In this thesis Direct Numerical Simulation (DNS) is used to investigate the development of turbulent premixed flame kernels during the early stages of growth typical of the period following spark ignition. Two distinct aspects of this phase are considered: the interaction of the expanding kernel with a field of decaying turbulence, and the chemical and thermo-diffusive response of the flame for different fresh-gas compositions. In the first part of the study, three-dimensional, repeated simulations with single-step chemistry are used to generate ensemble statistics of global flame growth. The surface-conditioned mean fluid-velocity magnitude is found to vary significantly across different isosurfaces of the reaction progress variable, and this is shown to lead to a bias in the distribution of the Surface Density Function (SDF) around the developing flame. Two-dimensional simulations in an extended domain indicate that this effect translates into a similar directional bias in the Flame Surface Density (FSD) at later stages in the kernel development. Properties of the fresh gas turbulence decay are assessed from an independent, non-reacting simulation database. In the second part of this study, two-dimensional simulations with a detailed 68-step reaction mechanism are used to investigate the thermo-diffusive response of pure methane-air, and hydrogen-enriched methane-air flames. The changes in local and global behaviour due to the different laminar flame characteristics, and the response of the flames to strain and curvature are examined at different equivalence ratios and turbulence intensities. Mechanisms leading to flame quenching are discussed and the effect of mean flame curvature is assessed through comparison with an equivalent planar flame. The effects of hydrogen addition are found to be particularly pronounced in flame kernels due to the higher positive stretch rates and reduced thermo-diffusive stability of hydrogen-enriched flames.

In this thesis Direct Numerical Simulation (DNS) is used to investigate the development of turbulent premixed flame kernels during the early stages of growth typical of the period following spark ignition. Two distinct aspects of this phase are considered: the interaction of the expanding kernel with a field of decaying turbulence, and the chemical and thermo-diffusive response of the flame for different fresh-gas compositions. In the first part of the study, three-dimensional, repeated simulations with single-step chemistry are used to generate ensemble statistics of global flame growth. The surface-conditioned mean fluid-velocity magnitude is found to vary significantly across different isosurfaces of the reaction progress variable, and this is shown to lead to a bias in the distribution of the Surface Density Function (SDF) around the developing flame. Two-dimensional simulations in an extended domain indicate that this effect translates into a similar directional bias in the Flame Surface Density (FSD) at later stages in the kernel development. Properties of the fresh gas turbulence decay are assessed from an independent, non-reacting simulation database. In the second part of this study, two-dimensional simulations with a detailed 68-step reaction mechanism are used to investigate the thermo-diffusive response of pure methane-air, and hydrogen-enriched methane-air flames. The changes in local and global behaviour due to the different laminar flame characteristics, and the response of the flames to strain and curvature are examined at different equivalence ratios and turbulence intensities. Mechanisms leading to flame quenching are discussed and the effect of mean flame curvature is assessed through comparison with an equivalent planar flame. The effects of hydrogen addition are found to be particularly pronounced in flame kernels due to the higher positive stretch rates and reduced thermo-diffusive stability of hydrogen-enriched flames.

Made available in DSpace on 2017-07-10T19:24:37Z (GMT). No. of bitstreams: 1 Luciano Aparecido Kempski.pdf: 1024512 bytes, checksum: 05341aec87667985a0d8254a3699a994 (MD5) Previous issue date: 2006-06-19 / The current work aimed the construction of a benches group for simulating displacement speeds of sowers. The speeds simulator was performed and was carried out in the mechanical trials laboratory located at UTFPR - campus Medianeira, and the assays of system´s evaluation were performed at the Agricultural Engineering Experimental Nucleous - AEEN, which belongs to West of the Paraná State University- campus Cascavel. The benches group of assay or speeds simulator is composed by two rolls: one of this set through a hydraulic engine brand TRW, and other one used as support for the wheels system of the sower. The hydraulical engine was connected to the hydraulical command of the tractor through fast connection, which become the coupling and withdraws of hoses easier when stationary assay of displacement speeds is performed. The assays were performed aiming the determination of the maximum rotation for the hydraulical engine without load and also with the sower on the rolls, in order to get ranges of displacement speeds in a fast and accurated form. The results obtained of the regulating valve´s opening and closing (A1 the A7) forms, in function of the hydraulic engine´s rotation and the displacement speed, are presented in figures, tables and relation ´s graphs. The tables present the average values and the hydraulical engine without load is presented by the comparision between the averages. For the hydraulical engine without load can be reach speeds ranged from 20 to 375 rpm in accordance to the results obtained, which is linked to the enough displacement