Dissertations / Theses on the topic 'Combustions'

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Zero-carbon powertrains development has become one of the main challenges for automotive industries around the world. Following this guideline, several approaches such as powertrain electrification, advanced combustions, and hydrogen internal combustion engines have been aimed to achieve the goal. Low Temperature Combustions, characterized by a simultaneous reduction of fuel consumption and emissions, represent one of the most studied solutions moving towards a sustainable mobility. Previous research demonstrate that Gasoline partially premixed Compression Ignition combustion is one of the most promising LTC. Mainly characterized by the high-pressure direct-injection of gasoline and the spontaneous ignition of the premixed air-fuel mixture, GCI combustion has shown a good potential to achieve the high thermal efficiency and low pollutants in compression ignited engines required by future emission regulations. Despite its potential, GCI combustion might suffer from low combustion controllability and stability, because gasoline spontaneous ignition is significantly affected by slight variations of the local in-cylinder thermal conditions. Therefore, to properly control GCI combustion assuring the maximum performance, a deep knowledge of the combustion process, i.e., gasoline auto-ignition and the effect of the control parameters on the combustion and pollutants, is mandatory. This PhD dissertation focuses on the study of GCI combustion in a light-duty compression ignited engine. Starting from a standard 1.3L diesel engine, this work describes the activities made moving toward the full conversion of the engine. A preliminary study of the GCI combustion was conducted in a “Single-Cylinder” engine configuration highlighting combustion characteristics and dependencies on the control parameters. Then, the full engine conversion was performed, and a wide experimental campaign allowed to confirm the benefits of this advanced combustion methodologies in terms of pollutants and thermal efficiency. The analysis of the in-cylinder pressure signal allowed to study in depth the GCI combustion and develop control-oriented models aimed to improve the combustion stability.

Ce travail présente l’étude de flammes turbulentes non-prémélangées et partiellement prémélangées par simulations numériques directes (DNS) en utilisant des modèles détaillés de chimie de transport. L’interaction entre une flamme H2/Air et un champ de turbulence est simulée et l’influence de la diffusion différentielle sur la structure de la flamme est qualifiée. On note en particulier l’absence de corrélation entre la température de flamme et le taux de dissipation scalaire quand un modèle de transport élaboré est utilisé, ainsi qu’une modification de la limite d’équilibre. Le ré-établissement de l’équation de flammelettes avec la prise en compte d’un nombre de Lewis non unitaire pour la fraction de mélange Z permet de prendre en compte, au moins partiellement, cet effet. Une simulation de l’interaction entre une flamme non-prémélangée H2/Air et une paire de tourbillons avec des modèles détaillés de chimie et de transport a été réalisée, post traitée et analysée. Une extinction de la flamme est observée et la structure partiellement prémélangée au bord de la zone réactive est étudiée. On montre que le radical OH est un bon traceur de la zone d’extinction de la flamme, mais qu’il ne « voit » pas l’intensification de l’activité chimique dans les zones partiellement prémélangées. L’auto-allumage d’une flamme turbulente non prémélangée a été examiné. Les résultats de DNS permettent d’extraire des informations sur la prévision de la localisation du premier site d’autoallumage, sur l’influence du modèle de transport et sur la structure partiellement prémélangée observée. La répétition des calculs permet une étude statistique de l’influence de la turbulence sur le temps d’allumage. Le test a priori d’un nouveau modèle de combustion turbulente basé sur le concept de densité de surface de flamme généralisée donne de premiers résultats prometteurs.

Cette thèse propose une modélisation aussi générique que possible de la combustion dans les moteurs automobiles dans un cadre de simulation aux grandes échelles. Une première étude aborde la fermeture du terme de transport non résolu pour la flamme de prémélange. Par la suite, un couplage entre les modèles ecfm-les et pcm-fpi est proposé et validé pour intégrer les effets de chimie complexe à la simulation de la flamme de prémélange. Ce travail est étendu par l'adjonction de modélisations spécifiques à l'allumage par bougie et de l'auto-inflammation, toujours en intégrant les effets de chimie détaillée. Des calculs d'application aux combustions anormales dans les moteurs à allumage commandé concluent ce travail.

Le moteur à allumage commandé fortement downsizé est une des solutions les plus prometteuses utilisée par les constructeurs automobiles pour augmenter le rendement et réduire les émissions de CO2. Cependant, les conditions thermodynamiques plus sévères rencontrées dans ces moteurs favorisent l’apparition de combustions anormales (cliquetis et rumble) qui sont difficiles à analyser expérimentalement vu les risques encourus par le moteur. La méthode Reynolds Averaged Navier-Stokes (RANS) s’est imposée depuis plusieurs années pour l’étude des moteurs à piston dans l’industrie, mais elle n’est pas la plus appropriée pour étudier des phénomènes locaux et sporadiques comme les combustions anormales qui n’affectent pas le cycle moyen simulé en RANS. Grâce à l’utilisation d’un code compressible LES et au développement d’une version améliorée des modèles ECFM-LES (Extended Coherent Flame Model) et TKI (Tabulated Kinetics of Ignition) qui permet un découplage total entre les taux de réaction liés à la propagation de la flamme et à l’auto-inflammation, ces travaux mettent en évidence pour la première fois la capacité de la LES à décrire le phénomène de cliquetis dans une configuration réaliste d’un moteur à allumage commandé. Contrairement aux études précédentes [S. Fontanesi and S. Paltrinieri and A. D’Adamo and G. Cantore and C. Rutland, SAE Int. J. Fuels Lubr., 2013-01-1082, pp. 98-118][G. Lecocq, S. Richard, J.-B. Michel, L. Vervisch, Proc. Combust. Inst. 33 (2011) 3105-3114], une étude quantitative du cliquetis est réalisée grâce à des post-traitements spécifiques et similaires pour les résultats expérimentaux et numériques. La LES est capable de prédire la variabilité de la pression cylindre, la fréquence mais également l’angle moyen d’apparition de l’auto-inflammation sur un balayage d’avance à l’allumage. Une analyse 3D démontre également que le cliquetis se déclenche à différents endroits, mais principalement dans la moitié de la chambre sous les soupapes d’échappement. De plus, l’intensité du cliquetis est proportionnelle à la masse de gaz frais brûlée en auto-inflammation pour les faibles intensités, alors qu’une croissance beaucoup plus forte est observée pour les intensités les plus élevées. Ceci suggère que des facteurs supplémentaires interviennent comme la localisation du cliquetis ou les interactions entre l’acoustique interne et l’auto-inflammation. L’utilisation d’un code LES compressible permet une visualisation directe de ces interactions mettant en évidence que les faibles intensités sont liées à des auto-inflammations locales sans couplage alors qu’une transition de la déflagration vers la détonation est possible en moteur automobile et correspond aux intensités les plus fortes.

Les techniques de mesures optiques non intrusives développées depuis plusieurs dizaines d'années permettent la mesure des paramètres physiques tels que la température, la concentration des espèces chimiques et la vitesse. Tous ces diagnostics optiques, bien que très performants, sont généralement appliqués en mesures ponctuelles.
Le but de la thèse est de développer une ou plusieurs techniques d'imagerie quantitatives et instantanées de température et de concentration. Deux axes d'études complémentaires ont été abordés au cours de ce travail. Il s'agit de la fluorescence induite par laser sur le radical OH pour l'étude des milieux en combustion et de la fluorescence induite par laser d'un traceur moléculaire (acétone) pour l'étude des écoulements non réactifs. Ces deux axes d'étude ont été menés en parallèle avec la même approche : après compilation des données bibliographiques, des modèles de fluorescence induite par laser de ces deux espèces ont été développés. Les résultats de ces modélisations ont servi à sélectionner les meilleures stratégies expérimentales.
Des expériences pilotes ont été mises en place en vue développer ces techniques d'imagerie. Elles consistent en l'utilisation des modèles proposés pour les deux traceurs étudiés afin d'obtenir des images instantanées et couplées de température et de concentration dans différents types d'écoulements (combustion hydrogène–air, mélange de jets, ...).
D'autres applications ont été réalisées sur des bancs d'essais à caractère semi-industriel afin de caractériser l'utilisation de ces techniques dans des conditions de mesures sévères.
Les résultats obtenus au cours de ces différentes expériences montrent que l'outil d'imagerie quantitative et instantanée développé est opérationnel, répondant ainsi à un besoin d'informations quantitatives et spatialement résolues et complétant les possibilités offertes par les autres diagnostics optiques.

Les techniques de mesures optiques non intrusives développées depuis plusieurs dizaines d'années permettent la mesure des paramètres physiques tels que la température, la concentration des espèces chimiques et la vitesse. Tous ces diagnostics optiques, bien que très performants, sont généralement appliqués en mesures ponctuelles. Le but de la thèse est de développer une ou plusieurs techniques d'imagerie quantitatives et instantanées de température et de concentration. Deux axes d'études complémentaires ont été abordés au cours de ce travail. Il s'agit de la fluorescence induite par laser sur le radical OH pour l'étude des milieux en combustion et de la fluorescence induite par laser d'un traceur moléculaire (acétone) pour l'étude des écoulements non réactifs. Ces deux axes d'étude ont été menés en parallèle avec la même approche : après compilation des données bibliographiques, des modèles de fluorescence induite par laser de ces deux espèces ont été développés. Les résultats de ces modélisations ont servi à sélectionner les meilleures stratégies expérimentales. Des expériences pilotes ont été mises en place en vue de développer ces techniques d'imagerie. Elles consistent en l'utilisation des modèles proposés pour les deux traceurs étudiés afin d'obtenir des images instantanées et couplées de température et de concentration dans différents types d'écoulements (combustion hydrogène-air, mélange de jets,). D'autres applications ont été réalisées sur des bancs d'essais à caractère semi-industriel afin de caractériser l'utilisation de ces techniques dans des conditions de mesures sévères. Les résultats obtenus au cours de ces différentes expériences montrent que l'outil d'imagerie quantitative et instantanée développé est opérationnel

Pour améliorer le rendement des moteurs essence, une méthode efficace est le downsizing qui consiste en la diminution de la cylindrée moteur compensée par l’ajout d’un compresseur pour maintenir la puissance. Lorsque le niveau de downsizing est trop important les fortes pression et températures rencontrées favorisent l’apparition de phénomènes d’auto-allumage de type cliquetis ou rumble néfastes pour l’intégrité du moteur. Ce type de phénomène, aujourd’hui encore mal compris, constitue une limite à l’utilisation du downsizing. Dans cette thèse la Simulation aux Grandes Echelles est utilisée pour étudier ce type de combustion dite anormale. L’objectif est de proposer une méthodologie numérique capable de reproduire leurs apparitions pour en étudier les mécanismes. L’auto-allumage est un mode de combustion sensible aux variations des conditions thermodynamiques locales. Des méthodes numériques précises et des modèles appropriés, en particulier pour la thermique paroi doivent donc être utilisés. La première partie de ce manuscrit présente la méthodologie numérique proposée et en particulier deux aspects développés lors de cette thèse: un modèle d’auto-allumage qui permet de reproduire le délai d’auto-allumage des gaz frais avec un schéma cinétique réduit et une méthodologie de couplage entre la chambre de combustion et la culasse permettant de définir des champs de températures paroi réalistes. La seconde partie de ce manuscrit présente les résultats de deux études numériques reproduisant certains points de fonctionnement d’un moteur expérimental. La première étude est réalisée à l’aide de modèles de combustion de la littérature et vise à reproduire le comportement expérimental pour diverses variations paramétriques influant sur la combustion. La seconde étude est réalisée à l’aide des modèles développés dans cette thèse afin d’étudier l’impact de la thermique paroi dans les mécanismes d’apparition des combustions anormales.

