Tesi sul tema "Laser Diagnostics"

The research presented in this thesis set out to contribute to knowledge seeking to advance the state-of-the-art in laser based, multi-functional, non-invasive diagnostic systems. The results of the work have contributed to the development of methodological generic approaches to the development of devices using light to detect and analyse biomarkers relevant to human health and disease conditions. Following the development of methodologies the research then progresses to examine in-vivo the potential of the integrated spectroscopic technologies to detect changes and rhythms in the micro-vasculature of the skin relevant to the response of the subjects to emotional and physical stress. The results uncover myogenic rhythm synchronisation as a potential marker of adaptive response. The complexity of monitoring and interpreting key biomarkers of metabolism, NADH and FAD and the derived redox ratio is addressed in detail. Analysis of results of around 3,000 functional scans, including tissue oxygen saturation and laser Doppler flowmetry, provides new insights into bio-technological issues. The challenges identified with biological characteristics include sampling zones and physiological features of the skin. Technological, photonics, electronics and computing challenges emerge from the results. These should be considered in advancing the integration of bio-photonic technologies toward realising meaningful diagnostic poly-bio-markers relevant to developing algorithms capable of delivering consistent, reliable and meaningful diagnostic information with utility in clinical practice for early diagnosis of disease conditions such as cancers and cardio-vascular diseases in individuals from the global population. The results have been published in peer-reviewed international journals and presented at major international conferences in the field.

An optical Thomson scattering diagnostic has been implemented on low temperature laser-produced plasmas. This is a novel diagnostic for these types of plasmas which provides a reliable non-intrusi~e means of determining absolute values for electron number density and temperature, with a minimal number of assumptions required compared to most diagnostics used so far. A frequency doubled Nd:YAG laser was used as a source of scattered light, then detected with a gated ICCD detector after being spectrally resolved by a 1 meter grating spectrometer. The density and temperature of an expanding KrF laser-ablated magnesium plume have been obtained. The e.lectron temperature was found to decay with the expected Te oc C1 dependence. However, it was found that the electron density has a time dependence ne oc t-4 . 95 which can be explained by strong recombination processes. Atomic Raman satellites were also observed; they were identified as originating from transitions between the different angular momentum levels of the metastable 3pO term in Mgl. Comparison with preliminary calculations of Rayleigh and Raman cross-sections of Mgl ground state and first excited state showed variations in the population of metastables relative to atoms and ions. The study was then extended further by adapting the system to an optical emission spectroscopy diagnostic. Up to - 40% discrepancy was found between the results given by each diagnostics, questioning the assumption of local thermodynamic equilibrium in the plasma, assumed to analyse the emission spectra. Supplied by The British Librawe world's knowledge'

Thesis (MSc (Physics))--University of Stellenbosch, 2005.
A tunable vacuum ultra-violet (VUV) laser source was recently developed for VUV spectroscopy using state selective excitation and total fluorescence detection. The VUV laser source makes use of a four-wave mixing process to provide tunable VUV radiation for the electronic excitation of the molecules. The theory of four-wave mixing, with the emphasis on parameters that are important for our experimental setup to generate efficient tunable VUV radiation is discussed. The experimental setup, and in particular the metal vapor heat-pipe, which provides Mg vapor as the nonlinear medium, is described. New diagnostic equipment described in this work was added to the experimental setup. This equipment was characterized and utilized together with the existing setup. The additional diagnostic equipment introduced enabled us to measure the tunable VUV output of the source (using a VUV monochromator), making it possible to significantly improve the efficiency of the existing tunable VUV laser source.

Quantitative Planar Laser Induced Fluorescence (QPLIF) is developed as a diagnostic technique and then applied to a prototype Jaguar optical internal combustion engine. QPLIF derives quantitative, two-dimensional, spatially-resolved measurements of fuel concentration. This work reports the first demonstration of a fully-fractionated surrogate fuel which exhibits all the characteristics of a typical gasoline. This 'pseudo' fuel, developed in association with Shell UK, is blended to accept a fluorescent tracer which may track one of the light, middle or heavy fractions of the fuel, each of different volatility. The traditional weaknesses of PLIF for quantitative measurements are addressed by use of a fired in-situ calibration method, which maps the quantum efficiency of the tracer and concurrently corrects for window fouling and exhaust gas residuals (EGR). Fuel distributions are presented with an estimated super-pixel accuracy of 10% at different operating conditions, and then compared to the computational fluid dynamics (CFD) predictions of an in-house Jaguar model. Fuel/Air Ratios by Laser Induced thermal Gratings (FARLIG) is developed theoretically, and results of validation experiments conducted in a laboratory setting are reported. FARLIG conceptually enables the measurement of fuel concentration, oxygen concentration and temperature within a spatially-localised probe volume. Uniquely, the technique exploits the dominant influence of molecular oxygen on non-radiative quenching processes in an aromatic tracer molecule. The changing character of a model quenching mechanism potentially allows the oxygen concentration in the measurement volume to be derived. Absolute signal strength is used to determine fuel concentration, while the oscillation period of the signal provides a precise measurement of temperature (~0.3% uncertainty), with accuracy limited by knowledge of the gas composition.

The interaction of an 8 ns, 10 mJ and 1.06 μm infrared pulse of radiation from a Q-switched Nd-YAG laser with water near a solid boundary is studied using high speed photographic techniques. The laser-liquid interaction has been used to generate high frequency sound waves by the mechanism of dielectric breakdown of the liquid around the beam waist of the focused laser beam. This leads to the production of a short duration plasma which rapidly heats and vaporises the surrounding liquid giving rise to a vapour cavity and the formation of a cavitation bubble resulting in the emission of a spherical acoustic wave. The acoustic transient associated with the breakdown, in turn interacted with a liquid-polymer interface leading to the generation of acoustic waves at this boundary and the propagation of stress-waves in the solid. Diagnostics of the laser-interaction events are recorded using a Mach-Zehnder interferometer illuminated by a sub-nanosecond nitrogen laser-pumped dye laser and computer-controlled video-imaging and capture systems. Measurements of the transient pressure distributions from the digitally recorded interferograms are carried out using a process known as Abel inversion. Dynamic photoelastic studies of the stress-waves propagation in the solid are performed using a circular polariscope arrangement thus producing the photoelastic fringe patterns. Identification of the wave structures are greatly enhanced by also recording the events in schlieren and focused shadowgraphy as well as by the combination of the above techniques. The initial part of the project also involved the design and development of a nitrogen laser and tunable dye laser system. The short-duration and high peak power output pulse of the nitrogen laser is then used to pump the dye laser giving sufficiently high power output with good spectral linewidth to provide an ideal light source for high-speed photography of the laser interaction events.

