Rozprawy doktorskie na temat „Hydrogen methane combustion”

Dans ce travail, les flammes stabilisées par tourbillonnement, assistées par hydrogène (enrichissement en hydrogène et pilotage) sont étudiées expérimentalement via l'expérience MIRADAS. Tout d'abord, les caractéristiques de stabilité statique, telles que les longueurs de flamme et les caractéristiques d'attachement de la flamme sont étudiées via des images de chimiluminescence CH * de flamme et les cas avec pilotage à l'hydrogène, pilotage au méthane et enrichissement en hydrogène sont comparés au cas de référence; d'une combustion méthane-air parfaitement prémélangée, pour une large gamme des richesse et des vitesses. On constate que le pilotage de l'hydrogène est la méthode la plus efficace pour fixer les flammes et étendre les plages de fonctionnement stables de la chambre de combustion. Ensuite, les caractéristiques de stabilité dynamique de l'installation sont étudiées expérimentalement via des cartes de stabilité et il est démontré que l'injection d'une très petite partie de la puissance thermique de l'hydrogène se traduit par un système plus stable ; une extension des points de fonctionnement stables dans les cartes de stabilité, ce qui signifie un fonctionnement global plus sûr. L'enrichissement en hydrogène et le pilotage du méthane sont également explorés et il est démontré que ces méthodes ne sont pas efficaces pour changer les cartes de stabilité, les cartes de stabilité ne sont pas effectuées. Par la suite, les réponses des flammes forcées sont étudiées expérimentalement et il est démontré que le pilotage de l'hydrogène et l'enrichissement en hydrogène provoquent une baisse du délai global de la fonction de transfert de flamme. Avec le pilotage de l'hydrogène, il y a une baisse globale du gain de la fonction de transfert de flamme, mais pour les cas enrichis en hydrogène, le gain est augmenté. Pour les cas pilotés au méthane, il y a une réduction globale du gain de la fonction de transfert de flamme, mais le délai n'est pas affectée. Par conséquent, pour explorer pourquoi et comment la fonction globale de transfert de flamme est modifiée avec différentes stratégies d'injection, des images de flamme forcée sont étudiées. Il est démontré que les changements dans la fonction de transfert de flamme sont causés par le comportement de compétition entre les réponses locales de dégagement de chaleur pour les cas pilotés par l'hydrogène. Autrement dit, il y a une différence de phase entre les réponses locales près du tube d'injection et les bords de la flamme, provoquant un effet de baisse, qui à son tour provoque une baisse du gain de la fonction de transfert de flamme. Ensuite, l'effet de différentes stratégies d'injection sur les émissions de polluants est étudié. Il est démontré que l'ajout d'hydrogène, en configuration d'injection pilote ou d'enrichissement d'hydrogène, entraîne une baisse des émissions de\mathrm{CO_2}pour la même puissance thermique. Les stratégies de pilotage provoquent une légère augmentation des émissions de NOx, mais les résultats montrent qu'une optimisation est possible pour obtenir des flammes stables, à faible \mathrm{CO_2} et à faible NOx. Enfin, les calculs LES et leurs comparaisons avec les résultats expérimentaux sont présentés. La capacité des calculs LES à prédire les réponses de la flamme est affichée et il est démontré que les réponses de la flamme proviennent des interactions des tourbillons qui se forment à la suite des pulsations acoustiques et des flammes. Des flammes sont enroulées autour de ces tourbillons, ce qui augmente la surface de la flamme. Plus loin dans le cycle de forçage, les parties enroulées des flammes commencent à toucher les parois de la chambre de combustion et s'éteignent, ce qui entraîne une perte de surface de la flamme. Ces changements dans la surface de la flamme se traduisent par un taux de dégagement de chaleur fluctuant, consistant en la réponse de la flamme
In this work, hydrogen assisted (hydrogen enrichment and piloting) swirl stabilized flames are studied experimentally via MIRADAS experiment. First of all, static stability characteristics, such as flame lengths and flame attachment characteristics are studied via CH* chemiluminescence flame images and cases with hydrogen piloting, methane piloting and hydrogen enrichment are compared to the reference case of perfectly premixed methane-air combustion for a wide range of equivalence ratios and bulk velocities. It is found out that hydrogen piloting is the most efficient method to attach the flames and extend operating ranges of the combustion chamber. Next the dynamic stability characteristics of the setup is studied experimentally via stability maps and it is shown that injection of a very small portion of the thermal power worth of hydrogen results in a more stable system and an extension in the stable operating points in the stability maps, meaning safer overall operation. Hydrogen enrichment and methane piloting are also explored, and it is demonstrated that these methods are not effective in changing stability maps, stability maps are not effected. Subsequently, the forced flame responses are studied experimentally and it is shown that hydrogen piloting and hydrogen enrichment causes a drop in the global time delay of the flame transfer function. With hydrogen piloting, there is a global drop in the flame transfer function gain, however for hydrogen enriched cases, the gain is increased. For methane piloted cases, there is a global reduction in the flame transfer function gain, however the time delay is not affected. Consequently, to explore why and how the global flame transfer function is changed with different injection strategies, forced flame images are studied. It is shown that the changes in flame transfer function is caused by the competition behavior between the local heat release responses for hydrogen piloted cases. Simply put, there is a phase difference between the local responses near the injection tube and the flame edges, causing a "pull-back" effect, which in turn causes a drop in the flame transfer function gain. Next the effect of different injection strategies on the pollutant emissions are investigated. It is demonstrated that adding hydrogen, in pilot injection or hydrogen enrichment configuration, causes a drop in \mathrm{CO_2} emissions for the same thermal power. Piloting strategies cause a slight increase in NOx emissions, however results show that an optimization is possible to obtain flames that are stable, low mathrm{CO_2} and low NOx. Finally, LES calculations and their comparisons with experimental results are presented. The capability of LES calculations in predicting flame responses is demonstrated and it is shown that the flame responses originate from the interactions of the vortices that are formed as a result of acoustic pulsations and the flames. Flames are wrapped around these vortices which increase the flame surface area. Further down the forcing cycle, the rolled up portions of the flames start touching the combustion chamber walls and gets quenched which causes a loss of flame surface area. These changes in flame surface area result in a fluctuating heat release rate, consisting the flame response

Indiana University-Purdue University Indianapolis (IUPUI)
This study contributes to a better understanding of ignition by hot combustion gases which finds application in internal combustion chambers with pre-chamber ignition as well as in wave rotor engine applications. The experimental apparatus consists of two combustion chambers: a pre chamber that generates the transient hot jet of gas and a main chamber which contains the main fuel air blend under study. Variables considered are three fuel mixtures (Hydrogen, Methane, 50\% Hydrogen-Methane), initial pressure in the pre-chamber ranging from 1 to 2 atm, equivalence ratio of the fuel air mixture in the main combustion chamber ranging from 0.4 to 1.5, and initial temperature of the main combustion chamber mixture ranging from 297 K to 500 K. Experimental data makes use of 4 pressure sensors with a recorded sampling rate up to 300 kHz, as well as high speed Schlieren imaging with a recorded frame rate up to 20,833 frame per seconds. Results shows an overall increase in ignition delay with increasing equivalence ratio. High temperature of the main chamber blend was found not to affect hot jet ignition delay considerably. Physical mixing effects, and density of the main chamber mixture have a greater effect on hot jet ignition delay.