Les feux de savanes et les combustions domestiques sont les principales sources de polluants atmospheriques en afrique. Afin de connaitre leur impact sur la chimie de l'atmosphere a l'echelle globale et regionale, il est necessaire d'estimer leurs emissions a ces differentes echelles. Pour cela, il faut determiner les quantites de biomasse brulees en fonction du temps et de l'espace et les caracteristiques de l'emission du compose atmospherique etudie, c'est a dire, la quantite de compose emis par unite de biomasse brule ou facteur d'emission. Ce travail propose la premiere quantification a l'echelle regionale et globale des emissions atmospheriques par les feux domestiques en afrique. Deux experiences en cote d'ivoire ont permis d'obtenir les facteurs d'emissions du dioxyde de carbone, du monoxyde de carbone, du methane, des hydrocarbures non methaniques, des acides organiques, des oxydes d'azote, du protoxyde d'azote, de l'ammoniac et du carbone particulaire emis par les feux traditionnels de bois, de charbon, et lors de la carbonisation du bois en meule artisanale pour la fabrication de charbon. Parallelement a ce travail, une etude theorique de la combustion permet de relier les diffrents procedes de combustion et les resultats experimentaux. Le principal processus mis en jeu lors de la carbonisation est une combustion lente, la combustion du charbon se fait en phase d'incandescence et les combustions du bois se font majoritairement en phase de flamme. En associant ces resultats et des donnees de consommation de bois et de charbon par pays, nous avons estime la quantite d'emission atmospherique due aux feux domestiques en afrique. Cette etude globale ne suffisant pas pour estimer l'impact de ces combustions sur la chimie reactive locale, nous proposons ensuite, une quantification des emissions a l'echelle spatiale et temporelle en presentant des cartes a 1 x 1 degre de resolution des emissions des principaux composes emis ainsi que les periodes maximums d'emissions. La comparaison de ces emissions negligeables a l'echelle regionale et globale de gaz traces et d'aerosols pouvant influencer la chimie de l'atmosphere

L'augmentation continue des charges de fonctionnement des moteurs à allumage commandé a conduit à l'apparition d'une nouvelle forme de combustion anormale à bas régime sous la forme d'un pré allumage. Dans des conditions de pression et de température extrêmes, une auto-inflammation incontrôlée du mélange carburé peut en effet se produire avant l'allumage normal à la bougie et conduire à une seconde auto-inflammation de type cliquetis donnant naissance à des oscillations de pression inacceptables même pour les moteurs les plus robustes. Cette anomalie constitue donc une véritable limite au downsizing des moteurs et à l'augmentation de leurs performances spécifiques. Cette dernière forme de combustion anormale est bien plus critique que le cliquetis car son apparition est aléatoire, le plus souvent sporadique et généralement très violente. Ces caractéristiques fondamentales expliquent que de nouveaux outils et de nouvelles méthodologies d'analyse aient dû être développés pour mieux caractériser le processus d'auto-inflammation dans ces conditions extrêmes. Des méthodes statistiques avancées ont notamment été mises au point pour quantifier de manière fiable la fréquence d'apparition du pré allumage malgré son caractère aléatoire. En parallèle, un travail expérimental important a été réalisé pour mettre au point une méthodologie de réalisation de visualisations endoscopiques permettant de mieux analyser le processus de combustion, et d'identifier de manière plus précise les zones préférentielles d'apparition du pré allumage dans la chambre de combustion. Les impacts des paramètres fondamentaux régissant l'auto-inflammation (aérodynamique interne, thermique et chimie du mélange) ont d'abord été analysés sur un monocylindre de recherche. Le processus de combustion a ainsi été détaillé et l'hypothèse d'une auto-inflammation spontanée en phase gazeuse a également pu être abordée en parallèle de l'analyse expérimentale par une approche numérique RANS. Une étude plus approfondie a ensuite montré qu'il était possible qu'un pré allumage conduise à une auto-inflammation de type détonation, ce qui explique qu'un nombre réduit d'occurrences suffise à détériorer irrémédiablement le moteur. La versatilité du monocylindre a également permis de mettre en évidence la diversité des phénomènes qui pouvaient conduire au pré allumage et d'autres hypothèses que celle d'une auto-inflammation spontanée en phase gazeuse ont ainsi pu être formulées. Celles-ci ont finalement été testées sur un multicylindre en appliquant des méthodologies d'essais et d'analyse éprouvées sur monocylindre. Les investigations tournées vers l'impact des réglages moteur ont alors notamment confirmé que les impacts du carburant sur les parois de la chambre de combustion conduisaient à la formation de films liquides dont les caractéristiques locales pouvaient être favorables à une auto-inflammation
The continuous increase of engine loads on SI engines has provoked the apparition of a new form of abnormal combustion at low engine speed in the guise of a pre-ignition. Under extreme conditions of pressure and temperature, an uncontrolled auto-ignition of the fresh mixture can happen well before the normal ignition at the spark and lead to a knocking-like second auto-ignition and to unacceptable pressure oscillations even for modern and robust engines. This anomaly constitutes thus a strong limit to the downsizing of gasoline engines and to the increase of their specific performance. This latter abnormal combustion is far more critical than knocking combustion since its apparition is random, most often sporadic and usually very violent. These fundamental characteristics explain that new tools and methodologies had to be developed to achieve a better characterization of the auto-ignition process under such extreme conditions. Advanced statistical methods have notably been defined to obtain a reliable quantification of the pre-ignition frequency despite its randomness. A significant work has simultaneously been realized to develop an experimental methodology dedicated to endoscopic visualizations allowing a better analysis of the combustion process and a more precise identification of the preferential areas of auto-ignition inside the combustion chamber. The impacts of fundamental parameters governing auto-ignition (the mixture's charge motion, thermal and chemical evolutions) have first been analyzed thanks to a research single cylinder engine. That way, the combustion process has been detailed and the hypothesis of a spontaneous auto-ignition of the gaseous mixture has also been tackled at the same time with the help of a numerical RANS approach. Then, a deeper analysis has showed that pre-ignition could lead to a developing detonation mode during the second auto-ignition, explaining so that a reduced number of events could cause irremediable damages. Thanks to the flexibility of the single cylinder engine, it has also been shown that a wide variety of phenomena could lead to pre-ignition and it has made possible the formulation of other hypotheses than a spontaneous auto-ignition of the gaseous mixture. These ones have finally been tested on a serial multi-cylinder engine with test and analysis methodologies validated on the single cylinder engine. The investigations focused on the impacts of settings have then confirmed that the fuel impacts on the liner and on the piston lead to the formation of liquid films whose local characteristics could be favorable to auto-ignition

Etude des effets de collision de CO2 et H2Osur les raies Q du spectre rovibrationnel de N2 à partir des largeurs et déplacements de raies mesures a l'aide d'un spectromètre Raman inverse et d'un lambdamètre (précision de quelques mhz). Mesure des coefficients d'élargissement à faible densité pour déduire les paramètres ajustables de trois modèles de relaxation rotationnelle de N2. Simulation des spectres N2-CO2 à haute densité et comparaison aux données expérimentales pour diviser la meilleure modélisation en vue de l'extrapolation à des températures et densités plus élevées

L'atmosphère terrestre est un milieu très complexe, perpétuellement en interaction, dont sa composition est fortement influencée par les activités humaines qui émettent de nombreux composés. Peu d'études liées aux émissions de composés organiques volatils (COV) en air intérieur à partir des sources de combustion (différents modes de chauffage, cuisine,. . . ) ont été conduites à ce jour. En effet, l'utilisation de cheminées ne peut que s'accentuer ces prochaines années compte tenu de l'augmentation importante du coût du pétrole et de la valorisation du bois en tant que source alternative. Une partie de la carence en études dans de domaine est liée au manque de techniques analytiques permettant d'accéder aux composés émis à des niveaux très faibles. Le travail entrepris a pour principal objectif l'évaluation de l'impact des émissions de COV dû à la combustion du bois, plus particulièrement dans les atmosphères intérieures. Afin de mieux appréhender le rôle des composés émis sur la qualité de l'air et la santé, une étude cinétique de photodégradation d'un traceur spécifique de la combustion a été réalisée : le créosol. Ainsi après avoir étudié les possibilités de nouveaux supports analytiques à base de nanostructures de carbone (NSC) nous nous sommes attachés à évaluer les caractéristiques des émissions de différents foyers individuels à bois. Cette étude a montré qu'il était possible d'isoler certains composés « traceurs » en relation avec le type de combustion et l'essence de bois brûlé. Les NSC ont montré des qualités analytiques inégales à ce jour et demande encore des études complémentaires. Un traceur type : le créosol, à été mis en évidence dont son étude cinétique a montré qu'il était très réactif avec une constante très élevée et qu'il était à l'origine de composés secondaires parfois plus toxiques pour la santé humaine (composés oxydés)
Currently, few studies related to Volatile Organic compounds (VOC) emissions in indoor air were realised from combustion sources (heating, cooking. . . ). Indeed, the use of fireplaces will increase next years due to oil price: wood valorisation is one of the alternative sources for residential heating. There are not many studies about this subject because analytical techniques to determine weak concentration are difficult to implement. The main goal of this work is to evaluate the impact of VOC emissions due to wood combustion, and more particularly in indoor air. In order to understand the role of compounds emitted on air quality, a kinetic study of a specific marker was carried out in an atmospheric simulation chamber. Thus, after having studied the possibilities of news analytical supports containing carbon nanostructures (CNS), we evaluated VOC emissions from different wood fireplace. This study showed it was possible to find a marker in relation to wood type burning. Creosol was highlighted as this marker and its kinetic study showed that it was very reactive (very high constant). This compound was also at the origin of secondary compounds sometimes more toxic for human health. Finally at this time the CNS showed unequalled analytical qualities and requires complementary studies for a reliable analytical application