The application of electronic-resonance enhanced (ERE) coherent anti-Stokes Raman scattering (CARS) for the detection of nitric oxide (NO) and acetylene (C2H2) is experimentally demonstrated and the effects of various parameters on the ERE CARS signal investigated. In addition, the detection of dipicolinic acid (DPA) using “normal” CARS is demonstrated. For NO detection, the frequency difference between a visible Raman pump beam and Stokes beam is tuned to a vibrational Q-branch Raman resonance of the No molecule to create a Raman polarization in the medium. The second pump beam is tuned into resonance with the rotational transitions in the (1,0) band of the A2Σ+-X2Π electronic transition at 236 nm, and the CARS signal is thus resonant with transitions in the (0,0) band. A NO gas cell was used for the experiment to detect NO at various pressure levels. A significant resonant enhancement of the NO CARS signal was observed and good agreement between calculated and experimental data was obtained. For C2H2 detection, ERE CARS experiments were performed in a roomtemperature gas cell using mixtures of 5000 ppm C2H2 in N2. Visible pump and Stokes beams were used, with the frequency difference between the pump and Stokes tuned to the 1974 cm-1 Ϡ2 Raman transition of C2H2. An ultraviolet probe beam with the wavelengths ranging from 232 nm to 242 nm is scattered from the induced Raman polarization to generate the ERE CARS signal. The effects of probe wavelength and pressure on signal generation are discussed. CARS was used to detect the 998 cm-1 vibrational Raman transition from a sample of polycrystalline DPA. The transition is the breathing ring vibration in the pyridine ring structure in the DPA molecule. The DPA 998 cm-1 transition is detected with excellent signal-to-noise ratio and the full-width-at-half-maximum is very narrow, approximately 4 cm-1.

In-situ optical techniques offer one of the most attractive options for measuring species concentration and spatial distribution profiles in reacting environments, such as flames. The generally non-intrusive nature and spatial resolution of these techniques are now preferred over on extractive sampling, followed by analysis using techniques such as gas chromatography. In this thesis two laser absorption measurement techniques are applied to measure the soot distribution, and acetylene concentration profiles in a flat-flame burner. The in-situ measurement of the distribution of particulate matter in flames is a key step in understanding the mechanism of its formation. Most in-situ measurement systems for this purpose are based on laser induced incandescence where particles are heated using high power laser sources and the increased incandescence emission of the soot particles is detected. However as the soot cools by heat transfer to the surrounding gas, following laser heating, the pressure of the gas is increased creating an acoustic effect. Photoacoustic detection has been applied to quantify low concentrations of particulate matter in ambient air but there have been few applications of photoacoustic detection to the in-situ measurement of particulate matter formation in combustion processes. A novel simple approach using a modulated continuous wave diode laser is presented in this thesis. The measurements taken using this new technique are compared to measurements of the visible emission from the flame, and previous soot distribution measurements using laser induced incandescence. Absorption spectroscopy using near-infrared tunable diode lasers has been applied to measure species in several harsh environments such as aero-engine exhaust plumes, flames, and other industrial processes. Simple single pass absorption techniques are not always suitable for this purpose due to the low absorption of the target species, either due to low concentration or weak absorption line-strength at high temperatures. One method to increase the sensitivity of such techniques is by using cavity enhanced methods which increase the effective path length of the laser through the absorbing medium. One such cavity enhanced method is Cavity Ring-Down Spectroscopy (CRDS). CRDS uses a cavity constructed of highly reflecting mirrors, laser light is then coupled into this cavity and absorption measurements can be evaluated from the decay rate of light from the cavity. The design and, novel application of continuous wave CRDS to measure the concentration profile of acetylene in the flat-flame burner is presented. Difficulties in deriving an absolute acetylene concentration from the measured ringdown times were encountered due to the large number of interfering features. Serveral fitting and extraction techniques are applied and compared to attempt to overcome these difficulties.

This thesis presents results from two strands of work towards realizing a free-electron laser (FEL) driven by electron bunches generated by a laser-wakefield accelerator (LWFA). The first strand focuses on selecting operating parameters for such a light source, on the basis of currently achievable bunch parameters as well as near-term projections. The viability of LWFA-driven incoherent undulator sources producing nanojoule-level pulses of femtosecond duration at wavelengths of 5 nm and 0.5 nm is demonstrated. A study on the prospective operation of an FEL at 32 nm is carried out, on the basis of scaling laws and full 3-D time-dependent simulations. A working point is selected, based on realistic bunch parameters. At that working point saturation is expected to occur within a length of 1.6 m with peak power at the 0.1 GW-level. This level, as well as the stability of the amplification process, can be improved significantly by seeding the FEL with an external radiation source. In the context of FEL seeding, we study the ability of conventional simulation codes to correctly handle seeds from high-harmonic generation (HHG) sources, which have a broad bandwidth and temporal structure on the attosecond scale. Namely, they violate the slowly-varying envelope approximation (SVEA) that underpins the governing equations in conventional codes. For this purpose we develop a 1-D simulation code that works outside the SVEA. We carry out a set of benchmarks that lead us to conclude that conventional codes are adequately capable of simulating seeding with broadband radiation, which is in line with an analytical treatment of the interaction. The second strand of work is experimental, and focuses on on the use of coherent transition radiation (CTR) as an electron bunch diagnostic. The thesis presents results from two experimental campaigns at the MPI für Quantenoptik in Garching, Germany. We present the first set of single-shot measurements of CTR over a continuous wavelength range from 420 nm to 7 μm. Data over such a broad spectral range allows for the first reconstruction of the longitudinal profiles of electron bunches from a laser-wakefield accelerator, indicating full-width at half-maximum bunch lengths around 1.4 μm (4.7 fs), corresponding to peak currents of several kiloampères. The bunch profiles are reconstructed through the application of phase reconstruction algorithms that were initially developed for studying x-ray diffraction data, and are adapted here for the first time to the analysis of CTR data. The measurements allow for an analysis of acceleration dynamics, and suggest that upon depletion of the driving laser the accelerated bunch can itself drive a wake in which electrons are injected. High levels of coherence at optical wavelengths indicate the presence of an interaction between the bunch and the driving laser pulse.

Turbulent flows and turbulent flames are inherently multi-dimensional in space and transient in time. Therefore, multidimensional diagnostics that are capable of resolving such spatial and temporal dynamics have long been desired; and the purpose of this dissertation is to investigate three such diagnostics both for the fundamental study of flow and combustion processes and also for the applied research of practical devices. These multidimensional optical diagnostics are a 2D (two dimensional) two-photon laser-induced fluorescence (TPLIF) technique, a 3D hyperspectral tomography (HT) technique, and a 4D tomographic chemiluminescence (TC) technique. The first TPLIF technique is targeted at measuring temporally-resolved 2D distribution of fluorescent radicals, the second HT technique is targeted at measuring temperature and chemical species concentration at high speed, and the third TC technique is targeted at measuring turbulent flame properties. This dissertation describes the numerical and experimental evaluation of these techniques to demonstrate their capabilities and understand their limitations. The specific aspects investigated include spatial resolution, temporal resolution, and tomographic inversion algorithms. It is expected that the results obtained in this dissertation to lay the groundwork for their further development and expanded application in the study of turbulent flow and combustion processes.
Ph. D.

