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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 [1], 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 hole commercial Gasoline Direct Injection (GDI) system running at 200 bar 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 shadowgraphy, laser sheet Mie scattering and back-fluorescence imaging. The proposed approach is very promising as a future imaging tool for detailed analysis of the dynamics of atomizing spray in the spray formation region.

"UNAC-LOW" is an ongoing project under EURAMET's EMPIR programme whose aim is to develop the European metrological capacity in underwater acoustics for the calibration of hydrophones and autonomous noise recording systems for frequencies below 1 kHz. The project will provide an improved framework to underpin the absolute measurement of underwater sound in support of regulation and EU Directives for which traceability is currently lacking. Methods for the calibration of hydrophones and autonomous recording systems in the frequency range from 20 Hz to 1 kHz will be developed and validated by comparison measurements between the project partners. Long-term operation of the calibration capabilities will be ensured by each partner, to provide a coherent metrology strategy for Europe within this field. Current activities regarding the design and preparation of calibration setup are here described, in view of round-robin calibrations and validation scheduled for year 2018.

This paper presents the application of several optical measurement techniques for the characterization of the combustion behavior of the pilot burner of a gas turbine combustor developed according to the lean premixed prevaporized concept. The vaporization of the kerosene fuel (Jet-A) injected by a pilot spray and its consequent mixing with air has been visualized using combined laser-induced fluorescence and Mie scattering measurements. The laser-induced fluorescence/Mie measurements can be used to estimate the length and time scales for evaporation and mixing with air of kerosene (Jet-A) for the lean, premixed, and prevaporized pilot burner. In addition, the feasibility of using laser-induced incandescence for soot characterization has been investigated. Finally, spontaneous flame emission (i.e., chemiluminescence and thermal radiation) have been measured providing information on the overall characteristics of the combustion., This work was supported by the European Union through the project entitled Low Pollutant Combustor Technology Program (LOPOCOTEP Contract G4RD-CT-2001-00447) and via the European Union (EU) Large Scale Facility in Combustion at Lund.