Experimental Investigation of Performance of an Air Blast Atomizer by Planar Laser Sheet Imaging Technique

It is widely recognized that the fuel-air mixing process is a critical factor in improving combustion efficiency and in minimizing pollutants such as NO_x. Enhancement of fuel-air mixing can lead to lower pollutant emissions and greater efficiency. However, swirling flows in lean combustors play the role of fuel-air mixing and flame stability. The complex fluid dynamic phenomena encountered in swirling two-phase flow contribute to the difficulty in complete understanding of the different processes occurring in combustors. Fortunately, optical and laser-based visualization techniques available in our lab are important nonintrusive tools for visualizing flow process, especially for fuel injection and fuel-air mixing. To provide for a better understanding of effects of counter-rotating flow on droplets in atomization process, this study is a detailed characterization of the spray generated by an airblast atomizer by planar laser sheet imaging method. Optical facility for spray diagnostics with fuel planar laser induced fluorescence (fuel-PLIF) method for fuel distribution and particle image velocimetry (PIV) method for the velocity of droplets is used to evaluate the performance of an airblast atomizer. The results show that the performance of secondary atomization is influenced by swirling flow and primary atomization simultaneously; the swirling flow exhibits significant influence on the droplet size and space distribution relative to that of primary atomization. The primary swirling air reopens the spray cone generated by pressure-swirl atomizer, and the secondary swirling air affects the fuel distribution by forming the recirculation zone. The results provide critical information for the design and development of combustion chambers.