Laser-induced blast waves in air and their effect on monodisperse droplet chains of ethanol and kerosene.

Weak spherical blast waves in static air and their breakup of ethanol and Jet A-1 kerosene droplets were investigated. The blast waves were created by laser-induced air breakdowns at ambient temperature and pressure. In the first part of this study, they were visualized with schlieren imaging, and their trajectories were tracked with high temporal resolution. The laser pulse energy was varied to create blast waves of different strengths. Their initial energies were determined by the application of a numerical and a semi-empirical blast wave model. In the second part, monodisperse ethanol and kerosene droplet chains were injected. Their interaction with the blast waves was visualized by the application of shadowgraph imaging. The perpendicular distance of the breakdown origin toward the droplet chains was varied to study the effect on the fuel droplets as a function of the distance. Droplets within a few millimeters around the breakdown origin were disintegrated into two to three secondary droplets. The blast-induced flow velocities on the post-shock side and the corresponding Weber numbers were calculated from the data of a non-dimensional numerical simulation, and a close look was taken at the breakup process of the droplets. The analysis showed that the aerodynamic force of the blast-induced flow was sufficient to deform the droplets into disk-like shapes, but diminished too fast to accomplish breakup. Due to the release of strain energy, the deformed droplets relaxed, stretched into filaments and finally disintegrated by capillary pinching. [ABSTRACT FROM AUTHOR]