Droplet characteristics of multi-plume flash boiling spray evaluation using SLIPI-LIEF/Mie planar imaging technique

Abstract

Flash boiling atomization is a promising approach whose primary breakup heavily relies on the phase change inside the nozzle. Droplet size measurement is crucial for fundamental studies of flash boiling sprays. However, the interference of the vapor phase and multiple scatterings in droplet-dense regions notably impact the accuracy of spray droplet size measurement. In this work, we utilized a three-phase structured laser illumination planar imaging, laser-induced exciplex fluorescence/Mie scattering (3p-SLIPI-LIEF/Mie) method in evaluating the droplet size distribution for a two-hole fuel injector and an ECN Spray G injector. The SMD characteristics of the fuel spray under various temperature and pressure boundary conditions were examined, and flash boiling spray collapse conditions were emphasized. The results show that the proposed SLIPI-LIEF/Mie method is superior to PDI techniques in providing more comprehensive results while maintaining satisfactory accuracy. The SLIPI-LIEF/Mie results show that the near-field plume expansion and SMD distribution strongly correlate with the flash boiling phase transition process. The droplet in the collapsed region was larger than that in the primary plume regions. However, whether or not the spray collapses, the SMD of the spray reduces as the fuel temperature increases, ambient pressure decreases, and injection pressure increases.