Les biocarburants et autres produits chimiques dérivés de la biomasse sont désormais considérés comme un élément essentiel du portefeuille énergétique durable, où ils promettent de contribuer à la sécurité énergétique de notre société. Malgré l'intérêt indéniable que présentent ces biocarburants, leurs processus de combustion sont susceptibles de favoriser la formation d'HAPOs (Hydrocarbures Aromatiques Polycycliques Oxygénés) qui peuvent à terme contribuer à la formation de suie, et peuvent également en modifier profondément les propriétés. Le travail réalisé dans cette thèse a porté sur l'identification et la quantification des aromatiques oxygénés formés lors de la combustion d'un biocarburant à base de lignine dans des conditions de flamme. Des flammes laminaires prémélangées d'anisole (composé modèle de substitution pour la biomasse) et de mélanges de carburants hydrocarbonés (iso-octane et méthane) ont été étudiées à l'aide de la chromatographie en phase gazeuse avancée. Dans ce contexte, nous avons mis en œuvre une technique d'enrichissement de l'échantillon (piège de préconcentration de l'échantillon) avec un ensemble d'analyses chromatographiques in situ et ex situ (1D GC-MS, 1D GC-SPT-FID et 2D GC-MS) qui nous ont permis d'identifier un large panel de différents aromatiques oxygénés (~100). Ces résultats ont ensuite été utilisés pour analyser les voies de décomposition du combustible qui conduisent à la formation d'HAPOs. Avec l'identification, cette thèse fournit une base de données expérimentale quantitative détaillée en termes d'évolution de la fraction molaire par rapport à la hauteur de la flamme pour plusieurs aromatiques oxygénés et non oxygénés associés. D'autres biocarburants comme le 2,5-DMF et l'éthanol ont également été étudiés et les résultats expérimentaux ont montré que les différentes structures moléculaires des biocarburants conduisent à des différences significatives dans la formation d'espèces intermédiaires et de polluants. Ce travail met également en lumière des informations cruciales concernant la quantité et la taille des particules de suie formées dans ces flammes en utilisant LII et SMPS. Les résultats préliminaires des mesures de suie indiquent que la taille des particules de suie dans ces flammes est très petite (<10 nm)
Biofuels and other biomass-derived chemicals are now considered as a vital part of sustainable energy portfolio, where they promise to contribute to our society’s energy security. Despite the undeniable interest presented by these biofuels, their combustion processes are likely to enhance the formation of OPAHs (Oxygenated Polycyclic Aromatic Hydrocarbons) which may eventually contribute to the formation of soot, and may as well profoundly modify its properties. The work carried out in this thesis focused on the identification and quantification of the oxygenated aromatics formed during the combustion of a lignin-based biofuel in flame conditions. Laminar premixed flames of anisole (surrogate model compound for biomass) and hydrocarbon fuel blends (iso-octane and methane) have been investigated using Advanced Gas Chromatography. In this context, we implemented a sample enrichment technique (sample pre-concentration trap) with a set of in situ and ex situ chromatographic analysis (1D GC-MS, 1D GC-SPT-FID and 2D GC-MS) which enabled us to identify a large panel of different oxygenated (~100) aromatics. These results were then used to analyze the fuel decomposition pathways that lead to the formation of OPAHs. Together with identification, this thesis provides a detailed quantitative experimental database in terms of the evolution of the mole fraction with respect to the flame height for several oxygenated and associated non-oxygenated aromatics. Other biofuels like 2,5-DMF and ethanol were also studied and experimental results showed that the different molecular structures of biofuels lead to significant differences in the formation of intermediate species and pollutants. This work also highlights crucial information concerning the amount and the size of soot particles formed in such flames using LII and SMPS. Preliminary results from soot measurements indicate that the soot particle size in these flames is very small (<10 nm)

Des capteurs en TiO2, sous forme de céramique, de couche épaisse obtenue par sérigraphie et de couche mince obtenue par pulvérisation cathodique, ont été étudiés sous l'action de flux gazeux en CO-CO2-O2-Ar hors équilibre thermodynamique. En régime stationnaire sous atmosphère oxydante autour de 600oc la résistance des capteurs suit la loi Po2 ½ P0,5/pco0,5 et autour de 830 oc la loi Po2 ½ Pc0 1/2 5. Sous atmosphère réductrice, dans l'intervalle de 600 à 830 oc, la réponse des échantillons massifs suit la loi (p c o 2/ p c o) 0,5 et celle des couches la loi fp o 2 0, 5 avec f fonction du taux de recouvrement (o a d s/sites de surface). En régime transitoire le temps de réponse des films de tio 2 dépend, lors d'un échelon de o 2, de la vitesse de diffusion de o 2 à travers la couche et, lors d'un échelon de Co, de l'interaction gaz-solide. Les couches obtenues par pulvérisation cathodique ont des constantes de temps de réponse de l'ordre de 30 MS.

In questo lavoro di tesi mi soffermerò, inizialmente, sul possibile futuro dei motori a combustione interna e sulle tecnologie innovative già presenti sul mercato (HCCI, VCR, ecc.). Mi concentrerò, poi, sull’analisi di due sistemi innovativi come gli Opposed Piston Engine (OPE) e gli Split Cycle Combustion Engine (SCCE).

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1985.
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Bibliography: leaf 26.
by Robert Phelps Bishop.
B.S.

As worldwide production of biodiesel fuel increases, one of the largest concerns is the abundance of waste glycerol. The price of crude glycerol has fallen drastically and many large biodiesel producers are currently paying to landfill this large waste stream. In the search to find a value added alternative, glycerol combustion may be one of the simplest solutions. Heat recovered from glycerol oxidation could easily be used to reduce heating costs inherent to large-scale biodiesel production. It has been stated ?Combustion of glycerol would be an elegant solution, if it worked?. Clean combustion of glycerol is difficult due to its high viscosity, high auto ignition temperature, and concerns of hazardous emissions. In particular, most in the biodiesel producing community share a fear that burning glycerol could produce acrolein, an aldehyde which is a thermal decomposition product of glycerol and is toxic at very low concentrations. This report will detail the design of a burner that can safely and easily burn crude glycerol for process heating. Emissions testing in the burner using glycerol sources of varying quality confirm that this burner design completely oxidizes the glycerol into CO2 and H2O with very low levels of pollutants, typical of other hydrocarbon fuels. These results show that safe, clean, and efficient combustion of a wide range of glycerol purities is possible with a properly designed burner.

The target of this master thesis is specify the requirements, which come up while summing the investment aim of a new 40MW energetic unit, and show the overall project management. Thesis is divided into two parts. First part deals with project management from the investors point of view. There is also detailed concept study, technological description of piston co-generation units and combined cycle, concept design of calculated variations and their economical analysis. Second part is taken from the point of view of the main supplier. There is defined the range of operations, documents and official permissions needed for successful finish of the civil part of the energetic unit project.

Les turbomachines actuelles ont atteint un niveau de maturité technique très élevé. De nouvelles architectures reposant sur des cycles thermodynamiques basés sur une combustion à gain de pression, comme la combustion à volume constant (CVC), ont le potentiel d’augmenter leur efficacité. Dans cette étude,une solution qui repose sur l’intégration dans une turbomachine de chambres de combustion à volume constant sans piston (CVCSP) est considérée. Les objectifs de ces travaux de thèse sont doubles : dans un premier temps de développer et de caractériser extensivement un nouveau dispositif (CV2) dédié à la Combustion à volume constant sans piston sur un cas de référence et, dans un second temps, de proposer à travers plusieurs études, une analyse de l’influence de l’aérodynamique et de la dilution sur les processus d’allumage et, plus généralement de combustion. Le dispositif CV2 permet la combustion aérobie en allumage commandé d’un mélange de propane ou de n-décane, injecté directement dans la chambre. Un point de référence est caractérisé en détail via : des mesures de champs de vitesse par PIV, de chimiluminescence pendant la combustion, une analyse 0D développée dans cette étude. La caractérisation détaillée de ce point de référence montre que le dispositif CV2 reproduit correctement une combustion à volume constant turbulente dans un mélange faiblement hétérogène en température et stratifié en composition, et ce sur un nombre de cycles permettant d’établir une convergence statistique raisonnable. Ces diagnostics et analyses sont employés dans 2 cas d’études pour caractériser successivement : l’influence de l’aérodynamique, via une variation de l’instant d’allumage, l’influence des gaz brûlés résiduels sur la combustion en allumage commandé et la stabilité cyclique, via une variation de la pression d’échappement.Dans un fonctionnement sans balayage, on montre que cette variabilité cyclique est liée au premier ordre à la variation de la dilution en gaz brûlé résiduel du mélange et à la vitesse locale. On montre notamment que, pour un mélange donné, il existe une corrélation statistique entre une vitesse statistique limite et la probabilité d’allumage moyenne. Pour représenter l’effet de pression dans un plénum en amont d’une turbine, on réalise une étude paramétrique sur la pression d’échappement. La dilution résultante, croissant avec la pression d’échappement, diminue la vitesse fondamentale de flamme et ralentit donc la combustion. Les niveaux de températures des gaz brûlés résiduels résultent des échanges de chaleur qui ont lieu sur toute la durée du cycle, de l’allumage du cycle N à celui du cycle N+1 suivant. Des extrapolations sur des cycles à température de paroi plus élevée et à échappement plus court montrent que l’adiabaticité du cycle est améliorée (de 20 %) et que l’effet de dilution en température est alors favorable à une vitesse de flamme turbulente qui est alors plus élevée. Un phénomène d’allumage par gaz brûlé résiduel est observé sur certains cycles de combustion. Ce phénomène est caractérisé dans des conditions favorables, i.e. faible richesse (0.66), allumage tardif et cycle plus court. Lors d’un allumage par gaz brûlés résiduels, un noyau de flamme se développe dans les zones présentant des gaz brûlés résiduels chauds et à basse vitesse autour du jet d’admission et se propage ensuite au reste du mélange identiquement à celui qui serait généré par allumage commandé.Ce travail prend place dans le cadre de la chaire industrielle CAPA sur la combustion alternative pour la propulsion aérobie financée par SAFRAN Tech, MBDA et l’ANR
Current turbomachines have reached a very high level of technical maturity. Thermodynamic cycles based on pressure-gain combustion, such as constant volume combustion (CVC), feature a clear potential for efficiency improvement. The present study considers the integration in a turbomachine of piston-lessCVC chambers. The thesis work is twofold. First, a new experimental setup (CV2) dedicated to cyclic piston-less CVC is developed and thoroughly characterized on a reference operating point. Second, the influence of the aerodynamics and dilution on the processes of ignition and, in a larger sense, on combustion is discussed through dedicated studies. The CV2 device allows for the spark-ignited air-breathing combustion of a mixture of either propane orn-decane, directly injected into the chamber. A reference condition is characterized in details using: PIV velocity field measurements, chemiluminescence of combustion and a 0D modeling of the device. This detailed characterization evidenced that the CV2 combustion chamber successfully replicates, on a number of cycles allowing a reasonable statistical convergence, a turbulent deflagrative constant-volume combustion in a mixture stratified in composition. Those diagnostics and analyses are applied to 2 cases of study to characterize successively : the influence of the aerodynamics, through a variation of the ignition timing, the influence of the residual burnt gases on spark-ignited combustion and the cyclic stability, through a variation of the exhaust backpressure.Operating the device without scavenging of the combustion chamber, we show that the cyclic variability correlates strongly with both the variation of residual burnt gases dilution and the local velocity. Particularly, we show that for a given mixture, a correlation exists between a statistical velocity limit and the average probability of ignition. The effect of a plenum backpressure upstream of a turbine, downstream of the combustion chamber, is simulated by varying the exhaust system backpressure. The resulting dilution, which increases with the exhaust backpressure, diminishes the fundamental flame velocity of the mixture and slows down the combustion. The residual burnt gases temperature results from the integrated heat exchanges that happen during the total cycle duration starting from the end of combustion of cycle N, to the ignition of cycle N+1. Enhanced cycles, with an increased wall temperature and reduced exhaust duration, are extrapolated by 0D analysis. Those cycles evidence a reduction of the cumulated heat exchanges of up to 20 %. The resulting dilutionis more favorable to higher turbulent flame velocity thus to shorter combustion duration. A phenomenon of ignition induced by the residual burnt gases is observed on certain combustion cycles. This phenomenon is characterized in favorable conditions, i.e. fuel-lean equivalence ratio (0.66), late ignition and shortcycles. During an ignition by residual burnt gases, a flame kernel is ignited in areas where the still hot residuals burnt gases meet fresh gases in low-velocity areas around the intake jet. The ignition kernel then propagates to the rest of the mixture in a similar manner as if it was spark-ignited.This work is part of the CAPA Chair research program on Alternative Combustion modes for Air-breathing Propulsion supported by SAFRAN Tech, MBDAFrance and ANR (French National Research Agency)