La combustion sans flamme est un régime de combustion massivement dilué associant forte efficacité énergétique et très faibles émissions polluantes dans les fours industriels. La composition du combustible et la température des parois de la chambre de combustion sont deux paramètres très influents de ce régime. Dans de précédents travaux menés au CORIA, l’étude du régime de combustion sans flamme des mélanges méthane-hydrogène à 18% d’excès d’air a mené à des résultats originaux et prometteurs. D’autre part, la haute température des parois s’est avérée un élément primordial pour la stabilisation de la combustion sans flamme. Dans le cadre du projet CANOE en collaboration avec GDF SUEZ et l’ADEME, cette thèse a pour objectif, d’une part de compléter l’étude de l’extension de ce régime à des mélanges méthane-hydrogène pour des conditions opératoires plus proches des conditions classiques de fonctionnement de brûleurs (10% d’excès d’air), et d’autre part, d'étudier les problèmes de stabilité de la combustion sans flamme en environnement à basse température pour envisager son application à des configurations de type chaudière industrielle.Sur le four pilote à hautes températures de parois du CORIA, l’ajout de l’hydrogène dans le combustible a permis de garder le régime de combustion sans flamme pour toutes les proportions méthane - hydrogène avec très peu d’émissions polluantes. Une augmentation de l’excès d’air est toutefois nécessaire pour certaines conditions opératoires. Les expériences réalisées avec abaissement progressif de la température des parois ont permis d’étudier l’influence de celle-ci sur le développement de la combustion sans flamme, et d’atteindre les limites de stabilité de ce régime. Des résultats similaires sont obtenus sur une installation semi-industrielle de GDF SUEZ. L’ajout d’hydrogène rend la combustion sans flamme moins sensible à l’abaissement de la température de parois. Une étude analytique de jets turbulents confinés a été développée pour représenter l'interaction entre les jets de réactifs et leur environnement dans la chambre de combustion permettant d'atteindre le régime de combustion sans flamme par entraînement, dilution et préchauffage. Ce modèle nous a permis d’établir une étude systématique permettant de mettre en valeur l’effet de chaque paramètre sur le développement des jets dans l’enceinte, et ainsi servir de moyen de pré-dimensionnement de brûleur à combustion sans flamme. L'apport de chaleur nécessaire à la stabilisation à basse température a ainsi été estimé. Sur cette base, un brûleur adapté aux configurations à parois froides a été dimensionné et fabriqué. L’applicabilité de la combustion sans flamme avec ce brûleur dans une chambre de combustion à parois froides, spécialement conçue et fabriquée dans cet objectif au cours de cette thèse, a été étudiée. Un régime de combustion diluée à basses températures a pu être stabilisé, mais le fort taux d'imbrûlés produits en sortie reste à réduire
Mild flameless combustion is a massively diluted combustion regime associating high energy efficiency and very low pollutant emissions from industrial furnaces. The fuel composition and walls temperature are two very influential parameters of this combustion regime. In previous works realized at CORIA, flameless combustion of methane - hydrogen mixtures at 18% of excess air has shown very promising results. In another hand, high walls temperature is an essential element for flameless combustion stabilization. Within the framework of the project CANOE in collaboration with GDF SUEZ and ADEME, the objective of this PhD thesis is to complete the study of flameless combustion for methane-hydrogen mixtures in operating conditions similar to classical operating conditions of burners (10% of excess air), and in another hand, to study the stability limits of this combustion regime in low temperature environment like in industrial boiler.Experiments realized on the CORIA high temperature pilot facility, have proved that hydrogen addition in the fuel keep flameless combustion regime stable for all methane - hydrogen proportions, with very ultra-low pollutant emissions. An increase of excess air is however necessary for some operating conditions.Experiments realized with wall temperature progressive decrease allowed to study the influence of this parameter on flameless combustion, and to reach its stability limits. Similar results are obtained on the semi-industrial facility of GDF SUEZ. With hydrogen addition, flameless combustion is less sensitive to wall temperature decrease. An analytical representation of confined turbulent jets has been then developed to represent interaction between the reactant jets and their environment in the combustion chamber allowing reaching fameless combustion regime by entrainment, dilution and preheating. The effect of each parameter on the development of the jets can be then studied, which can be used as convenient tool of flameless combustion burners design. The heat quantity necessary for the low wall temperature stabilization has been quantified. On this base, a burner adapted to the configurations with cold walls has been designed. The applicability of the flameless combustion with this burner has been studied in a combustion chamber with low wall temperature specially designed for this purpose during this thesis. A mild diluted combustion regime has been achieved, but the high levels of unburnt gases have to be reduced

This thesis investigates both hydrogen combustion and production, focusing on fundamentals of Pt-catalysed oxidation and steam methane reforming on nickelbased catalysts. On the first aspect, we started reporting and investigating discrepancies on the structure and predictions of detail surface kinetic models from Literature, for H2-O2 reaction on Pt. Quantitative comparisons have been carried out through a closed-vessel, well-stirred reactor model with catalytic internal surface. Discrepancies in the predictions of the microkinetic models apparently comes from disagreement in the experimental date they are based on. Differences in experimental set-ups and Pt surface structure prompted us to develop own data, using plane Pt surface in suitable reactors. A novel laboratory reactor to investigate hydrogen oxidation on Pt surfaces has been designed, based on modelling, and built. Experimental catalytic activity test proved that Pt activity can vary dramatically. Catalyst pretreatments with H2 and O2 revealed the mechanism of competition for surface sites as well as restructuring of the surface. Significantly long transformation was measured, particularly after catalyst O2 pretreatment, that are not included in the elementary chemistry models from Literature. Reaction lightoff at H2 lean compositions have been measured and compared with Literature experimental data, providing explanations for the differences among published data. Subsequently, transient simulation of hydrogen combustion in platinumcoated channel has been adopted to evaluate the behavior under heterogeneous and hetero-/homogeneous chemistries. Effects of catalyst support material properties, FeCr-alloy and cordierite, have been compared. Implication for the operation of various practical catalytic reactors are finally drawn. Concerning H2 production, we investigated the catalytic reforming of natural gas, by steam, both theoretically and experimentally. We identified relevant ranges of operative variables to study the catalyst at industrially relevant conditions. We designed by scaling down from industrial plants an original set-up to investigate the reaction kinetics at high-pressure (10 bars). We compared three nickel-based catalysts at low steam-to-carbon conditions, approaching S/C = 1, to collect activity and coking data for validation and development of detailed surface chemistry model.
Questa tesi investiga sia la combustion che la produzione di idrogeno, con particolare attenzione verso aspetti fondamentali della ossidazione catalizzata da platino e la reazione di steam reforming del metano su catalizzatori a base di nickel. Per quanto riguarda il primo aspetto, siamo partiti dall’osservare ed approfondire discrepanze sulla struttura e sui risultati di modelli cinetici di reazioni superficiali presenti in Letteratura, per la reazione di H2 e O2 su Pt. I confronti quantitativi sono stati fatti utilizzando un Modello di reattore chiuso ben mescolato con le superfici interne catalitiche. Le differenze nelle perizie dei diversi modelli sembrano discendere da differenze nei dati sperimentali su cui sono stati calibrati. Il fatto che se non state utilizzate diverse configurazioni sperimentali, e probabilmente strutture delle superfici di Pt , ci ha stimolato a intraprendere una campagna sperimentale per ottenere dati propri, utilizzando superfici di platino planari in opportuni reattori. Un nuovo reattore di laboratorio, a flusso stagnante, per indagare reazioni su Pt in forma di dischi e stato progettato sulla base di una` modellazione dettagliata e realizzato in laboratorio. I risultati sperimentali hanno dimostrato che l’attivita del Pt può variare enormemente. Pretrattamenti con H2 o O2 Hanno chiarito il meccanismo della competizione per siti superficiali e la possibilita di ristrutturazione la superficie. Sono state misurate trasformazioni di lunga durata, soprattutto dopo pretrattamenti con O2, che non trova una spiegazione in nessuno dei modelli cineticidettagliati di letteratura. Mediante misure in rampa di temperatura si e studiato` l’innesco di miscele povere di H2 in aria. Il confronto con dati di letteratura suggerisce una plausibile interpretazione della discrepanza dei dati riportati. Successivamente simulazioni transitorie della combustione di idrogeno in canali rivestiti di platino e stato utilizzato per valutare il comportamento della`reazione eterogenea con e senza reazione omogenea. L’effetto delle proprieta`del supporto del catalizzatore sono stati confrontati, considerando leghe Fe-Cre cordierite. Le implicazioni pratiche per l’operativita di questi reattori sono state`delineate. Per quanto riguarda la produzione di idrogeno abbiamo studiato sia dal punto di vista teorico che sperimentale la reazione di reforming di gas naturale mediante7 vapore. Abbiamo identificato intervalli significativi da un punto di vista industriale per le variabili operative, per studiare la cinetica dei catalizzatori. Abbiamo progettato un reattore di laboratorio mediante regole di scala rispetto a un impianto modello industriale di riferimento, con l’obiettivo di studiare la reazione a pressioni elevate (10bars). Abbiamo confrontato tre catalizzatori basati su Nickel con formulazioni diverse, modificando rapporto vapore/carbonio in alimentazione, per avvicinarsi alle condizioni stechiometriche. Si sono raccolti numerosi ,dati sia di attivita cataliticha che di formazione di carbone, utili per uno sviluppo di modelli` cinetici dettagliati della reazione superficiale.

