The usage of novel combustion technologies, such as Moderate or Intense Low-oxygen Dilution (MILD) combustion, in the future energy mix provides both a flexible and reliable energy supply, together with low emissions. The implementation though is highly situational and numerical studies can help in the assessment of said technologies. However, the existing uncertainties in numerical modeling of MILD combustion are quite significant, and as detailed kinetics should be considered while modeling MILD combustion, a major part of this uncertainty can be accredited to the kinetics. Combined with the fact that existing detailed mechanisms have been developed and validated against conventional combustion targets, there exists a gap between the performance of existing mechanism and experimental findings. To handle this discrepancy, Uncertainty Quantification (UQ) and Optimization are highly viable techniques for reducing this misfit, and have therefore been applied in this work. The strategy applied consisted of first determining the reactions which showed the largest impact towards the experimental targets, by not only considering the sensitivity, but also the uncertainty of the reactions. By using a so-called impact factor, the most influential reactions could be determined, and only the kinetic parameters with the highest impact factors were considered as uncertain in the optimization studies. The uncertainty range of the kinetic parameters were then determined using the uncertainty bounds of the rate coefficients, by finding the lines which intercepts the extreme points of these maximum and minimum rate coefficient curves. Based on this prior parameter space, the optimal combination of the uncertain parameters were determined using two different approaches. The first one utilized Surrogate Models (SMs) for predicting the behavior of changing the kinetic parameters. This is a highly efficient approach, as the computational effort is reduced drastically for each evaluation, and by comparing the physically viable parameter combinations within the pre-determined parameter space, the optimal point could be determined. However, due to limitations of the amount of uncertain parameters and experimental targets that can be used with SMs, an optimization toolbox was developed which uses a more direct optimization approach. The toolbox, called OptiSMOKE++, utilizes the optimization capabilities of DAKOTA, and the simulation of detailed kinetics in reactive systems by OpenSMOKE++. By using efficient optimization methods, the amount of evaluations needed to find the optimal combination of parameters can be drastically reduced. The tool was developed with a flexibility of choosing experimental targets, uncertain kinetic parameters, objective function and optimization method. To present these features, a series of test cases were used and the performance of OptiSMOKE++ was indeed satisfactory. As a final application, the toolbox OptiSMOKE++ was used for optimizing a kinetic mechanism with respect to a large set of experimental targets in MILD conditions. A large amount of uncertain kinetic parameters were also used in the optimization, and the optimized mechanism showed large improvements with respect to the experimental targets. It was also validated against experimental data consisting of species measurements in MILD conditions, and the optimized mechanism showed similar performance as that of the nominal mechanism. However, as the general trend of the species profiles were captured with the nominal mechanism, this was considered satisfactory. The work of this PhD has shown that the application of optimization to kinetic mechanism, can improve the performance of existing mechanism with respect to MILD combustion. Through the development of an efficient toolbox, a large set of experimental data can be used as targets for the optimization, at the same time as many uncertain kinetic parameters can be used contemporary. / Doctorat en Sciences de l'ingénieur et technologie / This work has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 643134, and from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 714605. / info:eu-repo/semantics/nonPublished

Mecanismos de cinética química detalhada são rotineiramente usados para descrever, a nível molecular, a transformação de reagentes em produtos de combustão, que ocorre através de muitas etapas elementares. Seu uso em modelos computacionais para simular processos de combustão pode gerar informações para melhorar o processo de uso do combustível e o desempenho do processo de combustão, e para quantificar as emissões a partir deste processo. Assim, para descrever um processo de oxidação, o esforço computacional se torna muito grande, exigindo simplificações do mecanismo. O desenvolvimento de mecanismos de cinética química reduzida para processos de combustão visa reduzir a esforço computacional na análise numérica de chamas. Os modelos cinéticos reduzidos podem substituir as equações diferenciais das espécies intermediárias, que são consideradas estarem em estado estacionário, através