Abstract

The effect of water-vapor addition to oxidizer on flame radiation is assessed experimentally and numerically through the study of laminar coflow ethylene-fueled non-premixed flames. Oxygen-deficient conditions were studied to closely represent real confined fire situations. Experimental soot volume fraction distributions, presented in a previous study, are complemented with temperature and radiation measurements. Experimental data are compared and complemented with numerical simulations. The relative importance of the thermal, chemical and dilution effects of water-vapor is also investigated through numerical modeling. Addition of water-vapor to oxidizer leads to a decrease in soot concentration, flame temperature, emitted radiation and radiant fraction, regardless of the Oxygen Index (OI). The measured temperatures in the sooting region by two-color pyrometry are in reasonably good overall agreement with the numerical predictions. Soot is the main radiation emitter in the ethylene flame under all the conditions studied, but its relative importance decreases with the water-vapor addition. CO2 is the second most important contributor. Depending on the OI, the relative importance of the water-vapor addition to flame radiation varies. At lower OI the dominant effect is thermal, while at higher OI (normal air condition) the effect of the water-vapor is shared by the three effects: dilution, chemical, and thermal.