In an investigation of the combustion behavior of biomass-derived liquids, we have performed single droplet experiments with two biomass oils, produced from the pyrolysis of oak and pine. The experiments are conducted at 1600 K on 320 pm diameter droplets introduced into a laminar flow reactor, operating at O2 concentrations of 14-33 mol %. In-situ video imaging of burning droplets reveals that biomass oil droplets undergo several distinct stages of combustion. Initially biomass oil droplets burn quiescently in a blue flame. The broad range of component volatilities and inefficient mass transfer within the viscous biomass oils bring about an abrupt termination of the quiescent stage, however, causing rapid droplet swelling and distortion, followed by a microexplosion. Droplet coalescence follows, and subsequent burning occurs in a faint blue flame with occasional smaller scale bursts of fuel vapor. At the late stages of biomass oil combustion, droplets are accompanied by clouds of soot, produced from gas-phase pyrolysis. Liquid-phase polymerization or pyrolysis of the oxygenate-rich biomass oils leads to the formation of carbonaceous cenospheres, whose burnout signifies the final stage of biomass oil droplet combustion. Oak and pine oils behave similarly during combustion, though differences in their physical properties cause pine oil to show more susceptibility to fragmentation 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 vast differences in combustion mechanisms, which are attributable to differences in the physical properties and chemical compositions of the fuels. Despite these differences, the biomass oils and No. 2 fuel oil exhibit surprisingly comparable burning times under the conditions of our experiments.
A 193 nm excimer laser and a custom fabricated cylindrical lens system is used to produce a plasma sheet of 8 cmX30 cmXO.4 cm in tetrakis(dimethylamino)ethylene (TMAE), a low ionization energy organic gas. Plasma density variation due to photon absorption is studied by scanning the filling pressure ofTMAE between 12 and 150 mTorr. A high density (n>2.OX 1013 cmp3), low temperature (T,w0.8 eV) plasma sheet of 4 mm thickness is obtained with less than 50% spatial density variation over the 30 cm axial length. Charge recombination is found to be the dominant process for tcl.2 /B with the plasma diffusion playing a perturbational role, A one-dimensional plasma model is utilized to model the experimental plasma data by treating the diffusion as a perturbation. This study shows that the recombination coefficient is 1.8+O.1X1O-7 cm3 s-l and the diffusion coefficient is 2.8+0.4X 10" cm* s-'. The plasma sheet has attractive properties for a microwave agile mirror. 0 1995 American Institute of Physics.
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