Experimental evidence for microexplosions in water/fuel oil emulsion flames inferred by laser light scattering

Abstract

Water fuel-oil emulsion flames have been studied on an experimental apparatus, conceived and realised in order to offer optical access all along a semi-industrial confined flame. The main objective of the work was to provide experimental evidence and gather information on the secondary atomisation mechanism, which was previously observed only in single droplet experiments. Laser light scattering diagnostic was applied to confined 600 kW fuel-oil and water/fuel-oil emulsion flames. The coexistence of fuel droplets, soot and cenospheres required a proper interpretation of the experimental results. The analysis of the scattered light intensities, of the polarization ratios and light extinctions enabled to localise, in semi-industrial scale turbulent diffusion flames, microexplosion phenomena, through which the water emulsions reduce solid particulate emissions. Unburned solid conventional sampling confirmed the amount and size reduction of the cenospheres, due to the microexplosions. The beneficial effect of water on soot formation has also been detected, showing a different behaviour between soot and cenosphere emissions by increasing the emulsified water content.