speeds. The benches group essay was showed as functional and also presented compact structure, with the flowing rangel of speeds verified through the pairs of gear. Its versatility is evidenced by the use of the hydraulic circuit of the tractor as energy source for the speeds simulator.It was observed that the regulating valve of outflow was efficient for the regulation of the hydraulical engine´s speed when it was assayed with load; it means that, with the sower on the cylinders. The results obtained allow to present the following conclusions: it is a too much suitable resource, considering the easiness, quickness and the capacity for obtaining several regulations, allowing the simulation of displacement speeds from 3,23 to 13,89 km.h-1; it fits perfectly in sowers with pneumatic wheels; the weight and size allow the transport without difficulties, provide conditions to evaluate the distribuition mechanisms of the seeds or fertilizer, and avaluation the longitudinal distribution of seeds, in accordance to the evaluation criteria of performing in spacements: normal, double and defective. / Este trabalho teve como objetivo a construção de uma bancada para simulação de velocidades de deslocamento de semeadoras. O simulador de velocidades foi projetado e montado no laboratório de processos mecânicos da UTFPR - campus Medianeira. Os ensaios de avaliação do sistema foram realizados no Núcleo Experimental de Engenharia Agrícola - NEEA, pertencente à Universidade Estadual do Oeste do Paraná campus Cascavel. A bancada de ensaio ou simulador de velocidades é formada por dois rolos: um acionado por meio de um motor hidráulico marca TRW e o outro utilizado como apoio para o rodado da semeadora. O motor hidráulico foi conectado ao comando hidráulico do trator por meio de engates rápidos, o que facilita o acoplamento e retirada das mangueiras, no momento da realização do ensaio estacionário de velocidades de deslocamento. Os ensaios foram realizados para a determinação da rotação máxima do motor hidráulico sem carga e com a semeadora sobre os rolos a fim de obter faixas de velocidade de deslocamento de forma precisa e rápida. Os resultados obtidos sobre a relação da abertura e fechamento da válvula reguladora (A1 a A7), em função da rotação do motor hidráulico e da velocidade de deslocamento, são apresentados em forma de figuras, tabelas e gráficos. As tabelas apresentam os valores médios e a comparação entre as médias está representada nos gráficos 21 e 22. Com o motor hidráulico sem carga podem-se alcançar velocidades desde 20 rpm até 375 rpm, conforme os resultados obtidos que se relacionam com as velocidades de deslocamento. A bancada de ensaio apresentou-se funcional e de estrutura compacta, com a faixa de escalonamento de velocidades verificada pelos pares de engrenagem. Sua versatilidade é evidenciada pelo uso do circuito hidráulico do trator como fonte de energia para acionamento do simulador de velocidades. Observou-se que a válvula reguladora de vazão foi eficiente na regulagem da velocidade do motor hidráulico quando ensaiado com carga, ou seja, com a semeadora sobre os cilindros. Os resultados obtidos permitem apresentar as seguintes conclusões: a bancada mostrou-se um recurso bastante adequado, considerando-se a facilidade, rapidez e a capacidade de conseguir várias regulagens, permitindo a simulação de velocidades de deslocamento de 3,23 a 13,89 km.h-1; adapta-se perfeitamente à semeadora com rodado pneumático, o peso e tamanho permitem o transporte sem dificuldades; fornece condições de avaliação de mecanismos distribuidores de sementes e fertilizantes; e avaliar a distribuição longitudinal de sementes, de acordo com os critérios de avaliação de desempenho em espaçamentos: normal, duplos e falhos.

Made available in DSpace on 2017-05-12T14:48:00Z (GMT). No. of bitstreams: 1 Luciano Aparecido Kempski.pdf: 1024512 bytes, checksum: 05341aec87667985a0d8254a3699a994 (MD5) Previous issue date: 2006-06-19 / The current work aimed the construction of a benches group for simulating displacement speeds of sowers. The speeds simulator was performed and was carried out in the mechanical trials laboratory located at UTFPR - campus Medianeira, and the assays of system´s evaluation were performed at the Agricultural Engineering Experimental Nucleous - AEEN, which belongs to West of the Paraná State University- campus Cascavel. The benches group of assay or speeds simulator is composed by two rolls: one of this set through a hydraulic engine brand TRW, and other one used as support for the wheels system of the sower. The hydraulical engine was connected to the hydraulical command of the tractor through fast connection, which become the coupling and withdraws of hoses easier when stationary assay of displacement speeds is performed. The assays were performed aiming the determination of the maximum rotation for the hydraulical engine without load and also with the sower on the rolls, in order to get ranges of displacement speeds in a fast and accurated form. The results obtained of the regulating valve´s opening and closing (A1 the A7) forms, in function of the hydraulic engine´s rotation and the displacement speed, are presented in figures, tables and relation ´s graphs. The tables present the average values and the hydraulical engine without load is presented by the comparision between the averages. For the hydraulical engine without load can be reach speeds ranged from 20 to 375 rpm in accordance to the results obtained, which is linked to the enough displacement speeds. The benches group essay was showed as functional and also presented compact structure, with the flowing rangel of speeds verified through the pairs of gear. Its versatility is evidenced