Numerically resolved line by line radiation spectrum of large kerosene pool fires

Abstract

A numerical model is presented for spectral characteristics of radiation coming from a pool fire flame. The case studies are 1.75 m × 1.75 m and 2.5 m × 2.5 m Kerosene pool fires. Transient heat and mass transfer of the system was solved using a CFD model of a 4 m × 4 m × 5 m rectangular domain built in Fire Dynamic Simulator (FDS) with LES of turbulence and a two-step combustion reaction. Transient profiles of gas compositions, soot concentration and temperature along a line of sight of an imaginary sensor were collected from the CFD simulations, and instantaneous solutions of the thermal radiation along the line were calculated using high-resolution LBL spectral absorption profiles of combustion gases together with a model for soot absorption coefficient, based on spectrally dependant complex index of refraction. The transient spectra, consisting of numerous instantaneous intensity solutions, were then averaged and compared against the similar experimentally measured data. The line of sight and other settings of the model were carefully checked to be consistent with the experiments performed for the same system. The modelling results revealed the strong absorption effect of cold atmospheric gases while the emission peak of hot CO2 at ~2200 cm−1 in fire is still quite distinguishable from the spectral profile of hot blackbody even at 23 m away from the centre of the flame. This emission peak can be therefore used for detection of the fire. The spectral changes of the spectrum are explained and a sensitivity analysis is performed to study the effects of the sensor's distance from the pool, pool size, and modelling and operational conditions, such as relative humidity and radiative fraction.