Pollutant control and efficiency improvement propel the need for clean combustion research on internal combustion engines. To design cleaner fuels for advanced combustion engines, gasoline combustion chemistry must be both understood and developed. A comprehensive examination of gasoline combustion chemistry in a jet stirred reactor is introduced in this dissertation. Real gasoline fuels have thousands of hydrocarbon components, which complicate numerical simulation. To mimic the behavior of real gasoline fuels, surrogates, composed of a few hydrocarbon components, are offered as a viable approach. In this dissertation, combustion chemistry of n-heptane, a key surrogate component, is investigated first, followed by an evaluation of a surrogate kinetic model. Finally, real gasoline fuels are assessed with the surrogate kinetic model. Mass spectrometry was employed to measure intermediates in n-heptane low temperature chemistry. Reaction pathways of the observed intermediates were proposed and clarified. n-Heptane low temperature oxidation reaction scheme was expanded by the proposed reactions. After surrogate proposal and formation, a surrogate kinetic model was examined. Low temperature and high temperature chemistry were observed and predicted. The octane number and composition effect on low temperature oxidation reactivity were revealed. High temperature combustion chemistry was found to be similar among the different surrogates, and the surrogate kinetic model reproduced surrogate behavior well in both low and high temperatures. Finally, the proposed surrogate model was examined using real gasoline fuels. Five real FACE (fuel for advanced combustion engines) gasolines were selected as target fuels to cover a wide range of octane number, sensitivity and hydrocarbon compositions. Low temperature oxidation chemistry was investigated for two intermediate octane number gasolines, FACE A and C. For a high octane number gasoline, FACE F, key pollutant production pathways were the focus of high temperature combustion chemistry. Two low octane number gasolines, FACE I and J, were compared with three other FACE gasolines to clarify gasoline combustion chemistry over a wide range. The gasoline surrogate chemical kinetic model proved to be a comprehensive, viable, accurate and powerful approach for numerical simulations. The proposed gasoline surrogate chemical kinetic model can aid in the numerical design of advanced combustion engines.

