This work investigates the extinction limits of laminar diffusion counterflow flames for various gaseous (methane, syngas, biogas) fuels using a high flow rate counterflow burner designed and built for this work. Equal momenta of the fuel and oxidizer streams were not maintained to provide data to check the fidelity of the numerical schemes and their chemical mechanisms at "non-standard" conditions. Strain rate values at extinction were obtained as a function of fuel mole fraction. Preliminary work with the new burner found that the methane extinction limit results were consistent with results from literature. The results provide insight into the extinction limit conditions of the aforementioned fuels. The strain rate was found to increase with increasing fuel mole fraction. Extinction limit results indicated that fuels with the highest concentration of hydrogen have the greatest extinction limit, which is believed to be attributed to the high diffusivity and reactivity of hydrogen.

This work investigates the extinction limits of laminar diffusion counterflow flames for various gaseous (methane, syngas, biogas) fuels using a high flow rate counterflow burner designed and built for this work. Equal momenta of the fuel and oxidizer streams were not maintained to provide data to check the fidelity of the numerical schemes and their chemical mechanisms at "non-standard" conditions. Strain rate values at extinction were obtained as a function of fuel mole fraction. Preliminary work with the new burner found that the methane extinction limit results were consistent with results from literature. The results provide insight into the extinction limit conditions of the aforementioned fuels. The strain rate was found to increase with increasing fuel mole fraction. Extinction limit results indicated that fuels with the highest concentration of hydrogen have the greatest extinction limit, which is believed to be attributed to the high diffusivity and reactivity of hydrogen.

Modern combustion systems benefit from constant technological advanceswhich aim at reducing the emissions of chemical pollutants and at wideningregimes of stable operation. Further progress in the combustion field requiresa better understanding and modelling of the combustion dynamics. In thesesystems, the combustible is often injected as a liquid polydisperse spray. Experimentaldata are thus required to validate simulation tools in configurationswith flames interacting with controlled structures in multi-phase flows.This thesis aims at studying some of these fundamental interactions in wellcontrolledlaminar flows submitted to upstream modulations. Two experimentalconfigurations are investigated comprising counterflow flames and free inertjets, fed with gaseous or liquid combustibles. The flows may be submittedto upstream velocity modulations to reproduce effects of unsteadiness. Dependingon the pulsation frequency, vortices of controlled sizes are shed fromthe burner lips and convected with the flow, while interacting with the sprayand the flame.In the first part of this thesis, the dynamics of a premixed stretched flameis analysed in a stagnation flow. The study focuses on determining the flowand flame structures under upstream modulations, and principally on studyingthe dynamics of flame/vortex interactions. Different responses of the flameare identified and analysed relative to the size of the vortex ring generated atthe burner outlet. Two propagation modes for the velocity perturbations areidentified, corresponding to a bulk oscillation of the entire reaction zone orto a flame perturbed only at its periphery. This leads to a discussion on thechoice of velocity boundary conditions to conduct 1D simulations of theseconfigurations. Comparisons between simulations and measurements of thevelocity field illustrate these conclusions. Flame transfer functions betweenheat release rate and velocity perturbations imposed at the burner outlet areestablished for different flow conditions. These measurements relying on localand global chemiluminescence of the flame show again a distinct behaviourof the emission originating from the flame region close to the burner axis andthe whole flame. Mechanisms of sound production by partially and perfectlypremixed flames are also identified and analysed relative to flame/vortex interactions.In the second part, the dynamics of a spray convected by a free inert jet or impinginga diffusion flame submitted to velocity modulations is analysed. Theoriginality of this work consists in characterizing the flow and spray dynamicsusing a set of advanced diagnostics. Phase-conditioned images at different instantsin the modulation cycle are used to analyse the interactions between thegaseous phase and the spray. The spatial distribution of combustible vapourand liquid phases is determined using Laser Induced Exciplex Fluorescence(LIEF). Velocities and sizes distribution of droplets from the spray are determinedlocally by Phase Doppler Anemometry (PDA) and in a plane by InterferometricParticle Imaging (IPI). Laser Doppler Velocimetry (LDV) andParticle Image Velocimetry (PIV) are also used to determine the response ofgaseous phase. These phase-conditioned analysis highlight some interactionsbetween the gaseous and liquid phases and constitute an interesting databasefor detailed simulation of these two-phase flows.