The development of Laser-Induced Thermal Grating Spectroscopy (LITGS) for diagnostics of combusting and non-combusting flows is described. The first use of LITGS to provide in situ calibration of 2-Dimensional temperature distributions generated using Two-Colour Planar Laser-Induced Fluorescence (TC-PLIF) is reported. Time-resolved measurements of temperature distributions in a firing GDI optical engine obtained by TC-PLIF were made during the compression stroke and calibrated to the absolute temperature scale by simultaneous LITGS measurements. The accuracy and precision of the temperatures derived from LITGS data are evaluated using alternative methods of data analysis - Fast Fourier Transform and Fitting to theoretical models of the experimental data. The relative merits of the two methods are examined for analysis of weak LITGS signals obtained under engine conditions of low pressure and high temperature. The combined TC-PLIF and LITGS system was demonstrated by performing repeated single-shot measurements for 1 in every 10 four-stroke cycles showing excellent correlation of the temperatures derived from both techniques. Direct measurement of the effect of 'charge cooling', of order 5 K, for operation with direct injection is reported. Inhomogeneous temperature distributions were observed during the compression stroke for fired operation with Port Fuel Injection (PFI) and also with Gasoline Direct Injection (GDI). The effects of varying the relative concentrations of toluene and iso-octane in the two-component fuel were investigated. Extension of the LITGS technique to multi-point measurements along a 1-D line is described. By recording signals from 4 points on separate detectors using a fibre-coupled photodiode array the limitations of Streak Cameras used previously for 1-D LITGS measurements were overcome. Demonstration of principle experiments are reported in which simultaneous 4-point measurements were made with 1 mm spatial resolution and a precision of 0.7 % in temperature gradients in gas flows and in boundary layers at surfaces.

Due to their scientific significance and practical applications, turbulent flows and flames have been under extensive and intensive research for a long time. Turbulent flows and flames of interests to practice inherently have three-dimensional (3D) spatial structures, and therefore diagnostic techniques that can instantaneously resolve their 3D spatial features have long been desired and probably are needed to ultimately answer some of the open research questions. The goal of this dissertation thus is to investigate such diagnostics and demonstrate their capability and limitations in a range of turbulent flows/flames. To accomplish this goal, this dissertation developed and evaluated the following three diagnostic methods: tomographic chemiluminescence (TC), volumetric laser induced fluorescence (VLIF), and super-resolution planar laser induced fluorescence (SR-PLIF). First, 3D flame topography of well-controlled laboratory flames was measured with TC method and validated by a simultaneous 2D Mie scattering measurement. The results showed that the flame topography obtained from TC and the Mie scattering agreed qualitatively, but quantitative difference on the order of millimeter was observed between these two methods. Such difference was caused by the limitations of the TC method. The first limitation involves TC's reliance on chemiluminescence of nascent radicals (mainly CH*) in reacting flows, causing ambiguity in the definition of flame front and limiting its applications to certain types of reactive flow only. The second limitation involves TC's inability to study an isolated region of interest because the chemiluminescence is emitted everywhere in the flame. Based on the above understanding of the TC technique, the second part of this dissertation studied a VLIF method to overcome the above limitations of the TC technique. Compared with the TC technique, the VLIF method can be used in either reacting or non-reacting flow and on any particular region of interest. In the VLIF technique, the fluorescence signal was generated by exciting a target species with a laser slab of certain thickness. The signal was recorded by cameras from different perspectives, and then a VLIF tomographic algorithm was applied to resolve the spatial distribution of the concentration of the target species. An innovative 3D VLIF algorithm was proposed and validated by well-designed experiment. This model enables analysis of VLIF performance in terms of signal level, size of the field of view in 3D, and accuracy. However, due to the limited number of views and the tomographic reconstruction itself, the spatial resolution of VLIF methods is limited. Hence, the third part of this dissertation investigated a SR-PLIF method to provide a strategy to improve the spatial resolution in two spatial directions, and also to extend the measurement range of scanning 3D imaging strategies. The SR-PLIF method used planar images captured simultaneously from two (or more) orientations to reconstruct a final image with resolution enhanced or blurring removed. Both the development of SR algorithm, and the experimental demonstration of the SR-PLIF method were reported.
Ph. D.

Oxygen enhanced oxy-fuel laminar and turbulent flame structure in a co-flow non-premixed jet burner are investigated. The measurement of intermediate species such as hydroxyl (OH) and formaldehyde (CH2O) and temperature are the focus of this work. The species concentrations were measured using planar laser induced fluorescence (PLIF) and the temperature using Rayleigh scattering. ‘Traditional Rayleigh’ requires a constant Rayleigh cross-section throughout the combustion process. This is impossible in high temperature oxy-fuel flames due to thermal decomposition. Derived temperature from Rayleigh signals is hence prone to inaccuracy. A direct comparison of measured and numerically-calculated Rayleigh signals can eliminate this error. Numerical Rayleigh signals are relatively easily calculated with knowledge of temperature and species concentration. The feasibility of adopting this procedure to validate the numerical model was investigated in laminar and turbulent flames. Sensitivity studies including radiation models, chemical kinetics mechanisms and the Soret effect were performed in laminar flames. Another Rayleigh technique, polarised/ depolarised Rayleigh was employed in a joint temperature, OH and CH2O measurement. The effect of varying O2 and jet Reynolds number on the flame structure was investigated. The applicability of determining heat release rate (HRR) using the product of [OH]x[CH2O] was also determined. [OH]x[CH2O] and HRR showed good spatial correlation in the main oxidation zone, but underestimated HRR in the secondary oxidation zone. Finally, analysis of thermal diffusion structures using high resolution polarised/ depolarised Rayleigh was performed. The analysis revealed the thickness of the diffusion layer is proportional to the temperature, axial location and O2 concentration. Increase of Reynolds number, however, reduces layer thickness. In summary, this work has used a suite of optical diagnostics to make the first structural survey of high temperature oxy-fuel flames, starting with overall flame shape through macroscopic localised extinction to microscopic thermal diffusion.