de relações algébricas. Desta forma, este trabalho desenvolve um método para reduzir a cinética química para a combustão do hidrogênio, monóxido de carbono, e hidrocarbonetos C1- C7, utilizando os pressupostos de estado estacionário. Um mecanismo cinético detalhado do processo de combustão de 439 reações elementares foi estudado e reduzido a mecanismos com, no máximo, 9 passos globais. Comparações de dados experimentais com simulações do perfil de fração de massa de CO2 e H2O, produzidos utilizando o mecanismo cinético reduzido do metano, propano e n-heptano demonstram boa concordância, validando estes mecanismos e, consequentemente, aumentando a confiabilidade dos demais mecanismos estudados. / Detailed chemical kinetic mechanisms are routinely used to describe, at the molecular level, the transformation of reactants to products of combustion, which occurs via many elementary steps. Its use in computer models to simulate combustion processes can generate information to improve the fuel quality and performance of the combustion process, and to quantify the emissions from this process. Thus, to describe a process of oxidation, the computational effort becomes very large, requiring simplifications of the reaction mechanism. The development of reduced kinetic mechanisms for combustion processes aims to reduce the computational effort necessary for the numerical analysis. The reduced models can replace the differential equations of the intermediate species, which are considered to be in steady state, through algebraic relationships. In this way, this work develops a method for reducing the kinetics of combustion for hydrogen, carbon monoxide and hydrocarbons C1-C7, using assumptions of steady-state. A detailed kinetic mechanism containing 439 elementary reactions was analysed and reduced mechanisms with up to 10 steps were developed. Comparisons between experiment and simulations for the reduced kinetic mechanism of methane and propane, show good agreement, validating these mechanisms, and consequently, increasing the reliability of the others mechanisms studied.

Mecanismos de cinética química detalhada são rotineiramente usados para descrever, a nível molecular, a transformação de reagentes em produtos de combustão, que ocorre através de muitas etapas elementares. Seu uso em modelos computacionais para simular processos de combustão pode gerar informações para melhorar o processo de uso do combustível e o desempenho do processo de combustão, e para quantificar as emissões a partir deste processo. Assim, para descrever um processo de oxidação, o esforço computacional se torna muito grande, exigindo simplificações do mecanismo. O desenvolvimento de mecanismos de cinética química reduzida para processos de combustão visa reduzir a esforço computacional na análise numérica de chamas. Os modelos cinéticos reduzidos podem substituir as equações diferenciais das espécies intermediárias, que são consideradas estarem em estado estacionário, através de relações algébricas. Desta forma, este trabalho desenvolve um método para reduzir a cinética química para a combustão do hidrogênio, monóxido de carbono, e hidrocarbonetos C1- C7, utilizando os pressupostos de estado estacionário. Um mecanismo cinético detalhado do processo de combustão de 439 reações elementares foi estudado e reduzido a mecanismos com, no máximo, 9 passos globais. Comparações de dados experimentais com simulações do perfil de fração de massa de CO2 e H2O, produzidos utilizando o mecanismo cinético reduzido do metano, propano e n-heptano demonstram boa concordância, validando estes mecanismos e, consequentemente, aumentando a confiabilidade dos demais mecanismos estudados. / Detailed chemical kinetic mechanisms are routinely used to describe, at the molecular level, the transformation of reactants to products of combustion, which occurs via many elementary steps. Its use in computer models to simulate combustion processes can generate information to improve the fuel quality and performance of the combustion process, and to quantify the emissions from this process. Thus, to describe a process of oxidation, the computational effort becomes very large, requiring simplifications of the reaction mechanism. The development of reduced kinetic mechanisms for combustion processes aims to reduce the computational effort necessary for the numerical analysis. The reduced models can replace the differential equations of the intermediate species, which are considered to be in steady state, through algebraic relationships. In this way, this work develops a method for reducing the kinetics of combustion for hydrogen, carbon monoxide and hydrocarbons C1-C7, using assumptions of steady-state. A detailed kinetic mechanism containing 439 elementary reactions was analysed and reduced mechanisms with up to 10 steps were developed. Comparisons between experiment and simulations for the reduced kinetic mechanism of methane and propane, show good agreement, validating these mechanisms, and consequently, increasing the reliability of the others mechanisms studied.