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Ce travail de Thèse est consacré à la caractérisation de la structure thermique des fronts de flammelaminaire de prémélange H2/CH4/Air et H2/CO/Air pauvres. L’étude a été réalisée sur un brûleur à jets opposés, permettant de stabiliser des flammes planes stationnaires, dans des conditions quasi-adiabatiques, pour différentes conditions d’étirement. Un diagnostic de Vélocimétrie par Imagerie de Particule (PIV) et un diagnostic bidimensionnel de diffusion Rayleigh induite par laser ont été utilisés successivement pour étudier l’influence de la richesse, de la concentration en hydrogène dans le combustible et de l’étirement sur le profil de température normal au front de flamme. Trois grandeurs fondamentales ont été étudiées : la température des gaz brûlés, le gradient maximum de température et l’épaisseur de flamme au sens de Spalding. Une attention particulière a été portée à l’interprétation du signal Rayleigh. Ce dernier dépendant notamment de la composition du gaz qui évolue à travers le front de flamme. Dans ce travaille de thèse, cette évolution a été évaluée numériquement (simulations 1D : CANTERA et OPPDIF) puis prise en compte pour améliorer le traitement des données expérimentales. Les résultats expérimentaux couvrent une gamme de richesses s’étalant pour H2/CH4/Air et H2/CO/Air, respectivement de 0.6 à 0.8 et de 0.4 à 0.6. Les concentrations en hydrogène dans le combustible s’étalent respectivement de 0 à 50% et de 10 à 50%. Une comparaison systématique a été faite avec les résultats de simulation numérique 1D (OPPDIF). / This Thesis is devoted to the characterization of the thermal structure of H2/CH4/Air and H2/CO/Air laminar flames. Counterflow flame setup has been used to study planar flames in steady and near-adiabatic conditions. Particle Image Velocimetry and laser induced Rayleigh scattering diagnostics has been successively applied to characterize the influence of equivalent ratio, hydrogen concentration in fuel and stretch on the temperature profile normal to the flame front. Three fundamental characteristics have been studied: the burned gas temperature, the maximum temperature gradient and the flame thickness defined by Spalding. Particular attention has been brought to the interpretation of the Rayleigh signal. Indeed, Rayleigh scattering depends on the gas composition which evolves across the flame front. This evolution has been numerical evaluated in this work (1D simulation: CANTERA and OPPDIF) and taken into account to improve Rayleigh data processing. Experimental results have been obtained for lean flames: equivalent ratio spreads from 0.6 to 0.8 and from 0.4 to 0.6 respectively for H2/CH4/Air and H2/CO/Air flames. A wide range of hydrogen concentration has been studied: from 0 to 50% of hydrogen in fuel for H2/CH4/Air flames and from 10 to 50% of hydrogen in fuel for H2/CO/Air flames. Experimental and numerical (OPPDIF) results have been systematically confronted.