[ES] Históricamente, el sector del transporte de servicio mediano y pesado ha sido desafiado por las regulaciones de emisiones que se han impuesto a lo largo de los años, lo que requirió intensificar el esfuerzo de investigación con el objetivo de avanzar en el desarrollo tecnológico para ofrecer una opción que cumpla con las normas a un precio similar para el propietario. No obstante, la reciente introducción de la normativa EUVI ha requerido la adición de un complejo sistema de postratamiento, agregando nuevos costes fijos al producto, así como costes operativos con el consumo de urea. Este avance fue necesario debido a la limitación de la combustión diésel convencional que no puede desacoplar las altas emisiones de NOx y la eficiencia. Esta limitación tecnológica ha impulsado la investigación sobre diferentes conceptos de combustión que podrían mantener niveles de eficiencia similares a los de la combustión diésel controlando la formación de emisiones durante el proceso de combustión. Entre las diferentes soluciones que han ido apareciendo a lo largo de los años, se demostró que la Ignición por Compresión Controlada por Reactividad (RCCI por sus siglas en inglés) tiene una ventaja competitiva debido a su mejor controlabilidad, alta eficiencia y bajas emisiones de hollín y NOx. A pesar de sus beneficios, la extensión de RCCI a la operación de mapa completo ha indicado limitaciones importantes como gradientes de presión excesivos a alta carga, o alta inestabilidad de combustión y productos no quemados a baja carga del motor. Recientemente, se introdujo el concepto de combustión Dual-Mode Dual-Fuel (DMDF) como un intento de resolver los inconvenientes de la combustión RCCI manteniendo sus ventajas. Los resultados preliminares obtenidos en un motor mono cilíndrico (SCE por sus siglas en inglés) han demostrado que el DMDF puede alcanzar niveles de eficiencia similares a los de la combustión diésel convencional al mismo tiempo que favorece niveles ultra bajos de hollín y NOx. Si bien, los requisitos de la condición límite son difíciles de encajar en el rango operativo de sistema de gestión de aire, así como inconvenientes como el exceso de HC y CO que aún persiste en la zona de baja y media carga, lo que puede ser un desafío para el sistema de postratamiento. Además, las futuras regulaciones a corto plazo exigirán una reducción del 15 % de las emisiones de CO2 en 2025, reto que la literatura sugiere que no se logrará fácilmente solo mediante la optimización del proceso de combustión. En este sentido, esta tesis tiene como objetivo general la implementación del concepto de combustión DMDF en un motor multicilindro (MCE por sus siglas en inglés) bajo las restricciones de las aplicaciones reales para realizar una combustión limpia y eficiente en el mapa completo a la vez que brinda alternativas para reducir la concentración de HC y CO y lograr un ahorro de CO2. Este objetivo se logra mediante un primer extenso procedimiento de calibración experimental que tiene como objetivo trasladar las pautas de la combustión DMDF del SCE al MCE respetando los límites operativos del hardware original, evaluando su impacto en los resultados de combustión, rendimiento y emisiones en condiciones estacionarias y condiciones de ciclo de conducción. A continuación, se realizan estudios específicos para abordar el problema relacionado con la concentración excesiva de productos no quemados mediante investigaciones experimentales y simulaciones numéricas para comprender las consecuencias del uso de combustibles con diferente reactividad en la eficiencia de conversión del catalizador de oxidación original y su capacidad para lograr emisiones en el escape menores que el límite EUVI. Finalmente, se busca la reducción de CO2 a través de la modificación del combustible, investigando tanto la mejora del proceso de combustión como el equilibrio entre el ciclo de vida del combustible.
[CA] Històricament, el sector del transport de servei mitjà i pesat ha sigut desafiat per les regulacions d'emissions que s'han imposat al llarg dels anys, la qual cosa va requerir intensificar l'esforç d'investigació amb l'objectiu d'avançar en el desenvolupament tecnològic per a oferir una opció que complisca amb les normes a un preu similar per al propietari. No obstant això, la recent introducció de la normativa EUVI ha requerit l'addició d'un complex sistema de postractament, agregant nous costos fixos al producte, així com costos operatius amb el consum d'urea. Aquest avanç va ser necessari a causa de la limitació de la combustió dièsel convencional que no pot desacoblar les altes emissions de NOx i l'eficiència. Aquesta limitació tecnològica ha impulsat la investigació sobre diferents conceptes de combustió que podrien mantindre nivells d'eficiència similars als de la combustió dièsel controlant la formació d'emissions durant el procés de combustió. Entre les diferents solucions que han anat apareixent al llarg dels anys, es va demostrar que la Ignició per Compressió Controlada per Reactivitat (RCCI per les seues sigles en anglés) té un avantatge competitiu a causa de la seua millor controlabilitat, alta eficiència i baixes emissions de sutge i NOx. Malgrat els seus beneficis, l'extensió del RCCI a l'operació de mapa complet ha indicat limitacions importants com a gradients de pressió excessius a alta càrrega, o alta inestabilitat de combustió i productes no cremats a baixa càrrega del motor. Recentment, es va introduir el concepte de combustió Dual-Mode Dual-Fuel (DMDF) com un intent de resoldre els inconvenients de la combustió RCCI mantenint els seus avantatges. Els resultats preliminars obtinguts en un motor mono-cilíndric (SCE per les seues sigles en anglés) han demostrat que el DMDF pot aconseguir nivells d'eficiència similars als de la combustió dièsel convencional al mateix temps que afavoreix nivells ultra baixos de sutge i NOx. Si bé, els requisits de la condició límit són difícils d'encaixar en el rang operatiu de sistema de gestió d'aire, així com inconvenients com l'excés de HC i CO que encara persisteix en la zona de baixa i mitja càrrega, la qual cosa pot ser un desafiament per al sistema de postractament. A més, les futures regulacions a curt termini exigiran una reducció del 15% de les emissions de CO¿ en 2025, repte que la literatura suggereix que no s'aconseguirà fàcilment només mitjançant l'optimització del procés de combustió. En aquest sentit, aquesta tesi té com a objectiu general la implementació del concepte de combustió DMDF en un motor multi-cilindre (MCE per les seues sigles en anglés) sota les restriccions de les aplicacions reals per a realitzar una combustió neta i eficient en el mapa complet alhora que brinda alternatives per a reduir la concentració de HC i CO i aconseguir un estalvi de CO¿. Aquest objectiu s'aconsegueix mitjançant un primer extens procediment de calibratge experimental que té com a objectiu traslladar les pautes de la combustió DMDF del SCE al MCE respectant els límits operatius del motor original, avaluant el seu impacte en els resultats de combustió, rendiment i emissions en condicions estacionàries i condicions de cicle de conducció. A continuació, es realitzen estudis específics per a abordar el problema relacionat amb la concentració excessiva de productes no cremats mitjançant investigacions experimentals i simulacions numèriques per a comprendre les conseqüències de l'ús de combustibles amb diferent reactivitat en l'eficiència de conversió del catalitzador d'oxidació original i la seua capacitat per a aconseguir emissions al tub d'escapament menors que el límit EUVI. Finalment, es busca la reducció de CO2 a través de la modificació del combustible, investigant tant la millora del procés de combustió com l'equilibri entre el cicle de vida del combustible.
[EN] The medium and heavy-duty transport sector was historically challenged by the emissions regulations that were imposed along the years, requiring to step up the research effort aiming at advancing the product development to deliver a normative compliant option at similar price to the owner. Nonetheless, the recent introduction of EUVI normative have required the addition of a complex aftertreatment system, adding new fixed costs to the product as well as operational costs with the urea consumption. This breakthrough was required due to the limitation of the conventional diesel combustion which cannot decouple high NOx emissions and efficiency. This technological limitation has boosted the investigation on different combustion concepts that could maintain similar efficiency levels than the diesel combustion while controlling the emission formation during the combustion process. Among the different solutions that have appeared along the years, Reactivity Controlled Compression Ignition (RCCI) was demonstrated to have a competitive edge due to its better controllability, high efficiency and low soot and NOx emissions. Despite the benefits, the extension of RCCI to full map operation has presented significant limitations, as excessive pressure gradients at high load and high combustion instability and unburned products at low engine load. Recently, Dual-Mode Dual-Fuel (DMDF) combustion concept was introduced as an attempt of solving the drawbacks of the RCCI combustion while maintaining its advantages. The preliminary results obtained in single cylinder engine (SCE) have evidenced that DMDF can achieves similar efficiency levels than those from conventional diesel combustion while promoting ultra-low levels of soot and NOx. Albeit, the boundary condition requirements are hard to fit in the operating range of commercial air management system as well as drawbacks like excessive HC and CO that still persists from low to medium load, which can be a challenge for the aftertreatment system. Moreover, short-term future regulations will demand a 15 % reduction of CO2 emissions in 2025 which was proven in the literature to not be easily achieved only by combustion process optimization. In this sense, this thesis has as general objective the implementation of the DMDF combustion concept in a multi-cylinder engine (MCE) under the restrictions of real applications to realize clean and efficient combustion in the complete map while providing alternatives to reduce the HC and CO concentration and accomplish CO2 savings. This objective is accomplished by means of a first extensive experimental calibration procedure aiming to translate the guidelines of the DMDF combustion from the SCE to the MCE while respecting the operating limits of the stock hardware, assessing its impacts on combustion, performance, and emission results under steady and driving cycle conditions. Next, dedicated studies are performed to address the issue related with the excessive concentration of unburned products by means of experimental investigations and numerical simulations, to understand the consequences of using fuels with different reactivity in the stock oxidation catalyst conversion efficiency and its ability in achieving EUVI tailpipe emissions. Finally, CO2 reduction is explored through fuel modification, investigating both combustion process improvement and well-to-wheel balance as paths to realize CO2 abatement.
This doctoral thesis has been partially supported by the Spanish Ministry of Science Innovation and Universities under the grant:"Ayudas para contratos predoctorales para la formación de doctores" (PRE2018-085043)
Lago Sari, R. (2021). Dual Mode Dual Fuel Combustion: Implementation on a Real Medium Duty Engine Platform [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/165366
TESIS