Characterisation of the ultra-short optical pulses produced by infrared ffee-electron lasers (FELs) is an important task, not only for the further development of free electron lasers and their theory, but also for their operation as a research tool. The setting up and optimisation of the FEL requires effective and reliable diagnostics tools. This thesis presents techniques for the measurement of sub-picosecond optical and electron pulses. A range of techniques is developed that allows measurements of the electric field of both optical pulses and electron bunches to be made with an accuracy of better than 100 fs. These techniques have been used to obtain the first complete electricfield characterisation of ultra-short pulses from a far-infrared FEL; to study the formation of singlesided exponential optical pulses in two FELs; and to obtain the longitudinal profile of electron bunches, both by probing the near-field transition radiation and by directly sensing the Coulomb field of the electron bunches. Although the techniques described are not truly single-shot - requiring measurements averaged over a period of a few microseconds - ways in which they could be extended to provide single-shot capability are discussed.

La technique laser-induced breakdown spectroscopy (LIBS), qui consiste à exploiter le spectre du plasma induit par laser sur la surface de l'échantillon pour déterminer sa composition élémentaire, a été inventée il y a plus de 50 ans. Récemment, elle connaît un développement rapide, poussée par des besoins d'application dans différents domaines, citons par exemple, exploration océanique, détection de pollution environnementale, ou contrôle de procédés industriels. Cette technique utilise le plasma généré par ablation laser comme la source spectroscopique. La particularité de LIBS est que le plasma induit par laser présente un comportement transitoire et une distribution spatiale qui ne soit pas uniforme en général. Bien que la détection résolue en temps puisse améliorer considérablement la performance de LIBS, surtout pour le procédé de LIBS autocalibration avec une meilleure détermination de température, l'évolution temporelle du plasma est souvent corrélée avec sa morphologie et son inhomogénéité spatiale. L'étude de la morphologie ainsi que la structure interne du plasma avec l'évolution pendant l'expansion de celui-ci dans un gaz ambiant, représente donc un point crucial pour l'optimisation du plasma entant qu'une source spectroscopique. Suite à la thèse de Qianli Ma réalisée dans notre équipe et soutenue en décembre 2012, qui a été notamment consacrée à l'étude de l'effet de la longueur d'onde du laser d'ablation sur les propriétés et l'évolution du plasma dans un gaz ambiant d'argon, la présente thèse s'intéresse aux effets des autres paramètres, la fluence du laser d'ablation, la durée de l'impulsion, et les différents gaz ambiants (argon ou air), sur la morphologie et la structure du plasma. Par ailleurs, les mécanismes microscopiques conduisant à l'onde de détonation soutenue par laser dans argon ou dans l'air sont aussi étudiés. Lors du refroidissant du plasma dans l'air, des oxydes métalliques peuvent se former. L'étude de la formation de molécules, au-delà de l'intérêt pratique pour la LIBS, fournit également un aperçu de la cinétique chimique dans le plasma, ce qui est intéressant pour l'étude de la transformation du plasma en phase gazeuse à une phase recondensée de nanoparticules
Laser-induced breakdown spectroscopy (LIBS) has been invented for more than 50 years, which analyzes the spectrum of the laser-induced plasma to determine the elemental composition of the ablated sample. Recently, LIBS technique has been well developed and applied in different domains, for example oceanic exploration, pollution monitoring in the environment. LIBS uses the ablation plasma as a light source that contains the elemental composition information of the sample. However, the laser-induced plasma exhibits a transient behavior. Although time-resolved and gated detection can greatly improve the performance of the LIBS technique especially that of calibration-free LIBS (CF-LIBS) with a better determination of plasma temperature, the temporal evolution of the plasma is correlated to its morphology and its spatial inhomogeneity. The determination of the morphology as well as the internal structure of the plasma together with their evolution during plasma expansion into the ambient gas is therefore crucial for the optimization of the use of ablation plasma as a spectroscopic emission source. Evolutions of the morphology and the internal structure of the ablation plasma are considered as the consequence of its hydrodynamic expansion into the ambient gas. Following the thesis of Qianli Ma which has studied the effect of laser wavelength on the behavior of the plasma induced in an ambient gas of argon, the present thesis has used the same diagnostic techniques (time- and space-resolved emission spectroscopy and fast spectroscopic images) together with 1064 nm ns laser pulse ablation of a target of aluminum to investigate the effects of other parameters, such as the fluence and the duration of laser pulse, the effect of different ambient gases (argon and air), on the morphology and internal structure of the plasma. Furthermore, in order to understand the effects of these parameters on the properties of the plasma, the microscopic mechanisms during post ablation and the propagation of the plasma are also studied. While the plasma cools down in air, molecules are formed, AlO for instance. So the thesis also studied the condition for the formation of the molecules in the plasma. Beyond the practical interest of this study for LIBS, it provides also insights to the kinetics of the AlO molecule formation in laserinduced plasma

