ID 182

Imaging atomizing sprays with high visibility using two-photon fluorescence laser sheet imaging

 

Abstract:

Two-photon excitation laser induced fluorescence (2p-LIF) is used here for imaging through an optically dense spray system. The main advantage of the approach is that a low level of unwanted fluorescence signal originating from multiple light scattering is generated. This leads to high visibility and image contrast even through scattering media, thus, providing faithful descriptions of the imaged fluid structures. While 2p-LIF imaging is a well-known point measurement approach in the field of life science microscopy, it has, to the best of the authors’ knowledge, never been tested for observing atomizing sprays. We take advantage of this process, here, at a macroscopic scale by imaging a light sheet of ~1cm height. To generate enough 2p-LIF signal at such large scale and for single-shot detection, ultra-short laser pulses of high pulse energy are needed. This is obtained by using a laser system providing 25 fs pulses centered at 800 nm wavelength and having 2.5 mJ pulse energy. The technique is demonstrated by imaging a single spray plume from a 6 holes commercial Gasoline Direct Injection (GDI) system running at 200 bars injection pressure. The injected liquid is water mixed with Fluorescein dye. We show the important image contrast improvement of 2p-LIF light sheet imaging in comparison with the traditional laser sheet Mie scattering and single-photon light sheet imaging. The proposed approach seems to be promising as a future tool for the detailed analysis of complex turbid two-phase flows systems.