Cette thèse traite le problème du contrôle de combustion des moteurs automobiles à combustion interne. On propose une méthode complétant les stratégies de contrôle existantes reposant sur des cartographies calibrées en régime stabilisé. Pendant les transitoires, cette méthode de contrôle utilise des variations de la variable rapide (moment d'allumage ou d'injection) pour compenser les déviations des conditions initiales des variables thermodynamiques dans les cylindres (variables lentes) par rapport à leurs valeurs optimales. Les corrections sont calculées grâce à une analyse de sensibilité d'un modèle de combustion. La stratégie de contrôle en résultant est utilisable en temps réel et, de manière intéressante, ne requiert ni capteur additionnel, ni phase de calibration supplémentaire. Plusieurs cas d'´etudes sont exposés: un moteur essence, un moteur Diesel dilué dans un cadre d'injection monopulse puis multipulse. Des simulations ainsi que des résultats experimentaux obtenus sur banc moteurs et véhicules mettent en valeur l'interêt de la méthode proposée.

Cycle to cycle variations in combustion and turbulence characteristics in a swirling flow were measured in a cylindrical vessel. The vessel was charged by rapid tangential injection using a shrouded valve for two valve lifts (7 mm and 12 mm). A premixed lean mixture of propane and air ($\phi$ = 0.8) was ignited at quarter radius from the center. Pressure rise as a function of time was measured using a pressure transducer. Mean flow, turbulence intensity and Taylor microscale were estimated by statistical analysis of a single hot wire anemometer signal using ensemble averaging and cyclic analysis. Results obtained indicate that changing the valve lift changes turbulence characteristics at mid-radius. However, turbulence characteristics at quarter radius from center and quarter radius to wall were found to be independent of valve lift. Mean time, standard deviation of mean time delay and Taylor microscale were estimated using combustion pressure traces. Results indicate that the mean time and the standard deviation ignition are weak functions of mean flow and turbulence intensity and strong functions of the Taylor microscale as implied by the Tennekes model. Cyclic variations at ignition were observed to contribute the most to cyclic variations.

The research work reported herein addresses the problem of mathematical modelling of fluid flow and combustion in internal combustion engines. In particular, the investigation of three topics that constitute prime sources of uncertainty, in current numerical models, namely turbulence modelling, inaccuracies in the solution procedure specific to moving grids, and combustion modelling. Two and three-dimensional computations of the in-cylinder turbulent flow in a diesel engine are described first, with emphasis on the modifications made to the standard k- model of turbulence to account for rapid compression/expansion, and on the k-W model also used in the computations. It is concluded that the standard k- model may lead to poor predictions when used for internal combustion engine simulations, and that the modified model leads to more reasonable length-scale distributions, improving significantly the overall agreement of velocity predictions with experiment. It is also demonstrated that the k-W model provides better turbulence predictions than the unmodified k- model for the cases considered. The moving boundary within a reciprocating engine poses the problem that as it moves toward the cylinder head it compresses the computational grid cells, creating large aspect ratios that can adversely affect the numerical accuracy and convergence. A conservative scheme has therefore been devised that allows for the removal or addition of grid cells during the simulation, so as to maintain reasonable aspect ratios. It is concluded that with the proposed scheme convergence is obtained within fewer iterations, computational cost is therefore reduced, and that the results are generally in better agreement with experimental data. The third part of this study investigates and compares the performance of the two most commonly used combustion models (the eddy-break-up and the Arrhenius models) and proposes a new formulation of a flame-front model. Calculations have been performed for a one-dimensional test case and for a representative spark-ignition engine in order to determine the grid and time step requirements for numerical accuracy, the sensitivity of results to empirical input and the physical realism of the predictions by comparison with experimental data. It has been found for the cases considered that neither the eddy-break-up nor the Arrhenius models are appropriate for predicting engine combustion. The Arrhenius model does not represent well the combustion process for the cases considered. The eddy-break-up model is not capable of predicting the observed flame front, and the empirical constants in the model require extensive tuning to obtain predictions that match experiments. The flame-front model however, in spite of many simplifications, produces much more realistic flame-front propagation and the empirical input of the model, i.e. the flame speed, can in principle be obtained by other means other than ad-hoc tuning. It is concluded that the flame-front model requires refinement, but for the cases considered, it provides the basis of a very promising combustion model for predicting premixed combustion in engines.

This thesis concerns numerical investigations of the combustion behaviour of various combustion regimes. The simulations are based on modelling the flow of the fuels in the combustion devices. Computational fluid dynamics (CFD) modelling and analysis were used in three different works. FLUENT software, which is based on the finite volume method, is used to carry out all the simulations. Firstly, numerical simulations were carried out to investigate the turbulent non-premixed combustion of a mixture of methane (CH4) 90% and nitrogen (N2) 10%, on volume basis, inside an axis-symmetric cylindrical chamber (base case). The objective is to investigate the turbulent flow, flame propagation, temperature and species concentration and evaluate the effects of different reduced reaction mechanisms of methane and the influence of various turbulence models on them. The turbulent combustion inside the chamber occurs under a condition for which the equivalence ratio (ɸ) of 1.04 is used. Instead of using fully detailed chemical kinetics schemes and to reduce the computational costs, four global reduced chemical kinetics mechanisms are employed in the combustion model and they are named as (M-I, M-II, M-III and M-IV). The simulations, in which M-I is used, are performed by Renolds-Averaged Navier Stokes (RANS) approach with the three two-equation k-ϵ closures (standard, realizable and RNG) employed to model the turbulent flow. Concerning the chemistry-turbulence interaction, the finite-rate/eddy-dissipation model (FR/ED) is used. The first two of the above kinetics schemes are two-step reaction mechanisms and the other two are first-step and five-step reaction mechanisms, respectively. The latter one is used to assess the capability of FR/ED model for modeling such a mechanism. The influence of thermal radiation is also investigated by means of P-1 model. The standard k-ϵ model and realizable k-ϵ model are also modified and used in the course of simulations. Moreover, the reaction mechanism (M-II) is optimized to see its effects on the combustion process. The results are compared with the experimental data and gave good agreement. It is found that the best results are generally obtained using the modified standard k-ϵ model. Moreover, the simulation results using the realizable turbulence model are found to have large discrepancies compared to the experimental data. In comparison with the experimental data, the optimization of M-II (Em = 1.6x108 J/kmol) is found to have good results in terms of temperature. Increasing the dilution of the fuel by N2 is investigated. Four cases, CH4 (85, 80, 75 and 100%) on volume basis, are performed. The latter one concerns the combustion of pure methane. The results are compared with the base case and found that the base case is the best compromise to obtain the highest temperature in inside the chamber. Secondly, an axis-symmetric combustion model based on the Euler-Lagrange approach was formulated to model the combustion of pulverized bituminous coal. Three cases with three different char oxidation models are presented. In case1 and case 2, the diffusion and kinetic/diffusion global char models are used, respectively. Whereas, to model char oxidation in case 3, the multi-surface reactions model is used. The volatiles released during the devolatilization stage, which is modelled using a single kinetic rate model, are treated as one species and its combustion is modelled using the FR/ED model. The predicted results have good agreement with the available experimental data and the best predictions are obtained from case 3. The results showed that the combustion inside the reactor was affected by the particulate size. It is found that the burnout of the particle with the diameter of 16 μm at the exit of the furnace is 100%. Whereas, the burnout of the particles with diameters of 84, 154, 222, 291 μm is approximately 86, 75, 35, 33, 29 %, respectively. A number of simulations were carried out to find the best values of parameters suitable for predicting NOx pollutants. The chemical formation and reduction rates of NO are calculated by post-processing data obtained from the previously reacting flow simulations. This method is computationally efficient. For volatile-N is assumed that the nitrogen is released via the intermediates HCN and NH3. For char-N path way, it is assumed that all the nitrogen is released via the intermediate HCN. It is found that the assumption of the partition of volatile-N by 52% HCN, 10% NH3 and 38% NO has the best agreement with the experiment data. The influence of different operating parameters on the combustion process and NOx formation was investigated as well. For the same operating conditions and the same particles size distribution, the combustion of pulverised biomass alone, represented by straw, was investigated followed by the investigation of its firing with coal. The former one show a promising results under such operating conditions. It is found that the temperature distribution when burning straw particles is nearly the same as that obtained from burning coal because all the saw particles are completely burned out inside the furnace when compared with the coal particles. The NOx model, in which the ratio of HCN to NH3 is suggested to be for the partitioning of volatile-N, shows that NO formation is reduced by approximately 20% for case I and 26% for case II at the exit of the furnace when compared to coal. For the latter one the results of co-firing blends of coal with 10, 20, 30 and 40% share of biomass are presented and show the influence of co-firing on the combustion process. Co-firing of straw with coal enhances the combustion behaviour and increases the burnout of coal particles compared to that of coal firing only. It is seen that the burnout of the particles with sizes 84, 154 and 222 μm is remarkably increased. On the other hand, the burnout of the other two particles (291 μm and 360 μm) does not show a great change. The share of 10% of straw shows the highest temperature. Thirdly, Two-phase computational modelling based on the Euler–Euler was developed to investigate the heterogeneous combustion processes of carbon particles inside a newly designed combustion chamber. A transient simulation was carried out for a small amount of carbon powder situated in a cup which was located at the centre of the combustion chamber. A heat source was provided to initiate the combustion with the air supplied by three injection nozzles. The combustion simulations are performed for particle sizes with different diameters (0.5mm, 1mm, 1.5mm, 2mm, 2.5mm and 3mm). The particle of 1mm diameter is assigned to the baseline case. The results show that the combustion is sustained in the chamber, as evidenced by the flame temperature. It is shown that, up to a time of 0.55 s, the higher temperature was gained from the case of carbon particles with the diameter of 3 mm and burning the carbon particles with a diameter of 0.5 mm produces lower temperature. This may be attributed to the residence time of the carbon particles and the design of the burner. The larger particles stay longer than the smaller ones inside the chamber. This may due to the reason that the smaller particles follow the streamlines of the continuous phase and increasing the particle size leads to that the larger particles may deviate from the streamlines of the continuous phase and their slip velocity may increase resulting in enhancing convective transports of heat and species concentrations. The influence of the chamber design was also investigated. The height of the chamber is doubled. With the same operating conditions, up to a time of approximately 0.55 s, it is found that burning carbon particles in the doubled height chamber produces higher temperature than the baseline case (particle diameter 1 mm) and after this time the opposite takes place. Most of the other cases do so.