Le contrôle de la production des particules de suies est aujourd'hui un enjeu industriel majeur en raison de leur impact néfaste tant sur le climat que sur la santé humaine et de leur forte contribution aux transferts radiatifs. Pour mieux comprendre et contrôler la production de ces polluants dans les foyers industriels, il est primordial d’améliorer nos connaissances à ce sujet dans un brûleur turbulent. L’objectif de cette thèse est donc de mettre en place des diagnostics optiques pour l’étude des flammes suitées turbulentes et pour caractérise la production de suies dans une nouvelle configuration de combustion prémélangée,confinée, swirlée turbulente académique tout en se rapprochant des configurations industrielles. Une première configuration expérimentale laminaire est donc considérée afin de valider la mise en place de la technique d’Incandescence Induite par Laser (LII) pour mesurer la fraction volumique de suies fv. Il s’agit d’un brûleur conçu à l’université de Yale qui permet la stabilisation d’une flamme laminaire de diffusion éthylène/air. Ce brûleur a été largement étudié dans la littérature nous permettant ainsi de comparer nos mesures aux résultats de différentes équipes internationales. La calibration du signal LII avec la technique MAE (Modulated Absorption Emission) a été effectuée via une collaboration avec l’UPMC, permettant de mesurer quantitativement fv et de comparer les techniques MAE et LII. Le brûleur a ensuite été équipé d’un haut-parleur afin de moduler l’écoulement et de pouvoir étudier les effets d’une perturbation contrôlée sur la production de suies, se rapprochant ainsi des phénomènes instationnaires caractéristiques des écoulements turbulents. Enfin, les effets d’élargissement de la nappe laser sur les résultats de la LII sont examinés afin de pouvoir appliquer ce diagnostic optique dans une configuration turbulente innovante caractérisée par de grandes dimensions. Ce brûleur (EM2Soot) a été développé pour mesurer la production de suies dans une flamme turbulente swirlée riche confinée prémélangée. Il permet de quantifier indépendamment les effets de la richesse, de la puissance et de l’environnement thermique sur la production de suies. Un point de fonctionnement représentatif a alors été étudié et, en parallèle avec la LII, les techniques de vélocimétrie par images de particules (PIV), et de mesure de température des parois par phosphorescence induite par laser (LIP) ont été employées afin de caractériser l’effet de la turbulence sur la production des suies et d’établir une base de données pour la validation de futures simulations numériques. Enfin, la géométrie du brûleur a été modifiée permettant une stabilisation différente de la flamme (en forme d’un V). Un nouveau point de fonctionnement a alors été étudié afin de mettre en évidence le rôle de la géométrie de l’injecteur sur la stabilisation de la flamme et, par conséquent, la production totale de suies
The control of soot particles production represents today a major industrial issue because of their harmful impact on both the climate and the human health and their strong contribution to the radiative transfers. To better understand and control the production of these polluting emissions, it is essential to improve our knowledge on this subject in a turbulent burner. The objective of this Ph.D. is to set up optical diagnostics for the study of turbulent flames and to experimentally characterize soot production in a new academic turbulent premixed combustion configuration while approaching industrial configurations, generally confined and swirled flows. For this, a laminar experimental configuration is first considered to validate the implementation of the Laser Induced Incandescence (LII) technique to measure the soot volume fraction fv. This burner designed at Yale University allows the stabilization of a laminar ethylene/air diffusion flame. This burner has been widely studied in the literature, so that it is possible to compare the quality of our measurements with the results of different international teams. Through collaborations with the UPMC, we calibrated the LII signal with the MAE (Modulated Absorption Emission) technique, making it possible to quantitatively measure fv and to compare the MAE and LII techniques. Finally, the burner was equipped with a loudspeaker to modulate the flow and to study the effects of a controlled perturbation on the soot production, thus approaching the unsteady phenomena characteristics of turbulent flows. Finally, the effects of the enlargement of the laser sheet on LII results were also investigated in order to be able to apply this diagnostic technique in an innovative large turbulent configuration. This experimental configuration, called EM2Soot, was developed to measure the production of soot in a turbulent swirled rich confined premixed ethylene/air flame. This burner makes it possible to independently quantify the effects of the equivalence ratio, the total flame power and the thermal environment on the total soot production. A representative operating point was then characterized, in parallel with LII measurements, Particle Image Velocimetry (PIV) and Laser Induced Phosphorescence (LIP) techniques have been employed in order to characterize the effect of the turbulence on soot production and to establish a database for the validation of future numerical simulations. Finally, the geometry of the burner has been modified allowing a different stabilization of the flame (V flame shape). A new operating point is then studied in order to highlight the role of the injector geometry on the stabilization of the flame and, consequently, on the total soot production

Optical Emission Spectroscopy (OES) and Mass Spectrometry (MS) were employed in tandem for diagnostic studies of Nd:YAG (532 nm) laser induced plasma plumes. OES measurements of laser-induced silicon plasmas were performed through a range of ambient pressure regimes from atmospheric pressure down to ~10-4 mbar. The temporal evolution of the plasmas was characterised in terms of electron excitation temperature Te, ionisation temperature Ti, and electron density Ne. Electron densities were determined in the range 2.86 × 1016 to 5.53 × 1019 cm-3, electron temperatures were calculated in the range 8794 to 21229 K, and ionic species temperatures calculated in the range 13658 to 22551K. The requirements for OES analysis based on the assumption of Local Thermal Equilibrium (LTE) conditions existing within the plasmas are discussed. The plasma morphology and expansion dynamics with respect to pressure are described. Response Surface Methodology (RSM) was employed to optimise Laser-Induced Breakdown Spectroscopy (LIBS) analyses of silicon at atmospheric pressure and under vacuum conditions. Multivariate analysis software was used to design and analyse several multi-level, full factorial RSM experiments. A Quality Factor (QF) was conceived as the response parameter for the experiments, representing the quality of the LIBS spectrum captured for a given hardware configuration. A full parametric study of the LIBS hardware configuration was performed to determine the true response of the system; the outcome of which compares favourably with the results yielded from the RSM investigation. MS analyses of silicon and copper laser-induced plasma plumes were performed using a commercially available Residual Gas Analyser (RGA). The RGA sampling configuration was investigated in order to maximise neutral and ionic species detection from the laser-induced plasmas.

Ce travail concerne le développement et l'utilisation de technique de mesures optiques bidimensionnelles non intrusives pour accéder, dans le champ proche de jets diphasiques, aux grandeurs scalaires telles que la fraction volumique de liquide (Y), le diamètre moyen de Sauter (D32) ou la densité d'interface nécessaire à la validation des codes de calcul. L'utilisation de la fluorescence induite par laser et d'une approche statistique basée sur des cumulatives à seuil variable a permis de reconstituer la PDF locale de Y en déconvoluant les fluctuations du bruit ; les distributions obtenues comportent deux pics d'intermittence encadrant une distribution continue qui par un simple changement de variable prend une forme canonique. L'application des principes de la physique statistique a fourni le nombre de degrés de liberté des éléments du spray. Un diagnostic similaire basé sur la diffusion Raman de l'oxygène liquide a été appliqué en combustion haute pression sur le banc cryogénique MASCOTTE de l'ONERA, mais les difficultés rencontrées dues principalement à la déflection et au piégeage par réflexion totale du rayonnement dans le jet dense déstabilisé ne nous ont pas permis d'interpréter les images quantitativement en terme de fraction volumique. La mesure 2D du D32, quant à elle, est basée sur le rapport entre les images de fluorescence du spray proportionnelles au D3 et les images de diffusion de Mie proportionnelles au D2, rapport qui devrait être indépendant de l'éclairement local I. Une vérification des principes de cette méthode a été réalisée numériquement et expérimentalement sur un train de gouttes monodisperse. Elle a montré la faisabilité du diagnostic en soulignant l'influence de la polarisation du laser, de la concentration en colorant et de l'angle de diffusion. L'application dans des conditions plus sévères sur un jet diphasique a fourni des images du D32 mais la densité du spray et la multidiffusion remettent en cause le caractère local de la mesure.

