Effect of water–kerosene emulsified fuel on radiation, NOx emission and thermal characteristics of a liquid burner flame in lean combustion regime

Abstract

A homogeneous stable emulsified fuel containing 5% water, 93% kerosene and 2% surfactant (1.68% span 80 and 0.32% tween 80) was prepared. Then, the effects of the fuel on the flame structure, radiation heat flux, thermal characteristics and NOx pollutant emission of a liquid burner were investigated in lean combustion regime. Light microscopy imaging of the stable water–kerosene emulsified fuel was used to analyze the micro-explosion phenomenon of the fuel droplets. Also, based on chemiluminescence technique, a TES-1332A digital luminance meter with spectral sensitivity close to CIE photopic curve was used to determine the effect of intermediate soot and carbonaceous particles on flame emissivity coefficient. The results indicate that the micro-explosion phenomenon of emulsified fuel droplets produces a large number of small-scale droplets which, compared with neat kerosene, enhance the mixing rate and decrease the flame reaction zone. Also, although the heat absorbed by the water content of emulsified fuel decreases the flame temperature, emulsified fuel enhances the average emissivity coefficient and radiation heat flux as much as 58% and 25%, respectively. The results also demonstrate that emulsified fuel increases the yellow luminous radiation of flame, which means the concentrations of intermediate soot and carbonaceous particles in the flame have been enhanced. Furthermore, in the case of emulsified fuel, in comparison with neat kerosene, decrease in flame temperature along with increase in OH radicals by water dissociation lead to decrease in the NOx pollutant emission as much as 34%.