Visualization of high-speed gas jets and their airblast sprays of cross-injected liquid

A planar and instantaneous visualization study of high-speed gas jets and t heir airblast sprays was performed to qualitatively examine the different a tomization performances of different gas nozzles. For the visualization of high-speed gas jets (with no liquid injected), Nd:YAG pulsed laser sheets i maged the clustered vapor molecules in the Rayleigh range (d much less than lambda), condensed from the natural humidity during the isentropic gas exp ansion through a nozzle. This method visualized both underexpanded sonic ga s jets from a converging nozzle (SN-Type) and overexpanded supersonic gas j ets from a converging-diverging nozzle (CD-Type). When liquid is cross-inje cted, the same laser sheet images the spray droplets of relatively large si zes (d greater than or equal to lambda). The present visualization results show that the SN-Type nozzle develops a wider spray than the CD-Type nozzle , quite probably because the SN-Type nozzle has a wider gas jet tin the abs ence of liquid) than the CD-Type. Also, the wider spray of the SN-Type nozz le lowers the probability of droplet coalescence and generates finer sprays compared to the CD-Type nozzle. These visualization results qualitatively agree with the previous quantitative finding of the different atomization c haracteristics of the two types of nozzles (Park et al. 1996).