A mathematical model representing the dynamic behaviour observed at the actual catalytic incineration plant at Perstorp was derived. The model equations for the two main process units, the heat exchanger and the incinerator, were based on the lumped systems approach in order to avoid using partial differential equations. The model was written in Matlab and implemented in Simulink using s-functions for the dynamic study. By analyzing the dynamic data from the actual plant, it was discovered that the possible source of the ocassional large temperature variations in the incinerator is the periodic variations in the inlet compositions, amplified the overly agressive air valve controller combined with a significant dead time. This results in oscillations due to overshooting. This behaviour was successfully reproduced using the derived model. Two possibilities for improving the control performance were investigated, both using already existing sensors and actuators. The first control improvement involved reducing the proportional gain according to the SIMC tuning rules for PI controllers. This resulted in a significant reduction in the amplitude of the oscillations in the temperatures throughout the reactor, and thus a more stable performance. Finally, cascade control was implemented using the faster-responding catalyst bed temperature for the inner loop, and the reactor outlet temperature for the outer loop. This provided the most optimal results with the best disturbance rejection as it is able to compensate for the disturbance before it is detected in the outlet temperature.

This thesis presents fundamental research about the combustion gas products and solid phase residue of switch grass combustion. To identify the compounds released during the combustion phase, tests were conducted using a Thermogravimetric Analyzer (TGA) coupled to a Fourier Transform Infrared Spectrometer. These test revealed that aromatic compounds as well as carbon dioxide and water were released.
High Pressure Liquid Chromatography (HPLC) and GCMS/GCFID were also used to identify and semi-quantify polycyclic aromatic hydrocarbons (PAH) and benzene derivatives. From these analyses it was concluded that thermal synthesis was not occurring within an oxidative environment and as such no PAHs were found.
Finally an infrared microscope and a scanning electron microscope were used to study functional group, morphology and metal content change resulting from the combustion process.
This research provided information about the combustion mechanism of switch grass and laid the foundation for pilot-scale testing.

In order to increase the validity of numerical models of the detonation of heterogeneous titanium explosives, experimental results are needed. The combustino of titanium is studied using two experimental techniques. The first technique is the study of the burn time for a single particle over a wide range of initial diameters while altering the oxygen concentration. To accomplish this a new flat flame burner to study particle burn time has been designed. Luminous tracks caused by the light emitted by the combustion of the particles are analyzed and burn time is inferred. Burn time in air and in an oxygen enriched atmosphere were determined. A second experiment involves the study of large scale detonation of heterogeneous charges. The charges are filled with nitromethane and a packed bed of titanium particles. The titanium particles varied in morphology and particles size. A critical charge diameter for charge ignition (CDPI) was found for irregularly shaped particles but was not found for spherical particles.
Pour augmenter la validit des modles numriques sur dtonation d'explosifs htrognes contenants du titane , des rsultats exprimentaux sont ncessaires. Le combustino de titane est tudi en utilisant deux techniques exprimentales. La premire technique est l'tude du temps brle pour une particule sur une large gamme de diamtres initiaux en changeant la concentration d'oxygne. Pour l'accomplir un nouveau brleur de flamme plat pour tudier la particule brle le temps a t conu. Les empreintes lumineuses provoques par la lumire mise par la combustion des particules sont analyses et brlent le temps est dduit. Brlez le temps dans l'air et dans l'atmosphre enrichie d'un oxygne ont t dtermins. Une deuxime exprience implique l'tude de grande dtonation d'chelle de charges htrognes. Les charges sont remplies de nitromethane et un lit emball de particules de titane. Les particules de titane variaient dans la grandeur de particules et la morphologie. Un diamtre de charge critique pour l'ignition de charge (CDPI) a t trouv pour les particules irrgulirement en forme de, mais n'a pas t trouv pour pour les particules irrgulirement en forme de mais n'a pas t trouv pour les particules sphriques.

The objective of this work is to better understand the operation of Submerged Flame Burners, commonly known as Submerged Combustion Burners. Two main aspects require consideration, namely: practical applications of the technology in industry; secondly, theoretical modelling of the flame behaviour within the Submerged Combustion Burner in order to ensure flame stability in the burner and hence heat transfer efficiency and reliable operation. The current status of the Submerged Combustion Technology has been reviewed, detailing the separation equipment items that, overall, make up an industrial Submerged Combustion package. The functionality of the different items has been considered in the context of the primary objective of the equipment, i.e. the establishment of a stable flame within the Submerged Burner. Cases detailing specific instances of the application of Submerged Combustion technology in industry are presented in order that practical aspects of the operation of such units can be better appreciated. The flame system within the Submerged Burner has been modelled using a commercially available Computational Fluid Dynamic Package. A simplified model was used in order to represent the processes occurring within the burner for the combustion of methane with air as the oxidant. The K- turbulence model was used for the prediction of turbulence behaviour within the system. The results of the Computational Fluid Dynamic modelling cover a range of operating parameter values that might be expected to be encountered in industrial applications of Submerged Combustion. The results of the theoretical analysis have been considered in terms of the significance to the design and operation of industrial Submerged Combustion units. The discussions of the practical application of the technology have also led to recommendations being made in respect of the design of the ancillary equipment associated with the Submerged Combustion Burners. The observations made and conclusions drawn in this work provide a better understanding of the processes involved with the production of a stable flame within a Submerged Combustion Burner. Recommendations have been made for future work building on the work reported here.

Current four stroke engine research objectives focus on increasing part load thermal efficiency while reducing exhaust emissions. Methods currently employed to achieve this are homogeneous charge lean burn technology, stratified charge lean burn technology and the use of alternative fuels. Of all possible alternative fuels hydrogen is viewed by many as being, ultimately, the fuel of the future. Methanol is regarded as being a likely transitional fuel between the current petroleum transport fuels and hydrogen. Hydrogen is known to be effective in extending the operating lean limit of an engine when used in small amounts in conjunction with conventional fuels. This thesis presents the results of an investigation into the use of hydrogen as a supplementary fuel in a methanol fuelled Ricardo E6 engine. Three methods of introducing supplementary hydrogen into the engine were investigated: Untimed manifold injection, early direct injection and injection through a modified spark-plug. Suitable injection systems were designed and tested on the Ricardo E6 engine. An engine management system, data acquisition system and post processing software were developed to enable data to be acquired and analyzed. The direct injection systems were the subject of schlieren visualization investigations of injected gas distribution to improve performance and elucidate engine related phenomena. Results detailing the effects of hydrogen supplementation on the engine performance, combustion and exhaust gas emissions are presented and discussed. The early direct injection of hydrogen through a dedicated cylinder head tapping proved to be the least effective method of introducing supplementary hydrogen in the Ricardo E6 engine. The position of the injector diametrically opposite the spark-plug coupled with low levels of bulk mixture motion in the cylinder resulted in the formation of an inversely stratified charge (lean near spark-plug) even when injection commenced very early in the compression stroke. The inversely stratified charge resulted in a given level of hydrogen supplementation not being as effective as was the case in the other two fuelling systems. The homogeneous air/fuel mixture formed by the untimed manifold injection of hydrogen was found to have a beneficial effect on both the combustion and emissions of the engine especially in lean air/fuel mixtures. Introducing supplementary hydrogen into the inlet manifold of the engine was however found to reduce the volumetric efficiency of the engine, reducing the level of output power produced by the engine. Injecting hydrogen through a modified spark-plug was found to be the most effective way of introducing supplementary hydrogen. The improved performance of the modified spark-plug system over the other two systems was found to be due to the presence of a localized hydrogen/air mixture at the spark-plug electrodes at the time of ignition. Extension of the lean limit past that possible with methanol alone was demonstrated whilst maintaining both a high thermal efficiency and low indicated specific unburned hydrocarbon emissions. Direct injection of supplementary hydrogen into the combustion chamber, either with the aim of forming a homogeneous charge, or forming a richer air/fuel mixture in the vicinity of the spark-plug without the use of a pre-chamber, has not been reported previously in the published literature. The investigation of both of these fuelling methods is presented in this thesis and constitutes an original contribution to the field of engine research.

A novel interconnected fluidized bed (IFB) reactor with a bypass line for chemical looping combustion (CLC) has been developed to overcome the problem of short residence time of oxygen carrier in the air reactor. A comprehensive hydrodynamic study was carried out on the cold-flow model of the proposed reactor. Detailed mapping of the operating conditions for the reactor system was studied. Pressure transducers were applied to investigate the pressure loops and the cross-sectional average solids hold-up along the air reactor. Solids circulation flux between the two reactors was measured using butterfly valves by estimating the time interval for collecting a given volume of solids. Helium was used as gas tracer for gas leakage measurement. The experiments examined the gas leakage from air reactor to fuel reactor, from fuel reactor to air reactor, from loop-seals to fuel reactor and from fuel reactor to the cyclone. For scaling consideration, the cold-flow reactor was operated with fluidizing gas mixture of helium and air to simulate the hydrodynamics of the hot unit. The effect of density ratio of solids to gas on the solids circulation flux, pressure loops and voidage distribution along the air reactor was investigated. The connection between cold unit and hot unit is achieved by applying a scaling law. It can be stated that the cold-flow model operated with fluidizing gas mixture of 96 vol% helium and 4 vol% air can be used to simulate the hydrodynamics of an atmospheric CLC hot unit. A comprehensive model for the investigation of the reactor is introduced by combining fluidization properties and a particle population balance for calculation of the bed particle conversion, considering the chemical reaction of a single particle. The dimensionless parameters, Mrfuel and Mrair, which represent the mass ratio of input oxidized-particles to the input fuel in unit time for the fuel reactor and the mass ratio of reduced-particles to the input oxygen in unit time for the air reactor, respectively, are introduced. The model shows that Mrfuel should be more than 50 for achieving fuel conversion of 90% in the fuel reactor and Mrair should be more than 60 for achieving oxygen conversion of 85% in the air reactor. A procedure for optimizing the performance of the atmospheric CLC reactor is developed. The modeling analysis indicated that the optimum operating condition of an atmospheric CLC reactor hot unit should be chosen as follows: fuel capacity is 80 kW, Ua0=6.6 m/s, Uf0= 0.076 m/s, UA1=4Umf, UA2=1Umf, and the temperature in air reactor is 1223 K and in fuel reactor is 1173 K.

