Planar laser-induced fluorescence imaging of the spatial vapor distribution around a monodisperse acetone droplet stream exposed to asymmetric radiant heating

The development of liquid fuelled microcombustors faces many challenges, one of which being high asymmetric heat flux across the combustion chamber. Typically, thin walls provide little resistance to convective heat transfer and therefore, allowing high heat loss rates. Insulating the walls results in high wall temperatures, which increases the likelihood that radiation plays an important role. Both of these effects have the potential to induce asymmetries and strong temperature gradients in the gas flow, relative to the more uniform environment of a conventional combustor. This investigation uses planar laser-induced fluorescence (PLIF) to reveal the spatial vapor distribution around a monodisperse acetone droplet stream that is exposed to asymmetric radiant heating. Droplets with diameters from 117 to 222 μm flow past a single-sided array of radiant heating elements to provide the asymmetric heating. A frequency-quadrupled Nd:YAG laser provides a 266 nm light sheet to excite the acetone vapor around the droplets, which are exposed to different experimental conditions by varying parameters such as the droplet diameter and temperature of the radiating elements for a fixed exposure time of the droplets in the heated region. A CCD camera captures the fluorescence of the excited acetone vapor molecules over a broadband wavelength range between 350 and 550 nm, to give the radial and axial vapor concentration around each droplet. After processing the PLIF images, we obtain contour plots of the spatial acetone vapor concentration around the droplets which depict asymmetric vapor distribution. The potential impacts on vaporization, combustion and pollutant formation are discussed.