Numerical simulation of a pool fire

Abstract

The thermo-fluid mechanical characteristics as well as flame structure in a small scale pool burning is numerically simulated in this study. Based on the fact that the pool fires are fires over the horizontal fuel surfaces in which flame spreading does not occur and that the heat transfer and reaction involved occur in the vapor phase, the small scale pool burning here is modeled like gaseous jet flame with low velocity as an approximation. The fires above 0.02 m, 0.05 m, and 0.1 m circular pools of ethylene have been studied in concurrent air. In order to simulate the unsteady behavior of the flames, all the governing equations are cast in a time-dependent form. Whereas the combustion model postulates infinitely fast chemical reaction, the soot formation model includes soot nucleation, surface growth, coagulation, thermophoresis, and oxidation. Radiative heat transfer is incorporated by the Discrete Ordinates Method (DOM) with the absorption coefficient evaluated using soot and gas species concentrations. The convection terms in the equations are solved by Barely Implicit Correction to Flux Corrected Transport (BIC-FCT) algorithm. First of all, the numerical results are validated by comparison with the experimental results for a low speed laminar diffusion flame. Then the calculations are extended for three flames having total heat release rate of 0.36, 2.26, 9.03 kW, respectively. Reasonably good agreements are found in the temperature distribution, velocity profiles, soot volume fraction and major species concentrations. Especially, the periodic formation of the large scale structures, which are characteristic of freely burning fires, are successfully simulated. Its frequency agrees well with an experimental result.