Mecanismos de cinética química detalhada são rotineiramente usados para descrever, a nível molecular, a transformação de reagentes em produtos de combustão, que ocorre através de muitas etapas elementares. Seu uso em modelos computacionais para simular processos de combustão pode gerar informações para melhorar o processo de uso do combustível e o desempenho do processo de combustão, e para quantificar as emissões a partir deste processo. Assim, para descrever um processo de oxidação, o esforço computacional se torna muito grande, exigindo simplificações do mecanismo. O desenvolvimento de mecanismos de cinética química reduzida para processos de combustão visa reduzir a esforço computacional na análise numérica de chamas. Os modelos cinéticos reduzidos podem substituir as equações diferenciais das espécies intermediárias, que são consideradas estarem em estado estacionário, através de relações algébricas. Desta forma, este trabalho desenvolve um método para reduzir a cinética química para a combustão do hidrogênio, monóxido de carbono, e hidrocarbonetos C1- C7, utilizando os pressupostos de estado estacionário. Um mecanismo cinético detalhado do processo de combustão de 439 reações elementares foi estudado e reduzido a mecanismos com, no máximo, 9 passos globais. Comparações de dados experimentais com simulações do perfil de fração de massa de CO2 e H2O, produzidos utilizando o mecanismo cinético reduzido do metano, propano e n-heptano demonstram boa concordância, validando estes mecanismos e, consequentemente, aumentando a confiabilidade dos demais mecanismos estudados. / Detailed chemical kinetic mechanisms are routinely used to describe, at the molecular level, the transformation of reactants to products of combustion, which occurs via many elementary steps. Its use in computer models to simulate combustion processes can generate information to improve the fuel quality and performance of the combustion process, and to quantify the emissions from this process. Thus, to describe a process of oxidation, the computational effort becomes very large, requiring simplifications of the reaction mechanism. The development of reduced kinetic mechanisms for combustion processes aims to reduce the computational effort necessary for the numerical analysis. The reduced models can replace the differential equations of the intermediate species, which are considered to be in steady state, through algebraic relationships. In this way, this work develops a method for reducing the kinetics of combustion for hydrogen, carbon monoxide and hydrocarbons C1-C7, using assumptions of steady-state. A detailed kinetic mechanism containing 439 elementary reactions was analysed and reduced mechanisms with up to 10 steps were developed. Comparisons between experiment and simulations for the reduced kinetic mechanism of methane and propane, show good agreement, validating these mechanisms, and consequently, increasing the reliability of the others mechanisms studied.

