Reliable LIF/Mie droplet sizing in sprays using structured laser illumination planar imaging

Area of Science:

• Fluid Dynamics
• Optical Diagnostics
• Spray Characterization

Background:

• Accurate measurement of droplet Sauter Mean Diameter (SMD) is crucial for understanding spray behavior.
• Conventional Laser-Induced Fluorescence (LIF)/Mie ratio techniques are susceptible to errors from multiple light scattering, especially in dilute sprays.
• Existing methods struggle to provide reliable 2D droplet size distribution mapping due to scattering effects.

Purpose of the Study:

• To develop and validate a robust 2D mapping technique for droplet SMD.
• To mitigate the impact of multiple light scattering on LIF/Mie measurements.
• To calibrate and compare the novel technique against established methods.

Main Methods:

• Structured Laser Illumination Planar Imaging (SLIPI) was employed to correct for multiple light scattering.
• The corrected LIF and Mie intensity images were used to calculate the 2D droplet SMD map via image ratio.
• Results were calibrated and validated using Phase Doppler Interferometry (PDI) measurements.

Main Results:

• SLIPI effectively removed unwanted light intensity from both LIF and Mie images, significantly reducing scattering-induced errors.
• The SLIPI-enhanced LIF/Mie ratio technique provided reliable 2D droplet SMD mapping even in dilute sprays.
• The results demonstrated excellent agreement between the SLIPI-LIF/Mie method and PDI measurements.

Conclusions:

• The combination of SLIPI and the LIF/Mie ratio technique offers a significant advancement for accurate 2D droplet SMD measurement.
• This approach overcomes the limitations of conventional LIF/Mie methods by effectively handling multiple light scattering.
• The validated SLIPI-LIF/Mie technique provides a reliable tool for spray diagnostics.