Droplet Transport in a Swirl-Stabilized Spray Flame

Droplet transport processes that occur in fuel sprays and spray flames were examined using laser velocimetry, phase Doppler interferometry, and laser sheet beam photography. Droplet size and velocity (axial and radial) distributions were obtained in a swirl-stabilized, pressure-atomized kerosene spray under nonburning and burning conditions. The results show that the introduction of swirl to the combustion air (under nonburning conditions) significantly modifies the spray structure and leads to the transport of smaller size droplets from downstream positions of the spray to upstream near the nozzle exit. Time-based velocity data at different spatial locations of the spray indicated some intermittency in the spray and clustering of droplets. In the center of the spray, near the nozzle exit, most of the droplets are recirculated; near the spray boundary, bimodal velocity distributions indicate the presence of recirculated droplets and droplets that arrive directly from the injector. Combustion results in a significant increase in droplet velocities, especially near the spray boundary where the flame sheet resides. The size of the recirculation zone is much reduced with combustion; however, a number of smaller droplets are still transported upstream. The data demonstrate the important role droplet transport plays in providing a fuel vapor feedback mechanism for flame stability.