Academic literature on the topic 'Laser-induced phosphorescence'

We report on long-lasting phosphorescence and photostimulated long-lasting phosphorescence phenomena in femtosecond laser-irradiated Mn2+-doped alumino-phosphofluoride glasses. Long-lasting phosphorescence was observed in the glass samples after the irradiation of the focused femtosecond laser. Photostimulated long-lasting phosphorescence was observed in the femtosecond laser pre-irradiated region by excitation of an ultraviolet light of 365 nm, after the femtosecond laser-induced long-lasting phosphorescence decayed completely. The mechanisms of these phenomena have been discussed. These phenomena have potential uses in three-dimensional ultra-high-density optical recording.

Temperature is one of the most important parameters in the combustion processes. Accurate surface temperature can help to gain insight into the combustion characteristics of various solid or liquid fuels, as well as to evaluate the operating status of combustion power facilities such as internal combustion engines and gas turbines. This paper mainly summarizes and compares the main surface thermometry techniques, from the aspects of their principles, current state of development, and specific applications. These techniques are divided into two categories: contact-based thermometry and non-intrusive thermometry. In contact-based thermometry, conventional thermocouples as well as thin-film thermocouples are introduced. These methods have been developed for a long time and are simple and economical. However, such methods have disadvantages such as interference to flow and temperature field and poor dynamic performance. Furthermore, this paper reviews the latest non-intrusive thermometry methods, which have gained more interest in recent years, including radiation thermometry, laser-induced phosphorescence, liquid crystal thermography, the temperature-sensitive paint technique, and the temperature-indicating paint technique. Among them, we highlighted radiation thermometry, which has the widest measurement ranges and is easy to acquire results with spatial resolution, as well as laser-induced phosphorescence thermometry, which is not interfered with by the emissivity and surrounding environment, and has the advantages of fast response, high sensitivity, and small errors. Particularly, laser-induced phosphoresce has attracted a great deal of attention, as it gets rid of the influence of emissivity. In recent years, it has been widely used in the thermometry of various combustion devices and fuels. At the end of this paper, the research progress of the above-mentioned laser-induced phosphorescence and other techniques in recent years for the surface thermometry of various solid or liquid fuels is summarized, as well as applications of combustion facilities such as internal combustion engines, gas turbines, and aero engines, which reveal the great development potential of laser-induced phosphorescence technology in the field of surface thermometry.

Laser-induced solid-surface room-temperature phosphorimetry (SSRTP) has been employed for the detection of polycyclic aromatic hydrocarbons. A nitrogen-pumped laser and a dye laser were used as excitation sources. The effects of sample volume, laser irradiation, and background reduction treatment on the precision and sensitivity of the method were studied. With the use of thallium(I) acetate as a phosphorescence enhancer, picogram limits of detection were estimated for phenanthrene, pyrene, benzo[ g,h,i]perylene, chrysene, coronene, and 1,2-benzofluorene. The study demonstrates that laser excitation can improve the sensitivity of SSRTP by up to three orders of magnitude.

