Fluorescence lifetime measurements applied to the characterization of the droplet temperature in sprays

Stiti, Mehdi; Liu, Yangpeng; Chaynes, Hadrien; Lemoine, Fabrice; Wang, Xishi; Castanet, Guillaume

doi:10.1007/s00348-021-03264-x

Cited by 5 publications

(5 citation statements)

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“…where is the fluorescence lifetime, which is on the order a few nanoseconds for organic dyes such as RhB, EY and Rh6G. In the literature, biexponential decays were sometimes used to describe the decay of some fluorophores including RhB (Boens et al 2007;Kristoffersen et al 2014;Stiti et al 2021b). In this case, the decay can be described using the following expression:…”

Section: Fluorescence Lifetime Measurements In the Time Domainmentioning

confidence: 99%

“…It consists in generating synthetic histograms of the photon arrival times, while taking into account the photon count rate, the acquisition time, the noise level, the IRF, and the time-channel width. Such method has been already employed by Stiti et al (2021b) for assessing the precision of temperature measurements in a single spray. In this study, a monoexponential function was used to describe the fluorescence decay.…”

Section: Appendixmentioning

confidence: 99%

“…Raman scattering was exploited to characterize the chemical composition and, in some cases, also the temperature using both the surface area and the position of the peaks in the Raman spectrum (Carns et al 1990;Schweiger 1990;Müller et al 2000). A second group of measurement techniques relies on photoluminescence processes like fluorescence (Stiti et al 2021b) or phosphorescence (Strizhak et al 2020) which are the consequence of the spontaneous relaxation of molecular species after these have been excited by a type of energy. Laser-induced fluorescence (LIF) offers unprecedented temperature sensitivity and versatility in its applications with a wide variety of fluorescent dyes excitable at various wavelengths and soluble in different solvents.…”

Section: Introductionmentioning

confidence: 99%

“…As an alternative to intensity-based measurements, Stiti et al (2021b) proposed a new approach based on the fluorescence lifetime. Contrary to the fluorescence intensity, the value of the fluorescence lifetime is not dependent on the measurement method and system.…”

Section: Introductionmentioning

confidence: 99%

“…It is closely dependent on the quenching rate of the fluorescence and therefore on the temperature for some dyes. The Time Correlated Single-Photon Counting method (TCSPC) was employed by Stiti et al (2021b) to measure the temperature of water droplets in a polydisperse spray. An ultrashort laser beam focused on the spray, and a fast-responding photodetector are used to detect the arrival times of the fluorescence photons.…”

Section: Introductionmentioning

confidence: 99%

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Two-photon fluorescence lifetime imaging applied to the mixing of two non-isothermal sprays: temperature and mixing fraction measurements

Wang

Stiti²,

Chaynes³

et al. 2022

Exp Fluids

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Droplets temperature is a key parameter for the study of heat and mass transfers in many spray applications. Time correlated single photons counting (TCSPC) is applied to monitor the fluorescence decay and determine the droplet temperature in the mixing zone of two sprays which are injected with significantly different temperatures. For some well-chosen fluorescent dye, like rhodamine B (RhB), the fluorescence lifetime strongly varies with the temperature. Provided sufficiently different fluorescence lifetimes for the droplets of the two sprays, the fluorescence decay is expected to follow a multiple exponential decay. In this study, different approaches are tested for measuring the temperature of the two sprays as well as their mixing fraction based on the analysis of the fluorescence decay. Firstly, the measurement of the mixture fraction alone is tested by considering a configuration where one spray is seeded with eosin Y (EY) and the other with rhodamine 6G (Rh6G). Given the very different lifetimes of these dyes, which are not temperature dependent, the fluorescence decay is function of the volume fraction of liquid from each spray in these tests. A calibration is necessary to evaluate the mixing fraction. Both sprays are mounted on an automated platform allowing 3D scanning and motions which allows obtaining maps of the fluorescence decay. The out-of-field fluorescence, observed in dense sprays when fluorescence is induced by one-photon absorption, is suppressed by using a two-photon fluorescence excitation. This approach significantly improves the spatial resolution of the measurements. Finally, both the droplet temperature and the mixing fraction are measured simultaneously using a single dye, namely RhB, whose fluorescence lifetime is temperature dependent. Special care must be paid to the fact that RhB does not have a purely monoexponential decay at a given temperature. The fluorescence decay in the mixing zone of the two sprays is considered as a combination of two biexponentials. Results show that the volume fraction of a spray must exceed about 10% to make it possible to determine its temperature with an accuracy of about 2-3 °C. Simultaneous measurements of the sprays temperatures and volume fractions provide a means to calculate the mixing temperature (the average between the temperatures of the two sprays weighted by their volume fractions).

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Section: Fluorescence Lifetime Measurements In the Time Domainmentioning

confidence: 99%

Section: Appendixmentioning

confidence: 99%