Les réglementations sur les NOx émis par les avions sont sévères. Les techniques les réduisant ont des inconvénients. Pour les supprimer, deux pistes sont explorées. La première modifie l'architecture des chambres de combustion et les stabilise par une cavité. La seconde dope le kérosène au ralenti.Peu d'information est disponible sur les mécanismes de stabilisation et sur la structure de flamme des Trapped Vortex Combustor. Pour y remédier, un TVC est construit. L'étude de l'écoulement à froid ainsi que l'étude temporellement résolue de la flamme, mettent en avant les éléments stabilisateurs et déstabilisateurs. L'impact de la structure de flamme sur les émissions est évalué.La seconde partie porte sur l'effet de l'ajout d'hydrogène et de gaz de reformeur dans une chambre conventionnelle. Malgré une légère augmentation des émissions de NOx, l'ajout de composés hydrogénés réduit fortement les émissions de CO, augmente la stabilité et réduit la limite d'extinction pauvre
Environmental standards on aircraff NOx emissions are strict. Technics for reducing them have drawbacks. Two options are explored in this study to supress them. The first one is to fundamentally change the current combustion chamber architecture, to stabilize them by a cavity, the second, to dope fuel at idle.Little information on the mechanisms of stabilization and on the flame structure on Trapped Vortex Combustor is available. To remedy this, a TVC is built. The stabilizing ans destabilizing parameters are pointed out by the cold flow investigation and the temporally resolved study of the combustion. The impact of the flame structure on pollutant emissions is also considered.The second part of this stud, deals with the addition of pure hydrogen an of reformer gas in a conventional combustuion chamber. Despite a slight increase in NOx emissions, the addition of hydrogenated compounds reduces drastically CO emissions, increases the flame stability and reduces the LBO limit

This body of research uses numerical and experimental investigative techniques to further the understanding of autoignition. Hydrogen/nitrogen and methane/air fuel configurations of turbulent lifted flames in a vitiated coflow burner are used as model flames for this investigation. Characterisation was undertaken to understand the impact of controlling parameters and the overall behaviour of the flames, and to provide a body of data for modelling comparisons. Modelling of the flames was conducted using the PDF-RANS technique with detailed chemistry incorporated using In-situ Adaptive Tabulation (ISAT) within the commercial CFD package, FLUENT 6.2. From these investigations, two numerical indicators for autoignition were developed: convection-reaction balance in the species transport budget at the mean flame base; and the build-up of ignition precursors prior to key ignition species. These indicators were tested in well defined autoignition and premixed flame cases, and subsequently used with the calculated turbulent lifted flames to identify if these are stabilised through autoignition. Based on learnings from the modelling, a quantitative, high-resolution simultaneous imaging experiment was designed to investigate the correlations of an ignition precursor (formaldehyde: CH2O) with a key flame radical (OH) and temperature. Rayleigh scattering was used to measure temperature, while Laser Induced Fluorescence (LIF) was used to measure OH and CH2O concentrations. The high resolution in the Rayleigh imaging permitted the extraction of temperature gradient data, and the product of the OH and CH2O images was shown to be a valid and useful proxy for peak heat release rate in autoigniting and transient flames. The experimental data confirmed the presence of formaldehyde as a precursor for autoignition in methane flames and led to the identification of other indicators. Sequenced images of CH2O, OH and temperature show clearly that formaldehyde exists before OH and peaks when autoignition occurs, as confirmed by images of heat release. The CH2O peaks decrease later while those of OH remain almost unchanged in the reaction zone.

Doctor of Philosophy(PhD)
This body of research uses numerical and experimental investigative techniques to further the understanding of autoignition. Hydrogen/nitrogen and methane/air fuel configurations of turbulent lifted flames in a vitiated coflow burner are used as model flames for this investigation. Characterisation was undertaken to understand the impact of controlling parameters and the overall behaviour of the flames, and to provide a body of data for modelling comparisons. Modelling of the flames was conducted using the PDF-RANS technique with detailed chemistry incorporated using In-situ Adaptive Tabulation (ISAT) within the commercial CFD package, FLUENT 6.2. From these investigations, two numerical indicators for autoignition were developed: convection-reaction balance in the species transport budget at the mean flame base; and the build-up of ignition precursors prior to key ignition species. These indicators were tested in well defined autoignition and premixed flame cases, and subsequently used with the calculated turbulent lifted flames to identify if these are stabilised through autoignition. Based on learnings from the modelling, a quantitative, high-resolution simultaneous imaging experiment was designed to investigate the correlations of an ignition precursor (formaldehyde: CH2O) with a key flame radical (OH) and temperature. Rayleigh scattering was used to measure temperature, while Laser Induced Fluorescence (LIF) was used to measure OH and CH2O concentrations. The high resolution in the Rayleigh imaging permitted the extraction of temperature gradient data, and the product of the OH and CH2O images was shown to be a valid and useful proxy for peak heat release rate in autoigniting and transient flames. The experimental data confirmed the presence of formaldehyde as a precursor for autoignition in methane flames and led to the identification of other indicators. Sequenced images of CH2O, OH and temperature show clearly that formaldehyde exists before OH and peaks when autoignition occurs, as confirmed by images of heat release. The CH2O peaks decrease later while those of OH remain almost unchanged in the reaction zone.

Mesures de profils de concentration des principales espèces stables et radicalaires dans les flammes CH4/O2/NH3 et CO/O2/H2NH3 par spectrométrie de masse. Comparaison avec des profils de concentration calculés à l'aide d'un programme numérique à partir d'un schéma cinétique complet. Proposition d'un modèle cinétique

Les réglementations sur les NOx émis par les avions sont sévères. Les techniques les réduisant ont des inconvénients. Pour les supprimer, deux pistes sont explorées. La première modifie l'architecture des chambres de combustion et les stabilise par une cavité. La seconde dope le kérosène au ralenti.Peu d'information est disponible sur les mécanismes de stabilisation et sur la structure de flamme des Trapped Vortex Combustor. Pour y remédier, un TVC est construit. L'étude de l'écoulement à froid ainsi que l'étude temporellement résolue de la flamme, mettent en avant les éléments stabilisateurs et déstabilisateurs. L'impact de la structure de flamme sur les émissions est évalué.La seconde partie porte sur l'effet de l'ajout d'hydrogène et de gaz de reformeur dans une chambre conventionnelle. Malgré une légère augmentation des émissions de NOx, l'ajout de composés hydrogénés réduit fortement les émissions de CO, augmente la stabilité et réduit la limite d'extinction pauvre.

La thèse étudie le vaporeformage catalytique du méthane avec captage de CO2. Les catalyseurs bi-fonctionnels choisis se composent de nickel, efficace en vaporeformage, de CaO pour la sorption de CO2 et d'aluminate de calcium (Ca12Al14O33) pour permettre une bonne dispersion du métal et de CaO. La méthode de synthèse privilégiée était la méthode d'autocombustion assisté par microondes. Le rapport Ca/Al a été optimisé et un large excès de CaO est nécessaire (75%CaO ; 25%Ca12Al14O33) pour la sorption de CO2. Le reformage du méthane est total dès 650 °C (H2O/CH4 de 1 ou 3) et la sélectivité en hydrogène de 100% durant 7h ou 16h selon les conditions opérationnelles, validant le concept de vaporeformage du méthane assisté par l'absorption de CO2.