The prospects of utilising the laser induced phosphorescence emission of common ketone tracers in the study of multi-phase (gas-liquid) flows are investigated within the context of this thesis. The quantification of evaporated fuel concentrations in the vicinity of liquid droplets by means of the laser induced fluorescence imaging technique, and the measurement of fuel concentrations in sprays containing sub-pixel sized droplets by means of the laser induced exciplex imaging technique suffer from well-known limitations; the former is plagued by low vapour phase signal intensities and halation, and the latter by liquid-vapour crosstalk and quenching. Therefore, a literature research was initially carried out, focusing on two main topics: the underlying photophysics of the processes involved in the excitation and deexcitation mechanism of the tracers under investigation, and the relevant optical techniques available for carrying out vaporized fuel concentration measurements in two-phase flow environments. Following a description of the experimental apparatus, a series of calibration experiments is presented. The liquid phase phosphorescence properties of acetone and 3-pentanone were investigated in the bulk and in liquid streams, and the phosphorescence emission characteristics of both tracers were quantified for different bath gas compositions. The phosphorescence signal of gaseous acetone was calibrated for the excitation energy and concentration dependencies. Based on the calibration data, a new technique was developed for the purpose of investigating the vapour phase concentration in the vicinity of liquid droplets. The proposed technique utilizes the phosphorescence rather than the fluorescence emission of vapour and liquid acetone, and is compared with the well-established laser induced fluorescence technique (LIF), in both evaporative and non-evaporative monodisperse droplet streams. The obtained results suggest that laser induced phosphorescence (LIP) imaging clearly improves upon laser induced fluorescence imaging, by successfully addressing both the high signal intensity disparity between the two phases and the ensuing halation that plague measurements carried out by deployment of LIF. The fluorescence and phosphorescence emission of acetone and 3-pentanone, the latter considered in order to demonstrate the feasibility of LIP imaging by deployment of other common ketone tracers apart from acetone, were also examined in sprays by means of a high-pressure gasoline direct injection system. Experiments examining the emission from both electronic states and their potential correlation are presented for non-evaporative sprays.; in particular, liquid phase corrections are carried out in LIF images by deployment of their corresponding LIP images and the obtained correlation functions, and the ensuing errors are quantified. Finally, mean and median filters are employed in limiting these errors and assessing the feasibility of the proposed technique. The obtained results are rendered encouraging, with suggestions for improvement focusing on reducing the noise observed in the LIP images by both signal augmentation and enhancement in the efficiency of the collection optics.

Thesis (Ph.D.)--Aerospace Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Seitzman, Jerry; Committee Member: Jagoda, Jechiel; Committee Member: Lieuwen, Tim; Committee Member: Menon, Suresh; Committee Member: Tan, David.

