L'optimisation des systèmes d'allumage est un paramètre critique pour la définition des foyers de combustion industriels. Des simulations aux grandes échelles (ou LES pour Large-Eddy Simulation) d'un brûleur de type bluff-body non pré-mélangé ont été menées afin de comprendre l'influence de la position de la bougie sur la probabilité d'allumage. La prise en compte de la combustion est basée sur une méthode de tabulation de la chimie détaillée (PCM-FPI pour Presumed Conditional Moments - Flame Prolongation of ILDM). Les résultats de ces simulations ont été confrontés des résultats expérimentaux disponibles dans la littérature. Dans un premier temps, les mesures de vitesse et du champ de richesse à froid sont comparées aux résultats de la simulation pour évaluer les capacités de prédiction en terme de structure de l'écoulement et de mélange turbulent. Un suivi temporel des vitesses et de la fraction de mélange est réalisé à différents points pour déterminer les fonctions de densité de probabilité (ou PDF)des variables caractéristiques de l'écoulement, à partir des champs résolus en LES. Les PDFs ainsi obtenues servent l'analyse des phénomènes d'allumages réussis ou déficients rencontrés expérimentalement. Des simulations d'allumage forcé ont été effectuées pour analyser les différents scénarios de développement de la flamme. Les corrélations entre les valeurs locales (fraction de mélange, vitesse) autour de la position d'allumage et les chances de succès de développement du noyau de gaz brûlés sont alors discutées. Enfin, une extension de la méthode PCM-FPI avec prise en compte des effets d'étirement est développée à l'aide d'une analyse asymptotique, puis confrontée aux résultats de mesures expérimentales. / The optimization of the ignition process is a crucial issue in the design of many combustion systems. Large eddy simulation (LES) of a conical shaped bluff-body turbulent non-premixed burner has been performed to study the impact of spark location on ignition success. The chemistry part of the simulation is done using tabulated detailed chemistry approach. This burner was experimentally investigated by Ahmed et al at Cambridge (UK). The present work focuses on the case without swirl for which detailed measurements are available. First, cold fkow measurements of velocities and mixture fraction are compared with their LES counterparts, to assess the prediction capabilities of simulations in terms of flow and turbulent mixing. Time history of velocities and mixture fraction are recorded at selected spots, to probe the resolved probability density function (pdf) of flow variables, in an attempt to reproduce, from the knowledge of LES resolved instantaneous flow conditions, the experimentally observed reasons of success or failure of spark ignition. A flammability map is also constructed from the resolved mixture fraction pdf and compared with its experimental counterpart. LES of forced ignition is then performed using flamelet fully detailed tabulated chemistry combined with presumed pdfs (PCM-FPI). Various scenarios of flame kernel development are analyzed and correlated with typical flow conditions observed in this burner. The correlations between velocities and mixture fraction values at the sparking time and the success or failure of ignition are then further discussed and analysed. The rate of flame development during successful or unsuccessful ignition events are analysed and compared against experimental observations. Finally, from asymptotic flame analysis, a novel approach has been proposed to include flame straining effects in the PCM-FPI method developped at CORIA-CNRS. The new model overcomes the problem associated with classical PCM-FPI closure to model kernel quenching due to intense local turbulence. Computations are done including the flame straining effects and the effect brought by the new model on kernel development is analysed in detail.