碩士
崑山科技大學
機械工程研究所
101
In this study, combustion characteristics of inverse methane jet diffusion flames were investigated using a triple-port Jet burner. The results showed that as the middle stream velocity of methane (V2) and the outer stream velocity of air (V3) are fixed, the gradual increase in the inner stream velocity of air (V1) will result in the transition of inverse diffusion flame from a single cone-shaped flame (Type A) to a double cone-shaped flame (Type B) to a M-shpaed flame with inner and outer open tips, so-called Type C flame, to a Type D flame with lifted inner flame. When V2 and V3 are kept constant, flame height decreases with increasing V1. As V3 was fixed, the critical velocities of inner air stream (V1) corresponding to the occurrence of Type B and Type C flames increased with V2, while the corresponding V1 for the onset of Type D flame decreased with increasing V2. With increasing central-flow air velocity or hydrogen concentration, radiative heat transfer rate (radiative heat flux) decreased for a fixed radial direction distance 50 cm at a constant fuel velocity. Additionally, with an increase in central-flow air velocity, the CO2 and NOx emissions increased, but the CO emission decreased. Moreover, the measurement of temperature distribution showed that, as V1=V2=V3=250 cm/s, the maximum temperature is about 1400 ℃ for pure methane but around 1600 ℃for the mixture of 80% methane and 20% hydrogen. Meanwhile, the latter also had a wider high temperature zone, leading to higher radiation for the latter.

碩士
國立中央大學
機械工程研究所
90
The lean combustion of hydrogen/methane mixtures within a highly porous medium has been investigated by experiment and numerical simulation. According to the ceramics arrangement and the gap, four burner structures are built. we use the LabView program to measure the flow rates, flame temperature, the NOx/CO emission. for the numerical simulation. we use STAR-CD to build a model and to compute the solution. results show that for burners without a gap, the flame tends to stabilize at the upstream half. for the burners with a gap, the flame can stabilized in either the upstream half ot the downstreams one. Using small-pore ceramics blocks at the inlet and exit can cut radiative heat loss and lower the lean limit. Addition of hydrogen in the fuel doesn't change the flame temperature greatly. the flame speed, however, increases with the hydrogen fraction in the fuel.

Indiana University-Purdue University Indianapolis (IUPUI)
Ignition by a jet of hot combustion product gas injected into a premixed combustible mixture from a separate pre-chamber is a complex phenomenon with jet penetration, vortex generation, flame and shock propagation and interaction. It has been considered a useful approach for lean, low-NOx combustion for automotive engines, pulsed detonation engines and wave rotor combustors. The hot-jet ignition constant-volume combustor (CVC) rig established at the Combustion and Propulsion Research Laboratory (CPRL) of the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) is considered for numerical study. The CVC chamber contains stoichiometric methane-hydrogen blends, with pre-chamber being operated with slightly rich blends. Five operating and design parameters were investigated with respect to their eff ects on ignition timing. Di fderent pre-chamber pressure (2, 4 and 6 bar), CVC chamber fuel blends (Fuel-A: 30% methane + 70% hydrogen and Fuel-B: 50% methane + 50% hydrogen by volume), active radicals in pre-chamber combusted products (H, OH, O and NO), CVC chamber temperature (298 K and 514 K) and pre-chamber traverse speed (0.983 m/s, 4.917 m/s and 13.112 m/s) are considered which span a range of fluid-dynamic mixing and chemical time scales. Ignition delay of the fuel-air mixture in the CVC chamber is investigated using a detailed mechanism with 21 species and 84 elementary reactions (DRM19). To speed up the kinetic process adaptive mesh refi nement (AMR) based on velocity and temperature and multi-zone reaction technique is used. With 3D numerical simulations, the present work explains the e ffects of pre-chamber pressure, CVC chamber initial temperature and jet traverse speed on ignition for a speci fic set of fuels. An innovative post processing technique is developed to predict and understand the characteristics of ignition in 3D space and time. With the increase of pre-chamber pressure, ignition delay decreases for Fuel-A which is the relatively more reactive fuel blend. For Fuel-B which is relatively less reactive fuel blend, ignition occurs only for 2 bar pre-chamber pressure for centered stationary jet. Inclusion of active radicals in pre-chamber combusted product decreases the ignition delay when compared with only the stable species in pre-chamber combusted product. The eff ects of shock-flame interaction on heat release rate is observed by studying flame surface area and vorticity changes. In general, shock-flame interaction increases heat release rate by increasing mixing (increase the amount of deposited vorticity on flame surface) and flame stretching. The heat release rate is found to be maximum just after fast-slow interaction. For Fuel-A, increasing jet traverse speed decreases the ignition delay for relatively higher pre-chamber pressures (6 and 4 bar). Only 6 bar pre-chamber pressure is considered for Fuel-B with three di fferent pre-chamber traverse speeds. Fuel-B fails to ignite within the simulation time for all the traverse speeds. Higher initial CVC temperature (514 K) decreases the ignition delay for both fuels when compared with relatively lower initial CVC temperature (300 K). For initial temperature of 514 K, the ignition of Fuel-B is successful for all the pre-chamber pressures with lowest ignition delay observed for the intermediate 4 bar pre-chamber pressure. Fuel-A has the lowest ignition delay for 6 bar pre-chamber pressure. A speci fic range of pre-chamber combusted products mass fraction, CVC chamber fuel mass fraction and temperature are found at ignition point for Fuel-A which were liable for ignition initiation. The behavior of less reactive Fuel-B appears to me more complex at room temperature initial condition. No simple conclusions could be made about the range of pre-chamber and CVC chamber mass fractions at ignition point.

The global energy consumption is estimated to reach around 262×1012 kWh/year by 2050 for 9 billion people. It is a challenge to meet global energy requirement via clean fuel (hydrogen) and by reducing/utilizing the CO2 emissions. Designing of efficient and stable catalysts could control the process economics, providing higher yields of H2 at low temperatures along with low CO2 emissions. Based on the current scenario of continuing fossil fuel utilization, researchers are developing technologies that can produce H2 efficiently from fossil fuels such as methane, diesel, glycerol and hydrocarbons. Developing efficient catalysts is a means of improving the process efficiency. Though the thermo-catalytic route can be beneficial for effective H2 generation, the purification steps (preferential CO oxidation, water-gas shift (WGS)) for H2 increases the CO2 concentration. On the other hand, H2 generation methods such as photocatalytic water splitting and electrochemical methods are attractive with no CO2 emissions, but these methods have low efficiencies and scalability that leaves the catalytic route of hydrogen generation to meet global energy requirement as the only viable option. It is important to understand the nature of the catalyst and its salient properties to design suitable catalysts for energy applications. In this thesis, we have addressed several factors such as strong metal support interaction (SMSI), morphology, oxygen storage capacity (OSC) and nature of the catalyst surface to improve the catalytic activity. The behavior of reactant molecules should be understood on the catalyst surface for developing the reaction mechanisms to determine its kinetics. To address the reactants behavior on catalyst surface, we have carried out reactions such as CO oxidation, preferential CO oxidation, water-gas shift (WGS) under reformate feed, catalytic hydrogen combustion, dry reforming of methane, autothermal reforming of methane and methane combustion. The structure of the thesis indicates the systematic approach of catalyst design by improving the salient properties to design thermally stable coke resistant catalysts. This thesis contains 7 chapters. Chapter 1 reviews the industrial approach for hydrogen generation, role of catalysts in each step of purification steps, brief review of other approaches for hydrogen generation and their limitations. Chapter 2 focuses on the synthesis of noble metal substituted titania catalysts for reforming of methane. Various reforming reactions such as partial oxidation, CO2 dry reforming and autothermal reforming of methane have been discussed. The mechanistic and kinetic aspects of reforming reactions are discussed elaborately. Further, the effective properties such as redox nature of the catalyst, SMSI, surface nature and OSC on the reaction mechanism and the stability were addressed. Chapter 3 emphasizes on the synthesis of other reducible catalysts such as cobalt oxide (Co3O4) and copper substituted cobalt oxide. These catalysts were subjected to low temperature reactions such as CO oxidation and preferential CO oxidation (PrOX) under H2 rich conditions. The redox nature and high OSC properties improved the catalytic activity and allowed reactions to occur below 170°C. Further, the role of intermediate species such as carbonates, carboxyl and formate groups in the reaction mechanism for CO oxidation under H2 rich conditions have been investigated to develop the rate expression and kinetics. Chapter 4 focuses on the development of Pt and Pd substituted Co3O4 – ZrO2 (CZ) catalysts using PEG – assisted sonochemical synthesis. Our objective is to design thermally stable catalysts and understand the behavior of the reactants on the catalyst surfaces. Hydrogen and oxygen activation are crucial steps in the mechanisms for hydrogen combustion, water-gas shift and reforming reactions and that can be achieved by modifying supports with suitable noble metals. The effect of oxygen vacancies in the reaction mechanism was found to be insignificant with Pt and Pd substituted CZ supports. This study is key for extending our work to design thermally stable catalysts for WGS and high temperature methane combustion reactions. Chapter 5 deals with the important industrial H2 upgradation step of low temperature WGS under reformate feed conditions using noble metal (Pt, Pd and Ru) substituted CZ catalysts. The objective of WGS is to upgrade H2 in the product stream by reacting CO with steam. However, low temperature WGS is a challenging reaction under reformate feed conditions. The reformate feed contains CO, CO2 and H2 in different concentrations and these can block the active sites of the catalyst and become favorable for side reactions such as methanation. In this study, the catalysts were modified by redesigning catalyst with potassium promoter. Thus the stable catalyst system was designed by eliminating the undesirable methanation reaction. Further, this chapter focuses on the mechanism of WGS on noble metal substituted CZ catalysts below 300°C. The role of promoter in the reaction mechanism and possible surface intermediates have been discussed in detail. This study gives insights of the behavior of reactant molecules on the catalyst surface, which further allowed us to design the catalysts for high temperature reactions such as methane combustion. Chapter 6 focuses on catalytic activity of composite catalysts for high temperature methane combustion reaction. The low cost transition metal substituted (Ni, Cu and Fe) CZ composites have been developed for methane combustion. Due to its oxygen storage capacity over a wide range of temperature, these catalysts were found to be stable at a temperature of 600°C without noticeable sintering. The spectroscopic studies gave an insight of possible reaction mechanism over the synthesized catalysts. Chapter 7 summarizes the major conclusions drawn from each chapter and highlights the further outlook of the work.