La réduction des émissions de CO2 et de polluants est un des enjeux essentiels pour faire face aux problèmes liés au changement climatique. Dans le secteur des transports, la technologie de recirculation des gaz d’échappement (EGR) est souvent utilisée dans les moteurs turbo-compressés à allumage commandé pour réduire la consommation de carburant, inhiber les risques de cliquetis et réduire les émissions de NOx. Cependant, des taux d’EGR élevés restent difficiles à atteindre car ils réduisent le dégagement de chaleur et la stabilité du moteur. L'augmentation du niveau de turbulence et la mise en oeuvre de systèmes à allumage commandé avancés n’apportant pas d'améliorations suffisantes dans des conditions aussi extrêmes, la chimie de la combustion pour les très hautes dilutions suscite un intérêt croissant. Le présent travail vise à comprendre la chimie de combustion des flammes prémélangées essence/air très diluées et à établir un mécanisme cinétique détaillé par modélisation multi-échelle afin de prévoir les caractéristiques de combustion avec une précision suffisante dans des conditions de forte dilution.Ce travail adopte une approche de modélisation multi-échelle et cible la vitesse de flamme laminaire (SL) d'un substitut d'essence, appelé TRFE et qui est constitué d'isooctane, de n-heptane, de toluène et d'éthanol. Pour la modélisation à l’échelle microscopique, la réaction entre le cétène et le radical hydroxyle, qui pourrait être importante pour la SL dans des conditions très diluées, est étudiée théoriquement à l'aide de méthodes de structure électronique ab initio pour la surface d'énergie potentielle (PES) et Rice -- Ramsperger -- Kassel -- Marcus Theory couplé à l'équation maîtresse (RRKM / ME) pour les coefficients de vitesse. Des PES détaillées sont obtenues, les voies dominantes sont identifiées et leurs coefficients de vitesse phénoménologiques sont dérivés pour être utilisés dans la modélisation de la combustion. Pour la modélisation à l'échelle macroscopique, les paramètres cinétiques, thermodynamiques et de transport importants pour la vitesse de la flamme laminaire dans des conditions très diluées sont d'abord identifiés à l'aide d'une analyse de sensibilité réalisée sur une version initiale du mécanisme TRFE de départ. Les réactions sensibles impliquent principalement HO2, les espèces C2 - C3 et des radicaux issus du carburant. Le mécanisme initial, via un travail spécifique à chacun des sous-mécanismes, est mis à jour à l'aide des paramètres cinétiques les plus récents issus de la littérature. Enfin, un mécanisme détaillé adapté aux calculs de vitesse de flamme laminaire dans des conditions de forte dilution est validé. Une corrélation mathématique de SL est établie pour l'utilisation dans des simulations numériques de la dynamique des fluides (CFD). / Reducing CO2 and pollutant emission is the essential challenge when dealing with climate change problems. In the transport sector, exhaust gas recirculation (EGR) technology is often used in turbocharged gasoline spark ignition (SI) engines to increase fuel economy, inhibit knock tendency, and reduce NOx emissions. However, high EGR ratios are still difficult to achieve, as they result in reduced heat release and engine stability. As increasing turbulence level and advance spark ignition systems could not bring sufficient improvements at such extreme conditions, growing interest is cast onto the combustion chemistry under high dilution. The present work aims to understand the combustion chemistry of highly-diluted gasoline premixed flames and to establish a detailed kinetic mechanism by multi-scale modeling to predict combustion characteristics with sufficient accuracy at highly-diluted conditions.This work adopts a multi-scale modeling approach, and targets on the laminar flame speed (SL) of a gasoline surrogate, which is named toluene reference fuel with ethanol addition (TRFE) and consist of isooctane, n-heptane, toluene, and ethanol. For micro-scale modeling, the reaction between ketene and hydroxyl radical, which might be important to the SL at highly-diluted conditions, is studied theoretically using ab initio electronic structure methods for the potential energy surface (PES) and Rice–Ramsperger–Kassel–Marcus Theory coupled with Master Equation (RRKM/ME) for the rate coefficients. Detailed PES is obtained, dominant pathways are identified, and their phenomenological rate coefficients are derived to be utilized in combustion modeling. For macro-scale modeling, firstly, important kinetic, thermodynamic, and transport parameters to the laminar flame speed at highly-diluted conditions, are firstly identified using sensitivity analysis based on a starting mechanism. Sensitive reactions are found to mostly involve HO2, C2--C3 species and fuel radicals. Secondly, in the sub-mechanisms where these reactions lies, diluted flames of the corresponding fuels are studied and chemical detail of the dilution effects are explored. The starting mechanism is updated by state-of-the-art kinetics parameters found in the literature for each sub-mechanisms. Finally, a detailed mechanism suitable for laminar flame speed calculations at highly-diluted conditions is established after validation. A mathematical SL correlation is generated for the use in computational fluid dynamic (CFD) simulations.

Cache County and the Wasatch Front, Utah have persistently experienced some of the nation’s worst air quality over the past decade. Elevated PM2.5 concentrations during wintertime “red air day” episodes frequently exceed the National Ambient Air Quality Standards (NAAQS). We investigate the possible effects of two different economic policies in controlling these regional problems. Adapting a model originally developed to calculate the social investment necessary to control nationwide disease outbreaks, we estimate an optimal preventative capital stock (for example, investment in public transportation) of between $4.1 million and $14.1 million to control red air day episodes in Cache County, and $133 million to $1.6 billion dollars to control such episodes in the Wasatch Front. Further, we find that a seasonal gasoline tax rate of roughly $8 per gallon is necessary for policy makers in the Wasatch Front to impose at the pump if their goal is to maintain concentrations below the NAAQS on average during a typical winter-inversion season. This rate is roughly $2 more than the rate calculated for Cache County in a previously published study.

