In many fire scenarios (such as a fully developed compartment fire), gaseous fuel burns in in vitiated environments. Changes of radiative and convective heat transfer from the flame to the environment or solid fuel surfaces due to vitiation need be better understood. This work presents an experimental study on the radiative characteristics of buoyant turbulent ethylene diffusion flames burning in a nitrogen-diluted atmosphere. The experiment was performed on a 15-cm diameter poollike ethylene fire enclosed in a water-cooled compartment. The ambient oxygen concentration was controlled by adding nitrogen to the air flow while maintaining the oxygen flow rate at ten times of the stoichiometric oxidant requirement of the flames. The fuel supply rate was constant while the ambient oxygen concentrations were reduced from atmospheric condition to 8 vol %. At different ambient oxygen concentrations, the radiant fraction, combustion efficiency, flame shape, and temperature along the central axis of the flame were measured. In addition, the radiative power per unit height was determined by measuring the radiative heat flux of flame sections using a slit radiometer, which facilitates the interpretation of radiant fraction. The global soot volume fraction and temperature were also determined by coupling measured spectral flame emission and RADCAL modeling. It was found that the radiant fraction reduces with decreasing ambient oxygen concentrations, which was mainlyattributed to reduced soot concentration.
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