Indiana University-Purdue University Indianapolis (IUPUI)
Investigations of a constant-volume combustor ignited by a penetrating transient jet (a puff) of hot reactive gas have been conducted in order to provide vital data for designing wave rotor combustors. In a wave rotor combustor, a cylindrical drum with an array of channels arranged around the axis spins at a high rpm to generate high-temperature and high-pressure product gas. The hot-gas jet ignition method has been employed to initiate combustion in the channels. This study aims at experimentally investigating the ignition delay time of a premixed combustible mixture in a rectangular, constant-volume chamber, representing one channel of the wave rotor drum. The ignition process may be influenced by the multiple factors: the equivalence ratio, temperature, and the composition of the fuel mixture, the temperature and composition of the jet gas, and the peak mass flow rate of the jet (which depends on diaphragm rupture pressure). In this study, the main mixture is at room temperature. The jet composition and temperature are determined by its source in a pre-chamber with a hydrogen-methane mixture with an equivalent ratio of 1.1, and a fuel mixture ratio of 50:50 (CH4:H2 by volume). The rupture pressure of a diaphragm in the pre-chamber, which is related to the mass flow rate and temperature of the hot jet, can be controlled by varying the number of indentations in the diaphragm. The main chamber composition is varied, with the use of four equivalence ratios (1.0, 0.8, 0.6, and 0.4) and two fuel mixture ratios (50:50, and 30:70 of CH4:H2 by volume). The sudden start of the jet upon rupture of the diaphragm causes a shock wave that precedes the jet and travels along the channel and back after reflection. The shock strength has an important role in fast ignition since the pressure and the temperature are increased after the shock. The reflected shock pressure was examined in order to check the variation of the shock strength. However, it is revealed that the shock strength becomes attenuated compared with the theoretical pressure of the reflected shock. The gap between theoretical and measured pressures increases with the increase of the Mach number of the initial shock. Ignition delay times are obtained using pressure records from two dynamic pressure transducers installed on the main chamber, as well as high-speed videography using flame incandescence and Schileren imaging. The ignition delay time is defined in this research as the time interval from the diaphragm rupture moment to the ignition moment of the air/fuel mixture in the main chamber. Previous researchers used the averaged ignition delay time because the diaphragm rupture moment is elusive considering the structure of the chamber. In this research, the diaphragm rupture moment is estimated based on the initial shock speed and the longitudinal length of the main chamber, and validated with the high-speed video images such that the error between the estimation time and the measured time is within 0.5%. Ignition delay times decrease with an increase in the amount of hydrogen in the fuel mixture, the amount of mass of the hot-jet gases from the pre-chamber, and with a decrease in the equivalence ratio. A Schlieren system has been established to visualize the characteristics of the shock wave, and the flame front. Schlieren photography shows the density gradient of a subject with sharp contrast, including steep density gradients, such as the flame edge and the shock wave. The flame propagation, gas oscillation, and the shock wave speed are measured using the Schlieren system. An image processing code using MATLAB has been developed for measuring the flame front movement from Schlieren images. The trend of the maximum pressure in the main chamber with respect to the equivalence ratio and the fuel mixture ratio describes that the equivalence ratio 0.8 shows the highest maximum pressure, and the fuel ratio 50:50 condition reveals lower maximum pressure in the main chamber than the 30:70 condition. After the combustion occurs, the frequency of the pressure oscillation by the traversing pressure wave increases compared to the frequency before ignition, showing a similar trend with the maximum pressure in the chamber. The frequency is the fastest at the equivalence ratio of 0.8, and the slowest at a ratio of 0.4. The fuel ratio 30:70 cases show slightly faster frequencies than 50:50 cases. Two different combustion behaviors, fast and slow combustion, are observed, and respective characteristics are discussed. The frequency of the flame front oscillation well matches with that of the pressure oscillation, and it seems that the pressure waves drive the flame fronts considering the pressure oscillation frequency is somewhat faster. Lastly, a feedback mechanism between the shock and the flame is suggested to explain the fast combustion in a constant volume chamber with the shock-flame interactions.

碩士
國立中興大學
環境工程學系所
105
Since Industrial Revolution, people use fossil fuel as energy sources. At present, the dependence on fossil fuels to meet energy demand have created environmental issues by the generation of anthropogenic greenhouse gases. As the demand for energy increases, it is important to seek alternative energy. Dry reforming of methane reaction has received much attention because it can provide a good way to convert the methane and carbon dioxide into a valuable synthesis gas, which is a mixture of hydrogen and carbon monoxide. However, because both reactants of CH4 and CO2 contain carbon, the dry reforming of methane reaction typically suffers deactivation from severe coke formation. In this study, MgAl2O4 spinel was synthesized by solution combustion method. Then, 10% nickel was impregnated onto the MgAl2O4−supported by impregnation method. We adjusted four parameters (magnesium metal precursor species, fuel type, fuel to oxidizer ratio and synthesis temperature) during the combustion process to realizing the influence of the spinel morphology. The effects of preparation parameters for the spinel supports on catalytic activity for dry reforming of methane reaction were studied. From the results, the MgAl2O4 spinel was highly effective prepared by magnesium nitrate and urea at 500 oC, and that nickel particles dispersed well on the MgAl2O4 support, and it has a strong interaction between Ni and spinel. The Ni/MgAl2O4 inhibited reverse-water shift reaction, which leads to a high catalytic performance and H2/CO. When the combustion reactions of fuel/magnesium metal precursor were carried out in stoichiometric condition, the Ni/MgAl2O4 catalyst generated high catalytic activity and hydrogen yield. As the fuel-to-metal precursor molar ratio increased, the catalyst exhibited high activity and superior anti-coking for dry reforming of methane due to the increased metal-support interaction.

