An optically accessible domestic-scale swirl-stabilized combustor has been developed to allow for the investigation of combustion characteristics of biomass derived pyrolysis oils in pressure-atomized and air-atomized spray flames. Pine and corn fiber derived pyrolysis oil have been studied, with light fuel oil (LFO) used as a baseline fuel for comparison. Gaseous and particulate exhaust emissions have been measured, and the particulate samples studied with scanning electron microscopy (SEM) to investigate morphology and composition. In-situ visualization studies have been performed by employing high speed imaging of flame luminosity and several laser diagnostic methods including Mie scattering, hydroxyl radical planar induced fluorescence (OH-PLIF), fuel planar laser-induced fluorescence (Fuel-PLIF), and laser induced incandescence (LII). Spray characteristics have been investigated by employing Mie scattering and phase Doppler particle analysis(PDPA). Particulate emissions in pyrolysis oil have been found to consist predominately of unburned fuel residues (cenospheres), rather than soot, with higher emissions than LFO. Cenosphere emissions have been found to be greater for pressure atomization compared to air atomization, lean conditions relative to rich conditions, and low atomization air flowrates compared to high atomization air flowrates. Variation in combustion air preheat temperature from 100 to 400 yC, variation in water content from 23 to 26%, and variation in fuel fixed carbon content from 15 to 51% did not show significant effects on cenosphere characteristics.