The exhaust valve system of combustion engines experiences a very complex contact situation of frequent impact involving micro sliding, high and varying temperatures, complex exhaust gas chemistry and possible particulates, etc. In addition, the tribological situation in the exhaust valve system is expected to become even worse due to strict future emission regulations, which will require enhanced combustion and cleaner fuels. This will substantially reduce the formation of combustion products that might ease the contact conditions by forming tribofilms on the contacting surfaces. The lack of protective films is expected to result in increased wear of the contact surfaces. The aim of the work presented in this thesis has been to increase the tribological understanding of the valves. The wear that takes place in the valve sealing interface and how the change in operating conditions affects it have been studied. Such understanding will facilitate the development of future valve designs. A test rig has been developed. It has a unique design with the ability to insert ppm amounts of media into a hot air flow, in order to simulate different environmental changes, e.g. varying amount and composition of combustion residue particles. PVD coated valves were evaluated in a dry atmosphere. It was concluded that although some of the coatings showed potential, the substrate could not support the thin, hard coatings. Investigations with an addition of different oils have been performed. Fully formulated oils proved to build up a protective oil residue tribofilm. This tribofilm has been in-depth analysed and proved to have similar composition and appearance as tribofilms found on low wear field tested valves. With a non-additivated oil, wear particles from the valve seat insert formed a wear particle tribofilm on top of the valve sealing surface. Without any oil the surfaces showed severe wear with wear particles spread over the surfaces. The results presented give a hint about what to be expected in the future, when the engine oils are replaced with ash less oils with reduced amount of additives and the consumed amount of oil within the cylinders are reduced.

While oxy-fuel combustion research is developing and large scale projects are proceeding, little information is available on oxy-biomass combustion and cocombustion with coal. To address this knowledge gap, this research conducted has involved comprehensive laboratory based fundamental investigation of biomass firing and co-firing under oxy-fuel conditions and compared it to conventional air firing conditions. First, TGA was employed to understand the fundamental behaviour of biomass devolatilisation, char combustion and nitrogen partitioning between volatiles and residual char. The results revealed that C02 did not have effect on the devolatilisation of sawdust at temperatures below 1100 grad. C due to higher mass transfer resistance of primary volatiles in C02 than in N2 at low temperatures. Secondly,. by optimising the devolatilisation procedure in a combustion system that simulates closely to an industrial scale such as drop tube furnace (DTF), the devolatilisation/char combustion characteristics of sawdust was investigated. The effect of CO2 on volatile yields, nitrogen partitioning and char burnout were all significant in relation to N2• While coal combustion additives are being used to enhance coal burnout, this study observed improved coal char burnout when biomass char was co-fired with coal char, again a faster burnout was observed in oxy-firing condition compared to air firing. This was due to the catalytic effect of biomass inherent alkali and alkaline earth metals. Similarly, improved volatile yields were observed during codevolatilisation. These fundamental results have provided insight into oxybiomass' firing and co-firing and the data can be used in appropriate CFD modelling to aid the design of oxy-biomass co-firing burners.

[EN] The research work presented on this thesis has been performed in the framework of the development and optimization of the combustion system of a novel two-stroke CI engine, with a scavenging configuration through poppet-valves, which has been specifically designed for a light-duty vehicle application. The main objective of this investigation is to improve the existing understanding about two-stroke poppet-valves engines, and assess the main relationships between the gas exchange and combustion processes in this type of architecture, with the aim of evaluating their impact on the exhaust emissions formation processes and on final engine efficiency. Then, the performance of this two-stroke engine is going to be optimized while operating in conventional diesel mixing-controlled controlled combustion; and in a second step, two advanced premixed combustion concepts will be evaluated to identify their potential for decreasing NOx and soot emissions compared to CDC as well as its main technological limitations. The methodology proposed on this thesis combines both a theoretical and experimental approach, that allows maximizing the available information about the basic phenomena involved in the various processes under study, while also keeping an efficient optimization approach to reduce as much as possible the number of necessary experimental tests. Additionally, to analyze in detail the physical relationships between the local cylinder gas conditions (such as the oxygen concentration, the combustion temperature and the equivalence ratio) and the formation of exhaust emissions, particularly NOx and soot, it was necessary to develop and setup different theoretical tools to complement and support the experimentally measured trends. To achieve these objectives, the research work has been divided in two sequential stages: first, the conventional diesel combustion is studied and optimized, based on a proper combination of engine settings that have a strong influence over the characteristics of the mixing-controlled combustion; and in a second step, two advanced combustion concepts are implemented and analyzed, the highly-premixed combustion (HPC) of diesel and the partially premixed combustion (PPC) using a fuel with higher resistance to autoignition (in this case it has been used a RON95 gasoline). In this phase of the research, special emphasis has been made to the gasoline PPC concept, since this combustion mode showed the highest potential and most promising results during the initial implementation studies. Accordingly, the last stage of the research was mainly focused on the detailed study of the effect of different injection settings over the characteristics of the gasoline PPC concept. Finally, the main results obtained with the gasoline PPC concept have been compared against the optimized points found in CDC, in regards to the final exhaust emissions levels, specific fuel consumption and indicated efficiency.
[ES] El trabajo de investigación presentado en esta tesis doctoral está enmarcado en el desarrollo y optimización del sistema de combustión de un novedoso motor de dos tiempos de encendido por compresión, que presenta una arquitectura de barrido por válvulas en culata, y que ha sido diseñado para aplicaciones de automoción dentro de la gama de coches compactos. El objetivo principal de esta investigación ha consistido en mejorar el conocimiento existente sobre los motores dos tiempos con arquitectura de barrido por válvulas, y a la vez identificar los principales vínculos entre los procesos de renovación de la carga y de combustión, con el fin de cuantificar su impacto sobre la formación de emisiones contaminantes y el rendimiento térmico del motor. Adicionalmente, se desea optimizar las prestaciones de este motor de dos tiempos operando con el proceso de combustión diésel convencional controlada por mezcla, así como evaluar el potencial de distintos conceptos avanzados de combustión de baja temperatura con fase de premezcla extendida, con el fin de reducir los niveles de emisiones contaminantes y mejorar el consumo específico de combustible del motor. La metodología utilizada en esta tesis ha sido concebida combinando un enfoque teórico-experimental, que permite maximizar la información que se puede obtener acerca de los fenómenos físicos involucrados en los diferentes procesos objeto de estudio, y a la vez conservar un enfoque de optimización eficiente reduciendo en la medida de lo posible el número de ensayos experimentales requeridos. Con la finalidad de analizar en detalle la relación que existe entre las condiciones en el cilindro (como lo es la concentración de oxígeno, la temperatura de combustión y el dosado local) y el proceso de formación de emisiones contaminantes, especialmente de NOx y hollín, se desarrollaron y utilizaron distintas herramientas teóricas para complementar y sustentar los comportamientos y tendencias observadas mediante los ensayos experimentales, tanto para el modo de combustión diésel convencional como para los conceptos avanzados de combustión. Para la consecución de dichos objetivos se ha seguido una estructura secuencial en la cual el trabajo de investigación ha sido desarrollado en dos grandes bloques: primero, se analizó y optimizó el proceso de combustión diésel convencional, mediante la combinación adecuada de parámetros de operación del motor que modifican apreciablemente las características del proceso de combustión controlada por mezcla; y segundo, se logró implementar y evaluar el desempeño de dos conceptos avanzados de combustión, específicamente el modo combustión altamente premezclado de tipo HPC utilizando diésel como combustible (acrónimo de "Highly-Premixed Combustion") y el modo de combustión parcialmente premezclada de tipo PPC ("Partially Premixed Combustion") utilizando un combustible con mayor resistencia a la auto-ignición (en este caso se utilizó gasolina de octanaje 95). En esta segunda fase, se hizo énfasis en el análisis del concepto de combustión PPC con gasolina, ya que este arrojó los resultados más prometedores durante la fase inicial de implementación. Consecuentemente, la última etapa de la investigación se centró en el estudio detallado del efecto de distintos parámetros de inyección sobre las características del proceso de combustión de tipo PPC. Finalmente, se ha comparado críticamente dicha operación en modo PPC con los resultados obtenidos operando con el modo de combustión diésel convencional, en cuanto al nivel final de emisiones contaminantes, al consumo de combustible y rendimiento indicado y al desempeño general del motor.
[CAT] El treball d'investigació presentat en esta tesi està emmarcat en el desenvolupament i optimització del sistema de combustió d'un nou motor dos temps d'encesa per compressió, amb configuració d'escombratge per vàlvules, i que ha estat dissenyat per a aplicacions d'automoció dins de la gamma de cotxes compactes. L'objectiu principal d'esta investigació ha consistit a millorar el coneixement existent sobre els motors dos temps amb configuració d'escombratge per vàlvules, així com també identificar els principals vincles entre els processos de renovació de la càrrega i de combustió, a fi de quantificar el seu impacte sobre la formació d'emissions contaminants i el rendiment tèrmic del motor. Addicionalment, es desitja optimitzar les prestacions d'este nou motor operant amb el mode convencional de combustió dièsel per difusió, així com avaluar el potencial de noves maneres de combustió de baixa temperatura amb fase de premescla extesa, per a controlar el nivell d'emissions i el consum de combustible. La metodologia utilitzada en esta tesi s'ha plantejat des d'un punt de vista teóric experimental, que permet maximitzar la informació que es pot obtindre sobre els fenòmens basics involucrats en els diferents processos objecte d'estudi, i al mateix temps conservar un enfocament d'optimització eficient reduïnt en la mesura del possible el nombre d'proves experimentals requerit. Amb la finalitat d'analitzar en detall la relació que existeix entre les condicions en el cilindre (com ho és la concentració d'oxigen, la temperatura de combustió i el dosatge local) i el procés de formació d'emissions contaminants, especialment de NOx i sutge, es van desenvolupar i van utilitzar distintes eines teòriques per a complementar i sustentar els comportaments i tendències observades per mitjà dels assajos experimentals, tant per al mode de combustió dièsel convencional com per als conceptes avançats de combustió. Per a abordar eixe objectiu, s'ha seguit una estructura seqüencial, en la qual el treball d'investigació s'ha desenvolupat en en dos grans blocs: en primer lloc, es va analitzar i va optimitzar el procés de combustió dièsel convencional, per mitjà de la combinació adequada de paràmetres d'operació del motor que modifiquen apreciablement les característiques del procés de combustió controlada per difusió; i en segon lloc, es va aconseguir implementar i avaluar les prestacions de dos conceptes avançats de combustió de baixa temperatura premesclats, específicament el mode combustió altament premesclat HPC (acrònim de "Highly-Premixed Combustion") utilitzant dièsel com a combustible i el mode de combustió parcialment premesclat PPC ("Partially Premixed Combustion") utilitzant un combustible amb major resistència a l'autoignició (en aquest cas s'ha utilitzat gasolina d'octanatge 95). En esta segona etapa, es va fer èmfasi en l'anàlisi del concepte de combustió PPC amb gasolina, ja que aquest va presentar els resultats més prometedors durant la fase inicial d'implementació. Conseqüentment, l'última etapa de la investigació es va centrar en l'estudi detallat de l'efecte de distints paràmetres d'injecció sobre les característiques del mode de combustió PPC. Finalment, s'ha comparat críticament la dita operació en mode PPC amb els resultats obtinguts operant amb el mode de combustió dièsel convencional, quant al nivell final d'emissions contaminants, al consum de combustible i rendiment indicat, i a les prestacions generals del motor.
De Lima Moradell, DA. (2016). Analysis of combustion concepts in a poppet valve two-stroke downsized compression ignition engine designed for passenger car applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68502
TESIS