A velocidade de queima laminar adiabática é um importante parâmetro da combustão que dita o comportamento de chamas pré-misturadas. Dos métodos disponíveis para a medição desse parâmetro, o método do fluxo de calor destaca-se pela simplicidade e precisão. No presente trabalho, esse método é utilizado para medir a velocidade de queima de biogás (modelado como CH4 com diferentes níveis de diluição com CO2) e de gás de síntese (modelado como uma mistura de CH4, H2, CO, CO2 e N2) em ar a 298 K e 1 atm. Tais gases são de crescente interesse para a sociedade em função de aspectos ambientais, porém, suas velocidades de queima não foram amplamente estudadas ainda. Os resultados obtidos são comparados com as previsões de cinco mecanismos cinéticos (GRI-Mech 3.0, Davis et al., Konnov, San Diego e USC Mech II) a fim de avaliar a sua capacidade preditiva. Os resultados experimentais e numéricos das velocidades de queima de biogás e ar apresentam uma boa concordância e as incertezas encontradas foram condizentes com as relatadas na literatura. Os resultados experimentais desse gás foram parametrizados em uma correlação empírica de fácil utilização em modelos numéricos. As medições da velocidade de queima de gás de síntese e ar, por outro lado, apresentaram valores inferiores às previsões numéricas de todos os mecanismos estudados. Os dados experimentais da literatura, para a mesma mistura, diferem tanto em valores quanto em comportamento dos resultados do presente trabalho. Tal comportamento está provavelmente relacionado a alguma contaminação no CO utilizado, já que quando esse gás está presente observa-se uma chemi-luminescência não relatada na literatura. / The adiabatic laminar burning velocity is an important combustion parameter that dictates premixed flames characteristics. Among the measuring methods available in literature, the heat flux method stands out for its simplicity and accuracy. In the present work, this method is used to measure the adiabatic laminar burning velocity of biogas (modeled as CH4 with different dilution levels with CO2) and syngas (modeled as a CH4, H2, CO, CO2 and N2 mixture) in air at 298 K and 1 atm. Such gases are of growing society interest due to environmental aspects, however, their adiabatic laminar burning velocity have not been widely studied yet. The experimental results are compared to predictions of five kinetic mechanisms (GRI-Mech 3.0, Davis et al., Konnov, San Diego e USC Mech II) to evaluate their predictive capacity. Experimental and numerical results of biogas/air mixtures adiabatic laminar burning velocity show good agreement and the found uncertainties are in agreement with literature. Experimental results of this gas were fitted in an empiric correlation of simple numerical application. Experimental results of the laminar burning velocity of syngas/air, on the other hand, show lower values than the numerical predictions of all studied kinetic mechanisms. Literature available data for the same mixture differ both in values and behavior of the present work results. Such behavior is probably related to some contamination on the CO used since a chemi-luminescence not reported in literature can be noted when this gas is present.

A velocidade de queima laminar adiabática é um importante parâmetro da combustão que dita o comportamento de chamas pré-misturadas. Dos métodos disponíveis para a medição desse parâmetro, o método do fluxo de calor destaca-se pela simplicidade e precisão. No presente trabalho, esse método é utilizado para medir a velocidade de queima de biogás (modelado como CH4 com diferentes níveis de diluição com CO2) e de gás de síntese (modelado como uma mistura de CH4, H2, CO, CO2 e N2) em ar a 298 K e 1 atm. Tais gases são de crescente interesse para a sociedade em função de aspectos ambientais, porém, suas velocidades de queima não foram amplamente estudadas ainda. Os resultados obtidos são comparados com as previsões de cinco mecanismos cinéticos (GRI-Mech 3.0, Davis et al., Konnov, San Diego e USC Mech II) a fim de avaliar a sua capacidade preditiva. Os resultados experimentais e numéricos das velocidades de queima de biogás e ar apresentam uma boa concordância e as incertezas encontradas foram condizentes com as relatadas na literatura. Os resultados experimentais desse gás foram parametrizados em uma correlação empírica de fácil utilização em modelos numéricos. As medições da velocidade de queima de gás de síntese e ar, por outro lado, apresentaram valores inferiores às previsões numéricas de todos os mecanismos estudados. Os dados experimentais da literatura, para a mesma mistura, diferem tanto em valores quanto em comportamento dos resultados do presente trabalho. Tal comportamento está provavelmente relacionado a alguma contaminação no CO utilizado, já que quando esse gás está presente observa-se uma chemi-luminescência não relatada na literatura. / The adiabatic laminar burning velocity is an important combustion parameter that dictates premixed flames characteristics. Among the measuring methods available in literature, the heat flux method stands out for its simplicity and accuracy. In the present work, this method is used to measure the adiabatic laminar burning velocity of biogas (modeled as CH4 with different dilution levels with CO2) and syngas (modeled as a CH4, H2, CO, CO2 and N2 mixture) in air at 298 K and 1 atm. Such gases are of growing society interest due to environmental aspects, however, their adiabatic laminar burning velocity have not been widely studied yet. The experimental results are compared to predictions of five kinetic mechanisms (GRI-Mech 3.0, Davis et al., Konnov, San Diego e USC Mech II) to evaluate their predictive capacity. Experimental and numerical results of biogas/air mixtures adiabatic laminar burning velocity show good agreement and the found uncertainties are in agreement with literature. Experimental results of this gas were fitted in an empiric correlation of simple numerical application. Experimental results of the laminar burning velocity of syngas/air, on the other hand, show lower values than the numerical predictions of all studied kinetic mechanisms. Literature available data for the same mixture differ both in values and behavior of the present work results. Such behavior is probably related to some contamination on the CO used since a chemi-luminescence not reported in literature can be noted when this gas is present.