Ce travail porte sur la stabilisation de flammes prémélangées et swirlées de mélanges combustibles méthane/hydrogène/air avec différents taux de dilution d’azote et de dioxyde de carbone. Une tige centrale permet de stabiliser des flammes pour de faibles nombres de swirl. Le sommet de la flamme interagît éventuellement avec les parois de la chambre de combustion. L’objectif ces travaux est d’améliorer la connaissance des mécanismes qui gouvernent la stabilisation et la topologie de ces flammes. Ces travaux démontrent que le nombre de swirl, la composition du mélange combustible, la géométrie de la chambre de combustion ainsi que les conditions aux limites thermiques ont une grande influence sur la forme prise par la flamme. Le dispositif expérimental permet de modifier la forme et la taille de la chambre de combustion, le diamètre du tube d’injection et le nombre de swirl. Des conditions opératoires propices aux transitions de forme de flamme sont ensuite étudiées pour différentes configurations de brûleur. Une caractérisation expérimentale fouillée d’un point de fonctionnement est réalisée grâce à la Fluorescence Induite par Laser sur le radical Hydroxyle (OH-PLIF), la Vélocimétrie par Images de Particules (PIV) et la Phosphorescence Induite par Laser de phosphores sensibles à la température (LIP). Une base de donnée de l’écoulement et des conditions aux limites associées est obtenue sans et avec combustion. Les mécanismes qui contrôlent les transitions de formes de flamme sont ensuite analysés lorsque la flamme interagit avec les parois de la chambre de combustion. L’influence de la composition du mélange combustible, de la vitesse débitante et du nombre de swirl est caractérisée et il est démontré que la transition d’une flamme en V vers une flamme en M est déclenchée par un retour de flamme dans la couche limite le long d’une des parois latérales de la chambre de combustion. Les nombres sans dimension contrôlant ces transitions sont identifiés et un modèle de prévision de la forme de ces flammes est développé. La physique déterminant les transitions de forme de flammes est différente lorsque celles-ci n’interagissent pas avec les parois de la chambre de combustion. En utilisant le signal de chimiluminescence OH* et la OH-PLIF, il est montré que la teneur en hydrogène dans le combustible a une grande influence sur la forme de flamme. L’utilisation de la LIP et de thermocouples a également permis de montrer que les conditions aux limites thermiques jouent un rôle prépondérant sur la forme de flamme. Les effets combinés de l’étirement et des pertes thermiques sont examinés par l’utilisation conjointe de la PIV et de la OH-PLIF. Il est montré que les limites d’extinction de flammes pauvres prémélangées sont réduites par les pertes thermiques et que la transition d’une flamme en M vers une flamme en V est consécutive à l’extinction du front de flamme situé dans la couche de cisaillement externe du jet soumis à un étirement trop important. Ces expériences sont complétées par une analyse de la dynamique de ces flammes. Des modulations de la vitesse débitante à basse fréquence et à haute amplitude modifient la forme de flamme. La stabilisation de flammes CH4/H2/air diluées par du N2 ou du CO2 est finalement examinée. La zone de recirculation produite par la tige centrale permet d’alimenter la base de la flamme avec des gaz brûlés chauds et de stabiliser des flammes fortement diluées. Augmenter la fraction molaire de diluant dans le combustible réduit l’intensité de lumière émise par le radical OH*. Il est également montré que la composition du diluant a un impact sur le champ de température des gaz brûlés et des surfaces de la chambre de combustion. La dilution par du CO2 augmente les pertes thermiques par rayonnement des gaz brûlés. Cela réduit l’efficacité de la chambre de combustion équipée de quatre parois transparentes. [...]
This work deals with the stabilization of premixed turbulent swirling flames of methane/hydrogen/air combustible mixtures with different dilution rates of nitrogen and carbon dioxide. A central bluff body helps stabilizing the flames at low swirl numbers. The flame tip eventually impinges the combustor peripheral wall. The general objective is to gain understanding of the mechanisms governing the stabilization and the topology of these flames. It is found that the swirl number, the combustible mixture composition, the geometry of the combustor, and the thermal boundary conditions have a strong impact on the shape taken by these flames. The experimental setup used to characterize flames topologies is first described. Flames prone to topology bifurcations are selected and are studied for different arrangement of the combustor when the combustion chamber shape and size, the injection tube diameter, and swirl number are varied. One operating condition is fully characterized under non-reactive and reactive conditions using Planar Hydroxyl Laser Induced Fluorescence (OH-PLIF), Particle Imaging Velocimetry (PIV), and Laser Induced Phosphorescence of thermographic phosphors (LIP) to generate a detailed database of the flow and the corresponding boundary conditions. An analysis is then conducted to understand the mechanisms controlling shape bifurcations when the flame interacts with the combustor peripheral wall. Effects of the combustible mixture composition, the bulk flow velocity, and the swirl number are analyzed. It is shown that the transition from a V to an M flame is triggered by a flashback of the V flame tip in the boundary layer of the combustor peripheral wall. Dimensionless numbers controlling these transitions are identified and a simplified model is developed to help the prediction of the flame shapes. The physics of these shape bifurcations differs when the flame does not interact with the combustor wall. The large influence of the hydrogen enrichment in the fuel on the flame shape is analyzed using flame chemiluminescence and OH-PLIF. LIP and thermocouple measurements demonstrate that the thermal boundary conditions still have a strong impact on the flame topology. The combined effects of strain and heat losses are investigated using joint OH-PLIF and PIV experiments. It is shown that flammability limits of premixed flames are reduced due to heat losses and the transitions from M to V shaped flames is consecutive to localized extinctions of flame front elements located in the outer shear layer of the jet flow that are submitted to large strain rates. These experiments are completed by an analysis of the dynamics of methane/hydrogen/air flames. It is shown that low frequency and high amplitude velocity modulations generated by a loudspeaker alter the shape taken by these flames. The stabilization of methane/hydrogen/air flames diluted by nitrogen and carbon dioxide is finally examined. It was possible to stabilize swirled flames featuring important dilution rates due to the presence of the bluff body, installed on the axis of the injection tube. The recirculation zone behind this element supplies hot burnt gases to the flame anchoring point. Using OH* chemiluminescence imaging, it is shown than increasing the molar fraction of diluent in the fuel reduces the light emission from excited OH* radicals. The influence of dilution on the flame chemistry is emphasized with experiments conducted at a fixed thermal power and fixed adiabatic flame temperature. It is also demonstrated that the composition of the diluent has a strong influence on the temperature field of the burnt gases and of the combustor wall surfaces. Dilution with carbon dioxide increases radiative heat losses from the burnt gases in comparison to dilution with nitrogen. This penalizes the combustor efficiency equipped with four transparent quartz walls. [...]