<p>A novel two-loop estimation and control strategy is proposed to reduce the natural gas (NG) spark-ignition (SI) engine tail pipe emissions, with focus on the outer loop development. In the outer loop, an fractional oxidation state (FOS) estimator consisting of a three-way catalyst (TWC) model and an extended Kalman-filter is used to estimate the real-time TWC's FOS, and a robust controller is used to control the first-half TWC's FOS by manipulating the desired engine lambda (i.e., air–fuel equivalence ratio; lambda=1 at stoichiometry). The outer loop estimator and controller are combined with an industry-production baseline inner loop controller, which controls the engine $\lambda$ based on the desired lambda value. This novel two-loop control strategy reduces more CH4 and NOx emissions over no-outer-loop control strategy and the conventional two-loop control strategies through simulation. </p> <p><br></p> <p>Engine with and without fuel cut-off are both investigated. Although fuel cut-off brings better fuel economy, it also over-oxidizes the TWC during fuel cut events, which makes the FOS-based controller's competence in NOx reduction over non-FOS-based controllers less significant. By comparing simulation results with and without fuel cut-off, it shows huge potential for much better emission result if fuel cut-off's side effect can be alleviated. Considering that fuel cut-off generally being cutting engine fueling during zero load periods and introducing unreacted oxygen into the after-treatment system, the best way of dealing with the issue is to cut off or reduce the oxygen input to the TWC during those events. Several advanced engine technologies such as cylinder deactivation and exhaust gas re-circulation are good candidates to approach this issue. </p> <p><br></p> <p>An industry-production Cummins B6.7N natural gas SI engine was installed in the Ray W. Herrick Laboratories for study of variable valve actuation (VVA) technology, for the purpose of evaluating/improving SI engine's fuel efficiency, emission reduction, and engine knock resistance. A one-dimensional, physics-based natural gas SI engine model was investigated and calibrated in GT-Power software. To calculate the burn rates in the cylinder, three different pressure analysis methods were investigated and implemented. It is observed that all six cylinders' pressure curves are different, which in turn render different burn rates cylinder-to-cylinder. Cylinder with a higher peak cylinder pressure has a faster burn rate. Each operating condition has its unique pressure curve, and their burn rates are different under different operating conditions. Considering that the burn rate profile can vary cylinder-to-cylinder and operation-to-operation, to make the GT combustion model work for a larger range of loads, a fixed burn rate model may help in the preliminary research phase, but a predictive combustion model is more preferable.</p> <p><br></p> <p>The GT-Power model's VVA capability is investigated, where intake valve closure (IVC) modulation and cylinder de-activation (CDA) are built and analyzed. To mitigate TWC's over-oxidation issue during engine's fuel cut-off events, the CDA is implemented and simulated to demonstrate its benefit on further emission and fuel consumption reductions.</p>

Call number: LD2668 .T4 1985 S335 / Master of Science

In this thesis, exergy based SI engine model optimisation (EBSIEMO) is studied and evaluated. A four-stroke bi-fuel spark ignition (SI) engine is modelled for optimisation of engine performance based upon exergy analysis. An artificial neural network (ANN) is used as an emulator to speed up the optimisation processes. Constrained particle swarm optimisation (CPSO) is employed to identify parameters such as equivalence ratio and ignition time for optimising of the engine performance, based upon maximising 'total availability'. In the optimisation process, the engine exhaust gases standard emission were applied including brake specific CO (BSCO) and brake specific NOx (BSNOx) as the constraints. The engine model is developed in a two-zone model, while considering the chemical synthesis of fuel, including 10 chemical species. A computer code is developed in MATLAB software to solve the equations for the prediction of temperature and pressure of the mixture in each stage (compression stroke, combustion process and expansion stroke). In addition, Intake and exhaust processes are calculated using an approximation method. This model has the ability to simulate turbulent combustion and compared to computational fluid dynamic (CFD) models it is computationally faster and efficient. The selective outputs are cylinder temperature and pressure, heat transfer, brake work, brake thermal and volumetric efficiency, brake torque, brake power (BP), brake specific fuel consumption (BSFC), brake mean effective pressure (BMEP), concentration of CO2, brake specific CO (BSCO) and brake specific NOx (BSNOx). In this model, the effect of engine speed, equivalence ratio and ignition time on performance parameters