With a goal toward a net-zero energy supply, hydrogen, hydrogen-enriched natural gas, and biofuels, which reduce the carbon footprint, are actively being considered for firing stationary gas turbine engines. In this regard, the longitudinally-staged combustion concepts have been demonstrated to achieve low emissions and good fuel flexibility while operating over a wide range of load conditions. A particular implementation of such a concept is the constant pressure sequential combustor in Ansaldo Energia’s GT36 gas turbine comprised of two fuel stages implementing lean premixed combustion with different characteristics. In the first stage, the flame is stabilized aerodynamically and combustion occurs mainly by premixed flame propagation. The product gases from the first stage combustion are then blended with additional air in a dedicated mixer before entering the second stage combustor (also called the reheat burner) where additional fuel is added and combustion takes place at reheat conditions, i.e. it is controlled by spontaneous ignition due to the high temperature of the reactants. The reheat burner operation plays an important role in achieving the overall desired combustion characteristics. Recently, a high fidelity three-dimensional direct numerical simulation of the reheat flame with hydrogen fuel was performed to identify the modes of combustion and quantify their contributions towards fuel consumption at atmospheric conditions. However, the pressure in the practical system varies between 15 and 20 bar. The primary objective of this work is to understand the pressure scaling of flame in a reheat combustor using two-dimensional simulations. The computational domain consists of a mixing duct followed by a sudden expansion into a combustion chamber. A nine species, twenty-one reactions hydrogen-air mechanism is used for the detailed chemistry. Results show that at higher pressures the flame position is very sensitive to small perturbations in pressure/temperature, and can easily transition to an unstable state of combustion. Further, results on the flame structure and the role of auto-ignition will be presented. Chemical explosive mode analysis (CEMA) was used to qualify the fuel consumption rate between the auto-ignition and the flame propagation modes. With the increase in pressure, a significant decrease in fuel consumption due to auto-ignition was observed. To assess the effects of three-dimensional small-scale structures that are absent in two-dimensional simulations, a comparison of results between the two simulations was performed at atmospheric pressure. To understand the performance compromises observed in the hydrogen-rich regime of hydrogen-natural gas blends, further simulations with methane blended hydrogen were performed. Results illustrate a significant change in the flame stability and its structure. A detailed analysis of these results is also presented.

The fact that there is an increase in the price of fossil fuels, and that environmental changes are occurring due to pollutant emissions, makes it imperative to find alternative fuels that are less polluting and cheaper. Gas turbines have been particularly developed as aviation engines, but nowadays they can find applicability in many areas and the fact that they have multiple fuel applications, makes them a very important subject of study. The main objective of this dissertation is to evaluate through a CFD analysis on FLUENT the performance of the combustion in a gas turbine can combustor, fed with methane, hydrogen and methane-hydrogen mixtures taking a particular interest in the pollutants emissions. In the end a fuel optimization was carried on to evaluate the average mass fraction of the pollutants CO, CO2 and NOx at the exit of the can combustor, and also a brief evaluation of the static temperature and pressure, and velocity magnitude in the several CFD simulations was executed.
O facto do preço dos combustíveis fósseis estar cada vez mais elevado, e de estarem a ocorrer mudanças ambientais devido à emissão de poluentes por parte destes combustíveis torna imperativo encontrar combustíveis alternativos mais baratos e menos poluentes. As turbinas de gás têm sido particularmente desenvolvidas como motores de aeronaves, no entanto nos dias que correm elas podem encontrar aplicabilidade nas mais diversas áreas, e aliando a isto o facto das turbinas de gás possuírem diferentes aplicabilidades de combustíveis faz delas um importante tema de estudo. Sendo assim o principal objectivo desta dissertação é avaliar através de uma análise CFD no FLUENT o desempenho da combustão num ?can combustor? de uma turbina de gás, quando alimentado com metano, hidrogénio e misturas de metano-hidrogénio, tendo especial interesse na emissão de poluentes. Posto isto foi realizada uma optimização do combustível por forma a avaliar os valores médios da fracção mássica dos poluentes CO, CO2 e NOx à saída do "can combustor", e de notar que uma breve análise à temperatura estática, à pressão estática e à magnitude da velocidade das várias simulações foi também executada.

Indiana University-Purdue University Indianapolis (IUPUI)
A chemically reactive turbulent traversing hot-jet issued from a pre-chamber to a relatively long combustion chamber is experimentally investigated. The long combustion chamber represents a single channel of a wave rotor constant-volume combustor. The issued jet ignites the fuel-air mixture in the combustion chamber. Fuel-air mixtures are prepared with different hydrocarbon fuels of different reactivity, namely, methane, propane, methane-hydrogen blend, methane-propane blend and methane-argon blend. The jet acts as a rapid, distributed and moving source of ignition, traversing across one end of the long combustion chamber entrance, induces complex flow structures such as a train of counter rotating vortices that enhance turbulent mixing. In general, a stationary hot-jet ignition process lack these structures due to absence of the traversing motion. The ignition delay of the fuels and fuel blends are measured in order to obtain insights about constant-volume pressure-gain combustion process initiated by a moving source of ignition and also to glean useful data about design and operation of a wave rotor combustor. Reactive hot-jets are useful to ignite fuel-air mixtures in internal combustion engines and novel wave rotor combustors. A reactive hot-jet or puff of gas issued from a suitably designed pre-chamber can act as rapid, distributed and less polluting ignition source in internal combustion engines. Each cylinder of the engine is provided with its own pre-chamber. A wave rotor combustor has an array of circumferentially arranged channels on a rotating drum. Each channel acts as a constant-volume combustor and produces high pressure combustion products. Implementation of hot-jet igniter in a wave rotor combustor offers utilization of available high temperature and high pressure reactive combustion products residing in each of the wave rotor channels as a distributed source of ignition for other channels, thus requiring no special pre-chamber in ultimate implementation. Such reactive products or partially combusted and radical-laden gases can be issued from one or more channels to ignite the fuel-air mixture residing in another channel. Due to the rotation of the rotor channels, the issued hot-jet would have relative motion with respect to one end of the channels and traverse across it. This thesis aims to investigate the effects of jet traverse time experimentally on ignition delay along with other important factors that affect the hot-jet ignition process such as fuel reactivity, fuel-air mixture preparation quality and stratification and equivalence ratio. In this study, the traversing motion of the hot-jet at one end of the main combustion chamber is implemented by keeping the main combustion chamber stationary and rotating a pre-chamber at speeds of 400 RPM, 800 RPM and 1200 RPM. The rotational speeds correspond to jet traverse times of 16.9 ms, 8.4 ms and 5.6 ms respectively. The fuel-air mixture inside the channel is at room temperature and pressure initially and its equivalence ratio is varied from 0.4 to 1.3. The cylindrical pre-chamber is initially filled with a 50%-50% methane-hydrogen blend fuel and air mixture at room pressure and temperature and at an equivalence ratio of 1.1. These conditions were chosen based on prior evidence of ignition rapidity with the jet properties. The hot-jet is issued by rupturing a thin diaphragm isolating the chambers. Using high frequency dynamic pressure transducer pressure histories, the diaphragm rupture moment and onset of ignition is measured. Pressure traces from two transducers are employed to measure the initial rupture shock speed and ignition delay. Schlieren images recorded by a high speed camera are used to identify ignition moment and validate the measured ignition delay times. Ignition delay is defined as time interval from the rupture moment to onset of ignition of fuel-air mixture in the main combustion chamber. The ignition system is designed to produce diaphragm rupture at almost exactly the moment when jet traverse begins. Ignition delay times are measured for methane, propane, methane-hydrogen blends, methane-propane blend and methane-argon blend. The equivalence ratio of the fuel-air mixtures varied from 0.4 to 1.3 in steps of 0.1 for stationary-hot jet ignition experiments and in steps of 0.3 for traversing hot-jet ignition experiments. Hot-jet ignition delay of fuel-air mixtures, for both stationary hot-jet ignition process and traversing hot-jet ignition process, generally increased with increasing equivalence ratio. For stationary hot-jet ignition delay, the minimum ignition delay occurs between Ф = 0.4 to Ф = 0.6 for the tested fuel-air mixtures. Both stationary and traversing hot-jet ignition delay depended on fuel reactivity. In particular, the shortest ignition delay times were observed for a fuel blend containing hydrogen. Among pure fuels propane exhibited slightly shorter ignition delay times, on average, compared to pure methane fuel. The addition of argon to pure methane, intended to control fuel density and buoyancy, increased the ignition delay. The traversing hot-jet ignition delay generally increased with increasing jet traverse times. To explain the variations in the measured hot-jet ignition delay and investigate qualitatively the effect of buoyancy on flame propagation and mixture stratification, the fuel-air mixture inside the main combustion chamber was ignited using a spark plug to generate a propagating laminar flame. The laminar flame propagated within the flammable regions of the channel in ways that sensitively reveal variations in local fuel-air mixture equivalence ratio. Flame luminosity images from a high speed camera and schlieren images revealed the fuel-air mixture being highly stratified depending on the density difference between the fuel and air and provided mixing time (0 s, 10s ,30s for most fuels). The lack of buoyancy-driven spreading caused the fuel to remain in the vicinity of the fuel injector resulting in significant longitudinal stratification of the fuel-air mixture. Lighter fuels stratified to the top of the chambers and heavier fuel stratified to the bottom of the chamber. Increasing the mixing time, which is defined as the time interval from end of fuel injection into the chamber to the triggering of the spark plug, improved the buoyancy-driven spreading and extended the flammable region as evidenced by the schlieren and flame luminosity images. The maximum pressure developed in the combustor for the three ignition processes, namely, stationary hot-jet ignition, traversing hot-jet ignition and spark ignition process in laminar flame propagation experiments were compared. Stationary hot-jet ignition process generally exhibited the highest pressure being developed in the chamber. Variations in heat loss, fuel-air mixture leakage and mass addition mechanisms reduced the maximum pressure for spark ignition and traversing hot-jet ignition process.

