of hydrocarbon fueld releases. II. Thermal radiation

The processes of radiative heat transfer in a fireball which develops upon ignition of a cloud of hydrocarbon fuel near the Earth’s surface are simulated numerically. The emissive characteristics of combustion products (mixtures of nitrogen dioxide, water vapor, and soot) are described using the weighted-sum-of-gray-gases model with temperature-dependent weighting coefficients. The radiation field in the fireball for individual gray gases is calculated in a diffusion approximation (gases for which the fireball is optically thick) or in a volume emission approximation (gases for which the fireball is optically thin). Results of calculations for propane fireballs with fuel masses of 1 g to 10$^3$ kg are presented. The role of scale effects is analyzed by comparing the spatial distributions of the radiative source term for fireballs of different dimensions. It is shown that the radiation of burning clouds of small scale proceeds uniformly over the volume, whereas fireballs of large scale radiate predominantly from the surface. The calculated fraction of energy converting to radiation is in good agreement with literature data. The radiation field outside fireballs and the fluxes on the surface are calculated by the Monte Carlo method. The dose of energy incident on the surface during burning of a fireball is calculated.