using gasoline and CNG fuels are analysed. In addition, the model is validated by experimental data using the results obtained from bi-fuel engine tests. Therefore, this engine model was capable to predict, analyse and useful for optimisation of the engine performance parameters. The exergy based four-stroke bi-fuel (CNG and gasoline) spark ignition (SI) engine model (EBSIEM) here is used for analysis of bi-fuel SI engines. Since, the first law of thermodynamic (the FLT), alone is not able to afford an appropriate comprehension into engine operations. Therefore, this thesis concentrates on the SI engine operation investigation using the developed engine model by the second law of thermodynamic (the SLT) or exergy analysis outlook (exergy based SI engine model (EBSIEM)) In this thesis, an efficient approach is presented for the prediction of total availability, brake specific CO (BSCO), brake specific NOx (BSNOx) and brake torque for bi-fuel engine (CNG and gasoline) using an artificial neural network (ANN) model based on exergy based SI engine (EBSIEM) (ANN-EBSIEM) as an emulator to speed up the optimisation processes. In the other words, the use of a well trained an ANN is ordinarily much faster than mathematical models or conventional simulation programs for prediction. The constrained particle swarm optimisation (CPSO)-EBSIEM (EBSIEMO) was capable of optimising the model parameters for the engine performance. The optimisation results based upon availability analysis (the SLT) due to analysing availability terms, specifically availability destruction (that measured engine irreversibilties) are more regarded with higher priority compared to the FLT analysis. In this thesis, exergy based SI engine model optimisation (EBSIEMO) is studied and evaluated. A four-stroke bi-fuel spark ignition (SI) engine is modelled for optimisation of engine performance based upon exergy analysis. An artificial neural network (ANN) is used as an emulator to speed up the optimisation processes. Constrained particle swarm optimisation (CPSO) is employed to identify parameters such as equivalence ratio and ignition time for optimising of the engine performance, based upon maximising 'total availability'. In the optimisation process, the engine exhaust gases standard emission were applied including brake specific CO (BSCO) and brake specific NOx (BSNOx) as the constraints. The engine model is developed in a two-zone model, while considering the chemical synthesis of fuel, including 10 chemical species. A computer code is developed in MATLAB software to solve the equations for the prediction of temperature and pressure of the mixture in each stage (compression stroke, combustion process and expansion stroke). In addition, Intake and exhaust processes are calculated using an approximation method. This model has the ability to simulate turbulent combustion and compared to computational fluid dynamic (CFD) models it is computationally faster and efficient. The selective outputs are cylinder temperature and pressure, heat transfer, brake work, brake thermal and volumetric efficiency, brake torque, brake power (BP), brake specific fuel consumption (BSFC), brake mean effective pressure (BMEP), concentration of CO2, brake specific CO (BSCO) and brake specific NOx (BSNOx). In this model, the effect of engine speed, equivalence ratio and ignition time on performance parameters using gasoline and CNG fuels are analysed. In addition, the model is validated by experimental data using the results obtained from bi-fuel engine tests. Therefore, this engine model was capable to predict, analyse and useful for optimisation of the engine performance parameters. The exergy based four-stroke bi-fuel (CNG and gasoline) spark ignition (SI) engine model (EBSIEM) here is used for analysis of bi-fuel SI engines. Since, the first law of thermodynamic (the FLT), alone is not able to afford an appropriate comprehension into engine operations. Therefore, this thesis concentrates on the SI engine operation investigation using the developed engine model by the second law of thermodynamic (the SLT) or exergy analysis outlook (exergy based SI engine model (EBSIEM)) In this thesis, an efficient approach is presented for the prediction of total availability, brake specific CO (BSCO), brake specific NOx (BSNOx) and brake torque for bi-fuel engine (CNG and gasoline) using an artificial neural network (ANN) model based on exergy based SI engine (EBSIEM) (ANN-EBSIEM) as an emulator to speed up the optimisation processes. In the other words, the use of a well trained an ANN is ordinarily much faster than mathematical models or conventional simulation programs for prediction. The constrained particle swarm optimisation (CPSO)-EBSIEM (EBSIEMO) was capable of optimising the model parameters for the engine performance. The optimisation results based upon availability analysis (the SLT) due to analysing availability terms, specifically availability destruction (that measured engine irreversibilties) are more regarded with higher priority compared to the FLT analysis.