La conception de chambres de combustion de nouvelles génération moins polluantes et fonctionnant sur des plages de stabilité plus grandes nécessite une meilleure connaissance et modélisation de la dynamique de la combustion.De nombreux systèmes sont alimentés avec des carburants liquides atomisés qui interagissent avec des grandes structures de l’écoulement d’air puis avec le front de flamme. Il existe cependant peu de données qui permettent de valider les outils de simulation dans des configurations mettant en jeu des flammes en interaction avec des structures contrôlées pour des écoulements polyphasiques.Certaines de ces interactions fondamentales sont étudiées dans ce travail pour des écoulements laminaires soumis à des modulations de vitesse. Les configurations expérimentales correspondent à des flammes à contre-courant et à des jets inertes libres, avec une injection de combustible liquide vaporisé ou sous la forme de sprays polydisperses. Ces écoulements peuvent être soumis à des modulations de vitesse de manière à reproduire les effets d’instationnarité. En fonction de la fréquence de la pulsation, des tourbillons de tailles contrôlées sont générés à la sortie des brûleurs et sont convectés par l’écoulement. Ils interagissent avec le spray de combustible ou la flamme.Une première partie de la thèse vise à caractériser la dynamique de flammes prémélangées dans des écoulements à point d’arrêt pour des combustibles gazeux. L’étude se concentre tout particulièrement sur l’interaction de structures tourbillonnaires avec une flamme plane. Différentes réponses de la flammes ont identifiées et analysées en fonction de la taille des tourbillons générés.Deux régimes de propagation des perturbations de vitesse sont mis en évidence correspondant à une oscillation en bloc de la zone de combustion ou à des perturbations limitées à la périphérie du front de flamme. Ces constatations remettent en cause le choix des conditions aux limites à imposer dans les simulations numériques unidimensionnelles de ces configurations. Des comparaisons entre des prévisions numériques et des mesures du champ de vitesse supportent nos conclusions. L’analyse de la réponse de ces flammes est ensuite poursuivie par la détermination de leurs fonctions de transfert entre le dégagement de chaleur et les perturbations vitesses imposées à la sortie du brûleur.Ces mesures basées sur l’étude du signal de chimiluminescence rayonné par la flamme mettent à nouveau en évidence une différence de comportement entre la région restreinte au centre de l’écoulement à point d’arrêt et le comportement global de l’ensemble de la zone de combustion. Ces configurations sont ensuite utilisées pour identifier les mécanismes de production de bruit par des flammes parfaitement et partiellement prémélangées.La deuxième partie des travaux est dédiée à la caractérisation de la réponse à des tourbillons d’un spray dilué convecté par un jet inerte ou d’un spray combustible alimentant une flamme plane de diffusion dans un écoulement à contre-courant lorsqu’ils interagissent avec des tourbillons. L’originalité du travail repose sur l’utilisation combinée de diagnostics optiques avancés pour caractériser la dynamique de la phase gazeuse et de la phase dispersée, ainsi que leurs interactions par une prise d’images en moyenne conditionnée à différents instants du cycle de modulation. La distribution de la vapeur de carburant injecté dans les phases gazeuses et liquides est notamment caractérisée grâce à la Fluorescence Exciplex Induite par Laser (LIEF). La distribution de vitesse et la granulométrie des gouttelettes du spray sont déterminées localement par effet Doppler (PDA) et dans un plan par Interférométrie par Imagerie de Particules (IPI). Ces diagnostics sont complétés par l’utilisation de la Vélocimétrie Laser Doppler (LDV) et la Vélocimétrie par Imagerie de Particules(PIV) pour déterminer la réponse de la phase gazeuse de ces écoulements. / Modern combustion systems benefit from constant technological advanceswhich aim at reducing the emissions of chemical pollutants and at wideningregimes of stable operation. Further progress in the combustion field requiresa better understanding and modelling of the combustion dynamics. In thesesystems, the combustible is often injected as a liquid polydisperse spray. Experimentaldata are thus required to validate simulation tools in configurationswith flames interacting with controlled structures in multi-phase flows.This thesis aims at studying some of these fundamental interactions in wellcontrolledlaminar flows submitted to upstream modulations. Two experimentalconfigurations are investigated comprising counterflow flames and free inertjets, fed with gaseous or liquid combustibles. The flows may be submittedto upstream velocity modulations to reproduce effects of unsteadiness. Dependingon the pulsation frequency, vortices of controlled sizes are shed fromthe burner lips and convected with the flow, while interacting with the sprayand the flame.In the first part of this thesis, the dynamics of a premixed stretched flameis analysed in a stagnation flow. The study focuses on determining the flowand flame structures under upstream modulations, and principally on studyingthe dynamics of flame/vortex interactions. Different responses of the flameare identified and analysed relative to the size of the vortex ring generated atthe burner outlet. Two propagation modes for the velocity perturbations areidentified, corresponding to a bulk oscillation of the entire reaction zone orto a flame perturbed only at its periphery. This leads to a discussion on thechoice of velocity boundary conditions to conduct 1D simulations of theseconfigurations. Comparisons between simulations and measurements of thevelocity field illustrate these conclusions. Flame transfer functions betweenheat release rate and velocity perturbations imposed at the burner outlet areestablished for different flow conditions. These measurements relying on localand global chemiluminescence of the flame show again a distinct behaviourof the emission originating from the flame region close to the burner axis andthe whole flame. Mechanisms of sound production by partially and perfectlypremixed flames are also identified and analysed relative to flame/vortex interactions.In the second part, the dynamics of a spray convected by a free inert jet or impinginga diffusion flame submitted to velocity modulations is analysed. Theoriginality of this work consists in characterizing the flow and spray dynamicsusing a set of advanced diagnostics. Phase-conditioned images at different instantsin the modulation cycle are used to analyse the interactions between thegaseous phase and the spray. The spatial distribution of combustible vapourand liquid phases is determined using Laser Induced Exciplex Fluorescence(LIEF). Velocities and sizes distribution of droplets from the spray are determinedlocally by Phase Doppler Anemometry (PDA) and in a plane by InterferometricParticle Imaging (IPI). Laser Doppler Velocimetry (LDV) andParticle Image Velocimetry (PIV) are also used to determine the response ofgaseous phase. These phase-conditioned analysis highlight some interactionsbetween the gaseous and liquid phases and constitute an interesting databasefor detailed simulation of these two-phase flows.

The combustion of petroleum-based fuels leads to the formation of several pollutants. Among them, soot particles are particularly harmful due to their severe consequences on human health. Over the past decades, strict regulations have been placed on automotive and aircraft engines to limit these particulate matter emissions. This work is primarily focused on understanding the fundamental behaviour of soot particles and their formation. Though the focus of this work is on soot formation and growth pathways, the study of the gas-phase combustion process was also an integral part to validate the mechanism. A reduced mechanism is developed with retaining the larger PAH species till coronene from KAUST-ARAMCO mechanism. Counterflow diffusion flames had emphasized the simulation of canonical configuration where the reduced mechanism is validated and the soot growth pathways are evaluated. The importance of the significant contribution of larger PAH species on the soot growth pathways in both SF and SFO flames is evident in this analysis. The sensitivity of these flames with respect to strain rates, dilution, and at higher pressures are analysed. Direct Numerical Simulation (DNS) of two-dimensional counterflow diffusion flames is conducted to understand the impact of vortex interactions on soot characteristics. The results indicate that the larger PAH species contributes to the soot formation in the air-side perturbation regimes, whereas the soot formation is dominated by the soot transport in fuel-side perturbation. The study is extended to simulate and compare coflow laminar flame using different statistical moment methods MOMIC, HMOM and CQMOM.