A velocidade de queima laminar adiabática é um importante parâmetro da combustão que dita o comportamento de chamas pré-misturadas. Dos métodos disponíveis para a medição desse parâmetro, o método do fluxo de calor destaca-se pela simplicidade e precisão. No presente trabalho, esse método é utilizado para medir a velocidade de queima de biogás (modelado como CH4 com diferentes níveis de diluição com CO2) e de gás de síntese (modelado como uma mistura de CH4, H2, CO, CO2 e N2) em ar a 298 K e 1 atm. Tais gases são de crescente interesse para a sociedade em função de aspectos ambientais, porém, suas velocidades de queima não foram amplamente estudadas ainda. Os resultados obtidos são comparados com as previsões de cinco mecanismos cinéticos (GRI-Mech 3.0, Davis et al., Konnov, San Diego e USC Mech II) a fim de avaliar a sua capacidade preditiva. Os resultados experimentais e numéricos das velocidades de queima de biogás e ar apresentam uma boa concordância e as incertezas encontradas foram condizentes com as relatadas na literatura. Os resultados experimentais desse gás foram parametrizados em uma correlação empírica de fácil utilização em modelos numéricos. As medições da velocidade de queima de gás de síntese e ar, por outro lado, apresentaram valores inferiores às previsões numéricas de todos os mecanismos estudados. Os dados experimentais da literatura, para a mesma mistura, diferem tanto em valores quanto em comportamento dos resultados do presente trabalho. Tal comportamento está provavelmente relacionado a alguma contaminação no CO utilizado, já que quando esse gás está presente observa-se uma chemi-luminescência não relatada na literatura. / The adiabatic laminar burning velocity is an important combustion parameter that dictates premixed flames characteristics. Among the measuring methods available in literature, the heat flux method stands out for its simplicity and accuracy. In the present work, this method is used to measure the adiabatic laminar burning velocity of biogas (modeled as CH4 with different dilution levels with CO2) and syngas (modeled as a CH4, H2, CO, CO2 and N2 mixture) in air at 298 K and 1 atm. Such gases are of growing society interest due to environmental aspects, however, their adiabatic laminar burning velocity have not been widely studied yet. The experimental results are compared to predictions of five kinetic mechanisms (GRI-Mech 3.0, Davis et al., Konnov, San Diego e USC Mech II) to evaluate their predictive capacity. Experimental and numerical results of biogas/air mixtures adiabatic laminar burning velocity show good agreement and the found uncertainties are in agreement with literature. Experimental results of this gas were fitted in an empiric correlation of simple numerical application. Experimental results of the laminar burning velocity of syngas/air, on the other hand, show lower values than the numerical predictions of all studied kinetic mechanisms. Literature available data for the same mixture differ both in values and behavior of the present work results. Such behavior is probably related to some contamination on the CO used since a chemi-luminescence not reported in literature can be noted when this gas is present.