La réduction des émissions de polluants et la diminution de la consommation sont deux challenges fortement liés auxquels les constructeurs automobiles doivent faire face tout en maintenant les performances des moteurs. Les nouvelles stratégies telle que la réduction de la cylindrée associée à une optimisation de la boucle d'air (forte suralimentation et recirculation de gaz brûlés) possèdent ce potentiel. Cependant elles affectent la stabilité du moteur en favorisant les variations cycle à cycle (VCC) qui correspondent à une fluctuation de la combustion d'un cycle sur l'autre. L'objectif de cette thèse est de développer une méthodologie s'appuyant sur la Simulation aux Grandes Echelles (SGE) capable de prédire les VCC d'un moteur à allumage commandé. Les prédictions sont validées grâce à une base de données expérimentale conçue à l'IFP qui leur est dédiée. Une approche graduelle est employée : l'outil numérique est tout d'abord évalué sur une configuration simplifiée de moteur à piston sans combustion, puis appliqué à un moteur à allumage commandé entraîné pour valider la prédiction de l'aérodynamique interne. Sur cette dernière configuration le couplage avec le modèle de combustion DTFLES est rajouté pour simuler deux points de fonctionnement réactifs. Chacune de ces simulations intègre un ou plusieurs points de modélisation (les tétraèdres en maillage mobile, les modèles de choc et d'allumage, et la cinétique chimique) au préalable testés sur des configurations académiques. Ce travail de recherche montre que l'approche SGE, dans un contexte de calcul massivement parallèle, est un outil prometteur dans l'étude des VCC d'un moteur à allumage commandé de conception récente. / A major challenge for the development of internal combustion engines is to improve fuel economy and to reduce pollutant emissions while maintaining or enhancing engine performances. New strategies using downsizing with high levels of exhaust gas recirculation have this potential, but can impact on the combustion stability and trigger high cycle-to-cycle variations (CCV). The objective of this thesis is to set a methodology based on Large Eddy Simulation (LES) to study CCV of a Spark-Ignition (SI) engine. A gradual approach is used : the numerical tool is first evaluated on a motored axisymmetric piston-cylinder assembly, and then applied on a motored SI engine to validate the in-cylinder aerodynamic predictions. On this last configuration, the coupling with the turbulent combustion model DTFLES is added to simulate two operating points of the indirect injection engine mode. Each of these simulations takes into account one or several modeling key points (tetrahedra with moving mesh, the modelings of shock and ignition, and chemical kinetics) previously tested in academic configurations. This research work shows that LES approach, in the context of massively parallel computing, can be used to study the CCV of a realistic SI engine.

L'allumage et le réallumage de haute altitude présentent de grandes difficultés dans le cadre des chambres de combustion aéronautiques. Le succès d'un allumage dépend de multiples facteurs, des caractéristiques de l'allumeur à la taille des gouttes du spray en passant par le niveau de turbulence au point d'allumage. Déterminer la position optimale de l'allumeur ou le potentiel d'allumage d'une source d'énergie donnée à une position donnée sont ainsi des paramètres essentiels lors du design de chambre de combustion. Le but de ces travaux de thèse est d'étudier l'allumage forcé des chambres de combustion aéronautiques. Pour cela, des Simulation numériques aux Grandes Echelles (SGE) d'écoulements diphasiques réactifs sont utilisées et analysées. Afin de les valider, des données expérimentales issues du banc MERCATO installé à l'ONERA Fauga-Mauzac sont utilisées. Cela permet dans un premier temps de valider la méthodologie ainsi que les modèles utilisés pour les SGE diphasiques évaporantes avant leur utilisation dans d'autres conditions d'écoulement. Le cas diphasique réactif statistiquement stationnaire est ensuite comparé aux données disponibles pour évaluer les modèles en condition réactives. Ce cas est étudié plus en détail à travers l'analyse de caractéristiques de la flamme. Celle-ci semble être le théâtre de régimes de combustion très différents. On note aussi que la détermination de la méthode numérique la plus appropriée pour le calcul d'écoulements diphasiques n'est pas évidente. De plus, deux