Cette thèse est un travail empirique sur la dispersion des prix, c'est-à-dire le fait qu'un bien identique puisse être vendu à des prix différents, en violation de la célèbre loi du prix unique. L'approche s'inscrit dans une littérature initiée par Stigler (1961), qui note que "la dispersion des prix est (...) la mesure de l'ignorance dans le marché". Il en découle que de simples observations de prix peuvent révéler beaucoup d'information sur le fonctionnement d'un marché.Le premier chapitre étudie l'impact de la création d'une enseigne à bas prix sur le marché français de la distribution de carburant. Cette création implique que de nombreuses stations sont confrontées à une baisse de prix importante d'un proche concurrent. La réaction agrégée mesurée au niveau national est faible, mais masque des hausses et des baisses en proportions équivalentes. L'hétérogénéité des réactions souligne l'importante segmentation du marché. Le second chapitre, utilisant le même jeu de de données, examine la pertinence de modèles qui identifient la dispersion des prix à des équilibres en stratégies mixtes. Empiriquement, on observe que l'ordre des prix des stations concurrentes tend en effet à varier dans le temps, et que sa volatilité croit lorsque la distance qui sépare les points de vente augmente. La dispersion est donc croissante d'un coût recherche supporté par les consommateurs. Par ailleurs, l'enseigne des stations détermine largement leur stratégie de prix. Les stations qui pratiquent les prix les plus bas sont relativement plus susceptibles de maintenir des prix parfaitement alignés sur ceux des proches concurrents, tandis que la dispersion mesurée entre les stations plus onéreuses est corrélée positivement avec le coût du diesel et le nombre de stations présentes sur le marché. Ainsi, les résultats renforcent la thèse de la coexistence d'un marché proche d'une concurrence à la Bertrand avec un marché moins concurrentiel, où des stations tirent parti de frictions importantes.Le dernier chapitre s'intéresse à la grande distribution, s'appuyant sur des données collectées sur un comparateur de prix en ligne. J'observe que les comparaisons réalisées entre chaînes de magasins par le site sont relativement peu informatives compte tenu de l'hétérogénéité des résultats au niveau local. L'échantillon de produits retenu peut en outre conduire à des résultats largement différents. La volatilité des comparaisons augmente avec la distance séparant les supermarchés, ce qui, comme dans le cas du carburant, dénote la présence de coûts de recherche. A l'échelle locale, le niveau des prix ne croit pas avec la concentration approximée par les parts de marché, ce qui conduit à remettre en question la pertinence de cet indicateur en matière de politique publique. La dispersion est positivement corrélée au niveau des prix, ce qui suggère que l'imperfection de l'information permet effectivement aux supermarchés de pratiquer des prix plus élevés qu'en concurrence parfaite. / This thesis is an empirical study of price dispersion, namely the fact that a homogenous good can typically be purchased at various prices, in violation of the famous law of one price. The approach belongs to a literature initiated by Stigler (1961), which notes that “price dispersion is (...) the measure of ignorance in the market”. A noteworthy consequence is that simple price observations can be very informative about competition in a market.The first chapter analyses the impact of the creation of a discount chain on the French retail gasoline market. This creation implies that many gas stations are confronted with a sharp price decrease by a competitor. The aggregate reaction, measured at the national level, is weak but it conceals increases and decreases in equivalent proportions The heterogeneity of measured reactions highlights an important market segmentation. Using the same data, the second chapter explores the relevance of models which identify price dispersion with an equilibrium in mixed strategies. Empirically, the rank of competing gas stations is indeed observed to vary over time, and its volatility is positively correlated with the distance that separates the outlets. Dispersion thus increases with a search cost incurred by customers. The chain affiliation of gas stations largely determines their pricing strategies. Retailers which have low price policies are more likely than others to keep prices aligned with nearby competitors, while dispersion measured between more expensive gas stations is positively correlated with diesel cost and the number of sellers in the market. Results thus provide further support the coexistence of a market close to Bertrand competition with a less competitive market, where gas stations take advantage of significant frictions.The last chapter focuses on grocery stores, using data collected from an online price comparison website. Aggregate national chain comparisons that are displayed on the website are found to provide information of little value to consumers given the heterogeneity observed within store level comparison results. These can furthermore vary significantly depending on the set of compared products. Volatility tends to increase with the distance that separates supermarkets, which, as in the case of gasoline, suggests that search cost influence competition. Within local markets, the measured concentration is negatively correlated with price levels, which leads to question its effective relevance in terms of public policies. Price dispersion is found to increase with market price levels, which is consistent with sellers taking advantage of consumer search costs to post higher prices.