This thesis reports on the development and application of a new method for the measurement of particles transported within a moving fluid and subjected to high fluxes of radiant heating. The comprehensive understanding of heat transfer in particle-laden flows is important as it is a key factor in enabling optimisation of various industrial and scientific applications such as combustion, mineral processing plants, and pharmaceutical manufacturing, as well as aid in the development of new technologies based on the two-phase flow. However, one of the major factors that limits the furtherance of understanding of the field is the difficulty in measuring temperatures of moving, micron-sized particles. Previously, most publications on heat transfer in particle-laden flows focus on gas temperature measurements, where the temperatures of particles are inferred through fundamental heat transfer equations. However, this technique is not applicable in systems where a large disparity exist between the gas and particle temperatures, and does not take into account inter-particle relationships which could have a significant effect on the overall heat transfer where the interparticle spacing is sufficiently low. In order to distinguish between the particle and gas phase temperatures, a radiative heat source capable of delivering continuous heat fluxes of up to 36.6MW/m2 in the form of a Solid-State Solar Thermal Simulator (SSSTS) was used throughout this dissertation. This is because the SSSTS operates at a wavelength of 910nm, which is only absorbed by the particle phase and not the gas phase. Importantly, the operation of the SSSTS at this wavelength does not interfere with the excitation signal (355nm) used in the LIP technique. However, the performance of the SSSTS is not well understood due to the system being the first of its kind. Chapter 4 of this dissertation addresses this by characterising in detail the SSSSTS. The next part of this dissertation describes the development and application of single-shot, nonintrusive particle temperature measurement techniques based on laser-induced phosphorescence (LIP), a thermometry that makes use of the phosphorescent emission properties of thermophosphors (TPs) governed by the temperature-dependent Boltzmann distribution. Here, ZnO:Zn TPs were selected to be used as they have the highest temperature sensitivity below 625°C. The TPs were suspended in unsteady flow in an optically-accessible fluidised bed and subjected to high radiative heat fluxes of up to 21.1 MW/m2. Two types of thermometry are reported – with Chapter 5 describing the development of an in-situ, areaaveraged, temporally-resolved particle temperature measurement technique by analysing the change in phosphorescent emission spectra of the selected TP with respect to wavelength, collected using a fibre-optic cable connected to a spectrometer; and Chapter 6 detailing a single-shot, planar particle temperature measurement. For the planar thermometry, the phosphorescent emissions of the TPs were collected using a single ICCD camera fitted with an image splitter and two interference filters specifically selected. Each measurement derives from two 15mm × 10.8mm images collected simultaneously to avoid errors associated with timedelays and/or angular distortions. The resultant spatial resolution for each image was 51pixels/mm, with an average of 30 particles recorded within the imaging region. It was demonstrated that the particle temperatures measured with the LIP technique was found to be approximately 44°C higher on average than the gas temperatures measured with a thermocouple in the same system. A strong dependence of heat flux, as well as particle attenuation (mass loading) on particle temperature was also reported. Additionally, a maximum particle temperature rise of 350°C was recorded with a heat flux of 21.1 MW/m2, where the maximum particle residence time in the heating region is 0.05s. The next section of this thesis details the study of application of the developed thermometry technique in a laminar particle-laden jet flow issued from a 12.8mm pipe downwards into a wind tunnel and the particles radiatively heated by the SSSTS. The measured data were analysed by comparison with the results from a simple first-order analytical model that considers the radiative heating, convective cooling, radiative heat loss and heat gain of a single particle. It was found that heat flux, particle concentration and to a lesser extent, particle diameter all affect particle temperatures. At low heat fluxes, 𝑄̇𝑟𝑎𝑑 ≤ 6.1 MW/m2, particle concentrations and temperatures were found to be higher in jet edge, consistent with previous investigations. At heat fluxes above that, where 𝑄̇𝑟𝑎𝑑 > 6.1 MW/m2, thermophoresis was observed, as evidenced by the migration of the smaller particles to the jet edge where the local temperature is lower. The effect of buoyancy was also observed at 𝑄̇𝑟𝑎𝑑 ≥ 20.6 MW/m2, as evidenced by two distinct regions of high particle temperatures upstream from the heating region (one at the jet axis, and one at the jet edge). These results were presented in Chapter 7 of the present dissertation.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2020