by the use of the hydraulic circuit of the tractor as energy source for the speeds simulator.It was observed that the regulating valve of outflow was efficient for the regulation of the hydraulical engine´s speed when it was assayed with load; it means that, with the sower on the cylinders. The results obtained allow to present the following conclusions: it is a too much suitable resource, considering the easiness, quickness and the capacity for obtaining several regulations, allowing the simulation of displacement speeds from 3,23 to 13,89 km.h-1; it fits perfectly in sowers with pneumatic wheels; the weight and size allow the transport without difficulties, provide conditions to evaluate the distribuition mechanisms of the seeds or fertilizer, and avaluation the longitudinal distribution of seeds, in accordance to the evaluation criteria of performing in spacements: normal, double and defective. / Este trabalho teve como objetivo a construção de uma bancada para simulação de velocidades de deslocamento de semeadoras. O simulador de velocidades foi projetado e montado no laboratório de processos mecânicos da UTFPR - campus Medianeira. Os ensaios de avaliação do sistema foram realizados no Núcleo Experimental de Engenharia Agrícola - NEEA, pertencente à Universidade Estadual do Oeste do Paraná campus Cascavel. A bancada de ensaio ou simulador de velocidades é formada por dois rolos: um acionado por meio de um motor hidráulico marca TRW e o outro utilizado como apoio para o rodado da semeadora. O motor hidráulico foi conectado ao comando hidráulico do trator por meio de engates rápidos, o que facilita o acoplamento e retirada das mangueiras, no momento da realização do ensaio estacionário de velocidades de deslocamento. Os ensaios foram realizados para a determinação da rotação máxima do motor hidráulico sem carga e com a semeadora sobre os rolos a fim de obter faixas de velocidade de deslocamento de forma precisa e rápida. Os resultados obtidos sobre a relação da abertura e fechamento da válvula reguladora (A1 a A7), em função da rotação do motor hidráulico e da velocidade de deslocamento, são apresentados em forma de figuras, tabelas e gráficos. As tabelas apresentam os valores médios e a comparação entre as médias está representada nos gráficos 21 e 22. Com o motor hidráulico sem carga podem-se alcançar velocidades desde 20 rpm até 375 rpm, conforme os resultados obtidos que se relacionam com as velocidades de deslocamento. A bancada de ensaio apresentou-se funcional e de estrutura compacta, com a faixa de escalonamento de velocidades verificada pelos pares de engrenagem. Sua versatilidade é evidenciada pelo uso do circuito hidráulico do trator como fonte de energia para acionamento do simulador de velocidades. Observou-se que a válvula reguladora de vazão foi eficiente na regulagem da velocidade do motor hidráulico quando ensaiado com carga, ou seja, com a semeadora sobre os cilindros. Os resultados obtidos permitem apresentar as seguintes conclusões: a bancada mostrou-se um recurso bastante adequado, considerando-se a facilidade, rapidez e a capacidade de conseguir várias regulagens, permitindo a simulação de velocidades de deslocamento de 3,23 a 13,89 km.h-1; adapta-se perfeitamente à semeadora com rodado pneumático, o peso e tamanho permitem o transporte sem dificuldades; fornece condições de avaliação de mecanismos distribuidores de sementes e fertilizantes; e avaliar a distribuição longitudinal de sementes, de acordo com os critérios de avaliação de desempenho em espaçamentos: normal, duplos e falhos.

The search for clean and efficient combustors is motivated by the increasingly stringent emissions regulations. New gas turbine engines are designed to operate under lean conditions with inhomogeneous reactants to ensure cleanliness and stability of the combustion. This ushers in a new mode of combustion, called the inhomogeneous reactants premixed combustion. The present study investigates the effects of inhomogeneous reactants on premixed combustion, specifically on the interactions of an initially planar flame with field of inhomogeneous reactants. Unsteady and unstrained laminar methane-air flames are studied in one- and two-dimensional simulations to investigate the effects of normally and tangentially (to the flame surface) stratified reactants. A three-dimensional DNS of turbulent inhomogeneous reactants premixed combustion is performed to extend the investigation into turbulent flames. The methaneair combustion is represented by a complex chemical reaction mechanism with 18 species and 68 steps. The flame surface density (FSD) and displacement speed S_d have been used as the framework to analyse the inhomogeneous reactants premixed flame. The flames are characterised by an isosurface of reaction progress variable. The unsteady flames are compared to the steady laminar unstrained reference case. An equivalence ratio dip is observed in all simulations and it can serve as a marker for the premixed flame. The dip is attributed to the preferential diffusion of carbon- and hydrogen- containing species. Hysteresis of S_d is observed in the unsteady and unstrained laminar flames that propagate into normally stratified reactants. Stoichiometric flames propagating into lean mixture have a larger S_d than lean flames propagating into stoichiometric mixtures. The cross-dissipation term contribution to S_d is small (~~10%) but its contribution to the hysteresis of S_d is not (~~50%). Differential propagation of the flame surface is observed in the laminar flame that propagates into tangentially stratified reactants. Stretch on the flame surface is induced by the differential propagation, which in turn increases the flame surface area.