méthodes numériques différentes peuvent donner des résultats en bon accord avec l'expérience et pourtant avoir des modes de combustion différents. Les capacités de la SGE à correctement calculer un écoulement diphasique réactif étant validé, des SGE du phénomène transitoire d'allumage sont effectuées. La sensibilité observée expérimentalement de l'allumage aux conditions initiales, i.e. à l'instant de claquage, est retrouvé par les SGE. L'analyse met en évidence le rôle prépondérant de la dispersion du spray dans le développement initial du noyau de flamme. L'utilisation des SGE pour calculer les séquences d'allumage fournie de nombreuses informations sur le phénomène d'allumage, cependant d'un point de vue industriel, cela ne donne pas de résultat optimal, à moins de ne tester toutes les positions, ce qui rendrait le coût CPU déraisonnable. Des alternatives sont donc nécessaires et font l'objet de la dernière partie de ces travaux. On propose de dériver un critère local d'allumage, donnant la probabilité d'allumage à partir d'un écoulement diphasique (air et carburant) non réactif instationnaire. Ce modèle est basé sur des critères liés aux différentes phases menant à un allumage réussi, de la formation d'un premier noyau à la propagation de la flamme vers l'injecteur. Enfin, des comparaisons avec des données expérimentales sur des chambres aéronautiques sont présentées et sont en bon accord, indiquant que le critère d'allumage proposé, couplé avec une SGE d'écoulement diphasique non réactif, peut être utilisé pour optimiser la puissance et la position du système d'allumage. / Ignition and altitude reignition are critical issues for aeronautical combustion chambers. The success of ignition depends on multiple factors, from the characteristics of the igniter to the spray droplet size or the level of turbulence at the ignition site. Finding the optimal location of the igniter or the potential of ignition success of a given energy source at a given location are therefore parameters of primary importance in the design of combustion chambers. The purpose of this thesis is to study forced ignition of aeronautical combustion chambers. To do so, Large Eddy Simulations (LES) of two-phase reacting flows are performed and analyzed. First, the equations of the Eulerian formalism used to describe the dispersed phase are presented. To validate the successive LES, experimental data from the MERCATO bench installed at ONERA Fauga-Mauzac are used. It allows to validate the two-phase evaporating flow LES methodology and models prior to its use to other flow conditions. The statistically stationary two-phase flow reacting case is then compared to available data to evaluate the model in reacting conditions. This case is more deeply studied through the analysis of the characteristics of the flame. This last one appears to experience very different combustion regimes. It is also seen that the determination of the most appropriate methodology to compute two-phase flow flame is not obvious. Furthermore, two different methodologies may both agree with the data and still have different burning modes. The ability of the LES to correctly compute burning two-phase flow being validated, LES of the transient ignition phenomena are performed. The experimentally observed sensitivity of ignition to initial conditions, i.e. to sparking time, is recovered with LES. The analysis highlights the major role played by the spray dispersion in the development of the initial flame kernel. The use of LES to compute ignition sequences provides a lot of information about the ignition phenomena, however from an industrial point of view, it does not give an optimal result, unless all locations are tested, which brings the CPU cost to unreasonable values. Alternatives are hence needed and are the objective of the last part of this work. It is proposed to derive a local ignition criterion, giving the probability of ignition from the knowledge of the unsteady non-reacting two-phase (air and fuel) flow. This model is based on criteria for the phases of a successful ignition process, from the first kernel formation to the flame propagation towards the injector. Then, comparisons with experimental data on aeronautical chambers are done and show good agreement, indicating that the proposed ignition criterion, coupled to a Large Eddy Simulation of the stationary evaporating two-phase non-reacting flow, can be used to optimize the igniter location and power.