In questa tesi verrà descritto come sia possibile aumentare la performance di sistemi di misura basati sulla vibrometria laser, realizzando dei comportamenti auto-adattativi con lo scopo di ridurre l’incertezza di misura. I test sulle vibrazioni sono delle procedure ben note e largamente utilizzate per verificare la conformità a specifiche di qualità dei prodotti che contengono parti in movimento. Questi test posti alla fine di una linea di produzione forniscono delle informazioni utili per descrivere la qualità di un prodotto prima del suo stoccaggio e vendita. Nell’industria moderna la flessibilità e l’adattabilità sono dei fattori chiave per migliorare l’efficienza del processo produttivo. Sia il controllo del processo industriale che il controllo qualità dipendono dalla disponibilità di informazioni affidabili ottenute attraverso i test effettuati sui prodotti finiti. Grazie alle elevate prestazioni di misura alle sue caratteristiche, la vibrometria laser Doppler può giocare un ruolo fondamentale permettendo di realizzare sistemi di misura flessibili che posso contenere algoritmi modulari e che possono attuare (i sistemi soggetto) procedure auto-adattative. Questo sistema è stato ottenuto aggiungendo al vibrometro laser a scansione una telecamera. In questo modo il dispositivo è in grado di vedere e spostare il punto di misura in posizioni differenti. In questo sistema sono stati implementati diversi comportamenti auto-adattativi; spostando il fascio laser è possibile effettuare il riposizionamento del punto di misura sulla lavatrice, in modo da compensare gli eventuali posizionamenti errati che si hanno sulla linea di produzione quando la lavatrice in esame viene posizionata sotto il sistema di misura durante i controlli qualità. Dopo la compensazione di eventuali macro spostamenti della lavatrice, viene eseguito una fase di ricerca automatica del massimo segnale doppler. Questa ricerca viene condotta attraverso dei microspostamenti del fascio laser del vibrometro sulla superficie della vasca della lavatrice attorno al punto di misura prestabilito. L’obiettivo di questa fase è quello di minimizzare l’incertezza di misura andando a cercare la regione della superficie che massimizza il segnale Doppler. Un altro comportamento auto-adattativo consiste nella riconfigurabilità del sistema, cioè la possibilità di utilizzare differenti algoritmi diagnostici in base alla necessità di effettuare o meno un’analisi approfondita dell’elettrodomestico. Gli algoritmi scelti si riferiscono ai diversi scenari produttivi che possono presentarsi all’interno dello stabilimento durante il funzionamento della linea di produzione. Questo approccio modulare permette di considerare la realtà della linea produttiva in tutte la sua complessità, permettendo di svolgere un’analisi diagnostica che tiene in considerazione anche la qualità con cui si sono svolte le operazioni di assemblaggio della lavatrice che affronta il controllo qualità. Per poter utilizzare al meglio i comportamenti auto-adattativi, in questa tesi è stata effettuata una ricerca delle cause di incertezza nella diagnostica industriale, viene mostrato infatti come il valore RMS del segnale Doppler (signal quality-SQ) è fortemente correlato all’incertezza di misura. Infatti, maggiore è il decadimento del SQ e tanto più la velocità di vibrazione risulta essere affetta da incertezza. Gli esperimenti effettuati ci permettono di dire che durante la vibrazione il valore del SQ è legato alla morfologia della superficie di misura, e per intervalli di tempo sufficientemente brevi (10-15 secondi), il valore del SQ dipende solo dalla posizione X-Y del raggio laser sulla superficie di misura. Questi fatti permettono di utilizzare il valore del SQ(X.Y) come una funzione costo, e la diminuzione iii dell’incertezza di misura è un problema correlato all’ottimizzazione del valore del SQ durante la misura di vibrazione. Per la strategia di ottimizzazione è stato utilizzato l’algoritmo di down-hill (Nelder-Mead) e nella tesi vengono discussi i risultati ottenuti sul SQ dall’applicazione dell’algoritmo. Con le caratteristiche introdotte, il sistema di misura si trasforma in un Quality Control Agent (QCA) che diventa parte di un sistema multi-agente (MAS) che ha il compito di supervisionare l’operato della linea di produzione. In questa tesi vengono mostrati lo scambio dei dati tra il sistema di misura e gli agenti dando vita ad un sistema produttivo decentralizzato con caratteristiche di flessibilità e di auto-adattamento. In modo da poter fornire delle informazioni affidabili agli altri agenti dell’infrastruttura, il QCA associato al sistema di misura deve avere lapossibilità di capire il grado di confidenza con cui i risultati della diagnosi vengono calcolati. Per questo motivo è stato concepito e implementato un modello che permette di stimare il livello di confidenza delle informazioni diagnostiche estratte dalle caratteristiche del segnale acquisito durante i test. In questo modo, il QCA può fornire sia il valore globale della diagnosi che stimare il livello di confidenza con cui la diagnosi è stata effettuata. Le informazioni provenienti dal QCA vengo elaborate ed utilizzate dall’IMA (indipendent meta agent) per effettuare un controllo di processo in modo da migliorare l’esecuzione della produzione.
Vibration testing is a well established procedure for assessing the conformity to specifications of a variety of products, which contain moving parts. Typically at the end of an assembly line, a vibration test provides useful information for 100% quality control of products before packaging. In the appliance manufacturing sector vibration testing for online quality control is increasingly important. Laser Doppler Vibrometry (LDV) has been already used to perform such tests on-line and it has become an established measurement technique. In modern manufacturing industry flexibility and adaptability are key factors for the improvement of efficiency of production processes; both process control and product quality control depend on the availability of reliable information, and therefore on the quality of the data measured. For its non-contact nature and for its metrologic performance, laser vibrometry plays a more and more important and crucial role. This technique allows to realize flexible measurement systems that can implement adaptive and modular algorithms, comprising a large number of ready to use tools. In this thesis we will describe how it is possible to improve the performance of such systems by implementing self-adaptation and reconfigurability behaviors of the laser vibrometer aimed to reduce measurement uncertainty. Such behaviors are achieved by adding scanning mirrors and a dedicated camera, thus realizing a scanning LDV, which can displace the measurement beam at different locations. Self-adaptation (local adaptation) consists in the following behaviors: the system aims at the desired target point over the washing machine (WM) by displacing the laser beam so to compensate effects of WM mis-positioning due to production line inaccuracies. After this preliminary phase, the automatic search for sufficiently large Doppler signal starts. The system searches for an optimal optical signal by slightly displacing the laser beam in the surrounding of the desired target point thus optimizing measurement uncertainty. The system can support also reconfigurability (global adaptation), which consists in the possibility to plug-in/plug-out different post-processing algorithms for a deeper analysis of vibrations. For different production scenarios different diagnostic algorithms are chosen. This modular approach allows to consider the scenario of the production line and the quality of the operations carried out on the production line before the end product is made. In order to successfully use the self adaptation behavior to increase measurement accuracy, for this thesis a deep research of the causes correlated to uncertainty in industrial diagnostic has been made. It this work it is shown how the RMS amplitude of the Doppler signal (signal quality - SQ) is strictly correlated to measurement uncertainty, when SQ decreases then uncertainty affects the vibration velocity signal. Experimental data allow to say that SQ value is correlated to the morphology of the target surface and for a short period of time (10-15 s), so during the vibration the SQ value depends only on X-Y position of the laser beam on the target surface. These facts allow to use the SQ function as a cost function and the decrease the measurement uncertainty is a problem correlated to the optimization of the SQ value during the vibration measurements. The optimization strategy for the measurement enhancement achieved by the down-hill algorithm (Nelder-Mead algorithm) and its effect on signal quality (SQ) improvement are discussed. ii With these features, this system is designed as a Quality Control Agent (QCA) and it is part of a Multi Agent System (MAS) that supervises all the production line. This thesis also shows the data exchange between the measurement system and other agents in order to realize a decentralized manufacturing system. In fact, in a distributed system, the estimation of the confidence level of the information provided by other agents plays an important role. The QCA associated to the measurement system has to be able to understand the confidence level of the diagnostic results provided. To understand the confidence level of the diagnostic information extracted from a feature, an uncertainty estimate model applied to a vibration signal acquired from a washing machine has been conceived and implemented. In this way, the QCA can provide the overall diagnosis for the WM and estimate the uncertainty level with which the diagnosis has been performed. These information are used by the independent meta agent (IMA) to perform a trend analysis and elaborate suggestions and warnings to improve the process and product execution.