Indiana University-Purdue University Indianapolis (IUPUI)
A constant-volume combustor is used to investigate the ignition initiated by a traversing jet of reactive hot gas, in support of combustion engine applications that include novel wave-rotor constant-volume combustion gas turbines and pre-chamber IC engines. The hot-jet ignition constant-volume combustor rig at the Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) was used for this study. Lean premixed combustible mixture in a rectangular cuboid constant-volume combustor is ignited by a hot-jet traversing at different fixed speeds. The hot jet is issued via a converging nozzle from a cylindrical pre-chamber where partially combusted products of combustion are produced by spark- igniting a rich ethylene-air mixture. The main constant-volume combustor (CVC) chamber uses methane-air, hydrogen-methane-air and ethylene-air mixtures in the lean equivalence ratio range of 0.8 to 0.4. Ignition delay times and ignitability of these combustible mixtures as affected by jet traverse speed, equivalence ratio, and fuel type are investigated in this study.

Indiana University-Purdue University Indianapolis (IUPUI)
Ignition of a combustible mixture by a transient jet of hot reactive gas is important for safety of mines, pre-chamber ignition in IC engines, detonation initiation, and in novel constant-volume combustors. The present work is a numerical study of the hot-jet ignition process in a long constant-volume combustor (CVC) that represents a wave-rotor channel. The mixing of hot jet with cold mixture in the main chamber is first studied using non-reacting simulations. The stationary and traversing hot jets of combustion products from a pre-chamber is injected through a converging nozzle into the main CVC chamber containing a premixed fuel-air mixture. Combustion in a two-dimensional analogue of the CVC chamber is modeled using global reaction mechanisms, skeletal mechanisms, and detailed reaction mechanisms for four hydrocarbon fuels: methane, propane, ethylene, and hydrogen. The jet and ignition behavior are compared with high-speed video images from a prior experiment. Hybrid turbulent-kinetic schemes using some skeletal reaction mechanisms and detailed mechanisms are good predictors of the experimental data. Shock-flame interaction is seen to significantly increase the overall reaction rate due to baroclinic vorticity generation, flame area increase, stirring of non-uniform density regions, the resulting mixing, and shock compression. The less easily ignitable methane mixture is found to show higher ignition delay time compared to slower initial reaction and greater dependence on shock interaction than propane and ethylene. The confined jet is observed to behave initially as a wall jet and later as a wall-impinging jet. The jet evolution, vortex structure and mixing behavior are significantly different for traversing jets, stationary centered jets, and near-wall jets. Production of unstable intermediate species like C2H4 and CH3 appears to depend significantly on the initial jet location while relatively stable species like OH are less sensitive. Inclusion of minor radical species in the hot-jet is observed to reduce the ignition delay by 0.2 ms for methane mixture in the main chamber. Reaction pathways analysis shows that ignition delay and combustion progress process are entirely different for hybrid turbulent-kinetic scheme and kinetics-only scheme.

碩士
大同大學
化學工程學系(所)
99
In this work, tubular and plate reactors for carrying out methanol steam reforming reactions are simulated using Fluent software. The simulation results using Fluent software are confirmed by the performance of an isothermal plug flow tubular reactor in which the methanol steam reforming reactions are performed. Among the eight different reactor designs, the catalytic plate reactor packed with small catalyst particles coupling endothermic methanol steam reforming and hydrogen combustion system give the best performance. The conversion of methanol is 0.63 for the isothermal (250℃) plug flow tubular reactor while that for the catalytic plate reactor packed with small catalyst particles coupling endothermic methanol steam reforming and hydrogen combustion system is 0.6 if the mass transfer resistance between the gas reactants and the catalyst particles is not included in the simulation using Fluent software.

碩士
國立中興大學
機械工程學系所
100
In this paper, a single-cylinder motorcycle engine and a steam reformer were used as a test stand to investigate the effect of adding hydrogen mixture on the engine efficiency and exhaust pollution. Addition of reformed gas may have two effects on engine efficiency. One is the enhancement of combustion due to the high speed of flame propagation characteristics of hydrogen, and the other is attributed to the recovery of exhaust thermal energy to improve the fuel heating value. It was found in experiment that the engine efficiency can be improved at low load condition as well as high load condition. As the reformulated gas flow was 12.1 L/min, the engine efficiency was promoted to 24.8%, compared with the efficiency of 21.5% for gasoline engine at the same running condition. However, at high load condition, the NO emission was increased to 2550 ppm as the reformulated gas flow was 14.7 L/min. The heat transfer model of the reforming process was also developed in this paper to evaluate the effectiveness of the reformer. It was found that as the engine speed was 5000 rpm and the exhaust temperature was 450℃, if the methanol flow rate was set to 7.92 g/min, a distance of 56 cm is required to complete the physical change of methanol solution, in which the heating of methanol and water vapor from 100℃ to 270℃ takes the major share of 47.1%.

碩士
國立臺北科技大學
材料科學與工程研究所
105
The delafossite structure CuCr1-xFexO2 nanopowders (x = 0-1) was successfully synthesized by self-combustion glycine nitrate process (GNP) which has much higher surface area than bulk powder prepared by traditional solid state reaction. In this study, CuCr1-xFexO2 nanopowders as a precursor for copper based catalyst were applied to steam reforming of methanol (SRM) process for hydrogen production. Catalytic performance was enhanced with the nanoization of CuCr1-xFexO2 powders which leads to a higher surface area and the well dispersion of copper particles. Furthermore, CuCr1-xFexO2 nanopowders could be directly reduced by methanol steam without the typically activation process in hydrogen. Changes of CuCr1-xFexO2 nanopowders were determined by the X-ray diffraction (XRD) analysis. The cotton candy-like porous structure and the dispersion of Cu particles after the SRM process were revealed by scanning electron microscopy (SEM) together with the EDX elemental analysis. Microstructure of as-combusted nanopowders was determined by a transmission electron microscopy (TEM). The BET measurement showed the surface area of self-combusted CuCr1-xFexO2 nanopowders was over ten times larger than the powder prepared by traditional solid-state reaction and basically increased with the iron contents decreased. The production rate of hydrogen was analyzed with a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD).