Following stringent mandates from environmental regulatory authorities worldwide, various steps are being implemented to ensure clean combustion with minimum emissions, including fuel dilution, mild combustion and additives. Due to the need to understand combustion characteristics in primary applications (engines and turbines) with minimum emissions, the laminar burning velocity of natural gas has been measured with CO2 dilution and a wide range of blends with higher hydrocarbons. And because it has improved anti-knock quality to reduce greenhouse gas emissions (GHGE), the demand for oxygenated gasoline is now worldwide, making a compelling case for determining combustion behavior of oxygenated gasoline doped with hydrogen, ozone and carbon monoxide. The first section of this dissertation discusses dilution of methane with CO2 at elevated pressures, providing insight into comparative laminar burning characteristics in a wide range of equivalence ratios, particularly significant at elevated initial pressure. Utilizing CHEMKIN, a detailed kinetic study has been performed that explains the varying dependence on dilution ratio controlled by initial pressure. The second phase of this work reports the laminar burning velocity measurement of commercial gasoline. A TPRFE surrogate was used here to investigate burning characteristics and to provide detailed kinetic analysis of gasoline doped with additives (hydrogen, carbon monoxide and ozone). A study was also made of the behavior of gasoline with these additives in practical applications like engine and turbines. For this purpose, laminar burning velocity was measured at elevated pressures and temperatures, by varying the concentrations of synthetic EGR, and followed by measuring turbulent burning velocity at two turbulent intensities.

No description available.

Diesel-ignited gasoline and diesel-ignited methane dual fuel combustion experiments were performed in a single-cylinder research engine (SCRE), outfitted with a common-rail diesel injection system and a stand-alone engine controller. Gasoline was injected in the intake port using a portuel injector, whereas methane was fumigated into the intake manifold. The engine was operated at a constant speed of 1500 rev/min, a constant load of 5.2 bar IMEP, and a constant gasoline/methane energy substitution of 80%. Parameters such as diesel injection timing (SOI), diesel injection pressure, and boost pressure were varied to quantify their impact on engine performance and engineout ISNOx, ISHC, ISCO, and smoke emissions. The change in combustion process from heterogeneous combustion to HCCI like combustion was also observed.

Biomass-derived hydrocarbons that include gasoline, diesel, and jet fuel will help replace finite fossil fuel hydrocarbons of the same range. This study showed that temperature could be controlled in a scaled-up reactor system using three types of syngas. The CO conversion, selectivity and amount of product created from each type of syngas were examined. Clean syngas composed of 40% H2, 20% CO, 12% CO2, 2% CH4, and 26 % N2 was used to test ideal stoichiometric molar values. Clean syngas composed of 19% H2, 20% CO, 12% CO2, 2% CH4, and 47 % N2 was used to test an ideal contaminateree synthesis gas situation to mimic our particular downdraft gasifier. Gasifier wood syngas composed of 19% H2, 20% CO, 12% CO2, 2% CH4, 46 % N2, and 1% O2 was used in this study to determine the feasibility of using gasified biomass syngas to produce gasolinerange hydrocarbons.

Flash boiling may be defined as the finite-rate mechanism that governs phase change in a high temperature liquid that is depressurized below its vapor pressure. This is a transient and complicated phenomenon which has applications in many industries. The main focus of the current work is on modeling flash boiling in injectors used in engines operating on the principle of gasoline direct injection (GDI). These engines are prone to flash boiling due to the transfer of thermal energy to the fuel, combined with the sub-atmospheric pressures present in the cylinder during injection. Unlike cavitation, there is little tendency for the fuel vapor to condense as it moves downstream because the fuel vapor pressure exceeds the downstream cylinder pressure, especially in the homogeneous charge mode. In the current work, a pseudo-fluid approach is employed to model the flow, and the non-equilibrium nature of flash boiling is captured through the use of an empirical time scale. This time scale represents the deviation from thermal equilibrium conditions. The fuel composition plays an important role in flash boiling and hence, any modeling of this phenomenon must account for the type of fuel being used. In the current work, standard, NIST codes are used to model single component fluids like n-octane, n-hexane, and water, and a multi-component surrogate for JP8. Additionally, gasoline-ethanol blends are also considered. These mixtures are azeotropic in nature, generating vapor pressures that are higher than those of either pure component. To obtain the properties of these fuels, two mixing models are proposed that capture this non-ideal behavior. Flash boiling simulations in a number of two and three dimensional nozzles are presented, and the flow behavior and phase change inside the nozzles is analyzed in detail. Comparison with experimental data is performed in cases where data are available. The results of these studies indicate that flash boiling significantly affects the characteristics of the nozzle spray, like the spray cone angle and liquid penetration into the cylinder. A parametric study is also presented that can help understand how the two different time scales, namely the residence time in the nozzle and the vaporization time scale, interact and affect the phenomenon of flash boiling.

No description available.