Une étude expérimentale de la vaporisation de goutte d'éthanol et de propan-1-ol a été réalisée. Le dispositif expérimental est constitué d’une enceinte chauffée à l’intérieur de laquelle se trouve le support de goutte. Il est formé par deux fibres en quartz croisées. La goutte d'alcool se trouve à l'intersection de ces fibres. Le diamètre initial de la goutte est contrôlé, il varie entre 300 et 600µm. L’étude est faite de 298 à 973K et à pression atmosphérique. La théorie de l’état quasi-stationnaire est utilisée pour comparer et expliquer tous les résultats expérimentaux. L'impact réel de la concentration d'eau sur la vaporisation d'une goutte d'éthanol est également examiné. Deux périodes sont observées sur les courbes en d2. Ceci montre clairement que la vaporisation d'une goutte d'éthanol est accompagnée par la condensation de la vapeur d'eau à la surface de la goutte. L’évolution des taux instantanés de vaporisation du propan-1-ol et de l'éthanol confirme ce phénomène. Les délais d’autoinflammation de l'éthanol, du propan-1-ol et des mélanges d'éthanol et de l'eau ont été mesurés dans une machine de compression rapide. Les conditions de l’étude sont : une pression de compression de 30bar, la gamme de température variant de 750 à 860K, pour des mélanges stoechiométriques carburant/air. Les délais d’autoinflammation enregistrés diminuent lorsque la température augmente. Le propan-1-ol est plus réactif que l'éthanol, ce qui se traduit par des délais d’autoinflammation plus courts. Cependant, l'addition de l'eau à l'éthanol augmente la réactivité du mélange et se traduit par une réduction des délais d’autoinflammation / Detailed investigation of the vaporization of an isolated of ethanol and 1-propanol droplet was carried out in this experimental study. The experimental set-up consists of a heated chamber with a cross quartz fibers configuration as droplet support. An alcohol droplet is located at the intersection of the cross quartz fibre with a controlled initial diameter (300-600µm). Ambient temperature is varied from 298 to 973K at atmospheric pressure. The quasi-steady theory has been used to compare and to explain all experimental results. The real impact of the water concentration on the vaporization rate of an ethanol droplet is also examined, where two ‘quasi-steady’ periods are observed on the d2-curves, clearly showing that the vaporization of an ethanol droplet is accompanied by the simultaneous condensation of water vapour on the droplet surface and thus the temporal evolution of the droplet squared diameter exhibits an unsteady behavior. The histories of the instantaneous vaporization rates of both 1-propanol and ethanol droplets confirm this phenomenon. The autoignition experimental study of ethanol, 1-propanol and blends of ethanol and water have been carried out in a rapid compression machine at a compressed pressure of 30bar over a temperature range of 750-860K for stoichiometric mixture of fuel and air. The ignition delay times recorded show a significant decrease with increasing temperature. 1-propanol is more reactive than ethanol, which results in shorter ignition delay times. However, water addition to ethanol increases the reactivity of the mixture and results in a shorter ignition delay times than 1-propanol

Detailed investigation of the vaporization of an isolated of ethanol and 1-propanol droplet was carried out in this experimental study. The experimental set-up consists of a heated chamber with a cross quartz fibers configuration as droplet support. An alcohol droplet is located at the intersection of the cross quartz fibre with a controlled initial diameter (300-600µm). Ambient temperature is varied from 298 to 973K at atmospheric pressure. The quasi-steady theory has been used to compare and to explain all experimental results. The real impact of the water concentration on the vaporization rate of an ethanol droplet is also examined, where two 'quasi-steady' periods are observed on the d2-curves, clearly showing that the vaporization of an ethanol droplet is accompanied by the simultaneous condensation of water vapour on the droplet surface and thus the temporal evolution of the droplet squared diameter exhibits an unsteady behavior. The histories of the instantaneous vaporization rates of both 1-propanol and ethanol droplets confirm this phenomenon. The autoignition experimental study of ethanol, 1-propanol and blends of ethanol and water have been carried out in a rapid compression machine at a compressed pressure of 30bar over a temperature range of 750-860K for stoichiometric mixture of fuel and air. The ignition delay times recorded show a significant decrease with increasing temperature. 1-propanol is more reactive than ethanol, which results in shorter ignition delay times. However, water addition to ethanol increases the reactivity of the mixture and results in a shorter ignition delay times than 1-propanol