The present work aimed at designing a thermally efficient microreactor system coupling methanol steam reforming with methanol combustion for autothermal hydrogen production. A preliminary study was performed by analyzing three prototype reactor configurations to identify the optimal radial distribution pattern upon enhancing the reactor self-insulation. The annular heat integration pattern of Architecture C showed superior performance in providing efficient heat retention to the system with a 50 - 150 degrees C decrease in maximum external-surface temperature. Detailed work was performed using Architecture C configuration to optimize the catalyst placement in the microreactor network, and optimize reforming and combustion flows, using no third coolant line. The optimized combustion and reforming catalyst configuration prevented the hot-spot migration from the reactor midpoint and enabled stable reactor operation at all process flowrates studied. Best results were obtained at high reforming flowrates (1800 sccm) with an increase in combustion flowrate (300 sccm) with the net H2 yield of 53% and thermal efficiency of >80% from methanol with minimal insulation to the heatintegrated microchannel network. The use of the third bank of channels for recuperative heat exchange by four different reactor configurations was explored to further enhance the reactor performance; the maximum overall hydrogen yield was increased to 58% by preheating the reforming stream in the outer 16 heat retention channels. An initial 3-D COMSOL model of the 25-channeled heat-exchanger microreactor was developed to predict the reactor hotspot shape, location, optimum process flowrates and substrate thermal conductivity. This study indicated that low thermal conductivity materials (e.g. ceramics, glass) provides enhanced efficiencies than high conductivity materials (e.g. silicon, stainless steel), by maintaining substantial thermal gradients in the system through minimization of axial heat conduction. Final summary of the study included the determination of system energy density; a gravimetric energy density of 169.34 Wh/kg and a volumetric energy density of 506.02 Wh/l were achieved from brass architectures for 10 hrs operation, which is higher than the energy density of Li-Ion batteries (120 Wh/kg and 350 Wh/l). Overall, this research successfully established the optimal process flowrates and reactor design to enhance the potential of a thermally-efficient heat-exchanger microchannel network for autothermal hydrogen production in portable applications.

碩士
國立成功大學
系統及船舶機電工程學系
103
Exhaust emission from internal combustion engines is one of the major sources of air pollution, so the scholars at home and abroad in recent decades have put lots of effort on the pollution reducing technologies of engine and alternative fuels research. Because of the excellent combustion characteristics of hydrogen, the issue of it combined with the engine has received considerable attention. However, the carrying and storage problems of hydrogen still need to be resolved. This thesis is to explore diesel engine exhaust heat recovery system integrated with the methanol steam reforming method and discuss the performance and exhaust emission characteristics. Research is divided into two parts: the first part is to discuss the operating parameters of hydrogen-producing conditions and change feed rate of methanol-water solution under the appropriate working condition. Employing the concentration of hydrogen-rich gas and flow rate of carrier gas can obtain the hydrogen flow rate. The second part is to conduct experiments with diesel engine at different loads, and the author also adjusts the input rate of methanol water solution to control the hydrogen-rich gas production and changes the exhaust gas recirculation proportion for experiment. The inlet tank makes hydrogen-rich gas and air mix uniformly before conducting into cylinder. The cylinder gas pressure crank angle data, intake air temperature, exhaust gas temperature, air flow rate, exhaust flow rate, and exhaust pollution concentrations (NOX, Smoke, and PM2.5) are measured by changing exhaust gas recirculation (EGR) ratio and amount of hydrogen-rich gas for diesel engine operating under fixed engine speed and various loads. The BTE, heat release rate, and the concentrations of exhaust pollution are then analyzed. In addition, this thesis applies KIVA3V-RELEASE2 adding detailed chemical reaction for numerical computation to analyze effect of using hydrogen-rich gas reformed from aqueous methanol solution. Comparison of experimental results with numerical results can confirm the reliability of the experiment. Experimental results indicate that the reaction temperature directly influences hydrogen production. If there is insufficient supply of heat to decrease the reaction temperature, the production of hydrogen-rich gas will decrease significantly. While the temperature and S/C ratio is set up under the optimal working condition, the author changes the feed rate of the aqueous methanol solution to adjust the producing amount of hydrogen. The simulation and experimental results show that adding hydrogen-rich gas in diesel engines can increase the heat release rate under the premixed combustion phase. The appropriate proportion of exhaust gas recirculation helps reduce the exhaust pollution such as Smoke, PM2.5, and NOX. However, the higher peak pressures and temperatures in the engine cylinder will lead to harmful NOX when the hydrogen-rich gas is added.

Σκοπός της παρούσας διδακτορικής διατριβής ήταν η ανάπτυξη ενός αποτελεσματικού καταλυτικού συστήματος με βάση το χαλκό, για την αναμόρφωση της μεθανόλης. Για το σκοπό αυτό εξετάστηκαν οι καταλυτικές ιδιότητες τριών συστημάτων βασιζόμενων σε καταλύτες χαλκού και παρασκευασμένων με τη μη συμβατική μέθοδο της καύσης: CuO-CeO2, τροποποιημένων καταλυτών CuO-CeO2 και Cu-Mn-O για την προαναφερθείσα διεργασία, καθώς και τα βέλτιστα δείγματα των καταλυτών CuO-CeO2 και Cu-Mn-O υποστηριγμένων σε μεταλλικούς αφρούς Al. Τα φυσικοχημικά χαρακτηριστικά των καταλυτών CuO-CeO2, βρέθηκαν να εξαρτώνται από τις παραμέτρους σύνθεσης. Ο βέλτιστος καταλύτης παρασκευάστηκε με λόγο Cu/(Cu+Ce)= 0.15. Στους τροποποιημένους καταλύτες CuO-CeO2, ένα μέρος του τροποποιητή εισχωρεί στο πλέγμα της δημήτριας, οδηγώντας στο σχηματισμό στερεού διαλύματος. Αυτό είχε ως αποτέλεσμα να επηρεαστούν τα φυσικοχημικά χαρακτηριστικά των δειγμάτων, αλλά και η καταλυτική συμπεριφορά τους. Οι σπινελικοί καταλύτες Cu-Mn-O είναι πολύ ενεργοί παρά τη μικρή ειδική επιφάνειά τους. Η ενεργότητά τους είναι συγκρίσιμη με αυτή των εμπορικών καταλυτών Cu-Zn-Al. Ο βέλτιστος καταλύτης ήταν αυτός με λόγο Cu/(Cu+Mn)= 0.30. Εξίσου αποδοτικοί για την παραγωγή υδρογόνου μέσω αναμόρφωσης της μεθανόλης, μονολιθικοί καταλύτες Cu-Ce/Al foam και Cu-Mn/Al foam παρασκευάστηκαν με τη μέθοδο της καύσης. Με βάση τα ευρήματα της ισοτοπικής μελέτης, προτείνεται για τον καταλύτη Cu-Mn-O ότι η αναμόρφωση πραγματοποιείται αποκλειστικά μέσω μηχανισμού που περιλαμβάνει τον ενδιάμεσο σχηματισμό μυρμηκικού μεθυλεστέρα. Για τους καταλύτες Cu-Ce-O και Cu-Zn-Al πραγματοποιείται ταυτόχρονα και μηχανισμός που περιλαμβάνει ως ενδιάμεσο είδος το διοξομεθυλένιο.
The scope of the present thesis was the development of an effective catalytic copper-based system for methanol reforming. The catalytic properties of three different copper-based systems prepared via the non conventional combustion method, were investigated for the aforementioned process: CuO-CeO2, modified CuO-CeO2 and Cu-Mn-O, as well as the optimal CuO-CeO2 and Cu-Mn-O oxide cata¬lysts supported on Al metal foam. The physicochemical characteristics of CuO-CeO2 catalysts were found to be influenced by the parameters of the synthesis. The optimal catalyst was prepared with Cu/(Cu+Ce) ratio equal to 0.15. In the case of modified CuO-CeO2 catalysts, at least part of dopant cations gets incorporated into the CeO2 lattice leading to solid solution formation. As a result, the physicochemical characteris¬tics of the samples were influenced, as well as their catalytic performance. Cu-Mn spinel oxide catalysts were found to be highly active despite their low surface area. Their activity is comparable to that of commercial Cu-Zn-Al catalysts. The optimal catalyst was prepared with a Cu/(Cu+Mn) ratio equal to 0.30. Structured Cu-Ce/Al foam and Cu-Mn/Al foam catalysts prepared via in situ combustion method were equally effective for hydrogen production via methanol reforming. Based on the findings of an isotopic study, a mechanism has been proposed for the reforming reaction over Cu-Mn-O, where methyl formate is formed as a reaction intermediate. An additional reaction mechanism is taking place over Cu-Ce-O and commercial Cu/ZnO/Al2O3 catalysts, resulting in the intermediate dioxomethylene.