SINGLE DROPLET COMBUSTION OF BIOMASS PYROLYSIS OILS

In an investigation of the combustion behavior of biomass-derived liqu ids, we have performed single droplet experiments with two biomass oil s, produced from the pyrolysis of oak and pine. The experiments are co nducted at 1600 K on 320 mu m diameter droplets introduced into a lami nar flow reactor, operating at O-2 concentrations of 14-33 mol %. In-s itu video imaging of burning droplets reveals that biomass oil droplet s undergo several distinct stages of combustion. Initially biomass oil droplets burn quiescently in a blue flame. The broad range of compone nt volatilities and inefficient mass transfer within the viscous bioma ss oils bring about an abrupt termination of the quiescent stage, howe ver, causing rapid droplet swelling and distortion, followed by a micr oexplosion. Droplet coalescence follows, and subsequent burning occurs in a faint blue flame with occasional smaller scale bursts of fuel va por. At the late stages of biomass oil combustion, droplets are accomp anied by clouds of soot, produced from gas-phase pyrolysis. Liquid-pha se polymerization or pyrolysis of the oxygenate-rich biomass oils lead s to the formation of carbonaceous cenospheres, whose burnout signifie s the final stage of biomass oil droplet combustion. Oak and pine oils behave similarly during combustion, though differences in their physi cal properties cause pine oil to show more susceptibility to fragmenta tion during the microexplosion. Changes in oxygen concentration alter the timing of the events during biomass oil combustion, but not their nature. Comparison of the biomass oils with No, 2 fuel oil reveals vas t differences in combustion mechanisms, which are attributable to diff erences in the physical properties and chemical compositions of the fu els. Despite these differences, the biomass oils and No. 2 fuel oil ex hibit surprisingly comparable burning times under the conditions of ou r experiments.