Secondary atomization of small hydrocarbon droplet by fourth harmonic generation of Nd:YAG pulsed laser

Atomization of small fuel droplets using a UV laser is considered experimentally under atmospheric conditions. The droplet diameters in the experiments are 30 µm, 20 µm, and 15 µm. The maximum spatial resolution is 232 nm/pixel. The temporal resolution is 100 ns. The fuels under test are diesel oil (JIS K2204, No. 1), hexadecane (99.5%) and o-Xylene (98%). A Nd:YAG pulse laser operating at 266 nm is used in the experiments. The maximum laser energy is 10 mJ. The laser beam diameter is 5 mm, and the flash time is 7 ns. As a result, the diesel oil droplets of all diameters are atomized using 10 mJ of laser energy. The 15-µm-diameter hexadecane droplets are not atomized. The laser energy threshold for atomization of the 30-µm-diameter o-Xylene droplets is 4.5 mJ, and the calculated laser intensity is 450 J/m2 under the assumption of a Gaussian distribution. The atomization delay time is almost 8 µs. Moisture is observed just before atomization occurs. The moisture indicates that this phenomenon can be explained based on the heat transfer process of the laser energy.