L'amélioration des moteurs à allumage commandé représente un défi de première importance pour les ingénieurs afin de produire plus d'énergie, de consommer moins de matière première et de réduire les émissions polluantes. Les nouvelles technologies apparues ces dernières années amènent les moteurs de plus en plus proches de leurs limites de fonctionnement, favorisant ainsi des phénomènes néfastes qui doivent être contrôlés. Parmi ces phénomènes, les variations cycle-à-cycle (VCC) doivent être minimisées pour garder une performance optimale et éviter une dégradation rapide du moteur. La Simulation aux Grandes Echelles (SGE) est un outil prometteur afin de prédire numériquement les niveaux de variabilités obtenues lors du design d'un moteur (limitant ainsi les coûteuses campagnes de mesures expérimentales). Ce manuscrit s'est attaché à développer une méthodologie numérique pour la prédiction des variabilités cycliques, à simuler un nombre suffisant de cycles pour pouvoir estimer les niveaux de VCC et à valider les résultats obtenus par rapport aux résultats expérimentaux. La SGE semble capter les points de fonctionnements stable et instable étudiés. Les sources qui provoquent ces VCC ont aussi été analysées et une modification du fonctionnement du moteur a été proposée afin de réduire les VCC. / The improvement of the spark ignition engines is a major challenge for engineers in order to produce more energy, to minimize fuel consumption and to reduce the pollutant emissions. The new technologies which appear in the last years bring the engines closer to their stability limit while increasing various unwanted phenomena. Among these phenomena, cycle-to-cycle variation (CCV) need to be minimized in order to keep the performances as high as possible and avoid damages on the engines. Large Eddy Simulation (LES), which is a very promising tool in order to predict the level of CCV of a given engine, has been used in the present document to simulate a mono-cylinder spark ignition engine. The present document presented a numerical methodology for the prediction of CCV, numerous engine cycles were simulated by LES in order to validate the results in comparison to the experimental findings. The LES seems to be able to capture stable and instable (in terms of CCV) operating points of the engine. In addition, the sources of CCV were also analyzed and a modification of the engine has been proposed to reduce CCV.

O presente trabalho aborda o gerenciamento eletrônico de motores de combustão interna flex, com foco no desenvolvimento de uma estratégia de controle do avanço de ignição em função da ocorrência de combustão anormal conhecida como detonação, para se maximizar o torque de saída do motor. Primeiramente, é desenvolvido um método para a medição da composição de combustível e correção dos parâmetros de tempo de injeção e avanço de ignição, através de um sensor de composição de combustível. Tais parâmetros são definidos através de mapas que trabalham como um sistema de malha aberta. Em seguida, é desenvolvido um método para a leitura e detecção de detonação, em que são estudadas as particularidades do fenômeno para diferentes composições de combustível e a sua relação com a variação da temperatura do gás de escape e torque de saída do motor. Através do método de detecção e do estudo do fenômeno, é desenvolvido uma estratégia para controle do avanço de ignição em função da ocorrência da detonação. Esta abordagem permite ao sistema aumentar o avanço quando não há ocorrência de detonação, mas este avanço adicional é cancelado quando ocorre detonação. O gerenciamento do motor é realizado através de uma ECU de desenvolvimento modelo Flex-ECU, as estratégias de gerenciamento são desenvolvidos através da plataforma ASCET e a aquisição de dados e calibração de parâmetros são executados em uma ferramenta de medição e calibração. Os benefícios que o controle do avanço de ignição traz ao torque do motor são analisados e discutidos em função da rotação e da composição de combustível utilizado. / The present investigation explores the electronic management of internal combustion engines flex fuel, in which the focus is the development of a strategy for the spark advance angle as function of the abnormal combustion occurrence known ad Knock, in order to maximize the output torque. First, a method is developed for measuring the fuel composition and correction of the injection time and spark advance angle parameters through a fuel composition sensor. This parameter is defined through maps that work as an open loop system. Then, a method for detection of knock is developed, the peculiarities of the phenomenon are studied for different fuel compositions and the relationship of the phenomenon with the variation of the exhaust gas temperature and the engine output torque. Through the method of detection and the study of the phenomenon, an algorithm is developed to control the spark advance angle due to the knock occurrence, in which the approach allows the system to increase the angle when there is no occurrence of knock, but this additional angle is reduced when knock is detected. Engine management is performed through a development ECU model Flex-ECU, management algorithms are developed through the ASCET platform and data acquisition and calibration of and parameters is performed through a measurement and calibration platform. The result that the spark advance angle control brings to the engine torque output is analyzed and discussed depending on the rotation and the fuel composition used.