Controlled auto-ignition (CAI) combustion in the gasoline engine has been extensively studied in the last several years due to its potential for simultaneous improvement in fuel consumption and exhaust emissions. At the same time, there has been increasing interest in the use of alternative fuels in order to reduce reliance on conventional fossil fuels. Therefore, this study has been carried out to investigate the effect of alcohol fuels on the combustion characteristics and in-cylinder processes of CAI combustion in a single cylinder gasoline engine. In order to study the effect of alcohol fuels, combustion characteristics were investigated by heat releases analysis in the first part. The combustion process was studied through flame structure and excited molecule by chemiluminescence imaging. Furthermore, in-cylinder gas composition was analysis by GC-MS to identify the auto-ignition reactions involved in the CAI combustion. In addition, the influence of spark-assisted ignition and injection timings were also studied. Alcohol fuels, in particular methanol, resulted in advanced auto-ignition and faster combustion than that of gasoline. In addition, their use could lead to substantially lower HC, NOX and CO exhaust emissions. Spark-assisted ignition assisted gasoline combustion by advancing ignition timing and initiating flame kernel at the centre of combustion chamber but it had marginal effect on alcohol fuels. Auto-ignition always took place at the perimeter of the chamber and occurred earlier with alcohol fuels. Fuel reforming reactions during the NVO period were observed and they had significant effect on alcohol combustion.

The combustion and emissions performance of fuel blends in modern combustion systems has been investigated with the intention of reducing emissions, improving efficiency and assessing the suitability of future automotive fuels. The combustion systems used in this study include Homogeneous Charge Compression Ignition (HCCI) and Direct Injection Spark Ignition (DISI). By adding a small quantity (10%) of diesel to gasoline, the HCCI combustion of this ‗Dieseline‘ mixture shows a 4% increase in the maximum and a 16% reduction in the minimum loads (IMEP) achievable. The NOX emissions are reduced, with greater than 30% savings seen for high engine loads. The addition of bio-fuels (ethanol and 2,5 di-methylfuran) to gasoline in HCCI combustion resulted in reduced ignitability giving rise to a 0.25 bar IMEP reduction of the maximum load. A 70% increase in NOX emissions is seen at an engine load of 3.5 bar IMEP. The addition of ethanol and to a lesser extent 2,5 di-methylfuran (DMF) to gasoline in DISI combustion shows increased combustion efficiency. The NOX emissions are reduced with ethanol, but are increased with the addition of DMF. At wide open throttle the bio-fuels show up to a 3 percentage point increase in efficiency through the use of more favourable spark timings brought about by the increased octane ratings and enthalpies of vaporisation. The PM emissions from DISI combustion can be reduced by up to 58% (mass) with the addition of ethanol. The soluble organic fraction forms a significant part of the total PM, particularly for the higher ethanol blends at wide open throttle. The addition of DMF however increases the total PM by up to 70% (mass) through the incomplete combustion of the ring structure.

Controlled Auto Ignition (CAI) combustion is a new combustion principle in internal combustion engines which has in recent years attracted increased attention. In CAI combustion, which combines features of spark ignition (SI) and compression ignition (CI) principles, air/fuel mixture is premixed, as in SI combustion and auto-ignited by piston compression as in CI combustion. Ignition is provided in multiple points, and thus the charge gives a simultaneous energy release. This results in uniform and simultaneous auto-ignition and chemical reaction throughout the whole charge without flame propagation. CAI combustion is controlled by the chemical kinetics of air/fuel mixture with no influence of turbulence. The CAI engine offers benefits in comparison to spark ignited and compression ignited engines in higher efficiency due to elimination of throttling losses at part and idle loads. There is a possibility to use high compression ratios since it is not knock limited, and in significant lower NOx emission (≈90%) and particle matter emission (≈50%), due to much lower combustion temperature and elimination of fuel rich zones. However, there are several disadvantages of the CAI engine that limits its practical application, such as high level of hydrocarbon and carbon monoxide emissions, high peak pressures, high rates of heat release, reduced power per displacement and difficulties in starting and controlling the engine. Controlling the operation over a wide range of loads and speeds is probably the major difficulty facing CAI engines. Controlling is actually two-components as it consists of auto-ignition phasing and controlling the rates of heat release. As CAI combustion is controlled by chemical kinetics of air/fuel mixture, the auto-ignition timing and heat release rate are determined by the charge properties such as temperature, composition and pressure. Therefore, changes in engine operational parameters or in types of fuel, results in changing of the charge properties. Hence, the auto-ignition timing and the rate of heat release. The Thesis investigates a controlled auto-ignition (CAI) combustion in internal combustion engines suitable for transport applications. The CAI engine environment is simulated by using a single-zone, homogeneous reactor model with a time variable volume according to the slider-crank relationship. The model uses detailed chemical kinetics and distributed heat transfer losses according to Woschini's correlation [1]. The fundamentals of chemical kinetics, and their relationship with combustion related problems are presented. The phenomenology and principles of auto-ignition process itself and its characteristics in CAI combustion are explained. The simulation model for representing CAI engine environment is established and calibrated with respect to the experimental data. The influences of fuel composition on the auto-ignition timing and the rate of heat release in a CAI engine are investigated. The effects of engine parameters on CAI combustion in different engine concepts fuelled with various fuels are analysed. The effects of internal gas recirculation (IEGR) in controlling the auto-ignition timing and the heat release rate in a CAI engine fuelled with different fuels are investigated. The effects of variable valve timings strategy on gas exchange process in CAI engine fuelled with commercial gasoline (95RON) are analysed.

In this thesis, a model that couples a reduced alkali kinetic mechanism for alkali sulphate formation during biomass combustion with an ash deposition model using computational fluid dynamics (CFD) techniques has been presented. Starting with a detailed gas-phase kinetic mechanism for the alkali chemistry, a systematic reduction procedure has been performed using a sensitivity analysis to reduce the reaction mechanism to a level that can be implemented into a CFD calculation. An ash deposition model that takes into consideration the ash-sticking probability and the condensation of potassium salts has been developed. The reduced mechanism and the deposition model developed are implemented into a CFD model to predict ash depositions in a 10 MWth biomass grate furnace. Also, a CFD model to predict the deposition rates for the co-combustion of coal with biomass has been developed. This deposition model is based on the combined sticking probabilities of the ash particle viscosity and the melting behaviour of the ash particles. A Numerical Slagging Index (NSI) is also employed to estimate the degree of the sintering of the deposits. Experimental data from the Entrained Flow Reactor (EFR) at Imperial College, London, have been used to validate the models. The predicted results from both the ash deposition models agreed with the experimental measurements, and the NSI has successfully ranked the investigated coal-biomass mixtures according to their degree of sintering.

Air pollution regulations have driven modern power generation systems to move from diffusion to premixed combustion. However, these premixed combustion systems are prone to combustion instability, causing high fluctuations in pressure and temperature. This results in shortening of component life, system failure, or even catastrophic disasters. A large number of studies have been performed to understand and quantify the onset of combustion instability and the limit cycle amplitude. However, much work remains due to the complexity of the process associated with flow dynamics and chemistry. This thesis focuses on identifying, quantifying and predicting mechanisms of flame response subject to disturbances. A promising tool for predicting combustion instability is a flame transfer function. The flame transfer function is obtained by integrating unsteady heat release over the combustor domain. Thus, the better understanding of spatio-temporal characteristics of flame is required to better predict the flame transfer function. The spatio-temporal flame response is analyzed by the flame kinematic equation, so called G-equation. The flame is assumed to be a thin interface separating products and reactant, and the interface is governed by the local flow and the flame propagation. Much of the efforts were done to the flame response subject to the harmonic velocity disturbance. A key assumption allowing for analytic solutions is that the velocity is prescribed. For the mathematical tools, small perturbation theory, Hopf-Lax formula and numerical simulation were used. Solutions indicated that the flame response can be divided into three regions, referred to here as the near-field, mid-field, and farfield. In each regime, analytical expressions were derived, and those results were compared with numerical and experimental data. In the near field, it was shown that the flame response grows linearly with the normal component of the velocity disturbance. In the mid field, the flame response shows peaks in gain, and the axial location of these peaks can be predicted by the interference pattern by two characteristic waves. Lastly, in the far field where the flame response decreases, three mechanisms are studied; they are kinematic restoration, flame stretch, and turbulent flow effects. For each mechanism, key parameters are identified and their relative significances are compared.

Catalytic combustion is an environmentally benign technologywhich has recently reached the stage of commercialization.Palladium is the catalyst of choice when considering gasturbines fuelled with natural gas because of its superioractivity for methane oxidation. Several fundamental issues arestill open and their understanding would result in animprovement of the technology. Hence, the work presented inthis thesis aims at the identification of some of theparameters which govern the combustion activity ofpalladium-based catalysts.

The first part of this work gives a background to catalyticcombustion and a brief comparison with other existingtechnologies. Paper I reviews some of the issues related tomaterial development and combustor design.

The second part of this thesis consists of an experimentalinvestigation on palladium-based catalysts. The influence ofthe preparation method onthe properties of these catalystmaterials is investigated in Paper II. Paper III examines theactivity of the following catalysts: Pd/Al2O3, Pd/Ba-Al2O3 andPd/La-Al2O3. Specific attention is given to the metal-supportinteraction which strongly affects the combustion activity ofpalladium. The effect of doping of the support by addition ofcerium is reported in Paper IV.

Finally, the deactivation of combustion catalysts isconsidered. The various deactivation processes which may affecthigh temperature combustion catalysts are reviewed in Paper V.Paper VI focuses on the poisoning of supported palladiumcatalysts by sulphur species. Palladium exhibits a higherresistance to sulphur poisoning than transition metals.Nevertheless, the nature of the support material plays animportant role and may entail a severe loss of activity whensulphur is present in the fuel-air mixture entering thecombustion chamber.

Keywords: catalytic combustion, gas turbine, methane,palladium, alumina, barium, lanthanum, oxidation, preparation,temperature-programmed oxidation (TPO), decomposition,reoxidation, X-ray photoelectron spectroscopy (XPS),metal-support interaction, deactivation, sulphur, poisoning.The cover illustration is a TEM picture of a 100 nm palladiumparticle supported on alumina