Experimental study on secondary breakup regimes and resultant droplet sizes for water and surrogate fuels

Secondary breakup of water and single-component surrogate fuels of diesel and biodiesel fuels, n-dodecane and n-hexadecane, has been experimentally investigated in the present study. The experiments are performed by introducing mono-disperse droplets into an air jet issuing from a contoured nozzle. Droplet size is around 200±4-µm which is close to the droplet sizes found in practical sprays. The aerodynamic Weber number (We) is varied by changing the air-jet velocity. In the present study, apart from the most-reported regimes namely-bag breakup, bag and stamen breakup, shear breakup and catastrophic breakup - two more regimes viz. dual-bag breakup and multi-bag breakup regimes have also been observed. The dual bag regime occurs in the Weber number range of 30 to 46 followed by the multi-bag regime in the Weber number of 46 to 80. These two regimes have been very rarely reported in the technical literature. The SMD of resultant droplets reduces for Weber numbers in the range of 12 to 18 and increases for the Weber numbers in the range of 18 to 24 and monotonically reduces for Weber numbers above 24. However, at a given Weber number, the variation in liquid properties has minimal effect on SMD of resultant droplets. The experimental data presented is useful to validate computational models formulated based on secondary breakup phenomenon for simulation of water sprays or sprays of diesel fuel surrogates such as n-dodecane and n-hexadecane. © 2018 Solar Turbines Incorporated.