O etanol (álcool etílico) tem sido cada vez mais estudado e testado como combustível alternativo para substituição do uso de alguns derivados de petróleo em motores de combustão interna. O presente trabalho procura abordar o emprego do etanol na forma vaporizada em motores do ciclo Otto, objetivando a obtenção de melhores níveis de rendimento térmico total. Deste modo, um motor para teste de octanagem (motor CFR) foi equipado com um vaporizador de álcool instalado no coletor de escapamento, e após uma série de ensaios, várias análises puderam ser feitas. Essas considerações procuraram se ater a aspectos como rendimento térmico, relação ar/combustível, ângulo de avanço da centelha, temperatura de escape, assim como potência e eficiência volumétrica, levando em conta, sempre, a sua influência no funcionamento geral do motor. Ficou constatado que o motor movido a etanol vaporizado apresenta rendimento consideravelmente maior, menor consumo de combustível e funcionamento mais suave que aqueles verificados quando o mesmo motor e alimentado com álcool líquido. / The ethanol (ethyl alcohol) has been studied more and more as alternative fuel to replace some petroleum derivatives for internal combustion engines. The attached study examines the application of vaporized ethanol for Otto cycle engines, searching for better levels of total thermal efficiency. Therefore, an engine for test of octane number (CFR motor) was equipped with an alcohol vaporizer installed inside the escape pipe, and after many experiences, several analysis were made. The various analysis included aspects as thermal efficiency, air/fuel ratio, advance ignition, escape temperature, power and volumetric efficiency, always considering their influence on the operation of the engine. It was confirmed that the engine moved by vaporized ethanol presents higher thermal efficiency, smaller fuel consumption and smoother working than in case of alimentation by liquid alcohol.

O álcool etílico ou etanol vem se tornando, neste novo século, uma importante referência para estudos e aplicações que procuram um combustível alternativo ao uso de derivados de petróleo em motores de combustão interna. Neste trabalho, o uso do etanol vaporizado pelos gases de escape em motores do ciclo Otto busca a obtenção de melhores níveis de rendimento térmico e emissões de poluentes. Assim sendo, um motor de 1.0 litro foi montado em laboratório com um trocador de calor instalado ao lado do coletor de escapamento, e uma série de testes foram feitos, possibilitando uma cuidadosa análise quanto a rendimento térmico, relação ar/álcool, ângulo de avanço da centelha, temperatura de escape e gases de emissão, entre outros aspectos. Conclui-se que o motor a álcool vaporizado, em certos regimes de funcionamento, apresenta rendimento maior e emissões menores que aqueles verificados no motor a álcool líquido. / The ethyl alcohol or ethanol is becoming, in this new century, an important reference for studies and applications that search for an alternative fuel to be used in internal combustion engines, replacing oil derivatives. In this study, an Otto cycle engine is fueled with ethanol vaporized by the exhaust gases, aiming for better levels of thermal efficiency and exhaust emissions. Therefore, a 1.0 liter engine with a heat exchanger connected to the exhaust manifold was prepared in a test bench, and several tests were made, which allowed a criterious analysis about air/alcohol ratio, spark ignition time, exhaust temperature and exhaust emissions, and others. It was concluded that the engine fueled with vaporized alcohol presents, in some operation points, higher thermal efficiency and less emissions compared to the case of engine fueled with liquid alcohol.