Ce travail constitue une contribution à la caractérisation expérimentale d'un spray dense et à grande vitesse de type spray diesel, au moyen de diagnostics optiques, par des mesures ponctuelles - anémométrie phase doppler (PDA) - ou planes - vélocimétrie par images de particules (PIV) et traitement et analyse d'images (DIP) -. Un écoulement stationnaire est produit par décharge d'eau pressurisée à 10 MPa, à travers un orifice de diamètre 0,2 mm, débouchant dans le milieu ambiant. Grace à des mesures PDA, cinq critères définissant la transition d'un écoulement dense vers un écoulement pleinement développé (semblable à un écoulement d'air charge en particules) ont été établis, bases sur : (i) la valeur asymptotique atteinte par la vitesse moyenne axiale ; (ii) l'évolution linéaire de la masse d'air entrainée ; (iii) l'équilibre atteint par les fluctuations de vitesse ; (iv) l'évolution linéaire du déplacement carré moyen ; (v) l'évolution linéaire de l'épaisseur de mélange. L'adaptation de la PIV a l'étude de ce spray difficile a nécessité de nombreux tests sur le type d'éclairement (deux nappes laser opposées et coplanaires), sur le choix des intervalles de temps entre deux images, sur les tailles de fenêtres d'interrogation pour l'inter corrélation le DIP a fourni des résultats de granulométrie en bon accord avec ceux issus des mesures ponctuelles. Une investigation originale combinant la PIV et le DIP a permis l'étude de la vitesse des gouttes conditionnée par leurs tailles. Enfin, à partir des intensités fluorescées et diffusées, enregistrées simultanément sur deux cameras CCD, l'analyse précédente par PIV et DIP a donne des résultats encourageants sur la dynamique de la phase continue : des écarts de vitesse longitudinale entre les deux phases de l'ordre de 30 m/s ont été mesurés sur l'axe. Les perspectives majeures sont les analyses quantitatives de la vitesse du gaz conditionnée par la vitesse des gouttes ou par leur géométrie
The present work is a contribution to the experimental characterisation of a dense and high speed spray, by means of optical diagnostics : one-point measurements - Phase Doppler Anemometry (PDA) - and planar visualisation measurements - Particle Image Velocimetry (PIV) and Digital Image Processing (DIP) -. A steady state spray is produced by discharge of pressurised water at 10 MPa through a 0. 2 mm diameter hole. The spray discharges into quiescent air, at atmospheric pressure and ambient temperature. With PDA measurements, five criteria defining the transition from a dense flow to a fully developped flow (similar to an airjet laden with droplets) have been established, based on : (i) the asymptote reached by the mean velocity on the axis ; (ii) the linear evolution of the air entrainment ; (iii) the equilibrium reached by the fluctuating velocity ; (iv) the linear evolution of the mean-squared displacement ; (v) the linear evolution of the integral thickness. The adaptation of PIV to the study of this dense spray necessitates numerous preliminary experiments concerning the illumination of the droplets (two opposite coplanar laser sheets), the choice of time interval between two images, the interrogation spot size for the cross-correlation process. . . DIP gives droplets size results which are in good agreement with the ones issued from the PDA measurements. An original investigation combining PIV and DIP allows to study the droplets velocity (10 to 100 m/s) conditioned by their size (a few um). Finally, with the fluoresced and diffused light simultaneously recorded on two CCD cameras, the previous analysis by PIV and digital image treatment gives encouraging results on the continuous phase dynamic : differences in longitudinal velocity of about 30 m/s between the two phases were measured on the axis. Future prospects are the quantitative analyses of the gas velocity conditioned by droplets velocity or droplets geometry

The ability to rapidly, sensitively, and accurately detect the presence of a pathogen is a vital capability for first responders in the assessment and treatment of scenarios such as disease outbreak and bioterrorism. Nucleic acid tests such as the polymerase chain reaction (PCR) are supplanting traditional techniques due to the improved speed, specificity, sensitivity, and simplicity. Still, amplification by PCR is often the bottleneck when processing genetic samples. Conventional PCR machines are bulky, slow, and consume large reagent volumes and an affordable, compact, efficient, easy-to-use alternative has yet to emerge. In this work, a microfluidic PCR platform was developed consisting of a low-cost, multi-chamber polymer microchip and a laser-mediated thermocycler capable of independent thermal control of each reaction chamber. Innovations in polymer microchip modeling, fabrication, and characterization yielded a low-cost solution for sample handling. A simple optical system featuring an infrared laser diode and solenoid-driven optical shutter was combined with a microfluidic temperature measurement system utilizing embedded thermocouples to achieve rapid thermocycling capable of multiplexed temperature control. We validated the instrument with sensitive amplifications of multiple viral targets simultaneously. This technology is a breakthrough in practical microfluidic PCR instrumentation, providing the foundation for a paradigm shift in low-cost, high-throughput genetic diagnostics.

The need to ignite within a very short time the aircraft engines led to many studies. However, the ignition process is not yet fully understood. Many experimental studies are based on obtaining ignition probability at different points and in different average flow conditions but few have focused on the study of a single ignition event. The reason for the lack of full understanding is transient nature of the the ignition process, which depends on many physical parameters, before, during and after the deposition of spark energy. The purpose of this study is to develop the tools necessary to understand unique events by simultaneously measuring multiple parameters that affect the ignition process. A new technique of measurement, two-dimensional laser-induced plasma spectroscopy (2D-LIPS) was developed for the spatially resolved concentration gradients of species and energy in a laser-induced plasma. This technique is based on the use of two cameras, each provided with an interference filter centered on a transition atomic emission. This technique provides the initial size of plasma containing the minimum fuel concentration, thereby justifying the success/failure of an event. It was first validated in a mixing layer of air/nitrogen mixture to determine and resolve the spatial uncertainty of the technique. It was then applied to an aviation fuel injection system. The flow of air, preheated to 200_C, was set at 10 g/s and drops of dodecane having a Sauter mean diameter between 30 and 40 _m were inserted. This injector has a aerodynamic instability type Precessing Vortex Core around 550 Hz, measured by 2D-PIV on the droplets at 20 kHz. Simultaneous measurements 2D-LIPS and 2D-PIV at 20 kHz have established a scenario of ignition. A minimum concentration of dodecane and a minimum size of plasma are necessary but not sufficient for a successful ignition. The strength of PVC also appears to play a role in the fate of the initial nucleus. The study proposes to establish conditional probabilities of ignition using measurements by 2D LIPS. It is shown that for ignition tests having an unconditioned probability of 33% show a conditional probability of 88% through the 2D-LIPS measurements.