AbstractPhysics of supercritical fluids is extremely complex and not yet fully understood. The importance of the presented investigations into the physics of supercritical fluids is twofold. First, the presented approach links the microscopic dynamics and macroscopic thermodynamics of supercritical fluids. Second, free falling droplets in a near to supercritical environment are investigated using spontaneous Raman scattering and a laser induced fluorescence/phosphorescence thermometry approach. The resulting spectroscopic data are employed to validate theoretical predictions of an improved evaporation model. Finally, laser induced thermal acoustics is used to investigate acoustic damping rates in the supercritical region of pure fluids.

This paper describes the development of the Planar Laser-Induced Phosphorescence (PLIP) technique for mapping the fuel temperature and concentration distributions in a jet-in-cross-flow (JICF) spray study. The spray was produced by injecting cold liquid Jet-A into hot cross-flowing air. The application of PLIP required the seeding of liquid fuel with micron-size thermographic phosphor particles before injection. The resulting spray produced phosphorescence and droplets Mie-scattering signals when illuminated by a 355nm planar UV laser sheet of 0.054J/pulse energy. The technique was investigated as a potential alternative to the use of Jet-A Planar Laser-Induced Fluorescence (PLIF) for the mapping of fuel concentration in sprays, because the low signal intensity of Jet-A’s fluorescence at high T prevents the use of the PLIF approach. In contrast, PLIP provides a strong signal at high T, and allows the simultaneous determination of local T and fuel concentration when two spectral bands of the phosphorescence emission are imaged and their ratio-of-intensities (RI) determined. In addition, the locations where liquid fuel droplets exist were imaged from the UV Mie-scattering of the laser-sheet (which can also be done in PLIF). In the present investigation, an optical system that imaged two spectral bands of phosphorescence and one wavelength of Mie-scattering was developed. It consisted of three CCD cameras with dichroic beam-splitters and interference narrow bandpass filters. The spray-pattern within a span of ∼80×30 orifice diameters was captured, with spatial resolution of about 0.1mm/px. The investigated jet-in-cross-flow spray was produced by injecting Jet-A fuel from a 0.671mm diameter orifice located on the wall of a rectangular channel (25.4×31.75mm cross-section). The cross-flow air was preheated to temperatures encountered in modern gas turbines (up to 480°C), while the temperature of the injected Jet-A fuel was in the T = 27–80°C range. YVO4:Eu phosphor particles with a median size of 1.8 microns were used to seed the fuel. Since the emissions of the commonly used Dy:YAG thermographic phosphor were found to be too weak and had wavelengths that overlapped with Jet-A fluorescence signals, YVO4:Eu was used for the JICF studies instead. It was observed that while the emissions of YVO4:Eu were stronger than Dy:YAG, the range of T where it can be applied in the PLIP technique was more limited — just sufficient for the investigated JICF. Preliminary results from the study showed rapid changes in fuel concentration and T from the injector up to z/dinj∼30 for momentum ratios of J = 5, 10 and 20, followed by a more gradual mixing/heat-up downstream. It was also found that deposition of phosphor particles on channel-walls interfered with the spray characterization, reducing the accuracy of the measurements.