A incorporação de novas ferramentas na área de saúde tem promovido uma grande atividade interdisciplinar. A Odontologia tem sido uma dessas áreas beneficiadas com a incorporação de novas tecnologias, principalmente, na área de detecção de cáries. Atualmente, a tecnologia para uso da fluorescência no diagnóstico da cárie utiliza apenas um comprimento de onda no espectro da fluorescência, relacionando com a intensidade, para a determinação da presença ou ausência de tecido cariado. No entanto, deve ser analisado o espectro de fluorescência como um todo e não a fluorescência em um único ponto, pois todos os comprimentos de onda na fluorescência contêm a informação mais precisa sobre a existência ou não de cárie. Neste trabalho descrevemos uma maneira de processarmos a fluorescência para diagnosticar com mais precisão a existência de cárie, para isso, estudamos o comportamento da fluorescência do esmalte e dentina sadios e dentina cariada através de duas formas de processamento dessa fluorescência, sendo primeiramente através da razão do pico elástico pelo pico inelástico e a razão da área inelástica pela área elástica. Utilizamos dentes que apresentavam esmalte e dentina sem cárie e uma face com dentina cariada que foram excitados com três fontes de laser com 442nm, 532nm e 632nm. Foi possível determinar que os três comprimentos de onda foram eficientes na detecção de cárie, porém quando os tecidos foram excitados com 442nm e 632nm os resultados apresentaram os melhores contrastes, além disso, apresentamos um segundo experimento, onde medimos a fluorescência do esmalte sadio com o aparelho comercial Diagnodent® antes e depois da irradiação com o laser de Er: YAG e mostramos que o aparelho mostra erros nessas medidas acusando cárie em esmalte sadio irradiado com o laser, isso identifica um problema quando a fluorescência é captada em um único comprimento de onda
The introduction of new tools in medicine has promoted an important interdisciplinar activity. In Dentistry, the improvement induced by this new technology is mainly observed at caries detection. Until now, the fluorescence procedure for caries detection is based on the investigation of only a specific region of the fluorescencespectrum. From this analysis the presence of caries or healthy tissues is inferred. However, all the fluorescence spectrum must be evaluated and not only a small part of it. The collected information will be important to the caries diagnosis. In this work we propose two ways to process the fluorescence spectrum in order to obtain a more accurate diagnosis. In this way, we study the fluorescence behavior of health enamel and healthy and decayed dentin. The fist way to process the fluorescence here proposed is obtained by the ratio of inelastic peak and elastic peak and the second one, the ratio of the inelastic and elastic areas. It were investigated human teeth with healthy enamel, decayed and healthy dentin surfaces at the same sample. The fluorescence was induced by three lasers excitation: 442nm, 532nm and 632nm. Ali the used wavelengths showed to be efficient for caries detection, however 442nm and 632nm presented better contrasts. A second study was performed, when the fluorescence of healthy enamel was investigated using a commercial device (Diagnodent®) previously and after Er: YAG irradiation. It was demonstrated that this device can present divergent results showing a caries diagnosis for a healthy irradiated enamel surface. This result identifies a problem when a single wavelength is evaluated from all the fluorescence spectrum

Master of Engineering
Turbulent propagating premixed flames are encountered in spark ignition engines, gas turbines, industrial burners, as well as in vented gas explosions. In all these applications, the flame fronts interact with complex solid boundaries which not only distort the flame structure but directly affect the propagation rate in ways that are not yet fully understood. This thesis aims to provide both a quantitative and qualitative understanding of the link between overpressure, flame front wrinkling and turbulence levels generated in the propagating medium. This is an issue of importance for the provision of improved sub-models for the burning rates of premixed flames. An experimental chamber was constructed where controlled premixed flames were ignited from rest to propagate past solid obstacles and/or baffle plates strategically positioned in the chamber. Laser Doppler Anemometry was used to measure the velocity field and turbulence fields while pressure transducers were used to obtain pressure-time traces. In addition to this Laser-Induced Fluorescence of the Hydroxyl radical is was to image the flame front as it consumes the unburnt fuel captured in the re-circulation zone behind the main obstruction. The thesis reports on the effects of various parameters such as the inclusion of grids and obstructions, blockage ratio, and repeated obstacles to explore possible correlations between the pressure and the flow-fields. Pressure, velocity and LIF images were correlated and analysed to prove the significance of grid location and number on overall turbulence intensity. Corresponding flow field parameters such as flame front wrinkling, peak overpressure and RMS all combine to conclusively demonstrate their interaction and influence to turbulence intensity. By progressively positioning more grids further downstream, consequent rises in the flow field parameters and the establishment of positive trends indicates the overall significance of kernel development and flow disturbances in relation to turbulence generation.

Cette thèse est une étude théorique et expérimentale des raies satellites diélectroniques de la raie lyman-α hydrogénoide observée dans les plasmas crées par laser. L’utilisation de méthodes expérimentales performantes nous a permis de mesurer l’émission locale du rayonnement X dans la zone de conduction de plasma. Des spectres expérimentaux, nous avons déduit la densité et la température électronique du plasma le long de l’axe laser. Les caractéristiques du plasma étant déterminées nous avons vérifié la validité des prédictions faites par le modèle collisionnel radiatif décrivant l’intensité des raies satellites diélectroniques en les comparant aux résultats expérimentaux. Le bon accord trouvé a permis de confirmer l’ensemble des modèles théoriques utilisés ainsi que l’importance de la prise en compte des effets de réabsorption
This thesis is a theoritical and experimental study of dielectronic satellites of the hydrogen-like lyman-α line in laser created plasmas. The use of performing experimental methods enabled the measurement of the localized X ray emission in the plasma conduction zone. We deduced the electronic density and temperature of the plasma along the laser axis from experimental spectra. The characteristics of the plasma being determined, we verified the validity of the predicted satellite line intensities by comparison to experimental results. The good agreement obtained confirmed the various theoretical models used and showed the importance of taking into account reabsorption effects